RU2320988C1 - Titrometric method for determining mass portion of major substance of beta-chlorovinylarsonic acid - Google Patents

Abstract

FIELD: analytical methods.

SUBSTANCE: invention relates to analysis of non-biological materials with chemical methods and can find use when solving tasks concerning environmental control on chemical weapon destruction objects. Method of determining mass portion of major substance of beta-chlorovinylarsonic acid in aqueous solutions comprises dissolving sample of beta-chlorovinylarsonic acid having mass 0.1-0.3 g in 50 mL water, to which two drops of 0.1% water-alcohol solution of phenolphthalein is added as indicator. Solution is titrated with 0.1 N sodium hydroxide solution to rose coloration and mass portion of major substance is calculated in terms of following equation: % (mass portion of major substance) = [(V₁-V₂)*K*0.00932135*100]/q, where V₁ is volume of 0.1 N sodium hydroxide solution utilized for titration of weighed sample of beta-chlorovinylarsonic acid, cm³; V₂ is volume of working solution utilized for titration of blank sample and decomposition of indicator, cm³; K is correction factor for titer of sodium hydroxide solution (K=1 when standard titer is used); 0.00932135 is quantity of beta-chlorovinylarsonic acid equivalent to 1 cm³ of 0.1 N sodium hydroxide solution, g/cm³, and q is mass of beta-chlorovinylarsonic acid sample. As measurement result, arithmetic mean of two parallel measurements is taken, wherein permissible deviation between the two measurements has not to exceed ±1%.

EFFECT: increased accuracy and simplified analytical procedure.

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Description

The invention relates to the study and analysis of non-biological materials by chemical methods, specifically to the determination of the mass fraction of the main substance β-chlorovinylarsonic acid (the degradation product of the lewisite poisonous substance) by titration in the presence of a chemical indicator.

To ensure environmental safety of the activities of facilities for the storage and destruction of chemical weapons, environmental monitoring is carried out, which involves the measurement of certain parameters and comparing them with relevant regulatory values. To solve the problems associated with the calibration and calibration of measuring instruments, the development and metrological certification of methods for measuring the content of the lewisite poisonous substance and its degradation products in controlled environments, to control the quality indicators of measurements performed by certified chemical analytical laboratories, metrological certification of standard samples is required. The main task of metrological certification is the accurate determination of the mass fraction of the main substance of the determined (investigated) product [1-4]. The main method for determining the mass fraction of the main substance according to MI 2574-2000 is considered to be the titrimetric method, which has the smallest determination error in comparison with photometric and gas chromatographic methods.

Known methods for the quantitative determination of arsenic-containing substances, including toxic ones, based on preliminary mineralization with the subsequent determination of either arsenic hydrogen or arsenic acid, mainly by the colorimetric method. The methods are characterized by the duration of sample preparation and the use of relatively toxic and expensive reagents [5, 6].

In the same works [5, 6], express methods for the quantitative determination of lewisites and their analogues by the amount of acetylene released during processing of the sample with alkali by volumetric determination are described [5, 6].

A more close way to determine the mass fraction of the main substance of β-chlorovinylarboxylic acid is considered to be the determination method described in the "Method for the separate determination of β-chlorovinyl dichloroarsine in water at the MPC and β-chlorovinylarsonic acid" [7]. The essence of this method lies in the fact that a separate determination of substances is achieved by alkaline hydrolysis of β-chlorovinyl dichloroarsine and β-chlorovinyl darsyl acid at different temperature conditions, the content of β-chlorovinyl dichloro rasine being determined at 20 ° C, and the total content is determined at 80 ° C, after which of this content, the content of β-chlorovinyl dichloroarasin is subtracted and the content of β-chlorovinylarsonic acid is determined. Acetylene released during alkaline hydrolysis of the test substances is determined by gas chromatography with a determination error of 5 to 35% depending on the concentration of substances in the solution. However, the relatively high error of this method excludes the possibility of its use for metrological certification of state standard samples.

The disadvantages of this method are the significant complexity of sample preparation, the need to maintain specified temperature conditions and expensive equipment for gas chromatographic analysis.

The aim of the invention is to eliminate the stage of complex sample preparation and the use of expensive equipment, ease of analysis in a factory laboratory (laboratory glassware and two chemicals), reducing the quantitative determination error to 1.0% when determining the mass fraction of the main substance in standard samples of β-chlorovinylarsone acids in various categories.

This goal is achieved by using the titrimetric method for determining the mass fraction of the main substance of β-chlorovinylarsonic acid by the neutralization method.

The essence of the proposed method lies in the fact that the analyte, β-chlorovinylarboxylic acid, which is an organic acid, is neutralized with a weak alkali solution at a temperature of (20 ± 5) ° С, which eliminates the alkaline hydrolysis of the chlorovinyl group. The equivalence point is determined by the acid-base indicator.

The proposed method for measuring the mass fraction of the main substance in the test sample is carried out in the following sequence.

In a conical flask with a volume of 100 cm ^{3, a} sample of β-chlorovinylarsonic acid weighing 0.1-0.3 g is taken, 50 cm ^{3 of} distilled water and 2 drops of an indicator of a 0.1% aqueous-alcoholic solution of phenolphthalein are added. After complete dissolution of β-chlorovinylarsonic acid, the solution was slowly titrated with 0.1 N. sodium hydroxide solution until a sharp color change indicator from colorless to pink. (A magnetic stirrer is allowed during the titration period.)

The calculation of the measurement results of the mass fraction of the main substance in the sample of β-chlorovinylarsonic acid is carried out according to the formula:

where: V ₁ is the volume of 0.1 N. a solution of sodium hydroxide, which went to the titration of a sample of β-chlorovinylarsonic acid, cm ³ ;

V ₂ - the volume of the working solution, which went to the titration of a blank sample and the decomposition of the indicator, cm ³ ;

K - correction factor to the titer of sodium hydroxide solution (K = 1 when using a standard titer);

0.00932135 - the amount of β-chlorovinylarsonic acid, equivalent to 1 cm ³ 0.1 N. sodium hydroxide solution, g / cm ³ ;

q is a sample of β-chlorovinylarsonic acid,

The measurement result is the arithmetic average of the results of two parallel determinations, the permissible difference between which should not exceed (when developing state standard samples, standard samples) ± 1.0%.

The results of the analysis of the mass fraction of the main substance in β-chlorovinylarsonic acid are presented in the table.

Table The results of determining the mass fraction of the basic substance of the composition of β-chlorovinylarsonic acid and its mixtures for certification with elements of statistical processing Sample Content KHA Result Number The results of parallel determinations,% Arithmetic mean of 2 parallel definitions,% The average definition (n = 12),% The confidence interval of the average value at P = 0.95,% one 2 one 2 3 four 5 6 7 96.0% one 96.2 95.8 96.00 96,025 0,110 2 96.1 96.3 96.20 3 95.9 95.7 95.80 four 96.3 96.0 96.15 5 95.7 96.3 96.00 6 96.0 95.9 95.95 7 96.4 95.7 96.05 8 95.8 96.1 95.95 9 96.2 95.6 95.90 10 96.5 96.1 96.30 eleven 95.5 96.0 95.75 12 96.4 96.1 96.25 Mixture for certification of 93.0% one 93.0 92.9 92.95 92,996 0.107 2 92.8 93.1 92.95 3 92.7 92.9 92.80 four 93.1 93,4 93.25 5 93.2 92.8 93.00 6 93.1 93.3 93.20 7 92.9 93.1 93.00 8 92.6 93.2 92.90 9 93.1 92.9 93.00 10 92.9 93.3 93.10 eleven 93.2 93.1 93.15 12 92.5 92.8 92.65 Mixture for certification 91.0% one 90.8 91.1 90.95 91,008 0,095 2 91.2 90.8 91.00 3 90.7 90.6 90.65 four 91.3 91.2 91.25 5 91.1 91.0 91.05 6 91.4 90.5 90.95 7 91.0 91.3 91.15 8 90.8 91.2 91.00 9 91.1 91.2 91.15 10 90.9 91.0 90.95 eleven 90.8 91.3 91.05 12 90.9 91.0 90.95

Information sources

1. Standard samples of the composition of pure substances. Certification Methods. The main provisions. MI 2574-2000, UrNIIM, 2000.10 s.

2. GOST 8.315-97. Standard samples of the composition and properties of substances and materials. Mn 1998.25 p.

3. GOST R ISO 5725-2002. Accuracy (correctness and precision) of measurement methods and results. M. 2002. Part 1-5.

4. Indicators of accuracy, correctness, precision of methods of quantitative chemical analysis. Evaluation Methods. MI 2336-2002. 48 sec

5. Soborovsky L.Z., Yakubovich A.Ya. The synthesis of toxic substances. M .: State. publishing house of the defense industry, 1939.252 s.

6. Franke Z., Franz P. et al. Chemistry of toxic substances. T.2. M .: Chemistry, 1973.406 p.

7. Polyakova G.Yu., Kuchinsky E.V. and others. Patent for the invention No. 2163016. Military unit 61469, 1998.

Claims (1)

A titrimetric method for determining the mass fraction of the main substance of β-chlorovinylarsonic acid in aqueous solutions, including dissolving a sample of β-chlorovinylarsonic acid weighing 0.1-0.3 g in 50 ml of water, adding 2 drops of a 0.1% aqueous-alcohol solution of phenolphthalein as an indicator, titration of 0.1 N. sodium hydroxide solution until pink and the calculation of the mass fraction of the basic substance by the formula

where V ₁ is the volume of 0.1 N. a solution of sodium hydroxide, which went to the titration of a sample of β-chlorovinylarsonic acid, cm ³ ; V ₂ - the volume of the working solution, which went to the titration of a blank sample and the decomposition of the indicator, cm ³ ; K is the correction factor to the titer of sodium hydroxide solution (K = 1 when using a standard titer); 0.00932135 - the amount of β-chlorovinylarsonic acid, equivalent to 1 cm ³ 0.1N. sodium hydroxide solution, g / cm ³ ; q is a sample of β-chlorovinylarsonic acid, g, the measurement result is the arithmetic average of the results of two parallel determinations, the permissible difference between which should not exceed ± 1%.