Chapter 4. Quantitative chemical analysis

Titrimetric analysis

Quantitative analysis of a substance is experimental determination (measurement) of content chemical elements, compounds or their forms in the analyte, expressed in numerical form. The purpose of quantitative analysis is to determine the content (concentration) of components in a sample. It can be carried out using various methods: chemical, physico-chemical, physical, biological.

Chemical Methods include gravimetric (weight) and titrimetric or volumetric types of analysis .

Gravimetric Methods based on accurate mass measurement the component being determined, or a compound quantitatively related to it with a precisely known composition.

Under titrimetric analysis understand the determination of the content of a substance by an accurately measured amount of a reagent (mass or volume) that has reacted with the component to be determined in an equivalent amount.

Methods of quantitative chemical analysis do not require sophisticated equipment, have good accuracy and reproducibility. Since the error of many titrimetric methods does not exceed ± 0.5 ¸ 0.1%, and gravimetric methods - no more than 0.1%, these methods are still used as metrological during the certification of analysis methods. However, they have a number of disadvantages. The most significant are the lack of selectivity and sensitivity, which requires careful preparation of the sample and the reagents used.

For chemical analysis, reagents of the following qualifications are used: h.(pure), analytical grade– pure for analysis; h.h.– chemically pure; o.s.h.- very clean. The lowest content of impurities have reagents brand o.s.h. And h.d.a., while reagents qualification h.h.(pure) and below are not always suitable for quantitative determinations and require additional purification.

The quality of the results obtained is largely determined by the correct selection of dishes and equipment. For quantitative analysis, a wide variety of laboratory glassware and scales are used. According to its purpose, it is classified into:

Ø special purpose dishes - used to perform a narrow range of operations. This various kinds of pycnometers, hydrometers, refrigerators, round-bottom flasks, Kjeldahl flasks;

Ø general purpose crockery - the most commonly used in various types of work: boiling, titration, filtration, etc. This test tubes, funnels, beakers, flat-bottomed round and conical flasks (Erlenmeyer), crystallizers, Petri dishes, weighing bottles, desiccators(fig. 4.1 and 4.2);

Figure 4.1 - General laboratory glassware used in various methods of analysis.

Figure 4.2 - general purpose dishes: a) glass bottles with lids for weighing and storing hygroscopic substances; b) various types of washers for rinsing dishes.

Ø measuring utensils - is used to measure the volume of liquid. It is divided into dishes accurate measurement : pipettes (Mora and graduated), burettes, volumetric flasks Mohr (Fig. 4.3) and inaccurate measuring utensils: measuring cylinders, beakers, glasses, flasks with divisions, graduated test tubes: cylindrical and conical or finger (Fig. 4.4).

Figure 4.3 - utensils for accurate volume measurement, used in

selection of aliquots, preparation of standard solutions and titration.

Figure 4.4 - Dishes for inaccurate volume measurement used

for the preparation of solutions to be standardized and reagents

in qualitative analysis.

For taking aliquots in titrimetry, during quantitative precipitation from solutions, as well as in the preparation of standard solutions for various purposes, always use only precision measuring glassware and analytical balances! crockery for inaccurate volume measurement And technochemical scales used: in preparation standardized solutions, measuring the volumes of solutions used to maintain the acidity of the medium (buffers), carry out precipitation and titration of aliquots. When working with measuring utensils, especially accurate , it must be kept clean. For this purpose, dishes before use Always rinse with distilled water and dry. Accurate the dishes are dried in air using ether or alcohol, and imprecise And general purpose– on heated dryers or in a drying cabinet. To eliminate errors in the selection of aliquots and work with burettes, they are additionally rinsed with the measured solution.

A change in the temperature of the medium leads to the occurrence of measurement errors: overestimation or underestimation of the determined volume, and hence the calculated concentration. Therefore, all measuring utensils have a stamp indicating their volume at 20ºС, and precise measurement dishes - optional calibrated with distilled water using an analytical balance and correcting for the density of water at a given temperature. Sometimes there is an additional marking indicating heat resistance and chemical resistance. The heat resistance of glass is indicated matte square or circle. In such dishes, liquids are heated and boiled on stoves and gas burners.

Scales. Devices used to determine the mass of bodies are called scales . In chemical analysis, two types of scales are used: technical and analytical. They can be both mechanical and electronic; have one cup (quadrant mechanical and electronic) or two (pan and damper scales). Under weighing understand comparison of the mass of a given object with the mass of calibrated weights (weights) or a measurement of the pressure that an object exerts on the scale pan in terms of its mass units. Weights are necessary when working on damper or pan balances, and in quadrant and electronic one pan balance the scales are already graduated in units of mass.

Scales differ in accuracy class and measurement limits. Technical scales - the least accurate and are used for weighing relatively large samples. For chemical purposes, quadrant or cup technical scales of 0.2–1 kg (sometimes up to 5 kg) are usually used. Their accuracy does not exceed 0.01 - 20 g. Technical scales with an accuracy of 0.1 - 0.01 g called technochemical and used in the laboratory for sampling from 1 to 500 g . In modern electronic technical scales the accuracy of measurements can be higher: with the maximum weight of an object of 500 g, it varies from 0.001 g to 0.2 g.

Analytical balance serve for exact definition sample mass in the preparation of standard solutions, carrying out gravimetric measurements, etc. The accuracy of damper balances is ± 2 × 10 - 4 - 2 × 10 - 5 g, and electronic - up to 2 × 10 - 6 g. On average, such scales are designed for the maximum mass object 50 - 200 g, but scales and increased accuracy are produced for the maximum mass of a sample of 1 - 20 g, which are used in some types of instrumental analysis, for example, in spectral analysis.

When working on scales, you must strictly follow the rules for handling them. Improper installation or careless handling can result in unreliable results and damage the balance. This is especially important to remember when using electronic and analytical damper balances.

Indicators and their selection

To detect the equivalence point in titrimetric analysis, use indicators(from lat. indicare- show, reveal). indicators Reagents are called reagents that can contrastly change their color depending on changes in the properties of the medium. Most often it is organic matter With reversible color change(exception - precipitation indicators).

Far from any substance that changes its color depending on the properties of the medium is suitable as a titration indicator. Moreover, the indicators change their color regardless of whether the equivalence point has been reached or not yet reached: the defining moment is only the parameters of the environment. Therefore, it is important choose the right indicator . TO necessary requirements When choosing an indicator, include the following:

Ø titration index pT (indicator color transition interval) should be located in the jump area and be as close as possible to the equivalence point, and the value of the indicator error cannot exceed 0.5%;

Ø indicator color- very intense and clearly fixed in the solution visually even with strong dilution (for 1 - 2 drops of the indicator);

Ø sensitivity of an indicator substance to changes in the properties of the medium- high, so that the color change occurs with a minimum excess of titrant in the solution (from 1 - 2 drops of titrant);

Ø transition interval- narrow and high contrast;

Ø indicator must be stable- do not decompose in air and in solution;

Ø indicator substance- indifferent to the titrated solution or titration products, i.e., reactions between them that affect the course of the titration curve should not occur.

Depending on the properties, indicators are classified by number transitions (single and multijunction) and by area of ​​application . TO unijunction refers to phenolphthalein (crimson - colorless), and to multijunction- methyl orange (yellow - orange and orange - pink). Examples of other multi-transition indicators are: a-Naphtholbenzein - two transitions: green - yellow (pH = 0 - 1) and yellow - blue (pH = 8.4 - 10); Methyl violet - three transitions (yellow - green, green - blue, blue - violet); Cresol red - two transitions (red - yellow and yellow - magenta). Multi-junction indicators also include universal indicators. Sometimes multi-transition indicators in titration are used as single-transition indicators if the color change of not all transitions occurs in a relatively narrow range of values ​​or they are not clearly fixed.

By Areas of use There are the following groups of indicators:

1. Acid - basic.

2. Redox indicators (redox indicators).

3. Metallochromic (complexing agents).

4. Precipitation.

5. Adsorption.

6. Specific.

7. Mixed.

8. Luminescent (fluorescent) and metal fluorescent.

9. Extraction.

10. Shielding.

This division is rather arbitrary, since during the titration, several parameters that correlate with each other often regularly change simultaneously. For example, pH and system potential E, pH and PR value (solubility products). There is also a more complete classification of indicators, taking into account both their chemical structure and the mechanism of color change, but such a classification is rather complicated and will not be considered by us.

Chromophore theory (HT)

The change in the color of the indicator according to CT is associated with reversible structural processes (isomerization) occurring due to intramolecular rearrangements of individual functional groups in the molecule. Each of the structural forms ( tautomers) is stable only in a certain range of pH values ​​or other environmental parameters, therefore, the addition or elimination of a proton leads to a rearrangement of the indicator molecule, as a result of which new functional groups (chromophores) that existed before appear or disappear. These features explain why the color change of a number of indicators does not occur instantly, but is extended over time, since tautomeric transformations are intramolecular rearrangements, which, unlike ionic reactions (dissociations), are slower.

Functional groups responsible for the color of the indicator substance, got the name chromomorphic(chromo - color). These include: nitro group (O = N -); an azo group (–N = N–), several closely spaced carbonyl groups (>C=O).

Functional groups, color enhancing or stabilizing indicators are called auxochromic. Similar properties are possessed by: amino groups (–NH 2) and amine derivatives; oxygen- and nitrogen-containing compounds (–O–CH 3; –N (CH 3) 2; –N (C 2 H 5) 2), hydroxo groups (electron donor). The color of the indicator appears brighter if the substance contains, in addition to auxochromic groups, also anti-auxochromic(electrophilic) groups that provide a shift in the electron density in the molecule. For example, some oxygen-containing radicals (-NO 2 , -NO, -COCH 3) have electrophilic properties. As an example, we present the structural formulas of tautomeric isomers of a single-transition indicator p-nitrophenol(Fig. 4.8)

Figure 4.8 - The structure of the tautomeric forms of the indicator substance

(p-nitrophenol) containing chromophoric and auxochromic groups.

The chromophore theory also has a number of disadvantages, in particular:

Ø does not explain why the color change and tautomeric transformations depend on the pH value of the medium;

Ø how the color of most indicators with chromophore groups changes almost instantly, which contradicts the mechanism of intramolecular rearrangement;

Ø and, finally, the chromophore theory is not amenable to quantitative description.

Ion-chromophoric theory.

This theory combined the representations of the ionic (dissociative) and chromophore theories. According to ion-chromophore theory, acid-base indicators are weak acids and bases, and neutral molecules and their ionized forms contain different chromophore groups. IN aqueous solution the indicator molecule is capable of either donating hydrogen ions (weak acid) or accepting them (weak base), while undergoing tautomeric transformations according to the scheme:

HInd Û H + + Ind - Û H + + Ind - B,

Where Hind- non-ionized indicator molecule (weak acid, tautomeric form I); Ind-B- anion of a strong acid having a tautomeric form II in a dissociated state (basic form II).

With a decrease in pH (acidification of the solution), the equilibrium in the system shifts to the left towards the non-ionized form Hind. As soon as it begins to dominate, the solution acquires its color.

If the solution is alkalized (pH increases, and the concentration of H + - decreases), the equilibrium in the system shifts to the right and the dominant form becomes Ind-B, which gives the solution a different color, already characteristic of the main form II. Thus, the acidic form of phenolphthalein (рН = 8.2) is colorless, and upon transition to an alkaline medium, an anion of the tautomeric basic form (рН = 10) is formed, colored in red-crimson color. Between these forms there is a range of pH values ​​(from 8.2 to 10), corresponding to a gradual change in the color of the indicator.

The human eye is able to perceive the color of only one of the two forms in the mixture, provided that their color intensity is the same, if the concentration of one of these forms is about 10 times higher than the second.

indicators.

1. Acid - basic indicators – they are weak organic acids or bases. The color of the indicators is reversible and is determined by the pH value of the medium. The transition interval is calculated using the dissociation constant:

DрН ind. = – logK a ± 1, where K a is the dissociation constant of the indicator.

Consider an example. Indicator dissociation constant alizarin yellow K a \u003d 10 -11. Let's determine the transition interval of the indicator DрН ind:

DрН ind. = – log (10 -11)± 1 =11 ±1 Þ DрН ind [(11-1) ¸ (11+1)] = .

Indicator transition interval DрН ind = 10 ¸ 12.

2. Redox indicators- organic substances that exhibit the properties of weak oxidizing or reducing agents. They can be both reversible (diphenylamine) and irreversible, the color of which is destroyed (methyl red, methyl orange, they are also known as acid-base indicators). A change in the color of the indicator corresponds to a reversible reaction: Ind + + ne Û Ind; Where +- oxidized (Ox), and Ind- restored (Red) indicator form, n is the number of electrons in a given half-reaction . Change redox potential (indicator transition interval) calculated according to the Nernst equation: DE \u003d E 0 ± 0.059 / n,

where E 0 - standard redox potential for the indicator; n is the number of electrons in the half-reaction.

For example: Redox indicator diphenylamine has E 0 \u003d + 0.76 V and n \u003d 2. Let us determine the interval of its transition.

According to the formula: DE = 0.76 ± 0.059/2 = 0.76 ± 0.0295 Þ DE = (0,76 –0,0295) ¸ (0.76 + 0.295) = 0.73 ¸ 0.79 (B).

3. Metal-chromic (metal indicators)- These are organic dyes (weak acids) that have their own chromophore groups and reversibly change their color when they form a complex salt with metal cations. They are mainly used in complexometry, for example, eriochrome black T. For these indicators, the condition must additionally be met: the stability of the complex of the titratable substance with the titrant is higher than that of the complexes formed by it with the indicator in solution. Transition interval calculated by the formula:

DрMe = – logK set. ± 1, where K mouth is the stability constant of the complex formed by this indicator with the titratable substance.

4. Precipitation indicators The group of indicators is insignificant in composition, since a colored precipitate should form in solution immediately after the almost complete precipitation of the analyte (residual concentration is less than 10–6 mol/dm 3), and there are few such substances.

The transition interval of the indicator is determined by the value of the solubility product (PR) of the precipitate formed by it:Dp(PR) = – logPR. ± 1.

Adsorption indicators are organic substances , exhibiting the properties of weak acids or bases, such as eosin or fluorescein.

The mechanism of action of the adsorption indicator is shown in the diagram (Fig. 4.9). As can be seen from figure 4.9, the appearance of coloration occurs as a result of changes in the composition of ions on the surface of the dispersed phase(precipitate or colloidal particle) due to processes of adsorption or desorption of indicator ions. This phenomenon is explained by the change in sign of the electrostatic charge on the surface of precipitate particles during titration. The reason for this is that in an under-titrated solution, the surface of the precipitate predominantly sorbs titratable ions, which are part of its composition (the AgCl precipitate sorbs untitrated Cl - ions) and acquires their charge. As a result, the sorption of indicator ions becomes impossible.

Figure 4.9 - Schematic representation of the structure of the sorbed layer on the surface of the AgCl precipitate formed during the titration of Cl ions - AgNO 3 solution.

A - up to the equivalence point(Cl - ions are sorbed by the surface, while indicator ions Ind - remain in solution);

b - after the equivalence point(the surface absorbs Ag + titrant ions, which attract indicator ions Ind -).

As soon as the equivalence point is reached, the solution will have excess of oppositely charged ions of the titrant, which will also begin to accumulate near the surface of the precipitate, attracting indicator ions from the solution. The resulting substance colors the surface of the precipitate.

5. Specific indicators – A relatively small group of indicators, since their use is based on specific reactions with the titratable substance. A starch solution has such properties in relation to J 2 molecules: the formation of a blue compound.

Titration methods.

Since far from any substance can be analyzed directly, by reaction with a titrant, especially if it is unstable in air, several methods have been developed to solve such problems. tricks (ways) analysis. They allow you to replace unstable, under given connection conditions, by an equivalent amount of a more stable one that does not undergo hydrolysis or oxidation. The following main titrimetric analysis methods:

Ø direct titration;

Ø reversible;

Ø back titration or titration on the residue;

Ø indirect titration or by substitution (by substituent).

Table 4.1 shows the applications various ways depending on the type of titration.

Table 4.1 - Application of various types and methods of titration.

method name	private method name; (working solution)	substances determined by titration
direct	reverse	indirect
Protolithometry	Acidimetry (acids: HCl)	grounds; salts formed by a strong base and a weak acid	salts of weak bases and strong acids; organic compounds	-
Alkalimetry (Alkalis: NaOH)	acids; salts formed by a weak base and a strong acid	-	-
Redox meter	Permanganatometry ()	reducing agents	oxidizers	substances that react with reducing agents
Iodometry ( and )	reducing agents	reducing agents	oxidizers; acids
Complex-metry	Complexometry (EDTA)	cations that form complexes with EDTA	cations in water-insoluble compounds; cations for which there is no indicator	cations that form a more stable complex with EDTA than with
Sedimentation method	Argentometry ()	Anions forming a precipitate	cations that form a sparingly soluble precipitate with halogen ions: , , ; ,	-

Let us consider in more detail the essence of various methods of titration.

1. Direct titration It consists in the direct interaction of the titrant and the titratable substance. In the process of titration, a titrant solution is gradually added to an aliquot or a sample of a substance, the volume of which is accurately fixed in T. E. A working solution of a known concentration is used as a titrant. The calculation of the content of a substance in a sample is performed according to the law of equivalents:

= (4.1)

where is the number of mole equivalents of the analyte in the titrated sample; A - the number of mole equivalents of the titrant that reacted with the component to be determined A.

component concentration A in solution is calculated by the formula:

(4.2)

where is the molar concentration of the equivalent (normality) of the titrated solution (determined component), mol-eq/l; is the volume of an aliquot of the titrated solution, ml; is the concentration and is the volume of the titrant at the equivalence point. Titration method of individual weights formula (4.2) is transformed into expression (4.3):

(4.3)

The method is applied in all cases where there are no restrictions. For example, when analyzing acids, determining the hardness of water.

2. Reverse titration – This is a type of direct titration, when the working and titrated solutions are interchanged. In this case, the analysis is aliquots of the working solution, and in T.E. measure the spent titration the volume of the analyzed solution. Calculations are carried out in the same way as in direct titration, according to formulas (4.2) or (4.3). The method makes it possible to limit the surface area of ​​the solution in contact with air when standardizing relatively unstable compounds, such as NaOH.

Substituent titration (indirect) and residue titration (reverse) based on the use auxiliary solution interacting with the component to be determined. This technique allows one to analyze chemically unstable objects or in the absence of a suitable indicator.

In an indirect titrationfirst, the reaction of the analyte is carried out A with auxiliary solution IN, and then titrated equivalent amount of reaction product formed WITH(deputy). This method can be represented as a diagram: A + B C + (t-t), based on which we write the expression for the law of equivalents:

= = . (4.4)

It follows from equality (4.4) that = and the calculation can also be performed using formulas (4.2) and (4.3) used for direct titration. For the completeness of the reaction, the auxiliary solution is always taken with a slight excess. This method of titration is implemented in iodometry.

In back titration Also the first reaction is between the analyte A and taken in excess auxiliary solution IN, but then titrated residue of unreacted auxiliary solution . Therefore, it is necessary to know exactly concentration auxiliary solution IN and his volume taken for analysis. Component definition A performed according to the scheme: A + B B ost + (t-t). Based on the titration conditions, the law of equivalents can be written as:

– = . (4.5)

Where do we get:

= - . (4.6)

If all substances are taken as solutions, then formula (4.6) takes the form

(4.7)

If at least one of the substances is taken in dry form (its mass is known), then expression (4.6) should be used and the value for each of the substances should be recorded individually.

And how to prepare them.

Titrimetry uses solutions the concentration of which is established by any method with a high degree of accuracy. Such solutions are called standard titrated or simply titrated . Solutions are classified by purpose and by the method of determining their concentration.

By appointment they are conditionally divided into working solutions and solutions standards (primary and secondary).

Workers called solutions that are used directly in the analysis when determining the content of a substance. If the working solution does not belong to the standard, then it must be standardized just before analysis, since the concentration during storage could change significantly. The exact concentration of the working solution is found by titration standard solution or adjusting substances (accurate weighing method). This applies, for example, to such working solutions as: NaOH, Na 2 S 2 O 3 × 5H 2 O.

Under standard solution understand such a titrated solution that stably maintains its concentration during long-term storage. The main purpose of standard solutions - determination of the exact concentration of working and other solutions used in titration.

The process of establishing the exact concentration of a solution by titrating it against a standard is called standardization.

According to the method of determining the concentration distinguish primary standards And standardized solutions .

Standardized solutions - these are solutions whose concentration is set according to the standard and cannot be accurately determined in advance. These include solutions of acids, alkalis, hydrolyzable and hygroscopic salts, as well as substances that can react with atmospheric oxygen and carbon dioxide. There are many ways to prepare standardized solutions. The most commonly used for this purpose are: preparation by an approximate sample (alkalis, salts), methods of diluting or mixing solutions (acids, salts), ion exchange methods (salt solutions).

Standard solutions are classified by the method of determining their concentration . Distinguish: primary standards or solutions with prepared titer And secondary standards - solutions with a fixed titer.

Primary standards are solutions that are prepared either according to the exact weight of the substance(Fig. 4.10), or by diluting specially prepared standardized reagents - fixanals(Fig. 4.11). Fixanal is a glass sealed ampoule produced by the industry and containing a strictly standardized amount of a reagent, usually calculated per 1 liter of 0.1 N. solution.

Solution preparation by exact hitch begin with the calculation of its mass according to a given concentration (titer or normality) and the volume of the flask. A sample of a standard substance is weighed on an analytical balance with an accuracy of 1 × 10 -4 g and quantitatively transferred to a volumetric flask, where it is dissolved with stirring (Fig. 4.10).

Figure 4.10 - The order of operations in the preparation of the primary solution

standard for accurate weighting: 1 - Mohr volumetric flask; 2 - funnel;

3 - bottle with a sample of the substance; 4 – washer with distilled water;

5 - pipette or dropper.

a - transfer of a sample of a substance into a volumetric flask; b - rinsing the funnel;

c – bringing the volume of the standard solution to the mark.

This method usually prepares solutions of salts such as borax (Na 2 B 4 O 7 × 10H 2 O), K 2 Cr 2 O 7 . The amount of a substance in a solution is found either by value precisely taken sample weight(when transferring it, it is necessary to thoroughly rinse the bottle), or calculate difference method, defining the exact weight of the weighing bottle, first with a sample, and then - empty, already after the transfer of the substance into the flask. If necessary, the concentration of the solution is recalculated taking into account the actually taken weight of the sample.

The procedure for preparing the solution dilution method from fixanal shown in Figure 4.11. In order for the standard obtained by this method to be of high quality and meet all the requirements, it is necessary to exclude the loss of the substance when opening the ampoule and transfer it to the flask, and also make sure that fragments of the ampoule do not get into the solution. This largely depends on the correct handling of the ampoule.

Figure 4.11 - Method of preparation of primary standard solutions

dilution method from fixanal: 1 - Mohr volumetric flask per 1 liter;

2 - lower striker; 3 - funnel; 4 - fixanal ampoule; 5 - upper striker.

Before use, the ampoule should be rinsed with distilled water and only then opened with a special striker. Immediately after transferring the substance to the flask, thoroughly rinse the ampoule with distilled water, at least 6 times its volume. This method of preparing a primary standard is simpler than using accurate weights, but inferior to it in accuracy. It is used not only to obtain solutions of salts, but also various acids.

Since for cooking primary standard solution suitable only precise measuring utensils And analytical balance, then to substances used for this purpose are subject to a number of mandatory requirements. Only reagents that are characterized by:

Ø high purity(usually not worse than 99.99 - 99.999% - qualifications of ch.d.a. and o.s.ch.);

Ø exact correspondence to the formula composition and relatively high molecular weight;

Ø storage stability both in solid form and in solution(lack of hydration, hydrolysis, oxidation and carbonization processes);

Ø easy to prepare and good solubility;

Ø irreversibility of the reaction during standardization, selectivity;

Ø the possibility of accurate fixation of T. E. by any method.

secondary standard called such standardized solutions, which are stable during storage and can be used to standardize other solutions.

Secondary standards are prepared as solutions approximate concentration by any known method, and before use - determine their exact concentration by standardization according to the primary standard. Therefore, when preparing secondary standards, high accuracy in measuring the mass of a substance or the volume of a solution is not required, as in the case of primary standards. Suitable for this purpose technochemical scales And inaccurate measuring utensils(cylinders, beakers, graduated test tubes).

An example of a solution with properties secondary standard , is hydrochloric acid. Its diluted solutions can be stored for a long time, up to 1 month or more, without a noticeable change in concentration. Bura, used in protolithometry to standardize HCl, refers to primary standards and is prepared according to the exact weight. Whereas NaOH working solution- does not possess the properties of a standard at all and its the concentration has to be reset each time it is used.

And their application in analysis

The normative document for the measurement method should regulate how many (one or more) single observations should be made, how they are averaged (arithmetic mean of the results of multiple observations, median or standard deviation) and how they are presented as a measurement result (or test result). It may be necessary to introduce standard corrections (for example, such as bringing the volume of gas to normal temperature and pressure). Thus, the result of measurements (tests) can be presented as a result calculated from several observed values. In the simplest case, the result of measurements (tests) is actually the observed value).

According to "PMG 96-2009 GSI. Results and characteristics of measurement quality. Representation forms”, the measurement result is represented by a named or unnamed number. Together with the measurement result, the characteristics of its error or their statistical estimates are presented. The presentation of measurement results obtained as the arithmetic mean of the results of multiple observations is accompanied by an indication of the number of observations and the time interval during which they were carried out.

The accuracy of the chemical analysis result. Standards for monitoring the accuracy of the result of measuring the content of the controlled component in the sample of the analyte, procedures and frequency of control

According to “GOST R ISO 5725-1-2002 Accuracy (correctness and precision) of measurement methods and results. Part 1. Basic Provisions and Definitions”:

accuracy –With the degree of proximity of the measurement result to the accepted reference value.

accepted reference value - the value that serves as the match for comparison and is obtained as:

a) a theoretical or established value based on scientific principles;

b) an assigned or certified value based on the experimental work of some national or international organization;

c) an agreed or validated value based on collaborative experimental work led by a scientific or engineering team;

d) the expected value of the characteristic being measured, i.e. the mean value of a given set of measurement results - only if a), b) and c) are not available.

The term "accuracy", when referring to a series of measurement (test) results, includes a combination of random components and a total systematic error.

right - the degree of closeness of the average value obtained from a large series of measurement results (or test results) to the accepted reference value. Notes: The indicator of correctness is usually the value of the systematic error.

systematic error is the difference between the mathematical expectation of the measurement results and the true (or, in its absence, the accepted reference) value. Notes: The true value of the quantity is unknown, it is used only in theoretical studies.

As components of the systematic measurement error, a non-excluded systematic error is distinguished, which is a component of the systematic measurement error due to the imperfection of the implementation of the accepted measurement principle, the calibration error of the measuring instrument used), etc.

precision - the degree of closeness to each other of independent measurement results obtained repeatedly in specific regulated conditions. Notes: Precision depends only on random errors and has nothing to do with the true or stated value of the measured quantity. A measure of precision is usually expressed in terms of uncertainty and is calculated as the standard deviation of the measurement results. Less precision corresponds to a larger standard deviation. "Independent results of measurements (or tests)" means results obtained by a method that is not influenced by any previous result obtained from testing the same or similar object. Quantitative values ​​of precision measures significantly depend on the regulated conditions. The extreme cases of sets of such conditions are the repeatability conditions and the reproducibility conditions.

repeatability (synonym convergence) is the precision under repeatability conditions.

repeatability (convergence) conditions- conditions under which independent measurement (or test) results are obtained repeatedly by the same method on identical test objects, in the same laboratory, by the same operator, using the same equipment, within a short period of time .

reproducibility – precision under reproducibility conditions.

reproducibility conditions – conditions under which measurement (or test) results are obtained repeatedly by the same method, on identical test objects, at different times, in different laboratories, by different operators, using different equipment, but reduced to the same measurement conditions (temperature, pressure, humidity, etc.).

Measurement result accuracy control standards are indicators of repeatability (convergence), reproducibility and correctness of the measurement result.

State system ensure
unity of measurements

TECHNIQUES FOR QUANTITATIVE
CHEMICAL ANALYSIS OF WATER SAMPLES

Moscow

Standartinform

3. APPROVED AND INTRODUCED BY Order No. 264-st of October 26, 2005 of the Federal Agency for Technical Regulation and Metrology

4. This standard implements the provisions of the Law Russian Federation"On Ensuring the Uniformity of Measurements" and the Law of the Russian Federation "On Technical Regulation"

5. INTRODUCED FOR THE FIRST TIME

Information about changes to this standard is published in the annually published information index "National Standards", and the text of changes and amendments - in monthly published information signs "National Standards". In case of revision (replacement) or cancellation of this standard, a corresponding notice will be published in the monthly published information index "National Standards". Relevant information, notification and texts are also posted in the public information system - on the official website of the national body of the Russian Federation for standardization on the Internet

1 area of ​​use. 2 3. Terms and definitions. 3 4. General provisions. 5 5. Development of a method for quantitative chemical analysis of water samples. 5 6. Certification of the method of quantitative chemical analysis of water samples. 7 Appendix A. Standards for the presentation of accuracy indicators (correctness and precision) of the method of quantitative chemical analysis of water samples. 8 Appendix B. Basic concepts and representation of uncertainty. 9 Appendix B. Methods for assessing the accuracy indicators (correctness and precision) of the method of quantitative chemical analysis of water samples. 10 Appendix D. Construction, content and presentation of documents regulating the methods of quantitative chemical analysis of water samples. 12 Appendix E. Examples of the design of sections of documents regulating the methods of quantitative chemical analysis of water samples. 14 Appendix E. Content of work in the course of metrological studies and certification of the method of quantitative chemical analysis of water samples. 17 Appendix G. Form of certificate of attestation of the method of quantitative chemical analysis of water samples. 18 Bibliography. 19

GOST R 8.613-2005

NATIONAL STANDARD OF THE RUSSIAN FEDERATION

State system for ensuring the uniformity of measurements TECHNIQUES FOR QUANTITATIVE CHEMICAL ANALYSIS OF WATER SAMPLES General development requirements State system for ensuring the uniformity of measurements. Procedures for quantitative chemical analysis of water samples. General requirements for development

Introduction date - 2006-07-01

1 area of ​​use

This standard applies to newly developed and revised methods for the quantitative chemical analysis of samples of natural, drinking, waste water (hereinafter referred to as the MCCA of water samples) and establishes general requirements for their development and certification.

2. Regulatory references

This standard uses normative references to the following standards:

GOST R 1.5-2004 Standardization in the Russian Federation. National standards of the Russian Federation. Rules for construction, presentation, design and designation

GOST R 8.563-96 State system for ensuring the uniformity of measurements. Measurement techniques

GOST R ISO 5725-1-2002 Accuracy (correctness and precision) of measurement methods and results. Part 1. Basic provisions and definitions

GOST R ISO 5725-2-2002 Accuracy (correctness and precision) of measurement methods and results. Part 2: Basic method for determining the repeatability and reproducibility of a standard measurement method

GOST R ISO 5725-3-2002 Accuracy (correctness and precision) of measurement methods and results. Part 3. Intermediate precision values ​​of the standard measurement method

GOST R ISO 5725-4-2002 Accuracy (correctness and precision) of measurement methods and results. Part 4: Basic methods for determining the validity of a standard measurement method

GOST R ISO 5725-5-2002 Accuracy (correctness and precision) of measurement methods and results. Part 5 Alternative Methods determining the precision of a standard measurement method

GOST R ISO 5725-6-2002 Accuracy (correctness and precision) of measurement methods and results. Part 6. Using precision values ​​in practice

GOST 1.2-97 Interstate standardization system. Interstate standards, rules and recommendations for interstate standardization. The order of development, adoption, application, updating and cancellation

GOST 8.315-97 State system for ensuring the uniformity of measurements. Standard samples of the composition and properties of substances and materials. Key points

GOST 8.417-2002 State system for ensuring the uniformity of measurements. Units

GOST 27384-2002 Water. Standards of measurement error of indicators of composition and properties

Note - When using this standard, it is advisable to check the validity of reference standards in the public information system - on the official website of the national body of the Russian Federation for standardization on the Internet or according to the annually published information index "National Standards", which was published as of January 1 of the current year, and according to the corresponding monthly published information signs published in the current year. If the reference standard is replaced (modified), then when using this standard, you should be guided by the replaced (modified) standard. If the referenced standard is canceled without replacement, the provision in which the reference to it is given applies to the extent that this reference is not affected.

3. Terms and definitions

In this standard, the following terms are used with their respective definitions:

3.7. quantitative chemical analysis of water samples: Experimental quantitative determination of the content of one or a number of components of the composition of a water sample by chemical, physico-chemical, physical methods (taking into account the recommendations).

3.8. result of a single analysis (determination): The value of the content of a component in a water sample, obtained during a single implementation of the analysis procedure.

3.9. analysis result (measurement): The arithmetic mean or median of the results of a single analysis (determination) (taking into account recommendations).

3.10. method of quantitative chemical analysis of samples of natural, drinking, sewage, treated wastewater; MKCA of water samples: A set of operations and rules, the implementation of which provides the results of a quantitative chemical analysis of samples of natural, drinking, sewage, treated wastewater with established error (uncertainty) characteristics (taking into account recommendations).

Note - MCCA of water samples is a kind of measurement technique.

3.11. quality indicators of MKCA water samples: Indicators of accuracy (correctness and precision) of the MKCA of water samples.

3.12. indicators of accuracy (correctness and precision) of MKCA of water samples: Assigned characteristics of the error (its components) of the MCCA of water samples (taking into account the recommendations).

3.13. assigned characteristics of the MKCA error of water samples and the characteristics of the error of its components: The established characteristics of the error and its components for any of the totality of the results of the analysis obtained in compliance with the requirements and rules of the certified ICCA water samples (taking into account the recommendations).

Note - The assigned error characteristics characterize the guaranteed accuracy of the MKCA of water samples.

3.14. measurement uncertainty: A parameter associated with a measurement result that characterizes the spread of values ​​that can be attributed to the measurand .

NOTE Uncertainty is the equivalent of an assigned error characteristic. In this case, the equivalent of the expanded uncertainty is the interval estimate of the assigned error characteristic, the equivalent of the standard uncertainty is the point estimate of the assigned error characteristic [see. Table A.1 (Appendix A) and Appendix B].

3.15. content range (measurement range): The interval of the content of the indicator of a water sample, provided for by the ICCA of water samples.

3.16. Scope of MKCA water samples: The range of contents and ranges of permissible values ​​of the influencing factors of water samples and MCCA of water samples.

3.17. influencing factors of water sample: Interfering components and other properties (factors) of the sample that affect the result and the error (uncertainty) of measurements.

3.18. influencing factors of MCCA of water samples: Factors, the values ​​of which determine the conditions for the analysis of water samples according to the ICCA and which affect the result and the error (uncertainty) of measurements.

4. General provisions

4.1. MKCA of water samples are developed and used in order to ensure the performance of measurements with an error (uncertainty) that does not exceed the standard of measurement error for indicators of the composition and properties of water, established by GOST 27384.

4.2. The ICCA of water samples is set out in the following documents:

National standards of the Russian Federation;

Standards of organizations (enterprises).

4.3. MKCA water samples are used:

Bodies of state control over pollution and the state of the natural environment;

Bodies of state sanitary supervision;

Bodies of the state service for monitoring the level of pollution of the natural environment;

Organizations, individual enterprises or groups of enterprises (related to the relevant industry, department or association of legal entities) to assess the quality and (or) pollution of water.

4.4. Standards for MCCA of water samples (hereinafter referred to as documents for MCCA of water samples) are developed in accordance with the requirements of GOST R 1.5, GOST 1.2 and GOST R 8.563. Metrological supervision of water samples certified by the MKCA is carried out in accordance with GOST R 8.563 and,.

5. Development of a method for quantitative chemical analysis of water samples

5.1. The development of ICCA water samples consists of the following stages:

Development of terms of reference (TOR);

Choice of the method of analysis and technical means (measuring instruments, standard samples, certified mixtures, reagents and materials, volumetric utensils, equipment);

Establishing the sequence and content of operations in the preparation and performance of measurements, including the establishment of influencing factors of water samples and MCCA of water samples and methods for their elimination, the range of contents of the determined component and the permissible values ​​of influencing factors;

Experimental testing of the established algorithm for performing measurements (carrying out pilot measurements);

Planning and conducting an experiment (metrological studies) to assess the quality indicators of the ICCA of water samples to establish the attributed characteristics of the measurement error (uncertainty) and its components;

Establishing the values ​​of the assigned characteristic of the error (uncertainty) of measurements;

Selection and assignment of algorithms for operational control of the analysis procedure during the implementation of the ICA of water samples in a particular laboratory;

Development of a draft document for the ICCA of water samples;

MKCA certification of water samples;

Approval of the draft document for the ICCA of water samples.

5.2. The TOR provides the initial data for the development of the ICCA of water samples (names of the measured quantities, characteristics of the analyzed water samples, measurement error standards for indicators of the composition and properties of water samples, measurement conditions in the form of nominal values ​​​​and (or) boundaries of the ranges of possible values ​​​​of influencing quantities).

5.3. Methods and measuring instruments are chosen in accordance with. The types of measuring instruments chosen must be approved in accordance with:

Rules, if the MKCA of water samples is intended for use in the field of distribution of state metrological control and supervision;

The procedure established in the field of defense and security, if the ICCA of water samples is intended for use in the field of defense and security.

Standard samples must be approved in accordance with GOST 8.315, certified mixtures must be approved in accordance with.

5.4. For the MKCA of water samples used to measure the component at the level of the water quality standard, when setting the range of component contents, the lower limit of the range of contents of the determined component WITH n must satisfy the condition

WITH n? 0.5NKV, (1)

where NKV is the water quality standard.

Notes

1. An exception may be components for which it is impossible to achieve the values ​​indicated in formula (1). In this case WITH n can satisfy the condition WITH n? NKV.

2. In the absence of data on the value of the NKV, data on the background or average levels of the values ​​of this indicator are used as an indicative level of values ​​for the water quality component.

5.5. The planning of an experiment to assess the quality indicators of the MKCA of water samples is carried out in accordance with GOST R ISO 5725-1, GOST R ISO 5725-2, GOST R ISO 5725-4 and.

In general, the main stages of planning an experiment to assess the quality indicators of the MCCA of water samples are:

Drafting block diagram MKCA of water samples and analysis of possible sources of error (uncertainty) of measurements;

Studying the composition of initial water samples, studying the possible influence of the total composition of water samples on the measurement results;

Refinement of the range and scope of the ICCA of water samples based on the study;

Choosing a method for assessing the quality indicators of the MCCA of water samples based on the study, determining the availability of standard samples, the possibility of preparing certified mixtures, adding additives to the analyzed sample, the availability of a comparison method, etc.;

Determination of the number of laboratories that should be involved in a joint assessment experiment (if necessary, the introduction of ICCA water samples into the network of laboratories);

Determining the timing of the evaluation experiment.

5.6. Methods for expressing the attributed error characteristics of the MKCA of water samples must comply with the recommendations, taking into account Annex A and the requirements of GOST R ISO 5725-1. Uncertainty is expressed in accordance with , , and taking into account Annex B.

The methods for assessing the quality indicators of the MKCA of water samples are selected according to GOST R ISO 5725-1, GOST R ISO 5725-2, GOST R ISO 5725-4, GOST R ISO 5725-5, and also in accordance with the recommendations and Appendix B. Methods for assessing uncertainty choose according to , , .

5.7. The choice and assignment of algorithms for operational control of the analysis procedure during the implementation of the ICA of water samples in a particular laboratory is carried out in accordance with. The choice and assignment of algorithms for monitoring the stability of the measurement results obtained by the MKCA of water samples when it is implemented in a particular laboratory is carried out in accordance with GOST R ISO 5725-6 and.

5.8. Documents for the ICCA of water samples in the general case should contain the following sections:

Purpose and scope of ICCA water samples;

Assigned characteristics of measurement error (uncertainty);

Measuring instruments, auxiliary devices, reagents, materials;

Measurement method;

Requirements for the qualification of performers;

Measurement conditions;

Preparation for measurements;

Performing measurements;

Calculation of measurement results, including methods for checking the acceptability of single determination results obtained under repeatability conditions and measurement results obtained under reproducibility conditions;

Quality control of measurement results during the implementation of the MKCA of water samples in the laboratory;

Registration of measurement results.

The construction and presentation of documents for the ICCA of water samples - in accordance with Appendix D. Examples of the design of some sections of the documents for the ICCA of water samples are given in Appendix D.

6. Certification of the method of quantitative chemical analysis of water samples

6.1. Certification of the ICCA of water samples is carried out in order to confirm the possibility of performing measurements in accordance with the procedure regulated by the document for the ICCA of water samples, with the measurement error (uncertainty) characteristics not exceeding the assigned error (uncertainty) characteristics specified in the document for the ICCA of water samples.

6.2. Water samples are certified by the MKCA:

State Scientific and Metrological Centers (GNMC);

Bodies of the State Metrological Service (OGMS);

32 State Research and Testing Institute (hereinafter referred to as 32 GNIII MO RF) (in the field of defense and security);

Metrological services (organizational structures) of an organization (enterprise).

The metrological service (organizational structure) of an organization (enterprise) that carries out certification of the ICCA of water samples used in the field of distribution of state metrological control and supervision must be accredited for the right to certify the ICCA of water samples in accordance with the rules.

Note - Documents for the ICCA of water samples used in the areas of distribution of state metrological control and supervision are subjected to metrological examination at the SSMC or in organizations whose metrological services are accredited for the right to conduct metrological examination of documents for the ICCA of water samples used in the areas of distribution of state metrological control and supervision. Documents for the MKCA of water samples intended for use in the field of defense and security are subject to metrological examination at the 32nd State Research Institute of the Ministry of Defense of the Russian Federation. Metrological examination of documents for the MKCA of water samples is not carried out if the certification of the MKCA of water samples is performed by one of the GNMC or 32 GNIII MO RF.

6.3. Certification of the MCCA of water samples is carried out by metrological examination of the following materials for the development of the MCCA of water samples:

ToR for the development of ICCA water samples;

Draft document regulating the ICCA of water samples;

Programs and results of experimental and computational evaluation of quality indicators of the ICCA of water samples.

6.4. When conducting studies to establish the quality indicators of the ICCA of water samples, as well as during its certification, the performance of the work listed in Appendix E should be provided.

6.5. When conducting a metrological examination of materials for the development of the ICCA of water samples, they analyze the compliance of the methods for presenting the quality indicators of the ICCA of water samples with the main provisions of GOST R ISO 5725-1 - GOST R ISO 5725-4, recommendations and Appendix C (methods for presenting uncertainty to the recommendations, , and Appendix B ); in terms of quality control procedures for the measurement results, analyze and note in the expert opinion the use of procedures in accordance with GOST R ISO 5725-6 and. When conducting a metrological examination of documents for the MKCA of water samples, recommendations and are used.

6.6. With positive certification results:

Issue a certificate of attestation of the MKCA of water samples (except for the MKCA of water samples regulated by national standards). The form of the certificate is given in Appendix G. The procedure for registering certificates of certification of the ICCA of water samples is established by organizations (enterprises) that carry out the certification of the ICCA of water samples;

The document regulating the ICCA of water samples is approved in the prescribed manner;

The document regulating the MKCA of water samples (except for the state standard) indicates: “the method is certified” - with the designation of the organization (enterprise) whose metrological service carried out the certification, or the GNMC or the OGMS that performed the certification of the MKCA of water samples.

Annex A

(reference)

Forms of presentation of indicators of accuracy (correctness and precision) of the method of quantitative chemical analysis of water samples

Table A.1

Name of the quality indicator of the ICCA water samples	Form of presentation of the quality indicator of the ICCA water samples
The indicator of accuracy of the MKCA of water samples is the assigned characteristic of the error of the MKCA of water samples	1. The boundaries [lower, upper (D n, D c)], in which the error of any of the totality of the results of the analysis (measurements) is found with the accepted probability R,- interval estimation, or ±D, R, for D = |D n | =D in = Z s(D), Where Z- distribution quantile, depending on its type and accepted probability R. 2. Standard deviation - s(D) of the error in the results of analysis (measurements) obtained in all laboratories using this ICCA of water samples - point estimate
The indicator of the correctness of the MCCA of water samples is the assigned characteristic of the systematic error of the MCCA of water samples	where? is the mathematical expectation (estimate) of the systematic error; s c - standard deviation of the non-excluded systematic error of the MCCA of water samples - point estimate. Note - ? can be introduced into the result of a single analysis (determination) as a correction. 2. Boundaries (D s, n, D s, c), in which the systematic error of the MCCA of water samples is found with the accepted probability R, - interval estimate, or ± D s, R, where D s,v = |D s,n | =D with = Zs c
The indicator of the repeatability of the MCCA of water samples is the assigned characteristic of the random error of the results of a single analysis obtained under conditions of repeatability	1. Standard deviation of the results of a single analysis obtained under repeatability conditions (results of parallel determinations) - s r . 2. Repeatability limit - r for two single analysis results obtained under repeatability conditions (results of parallel determinations)
The reproducibility indicator of the MKCA of water samples is the assigned characteristic of the random error of the results of analysis (measurements) obtained under conditions of reproducibility	1. Standard deviation of the results of analysis (measurements) obtained under reproducibility conditions - s R. 2. Reproducibility limit - R for two analysis results (measurements)

NOTE If the MCCA of water samples is developed for use in a single laboratory, the assigned error characteristics of the MCCA of water samples are: accuracy score, intralaboratory precision score, repeatability score, and correctness score (laboratory bias). Presentation forms - in accordance with .

Annex B

(reference)

Basic concepts and representation of uncertainty

B.1. The uncertainty of the result of the analysis (measurements), expressed as the standard deviation, is the standard uncertainty and .

B.2. The method for estimating uncertainty by statistical analysis of series of observations is a type A estimate.

B.3. A method for estimating uncertainty, other than statistical analysis of series of observations, is a type B estimate.

B.4. The standard uncertainty of a measurement result, when the result is obtained from the values ​​of a number of other quantities, is positive square root the sum of the terms, the terms being the variances or covariances of these other quantities, weighted according to how the measurement result changes with the change in these quantities, is the combined standard uncertainty .

B.5. A value that defines the interval around the measurement result, within which (can be expected) is most of distributions of values ​​that could reasonably be attributed to the measurand is the expanded uncertainty .

B.6. The numerical factor used as a multiplier of the combined standard uncertainty to obtain the expanded uncertainty is the coverage factor. The coverage rate is usually between 2 and 3. Acceptance of the coverage rate k= 2 gives an interval that has a confidence level of approximately 95%, and acceptance k= 3 gives an interval having a confidence level of approximately 99%.

B.7. In accordance with when calculating the uncertainty, the result of the analysis (measurements) - X must be specified together with the expanded uncertainty u, which is calculated using the coverage factor k= 2. The following form is recommended:

X ± U, (B.1)

Where U is the expanded uncertainty, calculated using a coverage factor of 2, giving a confidence level of approximately 95%.

Methods for assessing accuracy indicators (correctness and precision) of the method of quantitative chemical analysis of water samples

IN 1. In general, the MCCA of water samples includes the following stages:

Sample preparation for analysis;

Direct measurements of analytical signals (intermediate measurements) and their processing;

Calculation of the result of measurements of the value of the indicator of the composition (properties) of waters, functionally related to the results of direct measurements.

Each of these operations is burdened with its own errors. Many factors can influence the formation of the error of the measurement result, including:

Random differences between the compositions of the samples taken;

Matrix effects and mutual influences;

Incomplete extraction, concentration;

Possible changes in the composition of the sample due to its storage;

Errors of the measuring instruments used, including standard samples (RM) or certified mixtures (AC), equipment, as well as the purity of the reagents used;

Inadequacy of the mathematical model underlying the measurement method to the physical phenomenon;

Inadequacy of samples for calibration to the analyzed samples;

Uncertainty of the blank correction value;

Operator actions;

Parameter variations environment when taking measurements (temperature, humidity, air pollution, etc.);

Random effects, etc.

AT 2. The assessment of the values ​​of the assigned error characteristic - the accuracy indicator of the MCCA of water samples - is carried out according to the established values ​​​​of the characteristics of its random and systematic components in the entire range of contents of the determined component, for all ranges of associated components (hereinafter referred to as the influencing factors of the sample), as well as the conditions for performing measurements given in document for ICCA water samples.

AT 3. The assessment of precision indicators (repeatability and reproducibility) can be carried out on homogeneous and stable working water samples using either RM for the composition of water according to GOST 8.315, or AC according to based on an interlaboratory experiment. The results of the analysis of the same samples or SS (AS) are obtained with random variations in the influencing factors of the methodology under reproducibility conditions (different times, different analysts, different batches of reagents of the same type, different sets of volumetric utensils, different instances of measuring instruments of the same type, different laboratories) .

Note - Working samples should be homogeneous and stable in composition throughout the duration of the experiment.

AT 4. The assessment of the indicator of correctness of the MCCA of water samples can be carried out in one of the following ways - using:

A set of samples for evaluation (ES) in the form of CO or AS;

The additive method and the additive method combined with the dilution method;

Certified methodology with known (estimated) measurement error characteristics (comparison methods);

Calculation method (by summing the numerical values ​​of the components of the systematic measurement error).

B.4.1. The use of a set of samples for evaluation in the form of CO or AC in the conditions of obtaining experimental data in several laboratories allows you to evaluate the constant part of the systematic error, as well as the variable part of the systematic error due to the influencing factors of the sample. The general composition of the TOE must correspond to the scope of the ICCA of water samples. The content of the indicator being determined and the levels of interfering factors of the sample in the TOE are selected in accordance with the requirements of the experimental design (single-factor or multi-factor).

B.4.2. The use of the addition method in combination with the dilution method makes it possible to estimate the additive (constant) and multiplicative (proportionately changing) parts of the systematic error of the MCCA of water samples. The use of the additive method makes it possible to estimate the multiplicative (proportionately changing) part of the systematic error of the MCCA of water samples. The use of the additive method is permissible if at the stage of preliminary studies or according to a priori data it is established that the additive (constant) part of the systematic error is not a statistically significant fraction of the error of the analysis result.

Samples for evaluation are working water samples, working water samples with a known additive, diluted working samples and diluted working samples with a known additive.

Note - The use of the addition method and the addition method in combination with the dilution method is acceptable if at the stage of preliminary studies or according to a priori data it is established that the influencing factors of the sample do not have a significant effect on the error of the analysis result.

B.4.3. The use of a method based on the use of certified ICCA water samples with known (estimated) error characteristics (hereinafter referred to as ICCA comparison) is possible under the following conditions:

The scope of the MCCA of comparison coincides with the scope of the investigated MCCA of water samples or overlaps it;

The value of the reproducibility indicator of the MCCA of comparison does not exceed the value of the reproducibility indicator of the investigated MCCA of water samples;

The systematic error of the MKCA comparison is insignificant against the background of its random error;

MKCA comparison meets the requirements of intralaboratory control of the accuracy of its results.

Note - The use of MCCA comparison is acceptable if at the stage of preliminary studies or according to a priori data it is established that the influencing factors of the sample do not have a significant effect on the error of the analysis result.

B.4.4. The application of the calculation method is based on the summation of the numerical values ​​of the components of the systematic error.

When calculating the method, the factors that form the systematic error of the MCCA of water samples can include all the factors listed in B.1, with the exception of random effects, the quantitative assessment of the influence of which is taken into account when calculating the standard deviation of the results of a single analysis (determination) obtained in repeatability conditions.

Construction, content and presentation of documents regulating the methods of quantitative chemical analysis of water samples

D.1. The name of the document for the MKCA of water samples must comply with the requirements of GOST R 1.5 and GOST R 8.563.

D.2. The document for the ICCA of water samples must contain introductory part and sections in sequence:

Norms of measurement error;

Method of analysis (measurements);

Measuring instruments, auxiliary devices, reagents and materials;

Safety requirements, environmental protection;

Operator qualification requirements;

Conditions for performing analysis (measurements);

Preparation for analysis (measurements);

Performing analysis (measurements);

It is allowed to exclude and (or) combine some sections.

D.3. In the introductory part, the purpose and scope of the ICCA of water samples should be established. The types of analyzed waters, the name of the analyzed component, the range of contents of the analyzed component and the ranges of variations of the influencing factors of the sample allowed by the ICCA of water samples should be indicated. If necessary, information on the duration and complexity of measurements can be given.

The first paragraph of the introductory part is stated as follows: “This document (indicate specifically the type of document for the ICCA of water samples) establishes a method for quantitative chemical analysis of water samples (indicates the types of analyzed waters) to determine in them (hereinafter - the name of the measured quantity, indicating the range of measured component and measurement method used)”.

D.4. The section "Norms of measurement error" should contain the permissible values ​​of the accuracy index, characterizing the required measurement accuracy. Measurement error rates are indicated in accordance with GOST 27384 for the entire range of measured contents of the analyte.

D.5. The section "Ascribed characteristics of the measurement error and its components" contains the numerical values ​​of the quality indicators of the MKCA of water samples. Methods for expressing the quality indicators of the ICCA water samples should comply with Appendix B and recommendations.

The values ​​of the assigned characteristics of the measurement error (the quality indicators of the MKCA of water samples) must be indicated for the entire range of measured contents. If the quality indicators of the MCCA of water samples depend on the measured content, their values ​​should be presented in the form of a functional dependence on the measured content or a table of values ​​for content intervals, within each of which changes in the values ​​of the quality indicators can be neglected.

Note - If the section gives the values ​​of uncertainty, then the methods of its expression are presented in accordance with and .

D.6. The section "Measurement method" should contain the name of the measurement method and a description of the principle (physical, physico-chemical, chemical) underlying it.

D.7. The section "Measuring instruments, auxiliary devices, reagents, materials" should contain a complete list of measuring instruments (including standard samples), auxiliary devices, materials and reagents necessary for performing measurements. In the list of these means, along with the name, designations of national standards (standards of other categories) or technical specifications, designations of types (models) of measuring instruments, their metrological characteristics (accuracy class, limits of permissible errors, measurement limits, etc.) are indicated.

If the measurements require special devices, devices, their drawings, descriptions and characteristics should be given in the reference appendix to the document for the ICCA of water samples.

D.8. The section “Requirements for safety, environmental protection” contains requirements, the fulfillment of which ensures labor safety, industrial sanitation standards and environmental protection when performing measurements.

D.9. The section "Requirements for the qualification of the operator" should include requirements for the level of qualification (profession, education, work experience, etc.) of persons allowed to perform measurements.

D.10. The section “Conditions for performing measurements” should contain a list of factors (temperature, pressure, humidity, etc.) that determine the conditions for performing measurements, the ranges of changes in these factors allowed by the ICCA of water samples or their nominal values, indicating the limits of permissible deviations.

D.11. The section "Preparation for measurements" should contain a description of all the preparations for measurements.

The section should describe the stage of checking the operating modes of the measuring equipment and bringing it into working condition, or give a link to regulatory documents that establish the procedure for preparing the equipment used.

The section should describe the methods of processing the analyzed samples of samples for calibration, the procedures for preparing solutions necessary for analysis. For solutions with limited stability, the conditions and periods of their storage should be indicated. It is allowed to give the method of preparation of solutions in the reference appendix to the document for the ICCA of water samples.

If the establishment of a calibration characteristic is provided for when performing measurements, the section should provide methods for its establishment and control, as well as the procedure for using samples for calibration.

If, in order to establish a calibration characteristic, it is necessary to use samples for calibration in the form of mixtures prepared directly during measurements, the section should contain a description of the procedure for their preparation, the values ​​(one or more) of the contents of the components of the mixture of initial substances and the characteristics of their errors.

It is allowed to give the method of preparation of such samples in the reference appendix to the document for the ICCA of water samples.

If the order of preparatory work is established by documents for measuring instruments and other technical means, then the section provides links to these documents.

D.12. In the "Performance of measurements" section, the requirements for the volume (mass) of sample portions, their number, methods of taking an analytical portion should be established, if necessary, an instruction is given to conduct a "blank experiment"; the sequence of carrying out and the content of operations that provide the measurement result, including operations to eliminate the influence of interfering sample components, if any, are determined.

D.13. In the section “Processing (calculation) of the measurement result”, methods for calculating the value of the content of the indicator in the analyzed water sample from the obtained experimental data should be described. Calculation formulas for obtaining the measurement result must be given with the indication of the units of the measured values ​​in accordance with GOST 8.417.

This section provides methods for checking the acceptability of the results of parallel determinations obtained under repeatability conditions and measurement results obtained under reproducibility conditions.

The numerical values ​​of the measurement result must end with a digit of the same digit as the value of the accuracy index of the MKCA of water samples.

D.14. The section "Formation of measurement results" contains requirements for the form of presentation of the obtained measurement results.

D.15. The section “Quality control of measurement results when implementing the methodology in the laboratory” should contain a description of control procedures, values ​​of control standards, requirements for control samples.

Annex D

(reference)

Examples of the design of sections of documents regulating the methods of quantitative chemical analysis of water samples

D.1. In accordance with Appendix A, this appendix provides examples of the design of the introductory part and the following sections of documents for the ICCA of water samples:

Assigned characteristics of measurement error and its components;

Processing (calculation) of the result of analysis (measurements);

Registration of analysis results (measurements);

Quality control of the results of analysis (measurements) during the implementation of the methodology in the laboratory.

D 2. An example of the design of the introductory part

"This standard of the organization (enterprise) establishes a method for the quantitative chemical analysis of wastewater samples to determine the mass concentration of sulfate ions in them from 25 to 400 mg / dm 3 by the gravimetric method."

D.3. An example of the design of the section "Ascribed characteristics of the measurement error and its components"

E.3.1. The method of quantitative chemical analysis provides the results of analysis (measurements) with an error, the value of which does not exceed the values ​​indicated in Table E.1.

Table E.1 - Measurement range, values ​​​​of indicators of accuracy, repeatability and reproducibility of the MCCA of water samples

E.3.2. The values ​​of the accuracy index of the MKCA of water samples are used for:

Registration of the results of analysis (measurements) issued by the laboratory;

Evaluation of the activities of laboratories for the quality of testing;

Assessing the possibility of using the results of analysis (measurements) in the implementation of the ICA of water samples in a particular laboratory.

D.4. An example of the design of the section "Processing (calculation) of the result of analysis (measurements)"

E.4.1. The result of a single analysis (determination) - the content of the determined indicator in the sample is found according to the calibration curve.

E.4.2. The result of the analysis (measurements) of the content of the determined indicator in the sample is taken as the arithmetic mean of the results of two parallel determinations obtained under repeatability conditions, the discrepancy between which should not exceed the repeatability limit. Repeatability limit values r for two results of parallel determinations are indicated in Table E.2.

When the repeatability limit is exceeded r need to get more n (n? 1) results of parallel determinations. If, in this case, the discrepancy ( X max- X min) results 2 + n parallel definitions less than (or equal to) the critical range CR 0.95 (2+ n) according to GOST R ISO 5725-6, then the arithmetic mean of the results 2 + n parallel definitions. Critical range values ​​for 2+ n the results of parallel determinations are indicated in Table E.2.

If the discrepancy ( X max- X min) more CR 0.95 (2+ n), as the final result of the analysis (measurement) take the median 2 + n results of parallel determinations.

Upon receipt of two consecutive results of analysis (measurements) in the form of a median, the reasons for the occurrence of such a situation are found out and operational control of the analysis procedure is carried out in accordance with .

Table E.2 - Measurement range, values ​​of the repeatability limit and the critical range at the assumed probability R = 0,95

E.4.3. The discrepancy between the results of the analysis (measurements) obtained in two laboratories should not exceed the reproducibility limit. If this condition is met, both results of the analysis (measurements) are acceptable and their total average value can be used as the final result. The values ​​of the reproducibility limit are indicated in Table E.3.

If the reproducibility limit is exceeded, methods for assessing the acceptability of the results of analysis (measurements) can be used in accordance with Section 5 of GOST R ISO 5725-6.

Table E.3 - Measurement range, values ​​of the reproducibility limit at the accepted probability R = 0,95

D.5. An example of the design of the section "Formatting the results of analysis (measurements)"

The result of the analysis (measurements), , in documents providing for its use, can be represented in the form

Where - the result of the analysis (measurements), obtained in accordance with the prescription of the methodology;

D is an indicator of the accuracy of the MKCA of water samples. The values ​​of D are given in section E.3 "Assigned characteristics of the measurement error and its components".

It is permissible to present the result of analysis (measurements) in the documents issued by the laboratory in the form

provided D l< D,

where ± D l - the value of the measurement results error characteristic, established during the implementation of the methodology in the laboratory, in accordance with the procedure adopted in the laboratory, taking into account the recommendations and ensured by monitoring the stability of the measurement results.

Note - When presenting the result of the analysis (measurements) in the documents issued by the laboratory, indicate the number of results of parallel determinations performed to obtain the result of the analysis (measurements), and the method of calculating the result of the analysis (measurements) - the arithmetic mean or median of the results of parallel determinations.

D.6. An example of the design of the section "Quality control of the results of analysis (measurements) when implementing the methodology in the laboratory"

D.6.1. Quality control of the results of analysis (measurements) when implementing the methodology in the laboratory provides for:

Operational control of the analysis procedure (measurements) - based on the assessment of the error in the implementation of a single control procedure;

Control of the stability of the measurement results - based on the control of the stability of the standard deviation of repeatability, the standard deviation of intralaboratory precision, error.

D.6.2. Algorithm for operational control of the analysis procedure (measurements) using control samples (CO or AS)

K to with control standard K.

K k is calculated by the formula

Where - the result of the control measurement of the content of the analyte in the control sample - the arithmetic mean of two results of parallel determinations, the discrepancy between which does not exceed the repeatability limit r. Meaning r indicate in table D.2;

WITH- certified value of the control sample.

Control standard K calculated according to the formula

K= D l, (D.2)

where ±D l - characteristic of the error of the measurement results, corresponding to the certified value of the control sample and set according to .

KTo ? K.(D.3)

If condition (D.3) is not met, the experiment is repeated. If the condition (D.3) is not met again, the analysis process is suspended, the reasons leading to unsatisfactory results are found out, and measures are taken to eliminate them.

D.6.3. Algorithm for operational control of the analysis procedure (measurements) using the method of additions

Operational control of the analysis procedure (measurements) is carried out by comparing the result of a single control procedure K to with control standard K d .

The result of the control procedure K k is calculated by the formula

(D.4)

where - the result of a control measurement of the content of the analyte in a sample with a known additive - the arithmetic mean of two results of parallel determinations, the discrepancy between which does not exceed the repeatability limit r. Meaning r indicate in table D.2;

The result of the control measurement of the content of the determined component in the working sample is the arithmetic mean value n results of parallel determinations, the discrepancy between which does not exceed the repeatability limit r;

WITH- additive.

Control standard K d is calculated by the formula

(D.5)

where are the values ​​of the error characteristic of the results of analysis (measurements) established in the laboratory when implementing the methodology, corresponding to the content of the analyte in the working sample and in the sample with the additive.

The procedure of analysis (measurements) is recognized as satisfactory if the condition is met

K To? K d . (D.6)

If condition (E.6) is not met, the experiment is repeated. If the condition (D.6) is not met again, the analysis process is suspended, the reasons leading to unsatisfactory results are clarified, and measures are taken to eliminate them.

The frequency of control of the analysis procedure (measurements), as well as the implemented procedures for monitoring the stability of the results of analysis (measurements) are established in the Laboratory Quality Manual.

Annex E

(reference)

The content of work in the course of metrological studies and certification of the method of quantitative chemical analysis of water samples

Table E.1

Name of works	Executor
1. Checking the availability of the conditions necessary for the metrological studies of the MKCA of water samples: Verification of the compliance of the draft document, which regulates the ICCA of water samples, submitted for metrological certification, with the requirements of the ToR and Appendix D of this standard; Checking the correctness of the choice of measuring instruments provided for by the ICCA of water samples; Checking the conformity of the conditions for the use of measuring instruments provided for by the ICCA of water samples, the conditions for their use specified in the regulatory documents for measuring instruments; Checking the availability, technical condition and compliance with the requirements of the ICCA of water samples of measuring instruments, auxiliary equipment, laboratory glassware, reagents, materials necessary for certification of the ICCA of water samples; Checking the compliance of the methods for preparing mixtures required for certification of the ICCA of water samples with the recommendations
2. Drawing up a program for the experimental and computational evaluation of the quality indicators of the ICCA of water samples	Developer of the MKCA of water samples, metrological service of the organization (enterprise), GNMC, OGMS
3. Conducting research to establish the values ​​of the quality indicators of the ICCA of water samples to assess the values ​​of the assigned error characteristic and its components, formalizing the results of the research	Developer of ICCA water samples
4. Validation: Carrying out studies to establish quality indicators of the MKCA water samples; Establishing the values ​​of quality indicators of the ICCA water samples; The choice (calculation) of the norms of measurement error for the determined component of the composition (properties) of water. Verification of the compliance of the calculated values ​​of the assigned characteristic of the measurement error with the standards of measurement error. Analysis of the validity of procedures and standards for quality control of measurement results in the implementation of the IQCA of water samples in the laboratory	Developer of the MKCA of water samples, metrological service of the organization (enterprise), GNMC, OGMS
5. Certification of water samples by the ICCA based on the results of the metrological examination of materials for its development, including materials for establishing quality indicators, in accordance with the recommendations	Organization that certifies the MKCA of water samples [metrological service of the organization (enterprise), GNMC, OGMS]

Form of certificate of attestation of the method of quantitative chemical analysis of water samples name of the organization (enterprise) that carried out the certification of the MKCA water samples CERTIFICATE No. on certification of water samples by the ICCA Method for quantitative chemical analysis of water samples ________________________________________________________________________ name of the measured quantity, measurement method, types of water developed by ____________________________________________________________ name of the organization (enterprise) that developed the ICCA of water samples and regulated by _____________________________________________________ designation and name of the document certified in accordance with GOST R 8.563-96. Certification was carried out based on the results of _____________________________________ type of work: metrological examination of materials for the development ________________________________________________________________________ MCCA of water samples, theoretical or pilot study ICAC of water samples, other types of work The results of certification of the MKCA of water samples that meet the metrological requirements for it are given in tables G.1 and G.2 (with the accepted probability P = 0,95). Table G.1 Table G.2 When implementing the MKCA, water samples in the laboratory provide: Operational control of the analysis procedure (based on the assessment of the error in the implementation of a single control procedure); Control of the stability of the results of the analysis (based on the control of the stability of the standard deviation of repeatability, the standard deviation of intralaboratory precision, error). The algorithm for operational control of the analysis procedure is given in the document for the ICCA of water samples. Procedures for monitoring the stability of the results of the analysis are established in the Quality Manual of the laboratory. date of issue Head of organization (enterprise) _________________ __________________ personal signature signature transcript Place of printing

Bibliography

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Keywords: methodology for quantitative chemical analysis of samples of natural, drinking, waste waters (MCCA of water samples), measurement error standards, attributed measurement error characteristics, quality indicators of MCCA of water samples

In practice, all the achievements of analytical chemistry as a science are realized in its final product - chemical analysis technique specific object.

There are methods of qualitative chemical analysis and methods of quantitative chemical analysis of the substance of the object of analysis. Qualitative and quantitative chemical analysis procedures can be described sequentially in one method.

Method of chemical analysis substances of the object of analysis - a document in which, in accordance with the method of analysis used, a sequence of operations and rules is described, the implementation of which ensures obtaining chemical analysis result a specific substance of a specific object of analysis with established error characteristics or uncertainty for methods of quantitative analysis, and for methods of qualitative analysis - with established reliability.

The result of chemical analysis can be presented, for example, in the following way: according to the method of qualitative analysis by conducting qualitative reactions it was found that with a 100% confidence in the sample of the substance of the ore of the Bakcharskoe deposit there is iron; according to the method of quantitative analysis by dichromatometry, it was established that the iron content in the sample of the ore substance of the Bakcharskoe deposit is (40 ± 1)% with a confidence level of 0.95.

Each method of chemical analysis is based on the use of any one method of chemical analysis.

Examples of names of chemical analysis methods:

Method for measuring the mass concentrations of cadmium, copper and lead ions in drinking, natural and sewage stripping voltammetry method .

Methodology for performing measurements of mass concentration polychlorinated dibenzo-p-dioxins and dibenzofurans in atmospheric air samples by chromato-mass spectrometry.

Method for measuring the mass fraction of heavy metals in soils and soils using X-ray fluorescence analyzers of the X‑MET type, METOREX (Finland).

Chemical analysis of a substance is a complex multi-stage process, it is carried out in a certain sequence, which is usually described in the analysis methodology specific object.

The analysis of any samples of a substance, including samples of the substance of environmental objects, is carried out in a certain sequence of its stages:

1. Sampling of a substance (in the field in ecology);

2. Obtaining a representative laboratory and analytical sample of the analyte;

3. Preparation of the sample of the analyte for the measurement of the analytical signal;

4. Creation of conditions for measurements and preparation of measuring instruments;

5. Preparation of the reference substance (standard);

6. Carrying out direct measurements of the analytical signal of standards and preparing a method for comparison with the standard when applying physical methods of analysis;

7. Carrying out direct measurements of the analytical signal of the analyzed sample of the substance;

8. Processing the results of direct measurements - identification of components and calculation of the content of the analyte in the sample of the analyte (indirect measurements);

9. Evaluation of the acceptability of the chemical analysis result by checking its precision (repeatability, reproducibility) and correctness;

10. Registration of the results of the chemical analysis of the sample of the substance of the object of analysis.

The ecologist is obliged to use the services analytical laboratories, accredited for the right to perform chemical analysis of environmental substances An accredited laboratory is considered to be a legally independent laboratory whose employees have repeatedly confirmed their technical competence. The methodology should be classified as a national (GOST) or industry (OST) standard or industry document (RD, PND F).

An example of requirements for organizational documents for the protection of atmospheric air in the laboratory of an enterprise to control the negative impact on the environment. The laboratory must have the following documents:

Regulations on the laboratory, its passport;

Documents on accreditation (attestation);

Certificates of verification of measuring instruments by state metrological authorities

Passports for state standard samples of the composition and properties of controlled objects;

Results of internal and external quality control of performed measurements;

Sampling acts and logs of their registration;

Certified measurement methods;

Logs of the results of environmental impact monitoring.

The result of a quantitative chemical analysis of a sample of a substance, including an ecological object, is expressed through mass fraction w (A) or mass concentration of the determined component A, C m (A).

An ecologist, for example, when assessing the pollution of a substance of environmental objects, submits for chemical analysis to an analytical laboratory selected samples of solid, liquid, gaseous, or heterophase substances weighing up to 1 kg. He is interested in complete chemical composition or the content of one or more components (in the form of atoms, isotopes, ions, molecules, or a group of molecules with the same properties) in a sample of the substance of the object of analysis - in soils, in plants, in bottom sediments, in natural waters, in atmospheric air and other ecological objects.

Mass fraction w (A) component A is the ratio of mass m (A) component A, of the substance present in the sample to the total mass of the sample of the substance m (thing), which went to the analysis:

w (A) \u003d m (A) / m(item), w / r

Mass fraction of the component A in a sample of a substance can be converted into its percentage:

w (A) \u003d × 100,%

Volume fraction of the liquid component A in a sample of a liquid substance or gaseous component A in a sample of a gaseous substance is calculated as:

w (A) \u003d 100,%,

Where V (A) - volume of liquid or gaseous component A in total V total samples of a liquid or gaseous substance;

In international practice, they use the way of expressing the mass fraction as one part of a component into a large number of other parts:

parts per hundred , %, pph, g∙100/kg;

parts per thousand , ‰, ppt, g/kg;

parts per million , ppm, mg/kg, g/t;

parts per billion , ppb, μg/kg, mg/t;

To quantify the content of the component A in liquid and gaseous matter, the concept component concentration A.

Component A concentration (C(A)) is a value that characterizes the relative content of a given component in a multicomponent substance and is defined as the ratio of the number of component particles A(molar concentration of the component A, molar concentration of component equivalent A) or the mass of the component A ( mass concentration of the component A), related to a certain volume of liquid or gaseous substance.

The concentration of a component is always a named value, it makes sense for the component A specific name. This is reflected in the definition of concentration, which emphasizes that we are talking about the relative content of a given component in the volume of a multicomponent liquid or gaseous substance.

The basic unit of measure for the number of particles of a component (n) in the International System of Units physical quantities(SI system), adopted for use in the USSR in 1984, is 1 mol. 1 mol particles of any component that is of interest to us in the form of such structural chemical units as an atom (element), isotope, functional group, including an ion, or molecule, contains 6.022 × 10 23 such particles in any volume or mass of matter. thousandth part 1 mol(multiple unit) is denoted mmol ( read millimole).

Number of component particles A (n (A)) in any mass of the component A (m(A)) calculated by the formula:

n (A) \u003d m (A) / M (A), mol,

Where m (A) - component mass A, g; M (A) - relative molar mass of the component A, g/mol;

In the international system of units of physical quantities, according to GOST 8.417-2002 “GSI. Units of quantities", the main names for the concentration of components in the volume of a liquid or gaseous substance are molar concentration of the component, mol / m 3, And mass concentration of the component, kg / m 3.

Molar concentration of component A in solution – C m (A) - is the particle number content of the component A n (A) per unit volume V

C m (A) \u003d n (A) / V; or C m (A) \u003d m (A) / [M (A) V . ]

The molar concentration of a component is measured in mol / m 3; mol / dm 3, mmol / dm 3 mol/l.)

An example of a recording form in documents: C m (NaCl) \u003d 0.1 mol / dm 3 \u003d 0.1 mmol / cm 3 (in analytical practice for internal use and use the following form of recording: 0.1 M NaCl).

Both in analytical practice and in various forms professional activity, including ecology, use the concentration expressed in mass units.

Mass concentration of component A is the mass content m (A) component A per unit volume V liquid or gaseous substance, is calculated as:

C m (A) \u003d m (A) / V. ,

The mass concentration of the component is measured in kg / m 3; submultiple units are also used - g / m 3, g / dm 3, mg / dm 3 etc. (for intralaboratory use, a unit is allowed g/l, g/ml).

An example of a recording form: C m (NaCl) \u003d 0.1 g / dm 3, (in analytical practice for internal use the notation form C m (NaCl) \u003d 0.1 g / l \u003d 0.1 mg / ml is allowed).

Knowing the mass concentration of the component A in solution, you can calculate its molar concentration and vice versa.

C m (A) \u003d C m (A) / M (A), If C m (A) expressed in g / dm 3,

C m (A) \u003d C m (A) M (A), If C m (A) expressed in mol / dm 3.

Ways of expressing the concentration of a component in a solution and the relationship between different types of concentration are given in Annex 3.

In ecology, the content of determined components in samples of a liquid substance is usually expressed through mass concentration in units g / dm 3, mg / dm 3, mcg / dm 3, in samples of a gaseous substance - in units g / m 3, mg / m 3 μg / m 3.

The mass of the sample m (thing) can be measured with the required accuracy on an analytical balance, the volume V can be measured with the required accuracy using measuring utensils. Weight of the component A, m (A), or the number of particles of the component A, n (A), it is impossible to directly measure the substances in the sample, they can only be measured indirectly (calculated using the appropriate formula, found from the calibration graph). To this end, various methods of quantitative chemical analysis.