Electrical conductivity of water is a very important property of water for each of us.

Every person should know that water, as a rule, is electrically conductive. Ignorance of this fact can lead to detrimental consequences for life and health.

Let us give several definitions to the concept of electrical conductivity, in general, and the electrical conductivity of water in particular.

Electrical conductivity is...

A scalar quantity that characterizes the electrical conductivity of a substance and is equal to the ratio of the density of the electrical conduction current to the electric field strength.

The property of a substance to conduct a time-invariant electric current under the influence of a time-invariant electric field.

Ushakov's Explanatory Dictionary

Electrical conductivity (electrical conductivity, pl. no, female (physical)) – the ability to conduct, transmit electricity.

Ushakov's explanatory dictionary. D.N. Ushakov. 1935-1940

Big Polytechnic Encyclopedia

Electrical conductivity or Electrical conductivity is the property of a substance to conduct, under the influence of an unchanging electric field, an electric current that does not change over time. Electromagnetic energy is caused by the presence of mobile electric charges in a substance - current carriers. The type of current carrier is determined by electron (for metals and semiconductors), ionic (for electrolytes), electron-ion (for plasma) and hole (together with electron) (for semiconductors). Depending on the specific electrical conductivity, all bodies are divided into conductors, semiconductors and dielectrics, physical. the reciprocal of electrical resistance. The SI unit of electrical conductivity is siemens (q.v.); 1 cm = 1 ohm-1.

Big Polytechnic Encyclopedia. – M.: Peace and Education. Ryazantsev V.D.. 2011

The electrical conductivity of water is...

Polytechnic terminological explanatory dictionary

Electrical conductivity of water is an indicator of the conductivity of electric current by water, characterizing the salt content in water.

Polytechnic terminological explanatory dictionary. Compilation: V. Butakov, I. Fagradyants. 2014

Marine encyclopedic reference book

Electrical conductivity of sea water is the ability of sea water to conduct current under the influence of an external electric field due to the presence of electrical charge carriers in it - ions of dissolved salts, mainly NaCl. The electrical conductivity of sea water increases in proportion to the increase in its salinity and is 100 - 1000 times greater than that of river water. It also depends on the water temperature.

Marine encyclopedic reference book. - L.: Shipbuilding. Edited by Academician N. N. Isanin. 1986

From the above definitions, it becomes obvious that the electrical conductivity of water is not a constant, but depends on the presence of salts and other impurities in it. For example, the electrical conductivity of water is minimal.

How to find out the electrical conductivity of water, how to measure it...

Conductometry - measuring the electrical conductivity of water

To measure the electrical conductivity of water, the Conductometry method is used (see definitions below), and the devices used to measure electrical conductivity have a name that is consonant with the method - Conductometers.

Conductometry is...

Explanatory dictionary of foreign words

Conductometry and many others. no, w. (German: Konduktometrie

Explanatory dictionary of foreign words by L. P. Krysin. - M: Russian language, 1998

encyclopedic Dictionary

Conductometry (from the English conductivity - electrical conductivity and the Greek metreo - I measure) is an electrochemical method of analysis based on measuring the electrical conductivity of solutions. They are used to determine the concentration of solutions of salts, acids, bases, and to control the composition of some industrial solutions.

Encyclopedic Dictionary. 2009

Specific electrical conductivity of water

And in conclusion, we present several values ​​of specific electrical conductivity for various types of water*.

The specific electrical conductivity of water is...

Technical Translator's Guide

Specific electrical conductivity of water is the electrical conductivity of a unit volume of water.

[GOST 30813-2002]

Specific electrical conductivity of water *:

• Tap water – 36.30 µS/m;
• – 0.63 µS/m;
• Drinking (bottled) – 20.2 µS/m;
• Drinking frozen – 19.3 µS/m;
• Water-frozen - 22 µS/m.

* Article “Electrical conductivity of drinking water samples of different degrees of purity” Authors: Vorobyova Lyudmila Borisovna. Magazine: “Interexpo Geo-Siberia Issue No. -5 / volume 1 / 2012.”

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1 microsiemens per centimeter [µS/cm] = 0.0001 siemens per meter [S/m]

Initial value

Converted value

siemens per meter picosiemens per meter mo per meter mo per centimeter abmo per meter abmo per centimeter statmo per meter statmo per centimeter siemens per centimeter millisiemens per meter millisiemens per centimeter microsiemens per meter microsiemens per centimeter conventional unit of electrical conductivity conventional coefficient of electrical conductivity ppm, coefficient. recalculation 700 ppm, coefficient. recalculation 500 ppm, coefficient. recalculation 640 TDS, ppm, coefficient. recalculation 640 TDS, ppm, coefficient. recalculation 550 TDS, ppm, coefficient. recalculation 500 TDS, ppm, coefficient. recalculation 700

More about electrical conductivity

Introduction and Definitions

Electrical conductivity (or electrical conductivity) is a measure of a substance's ability to conduct electric current or move electrical charges within it. This is the ratio of current density to electric field strength. If we consider a cube of conductive material with a side of 1 meter, then the conductivity will be equal to the electrical conductivity measured between two opposite sides of this cube.

Specific conductivity is related to conductivity by the following formula:

G = σ(A/l)

Where G- electrical conductivity, σ - specific electrical conductivity, A- cross-section of the conductor perpendicular to the direction of the electric current and l- length of the conductor. This formula can be used with any cylinder or prism shaped conductor. Note that this formula can also be used for a rectangular parallelepiped, because it is a special case of a prism, the base of which is a rectangle. Let us recall that electrical conductivity is the reciprocal of electrical resistivity.

It can be difficult for people far from physics and technology to understand the difference between the conductivity of a conductor and the specific conductivity of a substance. Meanwhile, of course, these are different physical quantities. Conductivity is a property of a given conductor or device (such as a resistor or plating bath), while conductivity is an inherent property of the material from which that conductor or device is made. For example, the conductivity of copper is always the same, no matter how the shape and size of a copper object changes. At the same time, the conductivity of a copper wire depends on its length, diameter, mass, shape and some other factors. Of course, similar objects made from materials with higher conductivity have higher conductivity (though not always).

In the International System of Units (SI), the unit of electrical conductivity is Siemens per meter (S/m). The unit of conductivity included in it is named after the German scientist, inventor, and entrepreneur Werner von Siemens (1816–1892). Founded by him in 1847, Siemens AG (Siemens) is one of the largest companies producing electrical, electronic, energy, transport and medical equipment.

The range of electrical conductivity is very wide: from materials with high resistivity such as glass (which, by the way, conducts electricity well if heated red) or polymethyl methacrylate (plexiglass) to very good conductors such as silver, copper or gold. Electrical conductivity is determined by the number of charges (electrons and ions), the speed at which they move, and the amount of energy they can carry. Aqueous solutions of various substances, which are used, for example, in plating baths, have average conductivity values. Another example of electrolytes with average conductivity values ​​is the internal environment of the body (blood, plasma, lymph and other fluids).

The conductivity of metals, semiconductors and dielectrics is discussed in detail in the following articles of the Physical Quantity Converter website: , and Electrical conductivity. In this article we will discuss in more detail the specific conductivity of electrolytes, as well as methods and simple equipment for measuring it.

Specific electrical conductivity of electrolytes and its measurement

The specific conductivity of aqueous solutions in which an electric current arises as a result of the movement of charged ions is determined by the number of charge carriers (the concentration of the substance in the solution), the speed of their movement (the mobility of ions depends on temperature) and the charge they carry (determined by the valency of the ions). Therefore, in most aqueous solutions, an increase in concentration leads to an increase in the number of ions and, consequently, to an increase in conductivity. However, after reaching a certain maximum, the specific conductivity of the solution may begin to decrease with a further increase in the concentration of the solution. Therefore, solutions with two different concentrations of the same salt can have the same conductivity.

Temperature also affects conductivity because as temperature increases, ions move faster, resulting in increased conductivity. Pure water is a poor conductor of electricity. Ordinary distilled water, which contains carbon dioxide from the air in equilibrium and a total mineralization of less than 10 mg/l, has a specific electrical conductivity of about 20 mS/cm. The specific conductivity of various solutions is given in the table below.

To determine the specific conductivity of a solution, a resistance meter (ohmmeter) or conductivity is used. These are almost identical devices, differing only in the scale. Both measure the voltage drop across the section of the circuit through which electric current flows from the device's battery. The measured conductivity value is manually or automatically converted into specific conductivity. This is done taking into account the physical characteristics of the measuring device or sensor. Conductivity sensors are designed simply: they are a pair (or two pairs) of electrodes immersed in an electrolyte. Sensors for measuring conductivity are characterized by conductivity sensor constant, which in the simplest case is defined as the ratio of the distance between the electrodes D to the area (electrode) perpendicular to the current flow A

This formula works well if the area of ​​the electrodes is significantly larger than the distance between them, since in this case most of the electrical current flows between the electrodes. Example: for 1 cubic centimeter of liquid K = D/A= 1 cm/1 cm² = 1 cm⁻¹. Note that conductivity sensors with small electrodes spaced apart over a relatively large distance are characterized by sensor constant values ​​of 1.0 cm⁻¹ and higher. At the same time, sensors with relatively large electrodes located close to each other have a constant of 0.1 cm⁻¹ or less. The sensor constant for measuring electrical conductivity of various devices ranges from 0.01 to 100 cm⁻¹.

Theoretical sensor constant: left - K= 0.01 cm⁻¹, right - K= 1 cm⁻¹

To obtain the conductivity from the measured conductivity, the following formula is used:

σ = K ∙ G

σ - specific conductivity of the solution in S/cm;

K- sensor constant in cm⁻¹;

G- conductivity of the sensor in siemens.

The sensor constant is not usually calculated from its geometric dimensions, but is measured in a specific measuring device or in a specific measuring setup using a solution of known conductivity. This measured value is entered into the conductivity meter, which automatically calculates the conductivity from the measured conductivity or resistance values ​​of the solution. Due to the fact that conductivity depends on the temperature of the solution, devices for measuring it often contain a temperature sensor that measures the temperature and provides automatic temperature compensation of the measurements, that is, normalizing the results to a standard temperature of 25 ° C.

The simplest way to measure conductivity is to apply a voltage to two flat electrodes immersed in a solution and measure the current flowing. This method is called potentiometric. According to Ohm's law, conductivity G is the ratio of current I to voltage U:

However, not everything is as simple as described above - there are many problems when measuring conductivity. If direct current is used, ions collect at the surfaces of the electrodes. Also, a chemical reaction may occur at the surfaces of the electrodes. This leads to an increase in polarization resistance on the electrode surfaces, which in turn leads to erroneous results. If you try to measure the resistance of, for example, a sodium chloride solution with a conventional tester, you will clearly see how the readings on the display of a digital device change quite quickly in the direction of increasing resistance. To eliminate the influence of polarization, a sensor design of four electrodes is often used.

Polarization can also be prevented or, in any case, reduced, if you use alternating current instead of direct current when measuring, and even adjust the frequency depending on the conductivity. Low frequencies are used to measure low conductivity, where the influence of polarization is small. Higher frequencies are used to measure high conductivities. Typically, the frequency is adjusted automatically during the measurement process, taking into account the obtained conductivity values ​​of the solution. Modern digital two-electrode conductivity meters typically use complex AC current waveforms and temperature compensation. They are calibrated at the factory, but recalibration is often required during operation, since the constant of the measuring cell (sensor) changes over time. For example, it can change when the sensors become dirty or when the electrodes undergo physical and chemical changes.

In a traditional two-electrode conductivity meter (this is the one we will use in our experiment), an alternating voltage is applied between two electrodes and the current flowing between the electrodes is measured. This simple method has one drawback - not only the resistance of the solution is measured, but also the resistance caused by the polarization of the electrodes. To minimize the influence of polarization, a four-electrode sensor design is used, as well as coating the electrodes with platinum black.

General mineralization

Electrical conductivity measuring devices are often used to determine total mineralization or solids content(eng. total dissolved solids, TDS). It is a measure of the total amount of organic and inorganic substances contained in a liquid in various forms: ionized, molecular (dissolved), colloidal and in suspension (undissolved). Solutes include any inorganic salts. Mainly these are chlorides, bicarbonates and sulfates of calcium, potassium, magnesium, sodium, as well as some organic substances dissolved in water. To be classified as total mineralization, substances must be either dissolved or in the form of very fine particles that pass through filters with pore diameters of less than 2 micrometers. Substances that are constantly suspended in solution, but cannot pass through such a filter, are called suspended solids(eng. total suspended solids, TSS). Total suspended solids are commonly measured to determine water quality.

There are two methods for measuring solids content: gravimetric analysis, which is the most accurate method, and conductivity measurement. The first method is the most accurate, but requires a lot of time and laboratory equipment, since the water must be evaporated to obtain a dry residue. This is usually done at 180°C in laboratory conditions. After complete evaporation, the residue is weighed on a precision scale.

The second method is not as accurate as gravimetric analysis. However, it is very convenient, widespread and the fastest method, since it is a simple conductivity and temperature measurement carried out in a few seconds with an inexpensive measuring instrument. The method of measuring specific electrical conductivity can be used due to the fact that the specific conductivity of water directly depends on the amount of ionized substances dissolved in it. This method is especially convenient for monitoring the quality of drinking water or estimating the total number of ions in a solution.

The measured conductivity depends on the temperature of the solution. That is, the higher the temperature, the higher the conductivity, since ions in a solution move faster as the temperature rises. To obtain temperature-independent measurements, the concept of a standard (reference) temperature is used to which the measurement results are reduced. The reference temperature allows you to compare results obtained at different temperatures. Thus, a conductivity meter can measure actual conductivity and then use a correction function that will automatically adjust the result to a reference temperature of 20 or 25°C. If very high accuracy is required, the sample can be placed in an incubator, then the meter can be calibrated at the same temperature that will be used in the measurements.

Most modern conductivity meters have a built-in temperature sensor, which is used for both temperature correction and temperature measurement. The most advanced instruments are capable of measuring and displaying measured values ​​in units of conductivity, resistivity, salinity, total salinity and concentration. However, we note once again that all these devices measure only conductivity (resistance) and temperature. All physical quantities shown on the display are calculated by the device taking into account the measured temperature, which is used for automatic temperature compensation and bringing the measured values ​​to a standard temperature.

Experiment: measuring total mineralization and conductivity

Finally, we will perform several experiments to measure conductivity using an inexpensive TDS-3 total mineralization meter (also called salinometer, salinometer, or conductivity meter). The price of the “unnamed” TDS-3 device on eBay including delivery at the time of writing is less than US$3.00. Exactly the same device, but with the manufacturer’s name, costs 10 times more. But this is for those who like to pay for the brand, although there is a very high probability that both devices will be produced at the same factory. TDS-3 carries out temperature compensation and for this purpose is equipped with a temperature sensor located next to the electrodes. Therefore, it can also be used as a thermometer. It should be noted once again that the device does not actually measure the mineralization itself, but the resistance between two wire electrodes and the temperature of the solution. It automatically calculates everything else using calibration factors.

A total mineralization meter can help you determine the solids content, for example when monitoring the quality of drinking water or determining the salinity of water in an aquarium or freshwater pond. It can also be used to monitor water quality in water filtration and purification systems to know when it is time to replace the filter or membrane. The instrument is factory calibrated with a 342 ppm (parts per million or mg/L) sodium chloride solution, NaCl. The measuring range of the device is 0–9990 ppm or mg/l. PPM - part per million, a dimensionless unit of measurement of relative values, equal to 1 10⁻⁶ of the base indicator. For example, a mass concentration of 5 mg/kg = 5 mg in 1,000,000 mg = 5 ppm or ppm. Just as a percentage is one hundredth, a ppm is one millionth. Percents and ppm are very similar in meaning. Parts per million, as opposed to percentages, are useful for indicating the concentration of very weak solutions.

The device measures the electrical conductivity between two electrodes (that is, the reciprocal of resistance), then converts the result into specific electrical conductivity (in English literature the abbreviation EC is often used) using the above conductivity formula, taking into account the sensor constant K, then performs another conversion by multiplying the resulting conductivity by a conversion factor of 500. The result is a total salinity value in parts per million (ppm). More details about this below.

This total mineralization meter cannot be used to test the quality of water with high salt content. Examples of substances with a high salt content are some foods (regular soup with a normal salt content of 10 g/l) and sea water. The maximum concentration of sodium chloride that this device can measure is 9990 ppm or about 10 g/l. This is the typical concentration of salt in foods. This device also cannot measure the salinity of seawater, as it is usually 35 g/l or 35,000 ppm, which is much higher than the device can measure. If you attempt to measure such a high concentration, the instrument will display the error message Err.

The TDS-3 salinity meter measures specific conductivity and uses the so-called “500 scale” (or “NaCl scale”) for calibration and conversion to concentration. This means that to obtain the ppm concentration, the conductivity value in mS/cm is multiplied by 500. That is, for example, 1.0 mS/cm is multiplied by 500 to get 500 ppm. Different industries use different scales. For example, in hydroponics, three scales are used: 500, 640 and 700. The only difference between them is in use. The 700 scale is based on measuring the concentration of potassium chloride in a solution and the conversion of specific conductivity to concentration is performed as follows:

1.0 mS/cm x 700 gives 700 ppm

The 640 scale uses a conversion factor of 640 to convert mS to ppm:

1.0 mS/cm x 640 gives 640 ppm

In our experiment, we will first measure the total mineralization of distilled water. The salinity meter shows 0 ppm. The multimeter shows a resistance of 1.21 MOhm.

For the experiment, we will prepare a solution of sodium chloride NaCl with a concentration of 1000 ppm and measure the concentration using TDS-3. To prepare 100 ml of solution, we need to dissolve 100 mg of sodium chloride and add distilled water to 100 ml. Weigh 100 mg of sodium chloride and place it in a measuring cylinder, add a little distilled water and stir until the salt is completely dissolved. Then add water to the 100 ml mark and stir thoroughly again.

To experimentally determine conductivity, we used two electrodes made of the same material and with the same dimensions as the TDS-3 electrodes. The measured resistance was 2.5 KOhm.

Now that we know the resistance and ppm concentration of sodium chloride, we can approximately calculate the cell constant of the TDS-3 salinity meter using the formula above:

K = σ/G= 2 mS/cm x 2.5 kOhm = 5 cm⁻¹

This value of 5 cm⁻¹ is close to the calculated constant value of the TDS-3 measuring cell with the electrode dimensions indicated below (see figure).

• D = 0.5 cm - distance between electrodes;
• W = 0.14 cm - width of electrodes
• L = 1.1 cm - length of electrodes

The TDS-3 sensor constant is K = D/A= 0.5/0.14x1.1 = 3.25 cm⁻¹. This is not much different from the value obtained above. Let us remember that the above formula allows only an approximate estimate of the sensor constant.

Do you find it difficult to translate units of measurement from one language to another? Colleagues are ready to help you. Post a question in TCTerms and within a few minutes you will receive an answer.

Distilled water- purified water, practically free of impurities and foreign inclusions. It is obtained by distillation in special apparatus - distillers.

Characteristics

Distilled water is standardized based on GOST 6709-72 “Distilled water”.

Physical

The specific electrical conductivity of distilled water is usually less than 5 µS/cm. The conductivity of deionized water can be less than 0.05 µS/cm.

Distilled water has pH =5.4-6.6

Peculiarities

Being very clean, in the absence of foreign mechanical inclusions, it can be overheated above the boiling point, or supercooled below the freezing point without undergoing a phase transition. The phase transition occurs intensively with the introduction of mechanical impurities or shaking.

Usage

Distilled water is used to adjust electrolyte density, safe battery operation, flushing the cooling system, diluting coolant concentrates and for other household needs. For example, to adjust the freezing temperature of non-freezing windshield washer fluid and for color photo printing.

Harm to human health

Constant consumption of distilled water causes irreparable harm to human health due to the creation of an imbalance of water-salt balance. Imbalance occurs when the pH - the pH value of human blood and distilled water - does not match.

The most important parameter of drinking water for health

pH - pH indicator

pH is a hydrogen indicator (from the Latin words potentia hydrogeni - the strength of hydrogen) - a measure of activity (in the case of dilute solutions, reflects the concentration) of hydrogen ions in a solution, quantitatively expressing its acidity, calculated as a negative (reversed) decimal logarithm of the concentration of hydrogen ions, expressed in moles per liter: pH = -log. Those. pH is determined by the quantitative ratio of H+ and OH- ions in water, formed during the dissociation of water. (A mole is a unit of measurement for the amount of a substance.) In distilled water, pH When the concentrations of both types of ions in a solution are the same, the solution is said to be neutral. When an acid is added to water, the concentration of hydrogen ions increases, and the concentration of hydroxide ions correspondingly decreases; when a base is added, on the contrary, the content of hydroxide ions increases, and the concentration of hydrogen ions decreases. When > the solution is said to be acidic, and when > it is alkaline.
The body balances the pH of internal fluids, maintaining values ​​at a certain level. The acid-base balance of the body is a certain ratio of acids and alkalis in it, which contributes to its normal functioning. The acid-base balance depends on maintaining relatively constant proportions between intercellular and intracellular waters in the tissues of the body. If the acid-base balance of fluids in the body is not constantly maintained, normal functioning and preservation of life will be impossible.
Optimal pH of drinking water = 7.0 to 8.0.
According to Japanese researchers, drinking water with a pH above 7 increases the life expectancy of the population by 20-30%.

How to determine the quality of distilled water? How are indicators analyzed and monitored? The concept of distilled water and its characteristics. Basic chemical indicators of this liquid. Regulatory documents for monitoring the quality of such water. Properties of distilled water and its effect on the human body. Methods of quality control in home and laboratory conditions. The quality of distilled water is checked by the remaining impurities. Analysis and control of indicators is directly related to the composition of the source liquid, the method of producing the distillate, the serviceability of the distillation device, as well as the conditions in which such water is stored.

Concept and characteristics

Distilled water is a liquid purified from substances of inorganic and organic origin. This includes compounds of mineral salts, suspended substances, pathogenic microorganisms, decomposition products from various living organisms, etc. It is important to understand that not every liquid that has undergone the process of evaporation and settled into condensate can be considered a distillate.

Distilled liquid is used to treat people, so its composition and quality are very important. Human health depends on this. In this regard, the quality of distilled water is regulated by standards, namely GOST 6709-72. The main characteristics of distilled water are described in these documents.

Basic indicators for distilled water

Concentration in mg per dm³	Item name
Not > 5	Residues of impurities after evaporation
Not > 0.02	Number of elements of ammonium salts and ammonia particles
Not > 0.2	Proportion of nitrates
Not > 0.5	Presence of sulfates
Not > 0.02	Chlorination level
Not > 0.05	Presence of aluminum particles
Not > 0.05	Iron residues
Not > 0.8	Proportion of calcium elements
Not > 0.02	Presence of copper particles
Not > 0.05	Presence of lead
Not > 0.2	Presence of zinc particles
Not > 0.08	Concentration of reducing elements
5,4-6,6	Liquid acidity
5 x 10 to the -4th power	Specific electrical conductivity of the composition

Distilled water comes in various stages of purification depending on the purpose of the liquid. Analysis of a liquid allows you to very accurately determine the degree of its purification and the presence of various impurities in the composition. So, there is a pyrogen-free liquid, which is distinguished by the complete absence of pyrogenic elements in its composition. These elements include substances of organic origin, as well as various bacterial components. Moreover, these components are able to negatively affect a person, causing symptoms such as increased body temperature, metabolic disorders, changes in the circulatory system, and the like. That is why the distillate, which is intended for the manufacture of injection formulations, must be cleaned of pyrogenic substances.

Distillate properties

It is very important to monitor the effect of the distilled liquid on the human body. As we have already said, the distillate is most often used for human treatment. That is why every pharmacy should keep a log of distilled water analysis. However, despite the medicinal properties of such a liquid, its uncontrolled use is contraindicated, since the composition can have a negative effect on the human body.

If you decide to use distilled water instead of regular drinking water, you risk causing serious harm to your health, namely:

• The distillate is capable of very quickly removing chloride compounds from the human body, which will lead to a persistent deficiency of this microelement.
• Such water can lead to disruption of the volumetric and quantitative balance between liquid volumes in the human body.
• Distilled water does not quench your thirst well, so you will drink more.
• This liquid causes frequent urination, which entails the loss of potassium, sodium and chloride compounds, and their lack in the body.
• The concentration of hormones responsible for water-salt balance is disrupted.

Distilled water quality control

You can control the composition of this liquid in several ways:

1. At home, using compact devices specially designed for this purpose.
2. Control of the amount of organic matter in the composition of water capable of reducing potassium permanganate.
3. Method of monitoring by specific electrical conductivity.

Let's look at each verification method in more detail.

At home, you can check the quality of distilled water using several devices at once. So, to control the hardness of the distillate, a device popularly called a salinity meter (TDS meter) is used. According to GOST number 6702-72, the permissible concentration of salts in distilled water is 5 mg/l. The percentage of chloride content in such water is determined using a chlorometer. According to GOST, this indicator should be equal to 0.02 mg/l. The acidity of water is measured with a pH meter, which allows you to very accurately determine the acid-base balance of the liquid. The norm for this indicator should be in the range of 5.4-6.6 mg/l. The specific electrical conductivity of distilled water is measured with a conductivity meter. The indicator is considered within normal limits if the device shows a value of 500.

The second control method can only be carried out in laboratory conditions. Its essence is that if substances capable of reducing potassium permanganate in a concentration of more than 0.08 mg/dm³ are detected in distilled water, the water is considered to be of poor quality. In such a situation, it is necessary to re-distill it with the addition of the necessary solutions.

A fairly common method for assessing the quality of distilled water is to test it by specific electrical conductivity. An indicator of at least 2 µS/cm indicates a solution of excellent quality.

Do you need to evaluate the quality of distilled water, but don’t have the necessary equipment to conduct the assessment yourself? Then contact our laboratory, where you will undergo all the tests necessary to control the quality of the liquid. To order an analysis, you just need to contact us at the numbers provided. You can check the cost of our services with the manager when you call.

STATE STANDARD OF THE USSR UNION

DISTILLED WATER

TECHNICAL CONDITIONS

GOST 6709-72

IPC PUBLISHING HOUSE OF STANDARDS

STATE STANDARD OF THE USSR UNION

Date of introduction 01.01.74

This standard applies to distilled water obtained in distillation apparatuses and used for the analysis of chemical reagents and the preparation of reagent solutions. Distilled water is a clear, colorless, odorless liquid. Formula: H 2 O. Molecular mass (according to international atomic masses 1971) - 18.01.

1. TECHNICAL REQUIREMENTS

1.1. In terms of physical and chemical indicators, distilled water must meet the requirements and standards specified in the table.

Indicator name
1. Mass concentration of the residue after evaporation, mg/dm 3, no more
2. Mass concentration of ammonia and ammonium salts (NH 4), mg/dm 3, no more
3. Mass concentration of nitrates (KO 3), mg/dm 3, no more
4. Mass concentration of sulfates (SO 4), mg/dm 3, no more
5. Mass concentration of chlorides (C l), mg/dm 3, no more
6. Mass concentration of aluminum (A l), mg/dm 3, no more
7. Mass concentration of iron (Fe), mg/dm 3, no more
8. Mass concentration of calcium (Ca), mg/dm 3, no more
9. Mass concentration of copper (C u), mg/dm 3, no more
10. Mass concentration of lead (P b), %, no more
11. Mass concentration of zinc (Zn), mg/dm 3, no more
12. Mass concentration of substances that reduce CM n O 4 (O), mg/dm 3, no more
13. Water pH
14. Specific electrical conductivity at 20 °C, S/m, no more

(Changed edition, Amendment No. 2).

2. ACCEPTANCE RULES

2.1. Acceptance rules - according to GOST 3885. 2.2. The manufacturer is allowed to determine indicators from 1 to 12 periodically. The frequency of inspection is set by the manufacturer. (Introduced additionally, Amendment No. 2).

3. METHODS OF ANALYSIS

3.1a. General instructions for carrying out the analysis are in accordance with GOST 27025. When weighing, use general-purpose laboratory scales of the types VLR-200 g and VLKT-500 g-M or VLE-200 g. It is allowed to use other measuring instruments with metrological characteristics and equipment with technical characteristics no worse , as well as reagents of quality not lower than those specified in this standard. 3.1. Samples are taken according to GOST 3885. The volume of the average sample must be at least 5 dm 3. 3.1a, 3.1. (Changed edition, Amendment No. 2). 3.2. (Deleted, Amendment No. 1). 3.3. Determination of the mass concentration of the residue after evaporation The determination is carried out according to GOST 27026. To do this, take 500 cm 3 of the analyzed water, measured with a 2-500 cylinder (GOST 1770). Water is considered to comply with the requirements of this standard if the mass of the dry residue does not exceed 2.5 mg. (Changed edition, Amendment No. 2). 3.4. (Deleted, Amendment No. 2). 3.5. Determination of mass concentration of ammonia and ammonium salts (Changed edition, Amendment No. 2). 3.5.1. distilled water according to this standard; checked according to clause 3.3; distilled water, not containing ammonia and ammonium salts; prepared as follows: 500 cm 3 of distilled water is placed in a round-bottom flask of a distillation device, 0.5 cm 3 of concentrated sulfuric acid is added, heated to a boil and 400 cm 3 of liquid is distilled off, discarding the first 100 cm 3 of distillate. Water that does not contain ammonia and ammonium salts is stored in a flask closed with a stopper with a “goose” containing a solution of sulfuric acid; sulfuric acid according to GOST 4204, concentrated and solution 1:3; sodium hydroxide, solution with a mass fraction of 20%, not containing ammonia; prepared according to GOST 4517; Nessler's reagent: prepared according to GOST 4517; solution containing NH 4 ; prepared according to GOST 4212; by appropriate dilution prepare a solution containing 0.001 mg/dm 3 NH 4 ; a distillation device consisting of a round-bottomed flask with a capacity of 1000 cm 3 refrigerator with a splash trap and a receiving flask; flat-bottomed test tube made of colorless glass with a ground stopper, diameter 20 mm and capacity 120 cm 3; pipette 4(5)-2-1(2) and 6(7)-2-5(10) according to GOST 29169; cylinder 1(3)-100 and 1-500 according to GOST 1770. (Changed edition, Amendment No. 1, 2). 3.5.2. Carrying out analysis 100 cm 3 of the water being analyzed is placed in a cylinder in a test tube, 2.5 cm 3 of sodium hydroxide solution is added and mixed. Then add 1 cm 3 of Nessler's reagent and mix again. Water is considered to comply with the requirements of this standard if the color of the analyzed solution observed after 20 minutes along the axis of the test tube is not more intense than the color of the reference solution prepared simultaneously with the analyzed solution and containing in the same volume: 100 cm 3 of water not containing ammonia and ammonium salts, 0.002 mg NH 4, 2.5 cm 3 sodium hydroxide solution and 1 cm 3 Nessler's reagent. 3.6. Determination of mass concentration of nitrates 3.5.2, 3.6. (Changed edition, Amendment No. 2). 3.6.1. distilled water according to this standard, tested according to clause 3.3; indigo carmine; the solution is prepared according to GOST 10671.2; sulfuric acid according to GOST 4204, chemical grade; sodium hydroxide according to GOST 4328, chemical grade, concentration solution With(NaOH) = 0.l mol/dm 3 (0.1 N), prepared according to GOST 25794.1 without establishing an adjustment factor; sodium chloride according to GOST 4233, solution with a mass fraction of 0.25%; solution containing NO 3; prepared according to GOST 4212; a solution containing 0.01 mg/cm 3 NO 3 is prepared by appropriate dilution; flask Kn-1-50-14/23 THS or Kn-2-50-18 THS according to GOST 25336; pipettes 4(5)-2-1 and 6(7)-2-5(10, 25) according to GOST 29169-91; evaporation cup 2 according to GOST 9147 or cup 50 according to GOST 19908; cylinder 1(3)-25(50) according to GOST 1770. 3.6.2. Carrying out analysis 25 cm 3 of the analyzed water is placed with a pipette in a cup, 0.05 cm 3 of sodium hydroxide solution is added, mixed and evaporated to dryness according to paragraph 3.3. The cup is immediately removed from the bath, 1 cm 3 of sodium chloride solution, 0.5 cm 3 of indigo carmine solution are added to the dry residue, and 5 cm 3 of sulfuric acid is added carefully while stirring. After 15 minutes, the contents of the cup are transferred quantitatively into a conical flask, the cup is rinsed in two doses with 25 cm 3 of distilled water, adding it to the main solution, and the contents of the flask are mixed. Water is considered to comply with the requirements of this standard if the color of the analyzed solution is not weaker than the color of the reference solution prepared as follows: 0.5 cm 3 of a solution containing 0.005 mg NO 3, 0.05 cm 3 of sodium hydroxide solution are placed in an evaporation cup and evaporated to dryness in a water bath. The cup is immediately removed from the water bath; then the dry residue is processed in the same way simultaneously with the dry residue obtained after evaporation of the analyzed water, adding the same amounts of reagents in the same order. 3.6.1, 3.6.2. (Changed edition, Amendment No. 1, 2). 3.7. Determination of mass concentration of sulfates (Changed edition, Amendment No. 2). 3.7.1. Reagents, solutions and equipment: distilled water according to this standard, tested according to clause 3.3; barium chloride according to GOST 4108, solution with a mass fraction of 10%; hydrochloric acid according to GOST 3118, concentration solution With(HC1) = 1 mol/dm 3 (1 n.), prepared according to GOST 25794.1 without establishing a correction factor; solution containing SO 4 ; prepared according to GOST 4212 on the water being analyzed by appropriately diluting the main solution with the same water to obtain a solution with a SO 4 concentration of 0.01 mg/cm 3 ; Rectified technical ethyl alcohol according to GOST 18300; pipettes 4(5)-2-2 and 6(7)-2-5(10) according to GOST 29169; glass V-1-50 TS according to GOST 25336; cylinder 1(3)-50 according to GOST 1770. 3.7.2. Carrying out analysis 40 cm 3 of the analyzed water is placed in a cylinder in a glass (with a 10 cm 3 mark) and evaporated on an electric stove to the mark. Then cool, add slowly with stirring 2 cm 3 of ethyl alcohol, 1 cm 3 of hydrochloric acid solution and 3 cm 3 of barium chloride solution, previously filtered through an ash-free “blue ribbon” filter. Water is considered to comply with the requirements of this standard if the opalescence of the analyzed solution, observed against a dark background after 30 minutes, is not more intense than the opalescence of a reference solution prepared simultaneously with the analyzed solution and containing: 10 cm 3 of analyzed water containing 0.015 mg SO 4, 2 cm 3 ethyl alcohol, 1 cm 3 of hydrochloric acid solution and 3 cm 3 of barium chloride solution. 3.7.1, 3.7.2. (Changed edition, Amendment No. 1, 2). 3.8. Determination of mass concentration of chlorides 3.8.1. Reagents, solutions and equipment: distilled water according to this standard, tested according to clause 3.3; nitric acid according to GOST 4461, solutions with mass fractions of 25 and 1%; prepared according to GOST 4517; sodium carbonate according to GOST 83, solution with a mass fraction of 1%; silver nitrate according to GOST 1277; solution with a mass fraction of about 1.7%; solution containing Cl; prepared according to GOST 4212; a solution containing 0.001 mg/cm 3 C l is prepared by appropriate dilution; test tube P4-15-14/23 HS according to GOST 25336; pipettes 4(5)-2-1 and 6(7)-2-5(10) according to GOST 29169; evaporation cup 3 according to GOST 9147 or cup 100 according to GOST 19908; cylinder 1(3)-50 according to GOST 1770. 3.8.2. Carrying out analysis 50 cm 3 of the analyzed water is placed in a cylinder in an evaporation cup, 0.1 cm 3 of sodium carbonate solution is added and evaporated to dryness according to clause 3.3. The residue is dissolved in 3 cm 3 of water; if the solution is cloudy, it is filtered through an ash-free “blue ribbon” filter, washed with a hot solution of nitric acid with a mass fraction of 1%, and transferred to a test tube. The cup is washed with 2 cm 3 of water, adding the washing water to the solution, adding 0.5 cm 3 of a solution of nitric acid with a mass fraction of 25% and 0.5 cm 3 of a solution of silver nitrate with stirring. Water is considered to comply with the requirements of this standard if the opalescence of the analyzed solution observed after 20 minutes against a dark background is not more intense than the opalescence of a reference solution prepared simultaneously with the analyzed solution and containing in the same volume: 0.001 mg Cl, 0.1 cm 3 sodium carbonate solution, 0.5 cm 3 solution of nitric acid with a mass fraction of 25% and 0.5 cm 3 solution of silver nitrate. 3.8.1, 3.8.2. (Changed edition, Amendment No. 1, 2). 3.9. Determination of the mass concentration of aluminum using stilbazo (Changed edition, Amendment No. 2). 3.9.1. Reagents, solutions and equipment: distilled water according to this standard, tested according to clause 3.3; ascorbic acid (vitamin C) solution with a mass fraction of 5%, freshly prepared; acetate buffer solution pH 5.4; prepared according to GOST 4919.2; hydrochloric acid according to GOST 3118, concentration solution With(HC l) = 0.1 mol/dm 3 (0.1 n.); prepared according to GOST 25794.1 without establishing an adjustment factor; solution containing A l; prepared according to GOST 4212; a solution containing 0.001 mg/cm 3 A l is prepared by appropriate dilution; stilbazo, solution with a mass fraction of 0.02%; good for two months; pipettes 4(5)-2-1(2) and 6(7)-2-5(10) according to GOST 29169; test tube P4-15-14/23 HS according to GOST 25336; evaporation cup No. 2 according to GOST 9147 or cup 40(50) according to GOST 19908; cylinder 1(3)-25(50) according to GOST 1770. 3.9.2. Carrying out analysis 20 cm 3 of the analyzed water is placed in a cylinder in an evaporation cup and evaporated to dryness according to clause 3.3. 0.25 cm 3 of hydrochloric acid solution is added to the residue, 2.25 cm 3 of water is quantitatively transferred into a test tube, and 0.15 cm 3 of ascorbic acid solution, 0.5 cm 3 of stilbazo solution and 5 cm 3 of acetate buffer solution are added with stirring. Water is considered to comply with the requirements of this standard if the color of the analyzed solution after 10 minutes is not more intense than the color of the reference solution prepared simultaneously with the analyzed solution and containing in the same volume: 0.001 mg Al, 0.25 cm 3 hydrochloric acid solution, 0.15 cm 3 solutions of ascorbic acid, 0.5 cm 3 stilbazo solution and 5 cm 3 buffer solution. 3.9.1, 3.9.2. (Changed edition, Amendment No. 1, 2). 3.9a. Determination of mass concentration of aluminum using xylenol orange 3.9a.1. Reagents, solutions and equipment: distilled water according to this standard, tested according to clause 3.3; acetate buffer solution pH 3.4; prepared according to GOST 4919.2; hydrochloric acid according to GOST 3118, chemical grade, concentration solution With(HC l) = 0.1 mol/dm 3 (0.1 n.); prepared according to GOST 25794.1 without establishing an adjustment factor; xylenol orange, solution with a mass fraction of 0.1%; prepared according to GOST 4919.1; solution containing A l; prepared according to GOST 4212; a solution containing 0.001 mg/cm 3 A l is prepared by appropriate dilution; flask Kn-1-50-14/23 THS or Kn-2-50-18 THS according to GOST 25336; pipettes 4(5)-2-1 and 6(7)-2-5(10) according to GOST 29169; evaporation cup No. 3 according to GOST 9147 or cup 100 according to GOST 19908; cylinder 1(3)-100 according to GOST 1770. 3.9a.2. Carrying out analysis 60 cm 3 of the analyzed water is placed in a cylinder in an evaporation cup and evaporated to dryness according to clause 3.3. The residue is dissolved in 0.25 cm 3 of hydrochloric acid solution, 2 cm 3 of water and quantitatively transferred 8 cm 3 of water into a conical flask. Then 10 cm 3 of acetate buffer solution and 1 cm 3 of xylenol orange solution are added to the solution, the flask is placed in a water bath (80 °C) for 5 minutes and cooled. Water is considered to comply with the requirements of this standard if the pinkish-orange color of the pink tint observed in transmitted light against the background of milky glass is no more intense than the color of the reference solution prepared simultaneously with the test solution and containing 0.003 mg Al, 0.25 cm in the same volume of water 3 solutions of hydrochloric acid, 10 cm 3 of acetate buffer solution and 1 cm 3 of xylenol orange solution. 3.9a. - 3.9a.2. (Changed edition, Amendment No. 1, 2). 3.10. Determination of mass concentration of iron (Changed edition, Amendment No. 2). 3.10.1. Reagents, solutions and equipment: distilled water according to this standard, tested according to clause 3.3; ammonium persulfate according to GOST 20478, solution with a mass fraction of 5%, freshly prepared; ammonium thiocyanate according to GOST 27067, a solution with a mass fraction of 30%, purified from iron by extraction with isoamyl alcohol (extraction is carried out after acidifying the solution with a solution of sulfuric acid until the alcohol layer becomes discolored); sulfuric acid according to GOST 4204, chemically pure, solution with a mass fraction of 20%; solution containing Fe; prepared according to GOST 4212; a solution containing 0.001 mg/cm 3 Fe is prepared by appropriate dilution; isoamyl alcohol according to GOST 5830; pipettes 4(5)-2-1(2) and 6(7)-2-5(10) according to GOST 29169; a test tube made of colorless glass with a ground stopper with a capacity of 100 cm 3 and a diameter of 20 mm; cylinder 1(3)-50(100) according to GOST 1770. (Changed edition, Amendment No. 1, 2). 3.10.2. Carrying out analysis 40 cm 3 of the analyzed water is placed in a cylinder in a test tube, 0.5 cm 3 of sulfuric acid solution, 1 cm 3 of ammonium persulfate solution, 3 cm 3 of ammonium thiocyanate solution are added, mixed, 3.7 cm 3 of isoamyl alcohol is added, thoroughly mixed and kept until stratification of the solution. Water is considered to comply with the requirements of this standard if the observed color of the alcohol layer of the analyzed solution is not more intense than the color of the alcohol layer of the reference solution prepared simultaneously with the analyzed solution in the same way and containing: 20 cm 3 of the analyzed water, 0.001 mg of Fe, 0.25 cm 3 of sulfuric solution acid, 1 cm 3 of ammonium persulfate solution, 1.5 cm 3 of ammonium thiocyanate solution and 3 cm 3 of isoamyl alcohol. 3.11. Determination of mass concentration of calcium 3.10.2, 3.11. (Changed edition, Amendment No. 2). 3.11.1. Reagents, solutions and equipment: distilled water according to this standard, tested according to clause 3.3; hydrochloric acid according to GOST 3118, solution with a mass fraction of 10%; prepared according to GOST 4517; murexide (ammonium salt of purple acid), solution with a mass fraction of 0.05%; good for two days; sodium hydroxide according to GOST 4328, concentration solution With(NaOH) = 1 mol/dm 3 (1 N), prepared according to GOST 25794.1 without establishing a correction factor; solution containing Ca; prepared according to GOST 4212; a solution containing 0.01 mg/cm 3 Ca is prepared by appropriate dilution; test tubes P4-15-14/23 HS according to GOST 25336; pipettes 4(5)-2-1 and 6(7)-2-5(10) according to GOST 29169; evaporation cup 1 according to GOST 9147 or cup 20 according to GOST 19908; cylinder 1(3)-25(50) according to GOST 1770. 3.11.2. Carrying out analysis 10 cm 2 of the analyzed water is placed in a cylinder in an evaporation cup and evaporated to dryness according to clause 3.3. The dry residue is treated with 0.2 cm 3 of hydrochloric acid solution and quantitatively transferred 5 cm 3 of water into a test tube. Then add 1 cm 3 of sodium hydroxide solution, 0.5 cm 3 of murexide solution and mix. Water is considered to comply with the requirements of this standard if the pinkish-violet color of the analyzed solution observed after 5 minutes is not more intense than the color of the reference solution, prepared simultaneously with the analyzed solution and containing in the same volume: 0.008 mg Ca, 0.2 cm 3 saline solution acid, 1 cm 3 sodium hydroxide solution and 0.5 cm 3 murexide solution. 3.11.1, 3.11.2. (Changed edition, Amendment No. 1, 2). 3.12. Determination of mass concentration of copper (Changed edition, Amendment No. 2). 3.12.1. Reagents, solutions and equipment: distilled water according to this standard, tested according to clause 3.3; sodium N, N-diethyldithiocarbamate 3-water according to GOST 8864, solution with a mass fraction of 0.1%; freshly prepared; hydrochloric acid according to GOST 3118, solution with a mass fraction of 25%; prepared according to GOST 4517; solution containing Cu; prepared according to GOST 4212; a solution containing 0.001 mg/cm 3 Cu is prepared by appropriate dilution; isoamyl alcohol according to GOST 5830; a test tube made of colorless glass with a ground stopper with a capacity of 100 cm 3 and a diameter of 20 mm or a cylinder 2(4)-100 according to GOST 1770; pipette 4(5)-2-1(2) and 6(7)-2-5(10) according to GOST 29169; cylinder 1(3)-50(100) according to GOST 1770. (Changed edition, Amendment No. 1, 2). 3.12.2. Carrying out analysis 50 cm 3 of the analyzed water is placed in a cylinder in a test tube, 1 cm 3 of hydrochloric acid solution is added, stirred, 3.8 cm 3 of isoamyl alcohol and twice 1 cm 3 of a solution of 3-aqueous N,N-diethyldithiocarbamate sodium are added, stirring immediately after adding each portions of a solution of 3-aqueous N,N-sodium diethyldithiocarbamate for 1 min and incubated until separation. Water is considered to comply with the requirements of this standard if the observed color of the alcohol layer of the analyzed solution is not more intense than the color of the alcohol layer of the reference solution prepared simultaneously with the analyzed solution in the same way and containing: 25 cm 3 of the analyzed water, 0.0005 mg of Cu, 1 cm 3 of saline solution acid, 3 cm 3 isoamyl alcohol and 2 cm 3 solution of 3-aqueous N,N-diethyldithiocarbamate sodium. 3.13. Determination of lead mass concentration 3.12.2, 3.13. (Changed edition, Amendment No. 2). 3.13.1. Reagents, solutions and equipment: distilled water according to this standard, tested according to clause 3.3; acetic acid according to GOST 61, chemically pure, solution with a mass fraction of 10%; potassium ferric sulfide 3-water according to GOST 4207, solution with a mass fraction of 1%, freshly prepared; sodium tetraborate 10-water according to GOST 4199, concentration solution With(Na 2 B 4 O 7 10 H 2 O) = 0.05 mol/dm 3 ; solution containing Pb; prepared according to GOST 4212; a solution containing 0.001 mg/cm 3 Pb is prepared by appropriate dilution; sulfarsazen (indicator), solution prepared according to GOST 4919.1; pipettes 4(5)-2-1(2) and 6(7)-2-5(10) according to GOST 29169; test tube P4-15-14/23 HS according to GOST 25336; evaporation cup 2 according to GOST 9147 or cup 50 according to GOST 19908; cylinder 1(3)-25(50) according to GOST 1770. 3.13.2. Carrying out analysis 20 cm 3 of the analyzed water is placed in a cylinder in an evaporation cup and evaporated to dryness according to clause 3.3. The dry residue is treated with 1 cm 3 of acetic acid solution and again evaporated to dryness. Then the cup is cooled, the residue is moistened with 0.1 cm 3 of acetic acid solution, quantitatively transfer 3 cm 3 of water into a test tube, add 0.2 cm 3 of potassium ferric sulfide solution, 0.25 cm 3 of sulfarsazene solution, mix, add 2 cm 3 of tetraborate solution sodium and mix again. Water is considered to comply with the requirements of this standard if the color of the analyzed solution, observed along the axis of the test tube in transmitted light on a white background, will not be more intense than the color of the reference solution prepared simultaneously with the analyzed solution and containing in the same volume: 0.001 mg P b, 0.1 cm 3 solutions of acetic acid, 0.2 cm 3 solution of potassium ferrous sulfide, 0.25 cm 3 solution of sulfarsazen and 2 cm 3 solution of sodium tetraborate. 3.13.1, 3.13.2. (Changed edition, Amendment No. 1, 2). 3.14. Determination of mass concentration of zinc (Changed edition, Amendment No. 2). 3.14.1. Reagents, solutions and equipment: distilled water according to this standard, tested according to clause 3.3; aqueous ammonia according to GOST 3760, solution with a mass fraction of 5%, freshly prepared; tartaric acid according to GOST 5817, solution with a mass fraction of 10%; citric acid monohydrate and anhydrous according to GOST 3652, solution with a mass fraction of 10%; solution containing Zn; prepared according to GOST 4212; a solution containing 0.001 mg/cm 3 Zn is prepared by appropriate dilution; sulfarsazen, solution with a mass fraction of 0.02%; prepared as follows: 0.02 g of sulfarsazen is dissolved in 100 cm 3 of water and 1 - 2 drops of ammonia solution are added; pipettes 4(5)-2-1(2) and 6(7)-2-5(10) according to GOST 29169; test tube P4-15-14/23 HS according to GOST 25336; evaporation cup 1 according to GOST 9147 or cup 20 according to GOST 19908; cylinder 1-10 according to GOST 1770 or pipette 6(7)-2-5(10) according to GOST 29169. (Changed edition, Amendment No. 1, 2). 3.14.2. Carrying out analysis 5 cm 3 of the analyzed water is placed with a cylinder or pipette in an evaporation cup and evaporated to dryness according to clause 3.3. The cup is cooled, the dry residue is transferred quantitatively to 3 cm 3 of water into a test tube, and 0.8 cm 3 of tartaric acid solution, 0.2 cm 3 of citric acid solution, 0.8 cm 3 of ammonia solution and 0.5 cm 3 of sulfarsazene solution are added with stirring. . Water is considered to comply with the requirements of this standard if the color of the analyzed solution, observed along the axis of the test tube, in transmitted light on a white background is not more intense than the color of the standard solution prepared simultaneously with the analyzed solution and containing in the same volume: 0.001 mg Zn, 0.8 cm 3 tartaric acid solution, 0.2 cm 3 citric acid solution, 0.8 cm 3 ammonia solution and 0.5 cm 3 sulfarsazen solution. 3.15. Determination of the mass concentration of substances that reduce potassium permanganate 3.14.2, 3.15. (Changed edition, Amendment No. 2). 3.15.1. Reagents, solutions and equipment: distilled water according to this standard, tested according to clause 3.3; potassium permanganate according to GOST 20490, concentration solution With(1/5 KM n O 4) = 0.01 mol/dm 3 (0.01 N), freshly prepared, prepared according to GOST 25794.2; sulfuric acid according to GOST 4204, solution with a mass fraction of 20%, prepared according to GOST 4517; flask Kn-1-500-24/29 THS or Kn-2-500-34 THS according to GOST 25336; pipettes 4(5)-2-1 and 6(7)-2-5 according to GOST 29169; cylinder 1(3)-250 according to GOST 1770. 3.15.2. Carrying out analysis 250 cm 3 of the water being analyzed is placed in a cylinder in a flask, 2 cm 3 of sulfuric acid solution and 0.25 cm 3 of potassium permanganate solution are added and boiled for 3 minutes. Water is considered to comply with the requirements of this standard if, when observed in transmitted light against a white background, a pink color is noticeable in the analyzed solution when compared with an equal volume of the same water to which the above reagents have not been added. 1 cm 3 solution of potassium permanganate, concentration exactly With(KM n O 4) = 0.01 mol/dm 3 corresponds to 0.08 mg of oxygen. 3.15.1, 3.15.2. (Changed edition, Amendment No. 1, 2). 3.16. Determination of water pH is carried out using a universal EV-74 ion meter with a glass electrode at 20 °C. (Changed edition, Amendment No. 2). 3.17. Specific electrical conductivity is determined using a conductometer of any type at 20 °C.

4. STORAGE

4.1. Water is stored in hermetically sealed polyethylene and fluoroplastic bottles or other containers that ensure stable water quality. (Changed edition, Amendment No. 2).

INFORMATION DATA

Good afternoon
Tell me, is there any theoretical method for determining the conductivity of water with compounds dissolved in it, if the initial conductivity of water and the exact quantitative content of compounds dissolved in water are known.

Thank you in advance!

Accurate calculation of specific electrical conductivity is carried out using special empirical formulas using calibrated solutions of potassium chloride with a previously known value of electrical conductivity. It is customary to display the measured value using the Siemens unit of measurement, 1 cm is the inverse of 1 ohm. Moreover, for salt water the research results are displayed in S/m, and for fresh water – in µS/meter, that is, in microsiemens. Measurement of electrical conductivity of aqueous solutions gives for distilled water a SEP value from 2 to 5 μS/meter, for atmospheric precipitation a value from 6 to 30 or more μS/meter, and for fresh river and lake waters in those areas where the air environment is heavily polluted, the SEP value can vary by within 20-80 µS/cm.

To mitigate this problem, four electrodes are often used instead of two. Electrode polarization can be prevented or reduced by applying alternating current and adjusting the measurement frequency. Low frequencies are used to measure low conductivity, where the polarization resistance is relatively small. Higher frequencies are used to measure high conductivity values. Modern digital two-electrode conductivity meters typically use complex AC waveforms and temperature compensation.

To approximate the SEP, you can use the empirically found relationship between the SEP and the salt content in water (salinity):

UEP ( µS/cm ) = salt content (mg / l) / 0,65

That is, to determine the SEP (μS/cm), the salt content (water mineralization) (mg/l) is divided by a correction factor of 0.65. The value of this coefficient varies depending on the type of water in the range of 0.55-0.75. Sodium chloride solutions conduct current better: NaCl content (mg/l) = 0.53 µS/cm or 1 mg/l NaCl provides electrical conductivity of 1.9 µS/cm.

Experiment: measuring total mineralization and conductivity

They are factory calibrated and often require recalibration in the field as the cell constant changes over time. It may be altered due to contamination or physicochemical modification of the electrodes. In a traditional two-electrode conductivity meter, an alternating voltage is applied between two electrodes and the resulting current is measured. This meter, although simple, has one drawback - it measures not only the resistance of the solution, but also the resistance caused by the polarization of the electrodes.

For an approximate calculation of the UEP based on the salt content in water (salinity), you can use the following graph (Fig. 1):

Rice. 1. Graph of the dependence of the electrical energy consumption on the salt content (salinity) in water.

The electrical resistance is also measured using a special device - a conductometer, consisting of platinum or steel electrodes immersed in water, through which an alternating current with a frequency of 50 Hz (in low-mineralized water) to 2000 Hz or more (in salt water) is passed, by measuring electrical resistance .

To minimize the effects of polarization, 4-electrode cells are often used, as well as platinized cells coated with platinum black. Electrical conductivity measuring devices are often used to measure total dissolved solids. It is a measure of the total mass of all organic and inorganic substances contained in a liquid in various forms: ionized, molecular, colloidal and suspended. Dissolved solids refer to any inorganic salts, mainly calcium, potassium, magnesium, sodium, chlorides, bicarbonates and sulfates and some organic matter dissolved in water.

The principle of operation of the conductometer is based on the direct dependence of the electrical conductivity of water (current strength in a constant electric field created by the electrodes of the device) on the amount of compounds dissolved in water. A wide range of appropriate equipment now makes it possible to measure the conductivity of almost any water, from ultrapure (very low conductivity) to saturated with chemical compounds (high conductivity).

Total dissolved solids are usually measured in water to determine its quality. There are two main methods for measuring total dissolved solids: gravimetric analysis, which is the most accurate method, and conductivity measurement.

The second method is not as accurate as gravimetric analysis. However, the conductivity method is the most convenient, useful, widespread and fast method because it is a simple measurement of conductivity and temperature that can be done in a few seconds using an inexpensive device. This method can be used because the electrical conductivity of water is directly related to the concentration of ionized substances dissolved in the water. This is especially useful for quality control purposes such as monitoring drinking water or estimating the total number of ions in a solution.

A conductivity meter can even be purchased at pet stores, and combinations of such a device with a pH meter are possible. In addition, such a device can be purchased at offices and companies selling equipment for environmental research www.tdsmeter.ru/com100.html.

Craftsmen who are good with a soldering iron can make their own device for measuring the electrical conductivity of I.I. Vanyushin’s design. (magazine "Fisheries", 1990, No. 5, pp. 66-67. In addition, this device and methods for its calibration are described in all details in the very useful book "Modern Aquarium and Chemistry", authors I.G. Khomchenko , A.V. Trifonov, B.N. Razuvaev, Moscow, 1997). The device is made on the common K157UD2 microcircuit, which consists of two operational amplifiers. The first one houses an alternating current generator, the second one houses an amplifier according to a standard circuit, from which readings are taken with a digital or analog voltmeter (Fig. 2).

Production and quality control of distilled water

Conductivity measurements are temperature dependent, i.e. As the temperature increases, conductivity also increases because the ions in the solution move faster. To obtain temperature-independent measurements, the concept of reference temperature was introduced. This allows conductivity results to be compared at different temperatures. If very high accuracy is required, the sample can be placed in an oven and the meter will then be calibrated to the exact same temperature used for the measurement.

Rice. 2. Homemade conductivity meter.

To eliminate the influence of temperature, electrical conductivity measurements are carried out at a constant temperature of 20 0 C, since the value of electrical conductivity and the measurement result depend on temperature, as soon as the temperature increases by at least 1 0 C, the measured value of electrical conductivity also increases by approximately 2%. Most often, it is recalculated in relation to 20 0 C according to the correction table, or reduced to it using empirical formulas.

Most modern conductivity meters contain a built-in temperature sensor that can be used for temperature correction as well as temperature measurement. However, they all only measure conductivity and temperature, and then calculate the required physical value and perform temperature compensation.

The same brand name device, probably made in the same factory, would cost 10 times more. But this is for those who like to pay only for the brand name. It should be noted that the two actual physical values ​​that this device measures are the resistance of the solution between the two electrodes and the temperature of the solution.

Correction table for calculating UEP.

Temperature, °C	Correction factor	Temperature, °C	Correction factor	Temperature, °C	Correction factor

The calculation of the specific electrical conductivity of water in this case is carried out using the formula :

This is a dimensionless quantity. Just as percentage means out of a hundred, parts per million units means out of a million. We will discuss these calculations below. Examples of substances with high salt concentrations are some foods and sea water. This is only the normal concentration of salt in many foods.

There are many different scales in many industries. The difference between them lies in their use. For our experiment, we will first measure the total dissolved solids in distilled water. To prepare 100 ml of solution, we need 100 mg of sodium chloride and up to 100 ml of distilled water. To make the solution, we place sodium chloride in a measuring cylinder, add some distilled water and stir until the sodium chloride is completely dissolved. Then add distilled water to the 100 ml mark and mix well again.

UEP = C p / R

where C p is the capacitance of the device sensor, which depends on the material and size of the electrodes and has a dimension of cm-1, determined when calibrating the device using solutions of potassium chloride with a known value of electrical conductivity; K is the temperature coefficient for bringing the measured value at any temperature to its accepted constant value; R is the measured electrical resistance of water by the device, in Ohms.

This is slightly less than the value of 5 cm-1. Note that the formula for calculating the cell constant can only give an approximate value. Do you have difficulty translating a unit of measurement into another language? Electrical conductivity estimates the amount of all dissolved salts or the total number of dissolved ions in water.

What in the world are microspheres per centimeter? These are units of electrical conductivity. The sensor simply consists of two metal electrodes that are exactly 0 cm apart and protrude into the water. A constant voltage is applied to the electrodes. An electrical current flows through the water due to this voltage and is proportional to the concentration of dissolved ions in the water - the more ions, the more conductive the water is resulting in a higher electrical current, which is measured electronically. Distilled or deionized water has very few dissolved ions and therefore almost no current flowing through the gap.

The device must be calibrated in resistance values. For calibration, the following resistances can be recommended: 1 kOhm (electrical conductivity 1000 µS), 4 kOhm (250 µS), 10 kOhm (100 µS).

In order to more accurately determine the specific electrical conductivity, you need to know the constant of the vessel for measuring CX. To do this, it is necessary to prepare a 0.01 M solution of potassium chloride (KCl) and measure its electrical resistance R KCl, (in kOhm) in the prepared cell. The capacity of the vessel is determined by the formula:

Classification of salt waters

You will find both sets of units in published scientific literature, although their numerical values ​​are identical. It is simply a scale symbol, from 0 to 14, that rates aqueous solutions based on their acidity or alkalinity. Pure water is given the number 7 - right in the middle of the scale - because it contains equal amounts of acidic and basic ions and is therefore neutral. As the alkalinity of a solution increases, the pH value increases; As acidity increases, pH decreases. Each step represents an increase or decrease by a factor of ten.

C p = R KC UEP KCl

where SEP KC is the specific electrical conductivity of a 0.01 M KCl solution at a given temperature in μS/cm, found from the correction table.

The UEP is then calculated using the formula:

UEP =C P (K T )/R

The pH of a water sample is a measure of the concentration of hydrogen ions. The term pH was derived from how the concentration of hydrogen ions is calculated - it is the negative logarithm of the concentration of hydrogen ions. What this means for those of us who are not mathematicians is that at higher pH there are fewer free hydrogen ions and that a change in one unit of pH represents a tenfold change in hydrogen ion concentrations. For example, the number of hydrogen ions is 10 times greater at pH 7 than at pH 7.

Establishing the value of total water mineralization

The pH range from 0 to a pH of 7 is considered neutral. Substances with a pH less than 7 are acidic; substances with a pH greater than 7 are basic. For example, in addition to influencing how much and what form of phosphorus is most abundant in water, pH can also determine whether aquatic life can use it. In the case of heavy metals, the degree of their solubility determines their toxicity.

where C p is the capacitance of the device sensor, which depends on the material and size of the electrodes and has a dimension of cm -1, is determined by calibrating the device using solutions of potassium chloride with a known value of the electrical conductivity; K t - temperature coefficient for bringing the measured value at any temperature to its accepted constant value; R is the measured electrical resistance of water by the device, in Ohms.

Metals tend to be more toxic at lower pH because they are more soluble. No need to adjust normally Easy to operate Reliable and stable Easy to carry. Deionized water is often used for precision cleaning. It's a proven process, but with a number of hidden pitfalls.

In general, there are three general levels of water: tap water, distilled water, and deionized water. From a precision cleaning standpoint, neither tap water nor distilled water are clean enough to do the job, as they are contaminated to a greater or lesser extent with minerals and organic matter.

The SEP of salt water is usually expressed in S/m (Sm - Siemens, the reciprocal of Ohm), for fresh water - in microsiemens (µS/cm). The SER of distilled water is 2-5 µS/cm, atmospheric precipitation - from 6 to 30 µS/cm or more, in areas with heavily polluted air, river and fresh lake waters 20-800 µS/cm.

The normalized mineralization values ​​approximately correspond to a specific electrical conductivity of 2 mS/cm (1000 mg/dm 3) and 3 mS/cm (1500 mg/dm 3) in the case of both chloride (in terms of NaCl) and carbonate (in terms of CaCO 3 ). mineralization.

Double-strand deionizers use separate tanks, one containing a cationic resin and another containing an anionic resin. Obviously, costs, energy consumption, end-to-end and control issues will increase exponentially as water purity increases. The purer the water, the hungrier it is for ions, and the more contaminants it will attract unless packaging and processing are tightly controlled.

Now you haven't specified any specifics of the application you were working on. If the water is clean enough to be a harsh cleaner, it will instantly become dirty as soon as the bottle or container is opened, at which point you can also clean with distilled water and save some money.

Pure water, as a result of its own dissociation, has a specific electrical conductivity at 25 C equal to 5.483 µS/m.

For more information about the methods for calculating the UEP, see the relevant sections of our website.

Ph.D. O.V. Mosin

Below are methodological methods for calculating total mineralization, ionic strength, hardness and determining the content of sulfate ions in natural and waste waters based on specific electrical conductivity as a general indicator of their quality.

This was because they found that after an hour or so the cleaning stopped no matter how long they ran the machines. The only viable option is a tightly closed loop system that treats the water, performs the treatment, and then recycles the water. They tend to be expensive, power hungry, and relatively slow end-to-end.

The reverse osmosis filter removes additional contaminants, while the mixed bed resin filter removes the final dissolved minerals. If you are cleaning high quality semiconductor final cleaning of optics or high end medical devices, then Type 1 is the right choice.

Determining the electrical conductivity (L) of water comes down to measuring its inverse value - the resistance (R) that water provides to the current passing through it. Thus, L= 1:R, and therefore the electrical conductivity value is expressed in inverse Ohms, and according to the modern SI classification - in Siemens (Sm).

The value of specific electrical conductivity remains unchanged within the permissible error (10%) in the presence of organic compounds of various natures (up to 150 mg/dm3) and suspended substances (up to 500 mg/dm3) in natural and waste waters.

How filtration and reverse osmosis systems work. Cartridge filter Next is the cartridge type filter. This type of filter usually has a removable housing into which different types of "elements" can be placed. The sediment filter cartridge element can be manufactured to remove particles of a certain size or larger. Most industrial and laboratory use items indicate removal of 15 to 15 microns or more. and add after it the words “Absolute”. This simply means that if it says it is 5 microns, it means!

To measure specific electrical conductivity (xi), any conductivity meters with a range from 1*10(-6) S/cm to 10*10(-2) S/cm can be used.

1. PRODUCTION AND QUALITY CONTROL OF DISTILLED WATER

1.1. QUALITY STANDARDS

In laboratories for quality control of natural and waste waters, distilled water is the main solvent for the preparation of reagents, a diluent for test samples, an extractant, and is also used for rinsing laboratory glassware. Therefore, for the successful operation of any chemical analytical laboratory, along with the fulfillment of such conditions as highly qualified specialists, the availability of accurate verified instruments, the use of reagents of the required degree of purity, standard samples and standard measuring glassware, great attention should be paid to the quality of distilled water, which in its own way physical and chemical parameters must comply with the requirements of GOST 670972 (see table).

STANDARDS

QUALITY OF DISTILLED WATER BY

pH ¦ 5.4-6.6 ¦

Substances that reduce KMnO4 ¦ 0.08 ¦

Residue after evaporation ¦ 5.0 ¦

Residue after ignition ¦ 1.0 ¦

Ammonia and ammonium salts ¦ 0.02 ¦

Nitrates ¦ 0.20 ¦

Sulfates ¦ 0.50 ¦

Chlorides ¦ 0.02 ¦

Aluminum ¦ 0.05 ¦

Iron ¦ 0.05 ¦

Calcium ¦ 0.80 ¦

Copper ¦ 0.02 ¦

Lead ¦ 0.05 ¦

Zinc ¦ 0.20 ¦

Specific electrical conductivity at 20 degrees. C no more than 5*10(-6) cm/cm

If all indicators comply with established standards, then distilled water is suitable for use in laboratory research, and its quality will not affect the metrological characteristics of analyzes performed in the laboratory. Standards for the frequency of quality control of distilled water have not been established.

1.2. RECEIVING AND QUALITY CONTROL

Distilled water is obtained in various brands of distillers. The distiller is installed in a separate room, the air of which should not contain substances that are easily absorbed by water (ammonia vapor, hydrochloric acid, etc.). During the initial start-up or when starting up the distiller after long-term preservation, the use of distilled water is permitted only after 40 hours of operation of the distiller and after checking the quality of the resulting water in accordance with GOST requirements.

Depending on the composition of the source water, distilled water of various qualities can be obtained.

With a high content of calcium and magnesium salts in water, scale forms on the surface of the heating elements, the internal walls of the steam generator and the refrigerating chamber, resulting in deterioration of heat exchange conditions, leading to a decrease in productivity and a shortening of the service life of the distiller. In order to soften the source water and reduce the formation of scale, it is advisable to operate the device in combination with an anti-scale magnetic device or a chemical water conditioner (based on ion-exchange resins in sodium form), for example the KU-2-8chs brand.

The question of the timing of periodic preventive flushing of the distiller and descaling is decided experimentally, guided by data on the quality of distilled water during periodic monitoring. After cleaning and washing the distiller, distilled water is again analyzed for all indicators in accordance with GOST.

All results of water tests should be entered into a journal, where at the same time it is necessary to reflect the operating mode of the distiller. Analysis of the results obtained will make it possible to establish for each source water its own mode of operation of the device: the period of operation, the period of its shutdown for preventive cleaning, washing, rinsing, etc.

If water with a high content of organic substances is used as source water, then some of them can be distilled into the distillate and increase the control value of oxidation. Therefore, GOST provides for the determination of the content of organic substances that reduce potassium permanganate.

To free the distilled water from organic impurities and improve the quality of the distillate, it is recommended to use chemical water conditioners with granulated sorbent made of birch activated carbon or with macroporous granulated anion exchanger brand AB-17-10P.

If substances that reduce potassium permanganate in a concentration of more than 0.08 mg/dm are detected in distilled water, it is necessary to carry out a secondary distillation of the distillate by adding 1% KMnO4 to it before distilling off the solution, at the rate of 2.5 cm3 per 1 dm of water. The total time spent on monitoring the quality of distilled water for all 14 indicators indicated in the table is 11 hours of analyst working time (65 laboratory units). Determining the specific electrical conductivity of water compares favorably in terms of time costs with traditional chemical analysis when determining individual indicators, because the time required for its determination is no more than 1 laboratory unit (10 minutes) and is recommended as an express method for monitoring the quality of distilled water.

Based on the value of specific electrical conductivity, one can generally characterize the entire sum of the components of the residual amount of mineral substances (including nitrates, sulfates, chlorides, aluminum, iron, copper, ammonia, calcium, zinc, lead).

If it is necessary to obtain express information about the content of sulfate ions in water, the latter can be calculated from the value of specific electrical conductivity and the content of hydrocarbonate chloride ions (see section 2).

According to GOST, the result of the intended value of distilled water is expressed at 20 degrees. WITH

1.3. STORAGE CONDITIONS

Distilled water for laboratory tests must be freshly distilled. If necessary, water can be stored in hermetically sealed polyethylene or fluoroplastic bottles. To prevent the absorption of carbon dioxide from the air, bottles with distilled water must be closed with stoppers with calcium chloride tubes. Ammonia-free water is stored in a bottle closed with a stopper with a “goose” containing a solution of sulfuric acid.

3. ESTABLISHING THE VALUE OF TOTAL MINERALIZATION OF WATER

3.1. NATURAL WATERS

One of the most important indicators of water quality is the value of total mineralization, usually determined gravimetrically from the dry residue. Using chemical analysis data on the content of chloride and hydrocarbonate sulfate ions, using conversion factors, it is possible to calculate the value of total mineralization (M, mg/dm3) of the water under study using formula (2):

M=[HCO(3-)*80+[Cl-]-55+*67

where [HCO(3-)], [Cl], are the concentrations of bicarbonate, chloride, and sulfate ions in mEq/dm.cub. respectively. The numerical factors approximately correspond to the arithmetic mean values ​​of the molar masses of the equivalents of salts of the corresponding anion with calcium, magnesium, sodium and potassium.

3. METHOD FOR ASSESSING THE IONIC STRENGTH OF AN AQUEOUS SOLUTION

In the practice of hydrochemical research, the value of the ionic strength of water is used to control the ionic composition of water using ion-selective electrodes, as well as in the express calculation of total hardness.

Calculation of the ionic strength (mu) of natural and waste waters is made based on the results of double measurements of the specific electrical conductivity of water: undiluted (xi1) and diluted in a ratio of 1:1 (xi2).

The ionic strength is calculated using formula (4):

(mu)=K*Cm10 (4)

Where Cm is the total mineralization of water, calculated from the specific electrical conductivity as a * 10(4) and expressed in mEq/dm3;

K is the ion indicator, established using an adjustment table based on the values ​​of Cm and xi2/xi1.

The values ​​(mu) of natural and waste waters (even those containing a large amount of suspended particles) calculated by this method are consistent with the values ​​(mu) determined from chemical analysis of the content of major ions; the discrepancy between the results of the two methods does not exceed 10%, which is consistent with the acceptable reproducibility standards.

This rapid method for determining the ionic strength of natural and waste waters is more economical and has an advantage in monitoring turbid and colored waters.

4. METHOD FOR ASSESSING THE TOTAL HARDNESS OF WATER

Displacement hardness is one of the most important group indicators of water quality for all types of water use. The generally accepted complex metric determination of hardness has a significant limitation and cannot be used when analyzing turbid and colored waters, as well as when there is a significant content of a number of metals. When determining the total hardness, such waters must undergo special treatment, which is associated with an increase in the consumption of chemical reagents and additional costs of working time for analysis.

An accelerated method for estimating the approximate value of total hardness (W total) is based on data obtained from electrical conductivity measurements. The calculation is made using the formula (5)%

F total = 2(mu) * 10(3) - (2Sm + SO4(2-)]) (5)

where (mu) is the value of the ionic strength of water (calculation based on electrical conductivity data, see section 4); cm - total mineralization, mEq/dm.cub. (calculation based on electrical conductivity data, see section 4); - concentration of sulfate ions, mEq/dm.cub. (calculation based on electrical conductivity data, see section 2, or another method). The error in determining rigidity using this method is within acceptable limits (5%). The method is recommended as an accelerated method for assessing total hardness in conditions of mass analysis of samples in an environmental monitoring system, especially in the case of turbid, colored waters and waters heavily contaminated with ions of a number of heavy metals.

LITERATURE

GOST 6709-72 "Distilled water".

Instructions for the organization and structure of laboratory control in the system of the Ministry of Housing and Communal Services of the RSFSR. M. 1986.

Vorobiev I.I. Application of electrical conductivity measurements to characterize the chemical composition of natural waters. M., Publishing House of the USSR Academy of Sciences, 1963-141 p.

Pochkin Yu.N. Determination of electrical conductivity of water when studying the salt regime of open reservoirs // Hygiene and Sanitation. 1967, N 5.

GOST 17403-72. Hydrochemistry. Basic concepts. Terms and Definitions.

Lurie Yu.Yu. Analytical chemistry of industrial wastewater. M., Chemistry, 1984.-447 p.

RD 52.24.58-88. Methodology for measuring the content of sulfate ions using the titrimetric method with barium salt.

RD 52.24.53-88. Methodology for measuring the content of sulfate ions with lead salt.

GOST 27384-87. Water. Measurement error standards are indicative of composition and properties.

GOST 26449.1-85. Stationary distillation and desalination plants. Methods of chemical analysis of salt waters.

Information leaflet N 29-83. Determination of boiler water content. CSTI, Arkhangelsk. 1983.

Manual for the chemical analysis of terrestrial surface waters. L., Gidrometeoizdat. 1977. - 537 p.

Accelerated determination of total mineralization, total hardness, ionic strength, content of sulfate ions and free CO2 by electrical conductivity. Kazan. GIDUV. 1989. - 20 p.

The product of the concentrations of hydrogen and hydroxyl ions in chemically pure water is a constant value equal to 10 -14 at a temperature of 25 °C. It remains unchanged in the presence of substances that dissociate to form hydrogen and hydroxyl ions. In pure water, the concentrations of hydrogen and hydroxyl ions are 10 -7 mol/dm 3, which corresponds to the neutral state of the solution. In acidic solutions [H + ] > 10 -7 mol/dm 3, and in alkaline solutions [H + ]

For convenience, expressing the concentration of hydrogen ions in water uses a value that is the decimal logarithm of their concentration taken with the opposite sign. This quantity is called pH value and is designated pH(pH = - log ¢).

The pH value is one of the most important indicators of water quality and characterizes the state of acid-base balance of water. The development and vital activity of aquatic biota, the forms of migration of various elements, and the aggressive effect of water on host rocks, metals, and concrete depend on the pH value.

The pH value of surface waters is influenced by the state of carbonate equilibrium, the intensity of the processes of photosynthesis and decay of organic substances, and the content of humic substances.

In most water bodies, the pH of the water usually ranges from 6.3 to 8.5. In river and lake waters, pH values ​​are lower in winter compared to summer.

The pH value of surface waters subject to intense pollution by wastewater or the influence of groundwater may vary within wider limits due to the presence of strong acids or bases in their composition.

Specific electrical conductivity (electrical conductivity) - quantitative characteristic of water’s ability to conduct electric current. In a purely physical sense, this is the reciprocal of the electrical resistance of water at a temperature of 25 ° C, located between two electrodes with a surface of 1 cm 2, the distance between which is 1 cm. The unit of electrical conductivity is Siemens per 1 m (S/m). For water, derived values ​​are used as a unit of measurement - milliSiemens per 1 m (mS/m) or microSiemens per 1 cm (μS/cm).

In most cases, the specific electrical conductivity of land surface waters is an approximate characteristic of the concentration of inorganic electrolytes in water - Na +, K +, Ca 2+, Mg 2+ cations and Clˉ, SO 4 2-, HCO 3 - anions . The presence of other ions, e.g. Fe (II), Fe (III), Mn (II), NO 3 - , HPO 4 2- usually has little effect on the value of electrical conductivity, since these ions are rarely found in water in significant quantities. Hydrogen and hydroxyl ions in the range of their usual concentrations in surface waters of land have practically no effect on the electrical conductivity. The influence of dissolved gases is equally small.

Thus, the specific electrical conductivity of land surface waters depends mainly on their mineralization and usually ranges from 50 to 10,000 µS/cm.

The pH of water is measured potentiometrically, and the specific electrical conductivity is measured by the conductometric method using appropriate instruments - pH meters (ionomers) and conductometers. Modern devices (ionomers-salin meters) are equipped with sensors for both indicators and allow them to be measured almost simultaneously.

RD 52.24.495-2005

GUIDANCE DOCUMENT

HYDROGEN INDICATOR AND SPECIFIC ELECTRICAL CONDUCTIVITY OF WATER. METHOD FOR PERFORMING MEASUREMENTS USING THE ELECTROMETRIC METHOD

Date of introduction 2005-07-01

Application area

This guidance document establishes methods for performing measurements (hereinafter referred to as the method) of the hydrogen index in the range from 4 to 10 units. pH and electrical conductivity in the range from 5 to 10,000 µS/cm in samples of land surface waters and treated wastewater by electrometric method.

Measurement error characteristics

Measurement method

When measuring the pH of water using the electrometric method, a system is used that consists of a glass electrode, the potential of which depends on the concentration (activity) of hydrogen ions, and an auxiliary electrode. When immersed in a water sample, the electrode system develops an emf that linearly depends on the activity of hydrogen ions.

The measurement of electrical conductivity is based on measuring the electrical resistance of a solution located between two platinum (platinized) electrodes with a surface area of ​​1 cm 2, the distance between which is 1 cm.

When the temperature changes by 1 °C, the value of the specific electrical conductivity changes (increases with increasing temperature) by approximately 2%. Therefore, to eliminate this error, measurements are carried out in a temperature-controlled sample or using an automatic temperature compensator. Otherwise, appropriate corrections are made to the results.

Safety and environmental requirements

where v t is the value of specific electrical conductivity at measurement temperature, µS/cm;

f - temperature correction (Appendix).

If the device is calibrated in other units, the measurement result must be converted to microsiemens per centimeter.

where pH is the arithmetic mean of two results, the difference between which does not exceed the repeatability limit r (0.06 pH units).

where: v is the arithmetic mean of two results, the difference between which does not exceed the repeatability limit r (2.77 s r);

±D - limits of measurement error ( table).

In this case, the actual measurement temperature is indicated if automatic or mathematical correction of the result was carried out. The numerical values ​​of the measurement result must end with a digit of the same digit as the values ​​of the error characteristic.

Quality control of measurement results when implementing the technique in the laboratory

When implementing the technique in the laboratory, the following is provided:

Operational control by the performer of the measurement procedure (based on an assessment of repeatability when implementing a separate control procedure);

Monitoring the stability of measurement results (based on monitoring the stability of the standard deviation of repeatability).

The algorithm for operational control by the performer of the measurement procedure is given in RD 52.24.495-2005.

The frequency of operational monitoring and procedures for monitoring the stability of measurement results are regulated in the Laboratory Quality Manual.

Chief metrologist of the State Chemical Institute A.A. Nazarova



Basic information. Measurement of the specific electrical conductivity of aqueous solutions has become widespread in laboratory practice, with automatic chemical control of the water regime of steam power plants, the operating efficiency of water purification plants and industrial heat exchange and other installations, as well as various quality indicators characterizing chemical technological processes.

Technical means designed to measure the specific electrical conductivity of aqueous solutions are usually called conductometric liquid analyzers. The scale of secondary instruments of liquid conductometers (laboratory and industrial) for measuring specific electrical conductivity is calibrated in units of siemens per centimeter or microsiemens per centimeter. Liquid conductometers, which are used in production conditions to measure quality indicators characterizing the salt content in steam, condensate and feed water of steam generators, are usually are called salt meters. The scale of secondary salt meter devices is calibrated according to the conditional content of these salts in a solution in the following units: milligram per kilogram microgram per kilogram or milligram per liter and microgram per liter Liquid conductometers used to measure the concentration of solutions of salts, acids, alkalis, etc. ., are often called concentration meters. The scale of secondary concentrator devices is graduated as a percentage of the mass concentration value. Conductometric liquid analyzers are also used as alarms.

With increased requirements for the quality indicators of feed water, steam and condensate, it is necessary to measure small values ​​of electrical conductivity, not exceeding 5-b. When monitoring the depletion of filters of treatment plants, the value of the measured electrical conductivity of water is , and when monitoring the concentration of reagent solutions - from to.

The electrical conductivity of aqueous solutions is usually measured using an electrode conductometric measuring transducer consisting of two electrodes,

located in a vessel into which a controlled aqueous solution flows. The design of these converters and the measuring circuits used for liquid conductometers are discussed below. Electrodeless liquid conductometers are also widely used to measure the electrical conductivity of solutions.

Electrical conductivity is the reciprocal of resistivity:

Here the electrical conductivity, resistivity, Ohm-cm, defined by the expression

where is the electrical resistance of a fixed volume of solution with concentration C between the metal electrodes, Ohm; effective cross-section of the solution through which current flows, distance between electrodes, see

According to equation (22-2-2), expression (22-2-1) takes the form:

where is the electrical conductivity of a fixed volume of solution, Ohm; constant of the electrode converter,

From expression (22-2-3) we have:

For converters with a simple electrode configuration, the constant can be determined by calculation. If the converter has a complex design, then the constant is determined experimentally.

It should be noted that based on the study of specific electrical conductivity, we are not able to compare the electrical conductivity values ​​of solutions with each other depending on their concentration. This becomes possible with the introduction of the concept of equivalent electrical conductivity. Kohlrausch called the equivalent electrical conductivity the quantity

where is the equivalent electrical conductivity, Sm -eq; -equivalent concentration of the dissolved substance, .

The value of electrical conductivity of solutions depends not only on the equivalent concentration and equivalent electrical conductivity, but also on the degree of electrolytic dissociation of the solution.

Therefore, in the general case, when not all molecules have broken up into ions, we obtain the following equation for specific electrical conductivity:

Here is the degree of electrolytic dissociation, i.e. the ratio of the number of dissociated electrolyte molecules to the total number of dissolved molecules. Electrolytes are substances whose aqueous solutions conduct electric current (salts, alkalis and acids). The degree of electrolytic dissociation a depends both on the nature of the solute and on the concentration of the solution. The numerical value of a increases with dilution of the solution. Depending on the degree of electrolytic dissociation, electrolytes are divided into strong (hydrochloric, sulfuric, nitric acids, alkalis, almost all salts) and weak (for example, organic acids). For strong electrolytes, which in aqueous solutions at low concentrations almost completely disintegrate into ions, the value of a is taken equal to unity.

Rice. 22-2-1. Dependence of the electrical conductivity of aqueous solutions of some substances on their concentration at 18° C.

Equation (22-2-6) can be represented as follows:

where is the mobility of cations and anions, respectively

Ion mobilities are the product of their absolute speed and the Faraday number

The electrical conductivity of aqueous solutions is complexly dependent on the concentration of the solution. In Fig. Figure 22-2-1 shows the dependence of the specific electrical conductivity of aqueous solutions of some substances on their concentration. From this graph it is clear that a clear relationship between the electrical conductivity of the solution and the concentration occurs only if the electrical conductivity measurements are performed in the region of relatively low concentrations. The concentrations of dissolved substances that have to be determined when monitoring the quality of steam, condensate, feed and boiler water correspond to the initial sections shown in Fig. 22-2-1 curves, where the electrical conductivity increases continuously with increasing concentrations.

When measuring the electrical conductivity of steam condensate and feed water, which are aqueous solutions with very low salt concentrations, the degree of electrolytic dissociation can be

take equal to one. In this case, a simplified equation can be used to determine electrical conductivity

Here the equivalent electrical conductivity at infinite dilution, which is determined by the equality

where are the mobility of cations and anions, respectively, with infinite dilution of the solution (for .

The values ​​and temperature coefficients of ion mobilities corresponding to a temperature of 18 ° C are given in. When measuring the specific electrical conductivity of aqueous solutions, the temperature is usually taken as normal (initial), for which electrical conductivity data are provided.

When measuring electrical conductivity, it is necessary to take into account the influence of the temperature of the solution on the readings of the device, since with a change in the temperature of the solution by 1 ° C, its electrical conductivity changes by to the instrument readings.

The dependence of the electrical conductivity of aqueous solutions on temperature at small deviations from 18° C is expressed by the formula

At temperatures differing from 18°C ​​by 10-25°C or more, it is necessary to use the equation

where is the temperature coefficient of electrical conductivity according to the formula

Here the temperature mobility coefficients of the cation and anion, respectively

The temperature coefficient of electrical conductivity according to Kohlrausch data is related to the coefficient by the ratio

The dependence of the electrical resistance of a fixed volume of solution between the electrodes of the converter on a temperature slightly different from 18 ° C is expressed by the formula

At temperatures differing from 18°C ​​by 10-25°C or more, the equation should be used

When monitoring water conditions in power plants, salt concentrations are usually expressed in milligrams per liter or micrograms per liter. The above equations use the equivalent concentration. These concentrations are recalculated using the formula

where the equivalent concentration, C-concentration, is the equivalent mass of solute ions, according to the formula

Here is the equivalent mass of the cation and anion of the solute, respectively (for . The values ​​of the equivalent masses of ions of substances encountered when measuring the electrical conductivity of aqueous solutions are given in.

It was noted above that the calibration of liquid conductometers (salin meters) is carried out according to the conditional content of this salt in the solution. This is due to the fact that among the various salts contained in steam condensate and feed water of steam generators, sodium chloride has an average electrical conductivity

The electrical conductivity of an aqueous solution at low concentrations and at an initial temperature C can be determined taking into account expressions (22-2-8), (22-2-9) and (22-2-16) according to the equation

Substituting values ​​into this expression we get:

Calibration of liquid conductometers (salin meters) is usually carried out at normal temperature. To convert to the temperature value, you can use the formula (22-2-10)

Substituting the values ​​into this equation we get:

The electrical resistance of a fixed volume of the converter solution at low concentration and at temperature C can be determined taking into account expressions (22-2-3) and (22-2-20) using the formula

In addition to a small amount of salts, the steam condensate and feed water of steam generators usually contain dissolved gases - ammonia and carbon dioxide and hydrazine. The presence of dissolved gases and hydrazine changes the electrical conductivity of the condensate and feed water, and the readings of the liquid conductometer (salin meter) do not clearly correspond to the conventional salt content, i.e., the value of the dry residue obtained by evaporation of the condensate or feed water. This leads to the need to amend the instrument readings or use an additional device to remove dissolved gases and hydrazine from the sample.

An additional device in the form of a degasser for removing dissolved gases from the sample does not exclude the influence of hydrazine on the readings of a conductometric hydrazine analyzer. The currently used filter filled with cation exchanger brand eliminates the influence of ammonia and hydrazine on the instrument readings.

Electrode conductometric transducers. Electrode transducers used to measure the electrical conductivity of solutions are manufactured for laboratory studies of various solutions and for technical measurements. Measurements in laboratory conditions are carried out using alternating current. It should be noted that the conductometric method of measuring alternating current remains generally accepted in everyday laboratory practice. Technical measurements of the electrical conductivity of solutions using electrode converters are usually carried out using alternating current with a frequency of 50 Hz.

The design, dimensions, and, consequently, the constant of electrode transducers largely depend on the measured value of the electrical conductivity of the solution. In technical measurements, the most common transducers are those with cylindrical coaxial and, to a lesser extent, those with flat electrodes. The design of converters with cylindrical coaxial electrodes is shown schematically in Fig. 22-2-2. The converter shown in Fig. 22-2-2, a, the outer cylindrical electrode is also its body. The second converter (Fig. 22-2-2, b) also has cylindrical coaxial electrodes, but they are located in its steel body, to which one electrode is welded. This converter

used in TsKTI salinity meters with small-sized concentrators. A degassed and enriched sample, having a constant temperature close to 100° C, enters the converter through the left fitting from the concentrator. The upper fitting of the converter is connected by a steel pipe to the vapor space of a small-sized concentrator, a salinity meter. A diagram of the device of a converter with flat electrodes is shown in Fig. 22-2-3. Feature of the converter shown in Fig. 22-2-3 is that the areas of its electrodes and the effective cross-section of the solution through which the current flows are not the same.

Rice. 22-2-2. Design of converters with cylindrical coaxial electrodes. 1 - clamps for connecting wires; 2 - electrodes; 3 - steel body; 4 - insulators.

Rice. 22-2-3. Transducer device with flat electrodes. 1 - converter housing; 2 - clamps for connecting wires; 3 - electrodes.

In addition to the considered flow-through electrode transducers, they are also of the submersible type, directly immersed in a pipeline with a liquid, the electrical conductivity (or concentration) of which must be controlled. Electrodes of transducers for technical measurements are made of stainless steel. Electrodes of transducers for laboratory studies of electrolyte solutions are made of platinum. To reduce the polarization of the electrodes, they are coated with a layer of platinum black. The vessels of these converters are usually made of glass. The dimensions of the vessels are selected depending on the expected value of the electrical conductivity of the solution being tested.

Complex electrochemical processes take place on the electrodes of the converter in contact with the solution. When measuring the electrical conductivity of aqueous solutions, the space between the electrodes is filled with a medium with a high dielectric constant. For these reasons, a fixed volume of solution between the electrodes of the transducer when measured on alternating current represents a complex electrical resistance - a combination of active

and capacitive components. The equivalent electrical circuit of the electrode converter, taking into account electrode processes, is shown in Fig. 22-2-4. Electrode processes include the process of electrolysis of a solution when an electric current passes through it and the process of formation of a double electrical layer at the “metal electrode - solution” interface. The formation of a double electric layer occurs due to the influence of an external electric field, the inequality of the chemical potentials of the metal ions of the electrodes and ions in the solution, and the specific adsorption of ions and polar molecules. In an alternating current circuit, the electrical double layer is equivalent to electrical capacitance. The electrical capacitance of the double layer does not depend on the frequency of the supply voltage and is a function of the concentration and size of the potential applied to the electrodes.

Rice. 22-2-4. Equivalent electrical circuit of the electrode converter.

The equivalent electrical circuit of the polarization process is represented in the general case by a nonlinear active-capacitive resistance, which is called the Faraday impedance. One of the equivalent circuit models is defined by the expression

where constant, Ohm - angular velocity, rad/s When carrying out technical measurements, they strive to create such a design of the electrode transducer so that its total resistance is determined by the active resistance of a fixed volume of solution between the electrodes and the influence of electrochemical processes and the reactive components of electrical resistance caused by these processes would be negligible . If these conditions are met with the required approximation, then the electrical resistance of a fixed volume of solution between the electrodes of the converter is determined according to expression (22-2-3) by the following formula:

Rice. 22-2-5. Simplified equivalent electrical circuit of the electrode converter.

Let's consider a simplified equivalent electrical circuit of an electrode converter, which does not take into account the effect of electrolysis. In this case, the total resistance of the converter will be determined, as follows from the circuit shown in Fig. 22-2-5, double layer capacitances on the electrodes with active electrical resistance of the solution between the electrodes and the capacitance shunting this resistance. The capacity can be called “constructive”. It should be noted that water has a higher relative dielectric constant compared to other liquids (for condensate, which leads to the need to take into account the capacitance between the electrodes.

Using the known relationship that determines the modulus of capacitive resistance, it is possible to conduct a qualitative analysis of the influence of capacitive components and frequency on the modulus of the impedance of the converter.

Assuming that the active resistance does not depend on the frequency of the voltage on the electrodes, it is easy to notice that as c increases, the relative influence of the double layer capacitance on the impedance modulus decreases, while the “constructive” capacitance increases. It can be shown that the relative influence of capacitance is practically independent of the shape of the electrodes, their mutual

locations and distances between them. Indeed, design changes affect almost equally the active resistance of the converter and the value of the capacitance. The degree of influence of the double layer capacitance can be changed by design techniques. As the area of ​​the converter electrodes increases, the capacity of the double layer increases, and a decrease in the effective cross-sectional area of ​​the solution through which the current passes leads to an increase in the active resistance of the solution. The relative influence of the double layer capacitance is reduced compared to a converter in which the electrode area and the effective cross section of the solution are the same.

To reduce the impact on the accuracy of measuring the electrical conductivity of electrode polarization solutions, four-electrode converters are used, for example, in conductometric analyzers for pure aqueous solutions, type converters with a measurement range are used. Two electrodes of this converter are current, supplied by alternating current voltage through a large limiting resistance, and the other two located between them are potential. In this case, the voltage measured at the potential electrodes uniquely determines the concentration of the controlled solution and does not depend on the partial polarization of the current electrodes.

Rice. 22-2-6. Schematic diagram of an electrode converter with temperature compensation.

Methods of temperature compensation and typical measuring circuits of conductometric analyzers. Temperature compensation is carried out using additional elements in the circuit of the electrode converter or in the measuring circuit of the liquid conductometer, which reduce the influence of a deviation of the solution temperature from 20 ° C on the readings of the device. Automatic temperature compensation does not completely eliminate the influence of the solution temperature on the instrument readings, which presents great difficulties, but it significantly reduces it.

Of the methods used for automatic temperature compensation in liquid conductometers, the most commonly used is an electrode converter with temperature compensation, the diagram of which is shown in Fig. 22-2-6. The temperature compensation circuit of the electrode converter is formed by resistors connected in parallel and in series with the resistance of the solution. The resistance of the solution with the resistor has a negative, and the series-connected resistor has a positive temperature coefficient of electrical resistance. The resistor is made of manganin wire, and the resistor is made of copper wire. To make a resistor, nickel or platinum wire is sometimes used. The resistor, performed similarly to the sensitive element of a resistance thermometer, is placed in the internal

transducer electrode (Fig. 22-2-2, a). A resistor connected in parallel with the resistance of the solution linearizes the dependence and at the same time reduces the temperature coefficient of the reduced resistance. This creates more favorable conditions for using a compensating resistor

Rice. 22-2-7. Dependence of the total resistance of the converter circuit on the concentration C for temperatures of 18 and 35 ° C.

The calculation of the parameters of the temperature compensation circuit is usually made from the condition of full temperature compensation for two given concentrations and certain temperature values ​​selected taking into account possible deviations of the solution temperature from this case, measurements of the concentration (electrical conductivity) must be made in the range from to since the error when the solution temperature changes beyond the boundaries this interval may be larger than within it (Fig. 22-2-7).

The total resistance of the converter circuit relative to terminals A to B (see Fig. 22-2-6) at solution concentration C and its temperature is determined by the expression

Here, as well as in subsequent equations, the indices indicate to what concentration of the solution and temperature the values ​​under consideration relate (resistance, electrical conductivity, electrical conductivity). The condition for complete temperature compensation is reduced to the equalities

In the last two expressions, the temperature coefficient of resistance of copper corresponding to 0° C. When calculating the parameters of the temperature compensation circuit, they are used to measure the electrical conductivity (salt content) of aqueous solutions at low concentrations; the values ​​of the quantities are the fourth arm of the bridge); asynchronous reversible motor; synchronous motor. The resistors are made of manganin wire. The resistor serves to establish the required range of resistance changes when measuring the electrical conductivity of a solution from the initial to the final scale value, which allows the use of commercially produced automatic balanced bridges KSM2 without changes to the flux cord and amplifier.

Rice. 22-2-8. Schematic diagram of a liquid conductometer using an electrode transducer (Fig. 22-2-2, 6).

The considered bridge measuring circuit of a secondary liquid conductometer device can also be used to measure the electrical conductivity of aqueous solutions using an electrode transducer with temperature compensation (see Fig. 22-2-6), if it is connected to the terminals instead of the transducer Liquid conductometers with such an electrode transducer, manufactured by Tulenergo , used at thermal power plants to measure the electrical conductivity of chemically demineralized water. These liquid conductometers use electrode transducers with temperature compensation from 15 to 35°C of flow-through and immersion types. The devices have a measurement range of specific electrical conductivity from 0.04 to 20° C.

Let's consider a method of temperature compensation using a thermistor included in the automatic measuring circuit.

balanced bridge liquid conductivity meter (Fig. 22-2-9). Here, the electrode converter of the EP is included in the measuring bridge circuit of the secondary device, just as in Fig. 22-2-8. In this case, the reduced resistance of the converter and the thermistor with a shunt connected to adjacent arms of the bridge have a negative temperature coefficient of resistance. It should be noted that for the thermistor the dependence is nonlinear, just like for

Rice. 22-2-9. Schematic diagram of a liquid conductometer using a thermistor for temperature compensation.

When measuring conductivity, the thermistor is at the same temperature as the solution being analyzed, since it is usually mounted inside the transmitter housing. The accuracy of temperature compensation will be determined by the degree of consistency between the temperature coefficients of the thermistor with shunt and the reduced resistance of the converter

The considered temperature compensation using a thermistor included in the measuring bridge circuit is used in the current conductometric liquid analyzers.

Temperature compensation can also be carried out using an additional electrode transducer, which is filled with an aqueous solution having a temperature coefficient of resistance close to the temperature coefficient of the analyzed solution. In this case, the working and compensating converters are included in adjacent arms of the bridge measuring circuit. In this case, the compensating transducer is washed from the outside by the analyzed solution and has the same temperature with it. This method of temperature compensation is not widely used, since the properties of the solution in the compensation converter change over time.

Automatic balanced bridges, designed to work in conjunction with electrode converters, can be equipped with an additional device for signaling (regulating) the limiting values ​​of the electrical conductivity of aqueous solutions of electrolytes.

In addition to the considered liquid analyzers with electrode transducers, a conductometric analyzer is available

Accuracy class 5 AK, developed by SKB AP, with a DC output signal. This conductometric analyzer, equipped with a filter filled with a cation exchanger brand, is designed to measure the specific electrical conductivity of aqueous solutions at a temperature of 30-40 ° C and the presence of mineral impurities, ammonia and hydrazine in them. An automatic milliammeter KSU2 with measurement ranges is used as a secondary device

Good afternoon
Tell me, is there any theoretical method for determining the conductivity of water with compounds dissolved in it, if the initial conductivity of water and the exact quantitative content of compounds dissolved in water are known.

Thank you in advance!

Accurate calculation of specific electrical conductivity is carried out using special empirical formulas using calibrated solutions of potassium chloride with a previously known value of electrical conductivity. It is customary to display the measured value using the Siemens unit of measurement, 1 cm is the inverse of 1 ohm. Moreover, for salt water the research results are displayed in S/m, and for fresh water – in µS/meter, that is, in microsiemens. Measurement of electrical conductivity of aqueous solutions gives for distilled water a SEP value from 2 to 5 μS/meter, for atmospheric precipitation a value from 6 to 30 or more μS/meter, and for fresh river and lake waters in those areas where the air environment is heavily polluted, the SEP value can vary by within 20-80 µS/cm.

To approximate the SEP, you can use the empirically found relationship between the SEP and the salt content in water (salinity):

UEP ( µS/cm ) = salt content (mg / l) / 0,65

That is, to determine the SEP (μS/cm), the salt content (water mineralization) (mg/l) is divided by a correction factor of 0.65. The value of this coefficient varies depending on the type of water in the range of 0.55-0.75. Sodium chloride solutions conduct current better: NaCl content (mg/l) = 0.53 µS/cm or 1 mg/l NaCl provides electrical conductivity of 1.9 µS/cm.

For an approximate calculation of the UEP based on the salt content in water (salinity), you can use the following graph (Fig. 1):

Rice. 1. Graph of the dependence of the electrical energy consumption on the salt content (salinity) in water.

The electrical resistance is also measured using a special device - a conductometer, consisting of platinum or steel electrodes immersed in water, through which an alternating current with a frequency of 50 Hz (in low-mineralized water) to 2000 Hz or more (in salt water) is passed, by measuring electrical resistance .

The principle of operation of the conductometer is based on the direct dependence of the electrical conductivity of water (current strength in a constant electric field created by the electrodes of the device) on the amount of compounds dissolved in water. A wide range of appropriate equipment now makes it possible to measure the conductivity of almost any water, from ultrapure (very low conductivity) to saturated with chemical compounds (high conductivity).

A conductivity meter can even be purchased at pet stores, and combinations of such a device with a pH meter are possible. In addition, such a device can be purchased at offices and companies selling equipment for environmental research www.tdsmeter.ru/com100.html.

Craftsmen who are good with a soldering iron can make their own device for measuring the electrical conductivity of I.I. Vanyushin’s design. (magazine "Fisheries", 1990, No. 5, pp. 66-67. In addition, this device and methods for its calibration are described in all details in the very useful book "Modern Aquarium and Chemistry", authors I.G. Khomchenko , A.V. Trifonov, B.N. Razuvaev, Moscow, 1997). The device is made on the common K157UD2 microcircuit, which consists of two operational amplifiers. The first one houses an alternating current generator, the second one houses an amplifier according to a standard circuit, from which readings are taken with a digital or analog voltmeter (Fig. 2).

Rice. 2. Homemade conductivity meter.

To eliminate the influence of temperature, electrical conductivity measurements are carried out at a constant temperature of 20 0 C, since the value of electrical conductivity and the measurement result depend on temperature, as soon as the temperature increases by at least 1 0 C, the measured value of electrical conductivity also increases by approximately 2%. Most often, it is recalculated in relation to 20 0 C according to the correction table, or reduced to it using empirical formulas.

Correction table for calculating UEP.

Temperature, °C	Correction factor	Temperature, °C	Correction factor	Temperature, °C	Correction factor

The calculation of the specific electrical conductivity of water in this case is carried out using the formula :

UEP = C p / R

where C p is the capacitance of the device sensor, which depends on the material and size of the electrodes and has a dimension of cm-1, determined when calibrating the device using solutions of potassium chloride with a known value of electrical conductivity; K is the temperature coefficient for bringing the measured value at any temperature to its accepted constant value; R is the measured electrical resistance of water by the device, in Ohms.

The device must be calibrated in resistance values. For calibration, the following resistances can be recommended: 1 kOhm (electrical conductivity 1000 µS), 4 kOhm (250 µS), 10 kOhm (100 µS).

In order to more accurately determine the specific electrical conductivity, you need to know the constant of the vessel for measuring CX. To do this, it is necessary to prepare a 0.01 M solution of potassium chloride (KCl) and measure its electrical resistance R KCl, (in kOhm) in the prepared cell. The capacity of the vessel is determined by the formula:

C p = R KC UEP KCl

where SEP KC is the specific electrical conductivity of a 0.01 M KCl solution at a given temperature in μS/cm, found from the correction table.

The UEP is then calculated using the formula:

UEP =C P (K T )/R

where C p is the capacitance of the device sensor, which depends on the material and size of the electrodes and has a dimension of cm -1, is determined by calibrating the device using solutions of potassium chloride with a known value of the electrical conductivity; K t - temperature coefficient for bringing the measured value at any temperature to its accepted constant value; R is the measured electrical resistance of water by the device, in Ohms.

The SEP of salt water is usually expressed in S/m (Sm - Siemens, the reciprocal of Ohm), for fresh water - in microsiemens (µS/cm). The SER of distilled water is 2-5 µS/cm, atmospheric precipitation - from 6 to 30 µS/cm or more, in areas with heavily polluted air, river and fresh lake waters 20-800 µS/cm.

The normalized mineralization values ​​approximately correspond to a specific electrical conductivity of 2 mS/cm (1000 mg/dm 3) and 3 mS/cm (1500 mg/dm 3) in the case of both chloride (in terms of NaCl) and carbonate (in terms of CaCO 3 ). mineralization.

Pure water, as a result of its own dissociation, has a specific electrical conductivity at 25 C equal to 5.483 µS/m.

For more information about the methods for calculating the UEP, see the relevant sections of our website.

Ph.D. O.V. Mosin

Below are methodological methods for calculating total mineralization, ionic strength, hardness and determining the content of sulfate ions in natural and waste waters based on specific electrical conductivity as a general indicator of their quality.

Determining the electrical conductivity (L) of water comes down to measuring its inverse value - the resistance (R) that water provides to the current passing through it. Thus, L= 1:R, and therefore the electrical conductivity value is expressed in inverse Ohms, and according to the modern SI classification - in Siemens (Sm).

The value of specific electrical conductivity remains unchanged within the permissible error (10%) in the presence of organic compounds of various natures (up to 150 mg/dm3) and suspended substances (up to 500 mg/dm3) in natural and waste waters.

To measure specific electrical conductivity (xi), any conductivity meters with a range from 1*10(-6) S/cm to 10*10(-2) S/cm can be used.

1. PRODUCTION AND QUALITY CONTROL OF DISTILLED WATER

1.1. QUALITY STANDARDS

In laboratories for quality control of natural and waste waters, distilled water is the main solvent for the preparation of reagents, a diluent for test samples, an extractant, and is also used for rinsing laboratory glassware. Therefore, for the successful operation of any chemical analytical laboratory, along with the fulfillment of such conditions as highly qualified specialists, the availability of accurate verified instruments, the use of reagents of the required degree of purity, standard samples and standard measuring glassware, great attention should be paid to the quality of distilled water, which in its own way physical and chemical parameters must comply with the requirements of GOST 670972 (see table).

STANDARDS

QUALITY OF DISTILLED WATER BY

pH ¦ 5.4-6.6 ¦

Substances that reduce KMnO4 ¦ 0.08 ¦

Residue after evaporation ¦ 5.0 ¦

Residue after ignition ¦ 1.0 ¦

Ammonia and ammonium salts ¦ 0.02 ¦

Nitrates ¦ 0.20 ¦

Sulfates ¦ 0.50 ¦

Chlorides ¦ 0.02 ¦

Aluminum ¦ 0.05 ¦

Iron ¦ 0.05 ¦

Calcium ¦ 0.80 ¦

Copper ¦ 0.02 ¦

Lead ¦ 0.05 ¦

Zinc ¦ 0.20 ¦

Specific electrical conductivity at 20 degrees. C no more than 5*10(-6) cm/cm

If all indicators comply with established standards, then distilled water is suitable for use in laboratory research, and its quality will not affect the metrological characteristics of analyzes performed in the laboratory. Standards for the frequency of quality control of distilled water have not been established.

1.2. RECEIVING AND QUALITY CONTROL

Distilled water is obtained in various brands of distillers. The distiller is installed in a separate room, the air of which should not contain substances that are easily absorbed by water (ammonia vapor, hydrochloric acid, etc.). During the initial start-up or when starting up the distiller after long-term preservation, the use of distilled water is permitted only after 40 hours of operation of the distiller and after checking the quality of the resulting water in accordance with GOST requirements.

Depending on the composition of the source water, distilled water of various qualities can be obtained.

With a high content of calcium and magnesium salts in water, scale forms on the surface of the heating elements, the internal walls of the steam generator and the refrigerating chamber, resulting in deterioration of heat exchange conditions, leading to a decrease in productivity and a shortening of the service life of the distiller. In order to soften the source water and reduce the formation of scale, it is advisable to operate the device in combination with an anti-scale magnetic device or a chemical water conditioner (based on ion-exchange resins in sodium form), for example the KU-2-8chs brand.

The question of the timing of periodic preventive flushing of the distiller and descaling is decided experimentally, guided by data on the quality of distilled water during periodic monitoring. After cleaning and washing the distiller, distilled water is again analyzed for all indicators in accordance with GOST.

All results of water tests should be entered into a journal, where at the same time it is necessary to reflect the operating mode of the distiller. Analysis of the results obtained will make it possible to establish for each source water its own mode of operation of the device: the period of operation, the period of its shutdown for preventive cleaning, washing, rinsing, etc.

If water with a high content of organic substances is used as source water, then some of them can be distilled into the distillate and increase the control value of oxidation. Therefore, GOST provides for the determination of the content of organic substances that reduce potassium permanganate.

To free the distilled water from organic impurities and improve the quality of the distillate, it is recommended to use chemical water conditioners with granulated sorbent made of birch activated carbon or with macroporous granulated anion exchanger brand AB-17-10P.

If substances that reduce potassium permanganate in a concentration of more than 0.08 mg/dm are detected in distilled water, it is necessary to carry out a secondary distillation of the distillate by adding 1% KMnO4 to it before distilling off the solution, at the rate of 2.5 cm3 per 1 dm of water. The total time spent on monitoring the quality of distilled water for all 14 indicators indicated in the table is 11 hours of analyst working time (65 laboratory units). Determining the specific electrical conductivity of water compares favorably in terms of time costs with traditional chemical analysis when determining individual indicators, because the time required for its determination is no more than 1 laboratory unit (10 minutes) and is recommended as an express method for monitoring the quality of distilled water.

Based on the value of specific electrical conductivity, one can generally characterize the entire sum of the components of the residual amount of mineral substances (including nitrates, sulfates, chlorides, aluminum, iron, copper, ammonia, calcium, zinc, lead).

If it is necessary to obtain express information about the content of sulfate ions in water, the latter can be calculated from the value of specific electrical conductivity and the content of hydrocarbonate chloride ions (see section 2).

According to GOST, the result of the intended value of distilled water is expressed at 20 degrees. WITH

1.3. STORAGE CONDITIONS

Distilled water for laboratory tests must be freshly distilled. If necessary, water can be stored in hermetically sealed polyethylene or fluoroplastic bottles. To prevent the absorption of carbon dioxide from the air, bottles with distilled water must be closed with stoppers with calcium chloride tubes. Ammonia-free water is stored in a bottle closed with a stopper with a “goose” containing a solution of sulfuric acid.

3. ESTABLISHING THE VALUE OF TOTAL MINERALIZATION OF WATER

3.1. NATURAL WATERS

One of the most important indicators of water quality is the value of total mineralization, usually determined gravimetrically from the dry residue. Using chemical analysis data on the content of chloride and hydrocarbonate sulfate ions, using conversion factors, it is possible to calculate the value of total mineralization (M, mg/dm3) of the water under study using formula (2):

M=[HCO(3-)*80+[Cl-]-55+*67

where [HCO(3-)], [Cl], are the concentrations of bicarbonate, chloride, and sulfate ions in mEq/dm.cub. respectively. The numerical factors approximately correspond to the arithmetic mean values ​​of the molar masses of the equivalents of salts of the corresponding anion with calcium, magnesium, sodium and potassium.

3. METHOD FOR ASSESSING THE IONIC STRENGTH OF AN AQUEOUS SOLUTION

In the practice of hydrochemical research, the value of the ionic strength of water is used to control the ionic composition of water using ion-selective electrodes, as well as in the express calculation of total hardness.

Calculation of the ionic strength (mu) of natural and waste waters is made based on the results of double measurements of the specific electrical conductivity of water: undiluted (xi1) and diluted in a ratio of 1:1 (xi2).

The ionic strength is calculated using formula (4):

(mu)=K*Cm10 (4)

Where Cm is the total mineralization of water, calculated from the specific electrical conductivity as a * 10(4) and expressed in mEq/dm3;

K is the ion indicator, established using an adjustment table based on the values ​​of Cm and xi2/xi1.

The values ​​(mu) of natural and waste waters (even those containing a large amount of suspended particles) calculated by this method are consistent with the values ​​(mu) determined from chemical analysis of the content of major ions; the discrepancy between the results of the two methods does not exceed 10%, which is consistent with the acceptable reproducibility standards.

This rapid method for determining the ionic strength of natural and waste waters is more economical and has an advantage in monitoring turbid and colored waters.

4. METHOD FOR ASSESSING THE TOTAL HARDNESS OF WATER

Displacement hardness is one of the most important group indicators of water quality for all types of water use. The generally accepted complex metric determination of hardness has a significant limitation and cannot be used when analyzing turbid and colored waters, as well as when there is a significant content of a number of metals. When determining the total hardness, such waters must undergo special treatment, which is associated with an increase in the consumption of chemical reagents and additional costs of working time for analysis.

An accelerated method for estimating the approximate value of total hardness (W total) is based on data obtained from electrical conductivity measurements. The calculation is made using the formula (5)%

F total = 2(mu) * 10(3) - (2Sm + SO4(2-)]) (5)

where (mu) is the value of the ionic strength of water (calculation based on electrical conductivity data, see section 4); cm - total mineralization, mEq/dm.cub. (calculation based on electrical conductivity data, see section 4); - concentration of sulfate ions, mEq/dm.cub. (calculation based on electrical conductivity data, see section 2, or another method). The error in determining rigidity using this method is within acceptable limits (5%). The method is recommended as an accelerated method for assessing total hardness in conditions of mass analysis of samples in an environmental monitoring system, especially in the case of turbid, colored waters and waters heavily contaminated with ions of a number of heavy metals.

LITERATURE

GOST 6709-72 "Distilled water".

Instructions for the organization and structure of laboratory control in the system of the Ministry of Housing and Communal Services of the RSFSR. M. 1986.

Vorobiev I.I. Application of electrical conductivity measurements to characterize the chemical composition of natural waters. M., Publishing House of the USSR Academy of Sciences, 1963-141 p.

Pochkin Yu.N. Determination of electrical conductivity of water when studying the salt regime of open reservoirs // Hygiene and Sanitation. 1967, N 5.

GOST 17403-72. Hydrochemistry. Basic concepts. Terms and Definitions.

Lurie Yu.Yu. Analytical chemistry of industrial wastewater. M., Chemistry, 1984.-447 p.

RD 52.24.58-88. Methodology for measuring the content of sulfate ions using the titrimetric method with barium salt.

RD 52.24.53-88. Methodology for measuring the content of sulfate ions with lead salt.

GOST 27384-87. Water. Measurement error standards are indicative of composition and properties.

GOST 26449.1-85. Stationary distillation and desalination plants. Methods of chemical analysis of salt waters.

Information leaflet N 29-83. Determination of boiler water content. CSTI, Arkhangelsk. 1983.

Manual for the chemical analysis of terrestrial surface waters. L., Gidrometeoizdat. 1977. - 537 p.

Accelerated determination of total mineralization, total hardness, ionic strength, content of sulfate ions and free CO2 by electrical conductivity. Kazan. GIDUV. 1989. - 20 p.

MINISTRY OF ENERGY AND ELECTRIFICATION OF THE USSR
MAIN SCIENTIFIC AND TECHNICAL DIRECTORATE OF ENERGY AND ELECTRIFICATION

MEASUREMENT PROCEDURE
SPECIFIC ELECTRICAL CONDUCTIVITY
WATER AND STEAM POWER INSTALLATIONS TPP
AUTOMATIC CONDUCTOMETER

The technique ensures obtaining reliable quantitative indicators of measurement accuracy in a stationary mode of operation of power equipment.

The methodology is mandatory for use at thermal power plants, as well as in design and commissioning organizations.

1. MEASURING INSTRUMENTS AND AUXILIARY
DEVICES

1.1. When performing SEP measurements, a set of measuring instruments and auxiliary devices must be used to ensure the selection and preparation of a sample for measurements and obtaining information about the SEP of the sample. The list of necessary measuring instruments and auxiliary devices, their purpose and technical characteristics are given in Appendix 1.

It is allowed to use other measuring instruments that are not inferior to those recommended in terms of technical and metrological characteristics.

1.2. Sampling of water and steam for UEP measurements is carried out using sampling devices OST 108.030.040-80 "Device for sampling steam and water from stationary steam boilers. Types, design, dimensions and technical requirements."

Transportation of samples is carried out via sealed sampling lines that meet the requirements of OST 108.030.04-80.

1.3. The block diagram of UEP measurements is shown in the figure.

Structural diagram of UEP measurements:
a - condensate; b - feed (boiler) water;
c - saturated and superheated steam;
1 - sampling device; 2 - pre-switched on
fridge; 3 - sample preparation system;
4 - automatic conductivity meter;
5 - sampling line

In the case of using computer technology to collect and process the measurement results of electrical conductivity, the output signal of the conductometer is transmitted to the information and computing complex.

2. METHOD OF MEASUREMENT

Measurement of electrical conductivity should be carried out by contact conductometry, based on the phenomenon of transfer of electrical charges by ions of dissolved substances when current passes through the analyzed solution.

3. SAFETY REQUIREMENTS

When performing UEP measurements, the requirements of the “Safety Rules for the Operation of Thermal Mechanical Equipment of Power Plants and Heating Networks” (M.: Energoatomizdat, 1985) must be observed.

4. REQUIREMENTS AND QUALIFICATIONS OF OPERATORS

Persons who have undergone special training and have the following qualifications may be allowed to service measuring instruments and process results:

when servicing measuring instruments - an electrician of at least the 3rd category, who knows the structural, installation and electrical diagrams of UEP measurement, the design and operating principle of the measuring instruments used, the location of sampling devices, sampling lines;

when processing measurement results - a technician or engineer who knows the features of the water-chemical regime of the power plant.

5. CONDITIONS FOR PERFORMING MEASUREMENTS

Availability of valid verification marks for measuring instruments.

6.2. Preparing measuring instruments for operation is carried out in accordance with the instructions contained in the operating instructions.

6.3. Preparation for operation of the N-cationite filter is carried out according to the method given in the "Methodological instructions for the use of conductometric monitoring for maintaining the water regime of power plants. MU 34-70-114-85" (M.: SPO "Soyuztechenergo", 1986).

7. TAKE MEASUREMENTS

7.1. When performing UEP measurements, you must:

maintain normal operation of the sample preparation system, including monitoring and, if necessary, adjusting the sample flow to the conductivity meter;

periodically check the accuracy of the conductivity meter readings and, if necessary, adjust it;

promptly regenerate the N-cation exchange filter;

periodically clean the primary converter.

7.2. The accuracy of the conductivity meter readings is checked by comparing its readings with the results of measurements performed with a laboratory conductivity meter.

7.3. Check the correctness of the conductivity meter readings, clean the primary converter and regenerate the H-cation exchange filter at the intervals specified in the "Regulatory material for the operation and repair of automatic chemical control devices AK-310 and pH-201. NR 34-70-009-82" (M .: SPO "Soyuztekhenergo", 1982).

7.4. Regeneration of the N-cation exchange filter depleted during operation, as well as cleaning of the contaminated primary converter, should be carried out in accordance with the instructions contained in the "Guidelines for the use of conductometric monitoring for maintaining the water regime of power plants. MU 34-70-114-85"

8. PROCESSING AND PRESENTATION OF RESULTS
MEASUREMENTS

8.1. The results of UEP measurements must be reduced to a sample temperature of 25 °C. In cases where the measuring instruments used do not have a device for automatically bringing the measurement results to a temperature of 25 °C, the reduction is carried out manually according to schedules. contained in the "Guidelines for the use of conductometric monitoring for maintaining the water regime of power plants. MU 34-70-114-85".

8.2. As an indicator of the accuracy of UEP measurements, an interval is taken in which, with a confidence probability R d the total measurement error is found.

The results of measurements of the electrical potential of water and steam are presented in the form:

where is the result of measuring the electrical conductivity, µS/cm;

Limit of permissible value of absolute measurement error, µS/cm;

R d- the probability with which the measurement error of the UEP is within the specified limits.

8.3. The numerical values ​​of the measurement result and the error must end with a digit of the same order.

When measuring UEP, the numerical values ​​of the measurement result and error must have two significant figures.

8.4. Limit of permissible value of total absolute measurement error ( D) UEP in the general case is determined by the formula:

(2)

Where D spp- absolute measurement error caused by changes in the physicochemical properties of the analyzed sample as it passes through various elements of the sampling system as it passes through various elements of the sampling and sample preparation system, µS/cm;

D AK- absolute error of the conductometer, µS/cm;

Dxi- additional error caused by deviation of operating conditions i- th measuring instrument included in the UEP measurement scheme, from normal, µS/cm;

n- the number of measuring instruments included in the UEP measurement scheme.

Limit of the permissible value of the total absolute measurement error of the UEP under normal operating conditions of measuring instruments ( DO) is determined by the formula:

(3)

Determination of additional errors caused by deviations in the operation of measuring instruments from normal (for example, ambient temperature, supply voltage and other external factors specified in the technical documentation for the measuring instruments used) is carried out as follows:

the mathematical expectation M of each influencing quantity is calculated using the formula

Where Yi- the value of the influencing quantity obtained when i- m dimension;

TO- number of measurements of the influencing quantity during the averaging interval.

The mathematical expectation of each influencing quantity is determined for the summer and winter seasons;

The values ​​of additional errors are determined based on the data from the technical documentation for the measuring instruments used and the obtained seasonal values ​​of the mathematical expectation of each influencing quantity.

An example of calculating the UEP measurement error is given in Appendix 2.

8.5. This technique ensures obtaining results of measurements of the electrical conductivity of water and steam with a limit of permissible value of the reduced measurement error ± 5% with a confidence level R d = 0,95.

Annex 1

MEASURING INSTRUMENTS AND AUXILIARY DEVICES, THEIR PURPOSE
AND TECHNICAL CHARACTERISTICS

Name	Main technical and metrological characteristics	Purpose
Sampling device		Sample selection
Sampling line	Material - stainless steel 12Х18Н12Т, diameter 10?2 mm, installation in accordance with the requirements of OST 108.030.04-80	Supplying a sample from the sampling device to the primary measuring transducer of the conductometer
Pre-plugged refrigerator	In accordance with OST 108.030.04-80	Cooling of feed water, boiler water, steam samples
Sample preparation system (SPP, SUPP)	Sample flow rate from 0.008 to 0.028 kg/s (from 30 to 100 l/h). Sample pressure at the inlet from 1 to 30 MPa; sample outlet pressure (0.1 ? 0.005) MPa. The sample temperature at the outlet is not higher than (40 ? 1) °C	Unification of sample parameters (pressure, temperature); alarm about exceeding the permissible values ​​of temperature and pressure of the sample and about stopping the sample supply; protection of measuring instruments from the arrival of samples of high parameters.
Automatic conductometer AK-310	Indication range from 0 to 1; from 0 to 10; from 0 to 100 µS/cm. The main reduced error is ± 5% of the upper limit of the reading range. Sample flow rate (5.6+0.3)?10 -3 kg/s ((20±1) l/h)	Measuring and recording the UEP of a sample

Appendix 2

Information

EXAMPLE OF CALCULATING ERROR OF EC MEASUREMENTS
ACCORDING TO TECHNICAL DOCUMENTATION

1. Measurement of electrical conductivity under normal operating conditions of measuring instruments.

The permissible value of the total absolute measurement error of the UEP under normal operating conditions of measuring instruments is determined by formula (3).

Initial data:

requirements for the sampling device and instrument sampling line are met in accordance with OST 108.030.04-80;

sample preparation system - SUPP type;

UEP measurements are performed with an automatic conductivity meter AK-310 in the range from 0 to 1 µS/cm.

Determination of the measurement error of the UEP.

Since all conditions for ensuring the duration of the test have been met, we can accept with sufficient accuracy for practice Dspp = 0.

According to clause 5 of Appendix 1 DAK- 0.05 µS/cm.

The total measurement error is determined by formula (3):

2. measurement of UEP when operating conditions of measuring instruments deviate from normal.

The permissible value of the total absolute measurement error of the UEP is determined by formula (2).

Initial data:

The UEP measurement conditions are assumed to be the same as in the previous example, with one difference - the intermediate converter of the conductometer is installed in a room with an air temperature of 35 °C.

Determination of UEP measurement error:

D spp=0 and D AK=± 0.05 µS/cm (see previous example);

the additional error caused by the deviation of the ambient air temperature at the installation site of the converter from normal, according to the passport for the automatic conductivity meter AK-310, will be DT= ± 0.025 µS/cm.

The total measurement error is determined by formula (2).