RU2354661C1 - Method of o-alkylmethylphosphonate analysis for mass fraction of ground substance - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention refers to method of standard sample O-alkylmethylphosphonates analysis for mass fraction of the ground substance to be used in ecological monitoring. Method consists in titration of their aqueous solutions by sodium hydroxide solution with using a potentiometric titration cell herewith automatically clamping an equivalence point in potential jump of titration curve.

EFFECT: method enhancement.

2 cl, 5 tbl

Description

The invention relates to the study or analysis of non-biological materials by chemical methods, specifically to the determination of the mass fraction of the main substance in standard samples of the composition of O-alkyl methylphosphonates (in particular, O-isopropylmethylphosphonate, O-isobutylmethylphosphonate, O-pinacolylmethylphosphonate) by titration of their aqueous solutions using automatic potentiometric ATP-02 titrator or its analogues.

Chemical compounds: O-isopropylmethylphosphonate, O-isobutylmethylphosphonate, O-pinacolylmethylphosphonate are products of the destruction of toxic substances - O-isopropyl fluoromethylphosphonate (sarin), O-isobutyl-S-2- (N, N-diethylamino-ethylmethyl-ethylmethyl) ethylmethyl , O-pinacolyl fluoromethylphosphonate (soman).

In the environmental safety system, when implementing a set of measures to monitor daily activities, as well as in order to prevent pre-emergency and emergency situations at chemical weapons storage and destruction facilities, one of the tasks is to measure certain parameters and compare them with the corresponding regulatory values. This task is reduced to metrological certification of samples to determine the mass fraction of the main substance in them in order to use them to solve measurement problems associated with the development, calibration and calibration of measuring instruments, development and metrological certification of methods for determining the content of toxic substances, their degradation products in controlled environments , monitoring the quality indicators of measurements performed by certified chemical analytical laboratories [1-4].

Known: a) methods for measuring mass concentrations of sarin, soman, substance of type Vi-X in the air of the working zone by gas chromatographic method with flame-photometric detection [5]. The disadvantage of these methods is: high measurement error from ± 21% to ± 24%; methods are recommended for assessing the compliance of the content of sarin, soman, Vi-X in the air of the working area with hygiene standards; the time of one analysis is more than 60 minutes; the methods involve determining only the organophosphorus poisonous substances themselves (sarin, soman, substance type Vi-X);

b) a method for determining the trace amounts of isopropyl ester of methylphosphonic acid fluoride in soil [6]. The method includes biochemical analysis, the error of which, as is known from [7], is up to ± 25%; the high cost of cholinesterase group drugs; fairly stringent temperature conditions during the analysis (+ 36.6 ° C); the calculation of the amount of sarin found is carried out taking into account the established extraction coefficient, which may vary depending on the composition and type of soil; regulation of the time of extraction carried out with distilled water using ultrasonic treatment (10 min). Failure to comply with the extraction time parameter leads to the destruction of methylphosphonic acid fluoride isopropyl ester, which leads to a distortion of the analysis result;

c) a method for determining methylphosphonic acid and its monoesters as chemical markers of organophosphorous toxic agents [8], which consists in determining acidic monoesters of methylphosphonic acid in bitumen-salt masses by gas-liquid chromatography using an external standard. Without dwelling on the complexity and duration of sample preparation, it should be noted that the error in the quantitative determination by this method is largely determined by the purity of the external standard used.

The closest analogue in technical essence is the method for determining the mass fraction of the main substance of acidic monoesters of methylphosphonic acid [9], which consists in the analysis of aqueous solutions of alkyl monoesters of methylphosphonic acid when processing the sample with an excess of 0.1 n. sodium hydroxide solution, after which the sample is incubated for 30 minutes and titrated with 0.1 N. hydrochloric acid solution in the presence of bromothymol blue as an indicator until its color changes to a yellow-green color. The disadvantages of this method are lengthy sample preparation, visual determination of the equivalence point by changing the color of the indicator, which undoubtedly depends on the individual characteristics of the operator, titration is done manually using routine manual labor.

The aim of the invention is to reduce the time and mass of the test substance for one analysis, obtaining more accurate, correct, precision analysis results, eliminating routine manual labor.

This goal is achieved by using an automatic potentiometric titrator, which, by reducing the unit volume of the titrant, increasing the accuracy of its measurement, automatically fixing the equivalence point by the potential jump, eliminates the individual error of the operator in the process of determining the color change of the indicator during analysis, replaces the reverse titration with direct, reduces time of one analysis.

The essence of the proposed method is that the solution of the analyte is titrated with a solution of sodium hydroxide using an automatic potentiometric titrator. The equivalence point in the proposed method is fixed automatically by the potential jump on the titration curve.

Chemical processes proceed according to the following reactions according to the schemes:

a) in general form for all O-alkylmethylphosphonates:

where R is alkyl radicals.

b) for O-isopropylmethylphosphonate:

c) for O-isobutylmethylphosphonate:

d) for O-pinacolylmethylphosphonate:

The proposed method for determining the mass fraction of the basic substance in standard samples of the composition of O-alkylmethylphosphonates (in particular, O-isopropylmethylphosphonate, O-isobutylmethylphosphonate, O-pinacolylmethylphosphonate) is carried out in the following sequence.

0.03-0.05 g of the corresponding O-alkylmethylphosphonate, depending on the molecular weight of the analyte in accordance with Table 1, is dissolved in 25 ml of distilled water in a 100 ml conical flask. For better dissolution of the test sample, the use of an ultrasonic bath is allowed. The combined electrode ESLK-01.7 is placed in the solution (it is a combination of silver chloride and glass electrodes) and the tip of the ATP-02 dispenser, where 0.1 n acts as a titrant. sodium hydroxide solution, turn on the magnetic stirrer and start the subroutine for titration of O-alkylmethylphosphonates with the parameters indicated below (the subroutine for ATP-02 with the indicated parameters is created once and is subsequently used without changes):

- titration method: direct, automatic mode, titration with determination of an equivalent point;

- titration rate, S: S _min = 0.016 ml / s;

S _max = 0.050 ml / s;

- drop volume: 0.002 ml;

- initial dose volume: 1.5 ml;

- potential stabilization level: 0.2000 mV;

- pause, sec: min = 1, max = 3;

- hitchhiking potential: - 10 mV.

These parameters are common to all automatic potentiometric titrators.

Upon completion of titration, the device gives the titrant volume corresponding to the potential jump on the titration curve. The calculation of the measurement results of the mass fraction of the main substance O-alkylmethylphosphonate (M _d , wt.%) Is performed according to the formula:

where V is the volume of 0.1 N. sodium hydroxide solution, which went to the titration of a sample of a standard sample of O-alkylmethylphosphonate, ml;

T is a titer of 0.1 N. sodium hydroxide solution according to O-alkylmethylphosphonate (in accordance with table 1), g / ml;

K - correction factor to a solution concentration of 0.1 N. sodium hydroxide;

m is the mass of a sample of a standard sample of O-alkylmethylphosphonate taken for measurements (in accordance with table 1),

Note: The choice of the correction coefficient K when calculating the mass fraction of the main substance (M _d ) by the formula (1) is due to the possibility of determining M _d in the absence of a standard titer of sodium hydroxide (TU 2642-001-49415344-99). The determination of the correction factor in this case is carried out in accordance with GOST 25794.1-83 - GOST 25794.3-83.

Table 1
Initial data for the analysis of O-alkylmethylphosphonates No. p / p Sample of O-alkyl methylphosphonate Title 0.1 n. sodium hydroxide solution for O-alkylmethylphosphonate ¹ , T, g / ml O-alkylmethylphosphonate ² , m, g The range of the measured mass fraction of the main substance,% one O-isopropylmethylphosphonate 0.013810 0.028-0.035 90-100 2 O-isobutylmethylphosphonate 0.015213 0,030-0,038 90-100 3 O-pinacolylmethylphosphonate 0.018019 0,036-0,045 90-100 Note: ¹ - Title 0.1 n. sodium hydroxide solution according to O-alkylmethylphosphonate, not shown in the table, is calculated by the formula:
T = M _r · 10 ^-4 ,
where M _r is the molar mass of the corresponding O-alkylmethylphosphonate.
² - The mass of the sample O-alkylmethylphosphonate, not shown in the table, is calculated by the formula:
m = (2.0-2.5)

The total duration of one analysis, taking into account the time for sample preparation, is up to 30 minutes.

To assess the precision of the claimed method for determining the mass fraction of the basic substance in standard samples of the composition of O-alkylmethylphosphonates, samples for evaluation (OO) with different contents of the mass fraction of the basic substance were prepared so that the content of the determined component in OO allowed to cover the measurement range [4], due to the requirements for state standard samples of the composition of substances [1].

The results of the determination of the mass fraction of the main substance of O-alkylmethylphosphonates with different values in OO are presented in tables 2-4.

table 2
The results of determining the mass fraction of the main substance in the samples for evaluating the composition of O-isopropylmethylphosphonate with elements of statistical processing Mass fraction of the main substance in the sample for evaluation M _d ,% KHA Result Number Determination result,% Arithmetic mean of the mass fraction of the main substance,% The confidence interval of the average value at P = 0.95,% one 2 3 four 5 99.0 one. 99.03 99,017 0,041 2. 98.84 3. 99.00 four. 99.03 5. 98.91 6. 99.05 7. 99.10 8. 98.93 9. 99.07 10. 99.22 eleven. 99.14 12. 99.11 13. 99.01 fourteen. 99.02 fifteen. 98.84 16. 99.13 17. 99.04 eighteen. 99.04 19. 98.92 twenty. 99.06 21. 98.91 22. 99.08 23. 99.08 24. 98.79 25. 98.93 26. 99.00 27. 98.88 28. 99.16 29. 98.95 thirty. 99.24 95.0 one. 94.93 95,019 0,040 2. 95.00 3. 95.04 four. 94.90 5. 95.05 6. 94.91 7. 94.89 8. 94.94 9. 95.28 10. 95,20 eleven. 95.00 12. 95.04 13. 95.16

Continuation of table 2 one 2 3 four 5 fourteen. 95.02 fifteen. 95.14 16. 95.03 17. 94.95 eighteen. 95.07 19. 94.77 twenty. 95.06 21. 94.87 22. 95.00 23. 94.90 24. 95.07 25. 94,99 26. 95.10 27. 95.03 28. 95.08 29. 95.11 thirty. 95.04 90.0 one. 90.04 90,019 0,042 2. 90.11 3. 90.15 four. 89.89 5. 90.28 6. 90.05 7. 89.89 8. 89.91 9. 90.07 10. 90.02 eleven. 89.90 12. 89.87 13. 90.02 fourteen. 89.91 fifteen. 89.73 16. 90.03 17. 90.04 eighteen. 89.93 19. 90.04 twenty. 89.95 21. 90.06 22. 90.16 23. 90.07 24. 90.08 25. 89,99 26. 90.13 27. 90.01 28. 90.00 29. 90.21 thirty. 90.03

Table 3
The results of determining the mass fraction of the main substance in the samples for evaluating the composition of O-isobutyl methylphosphonate with elements of statistical processing Mass fraction of the main substance in the sample for evaluation M _d ,% KHA Result Number Determination result,% Arithmetic mean of the mass fraction of the main substance,% The confidence interval of the average value at P = 0.95,% one 2 3 four 5 99.0 one. 99.11 99,021 0,045 2. 99.01 3. 98.83 four. 99.26 5. 98.90 6. 98.91 7. 99.14 8. 98.93 9. 99.09 10. 98.96 eleven. 99.01 12. 99.06 13. 99.01 fourteen. 99.08 fifteen. 98.95 16. 99.05 17. 98.93 eighteen. 98.76 19. 99.04 twenty. 98.88 21. 99.02 22. 99.07 23. 98.81 24. 99.02 25. 99.11 26. 99.11 27. 99.05 28. 99.17 29. 99.07 thirty. 99.28 95.0 one. 95.03 95,019 0,037 2. 94.86 3. 95.00 four. 95.04 5. 94.91 6. 94.93 7. 95.21 8. 95.01 9. 94.95 10. 94.98 eleven. 95.00 12. 95.24 13. 95.00

Continuation of table 3 one 2 3 four 5 fourteen. 94.89 fifteen. 95.02 16. 95.10 17. 95.04 eighteen. 95.10 19. 95.04 twenty. 95.16 21. 95.08 22. 94.93 23. 94.95 24. 95.07 25. 95.05 26. 94.90 27. 95.06 28. 94.80 29. 95.15 thirty. 95.06 90.0 one. 90.02 90,015 0,041 2. 89.87 3. 89.93 four. 89.89 5. 89.91 6. 90.17 7. 89.92 8. 89.93 9. 89,99 10. 89.95 eleven. 90.07 12. 90.00 13. 90.04 fourteen. 90.02 fifteen. 90.13 16. 90.02 17. 90.22 eighteen. 90.03 19. 90.25 twenty. 90.13 21. 90.11 22. 89.88 23. 89.91 24. 90.06 25. 90.08 26. 89.74 27. 90.03 28. 90.04 29. 90.09 thirty. 90.01

Table 4
The results of determining the mass fraction of the main substance in the samples for assessing the composition of O-pinacolylmethylphosphonate with elements of statistical processing Mass fraction of the main substance in the sample for evaluation M _d ,% KHA Result Number Determination result,% Arithmetic mean of the mass fraction of the main substance,% The confidence interval of the average value at P = 0.95,% one 2 3 four 5 99.0 one. 98.90 98,997 0,048 2. 98.79 3. 99.11 four. 98.83 5. 99.22 6. 98.90 7. 99.10 8. 98.93 9. 98,99 10. 98,99 eleven. 98.72 12. 99.00 13. 99.02 fourteen. 98.92 fifteen. 99.08 16. 99.02 17. 99.11 eighteen. 99.00 19. 99.14 twenty. 99.23 21. 98.81 22. 99.19 23. 98.94 24. 99.06 25. 98.91 26. 99.07 27. 98.86 28. 99.08 29. 98.91 thirty. 99.07 95.0 one. 94.92 94,979 0,043 2. 94,99 3. 94.87 four. 95.00 5. 94.89 6. 94.91 7. 94.83 8. 95.00 9. 94.92 10. 94.93 eleven. 95.16 12. 94.95 13. 94.93

Continuation of table 4 one 2 3 four 5 fourteen. 94.96 fifteen. 95.09 16. 94,99 17. 95.21 eighteen. 95.00 19. 95.26 twenty. 95.00 21. 95.01 22. 94.88 23. 94.74 24. 95.03 25. 94.93 26. 94.78 27. 95.07 28. 94.95 29. 95.04 thirty. 95.13 90.0 one. 90.00 89,998 0,046 2. 89.79 3. 89.82 four. 89.88 5. 89.88 6. 89.89 7. 89.94 8. 89.90 9. 89.95 10. 89.93 eleven. 90.23 12. 90.00 13. 90.08 fourteen. 90.01 fifteen. 89.71 16. 90.01 17. 90.24 eighteen. 90.04 19. 89,99 twenty. 90.01 21. 90.02 22. 90.12 23. 90.03 24. 90.09 25. 90.07 26. 90.10 27. 89.90 28. 90.03 29. 90.11 thirty. 90.17

The results of tables 2-4 indicate that certain average values of the mass fractions of the basic substance 0-isopropylmethylphosphonate, O-isobutylmethylphosphonate, O-pinacolylmethylphosphonate according to the proposed method have a discrepancy with the true value in the range up to 1.0%, which meets the requirements [1]. The results of the analyzes are more precise due to the automation of analysis in comparison with the method described in [9].

Table 5 shows data on a comparative assessment of the main characteristics of the proposed method and the closest analogue.

Table 5
A comparative assessment of the main characteristics of the proposed method for determining the mass fraction of the main substance in standard samples of the composition of O-alkylmethylphosphonates and the closest analogue Main characteristics The closest analogue The inventive method Titration method back straight The range of the determined mass fraction of the main substance,% 90-100 90-100 Time for one analysis, min fifty twenty Reagents Used 1.1.1 N NaOH
2.2.1 N Hcl
3. Bromthymol blue indicator 1.0.1 N NaOH
2. -
3. - Equivalence point indication Visual determination by the operator of a color change indicator Automatic fixation by potential jump on the combined electrode The possibility of using modern equipment - ATP-02 automatic potentiometric titrator with a computer interface and its analogues Sample sample for one determination, g 0.10-0.20 0.03-0.05

From the data shown in table 5, we can conclude that the use of the proposed method in comparison with the existing prototype method provides the following advantages:

- reduction of analysis time by at least 2.5 times;

- reduction in the weight of the sample of the determined O-alkyl methylphosphonate;

- no need to use a chemical indicator - the equivalence point is fixed automatically by a potential jump on the combined electrode;

- increasing the precision of measurements by reducing the individual error of the operator;

- the result of a single analysis is taken as the result of the analysis, which also reduces the consumption of the substance and the time for one determination.

Thus, the proposed method allows to determine the mass fraction of the main substance in the samples of the composition of O-alkylmethylphosphonates, in particular, O-isopropylmethylphosphonate, O-isobutylmethylphosphonate, O-pinacolylmethylphosphonate. The method is recommended for metrological certification of samples of their composition used at chemical weapons destruction facilities as state standard samples. Such samples are necessary to ensure the unity and the required accuracy of measurements in solving measurement problems associated with the development, calibration and calibration of measuring instruments, development and metrological certification of methods for determining the content of toxic substances, their degradation products in controlled environments, monitoring the quality of measurements performed by chemical analytical laboratories. The proposed method allows object laboratories to determine the mass fraction of the main substance with sufficient precision and with an error of up to 1%, increase labor productivity and automate the process of chemical analysis, while eliminating routine manual labor.

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. A collection of methods for performing measurements of organophosphorus toxic substances by the gas chromatographic method with PFD and the enzymatic method. Federal Office for the Safe Storage and Destruction of Chemical Weapons. FU / 5/90, M., 2005, 179 p.

6. N.I. Alimov, A.Yu. Lobur, S.A. Bazhenov, L.N. Solodkova, S.N. Shcherbin. RF patent No. 2213349. Military unit 61469, 2001.

7. E.I. Saveliev, A.S. Radilov, T.A. Kuznetsova, N.F. Volynets. Journal of Applied Chemistry. 2001.V. 74. Issue 10., P. 1671-1676.

8. E.I. Saveliev, I.G. Zenkevich, T.A. Kuznetsova, A.S. Radilov, G.V. Pshenichnaya. Russian Chemical Journal, a journal of the Russian Chemical Society named after D.I. Mendeleev. 2002.V. 46. Issue 6., Pp. 82-91.

9. V.G. Mandych, V.N. Davydova, S.N. Denisov, G.N. Kuranov, N.S. Denisov, S.N. Kobtsov, V.V. Brudnik, N.V. Fedorets. RF patent No. 2308030. SVIRKHBZ, 2007.

Claims (2)

1. A method for determining the mass fraction of the main substance in standard samples of the composition of O-alkylmethylphosphonates, which consists in titrating their aqueous solutions with sodium hydroxide solution using an automatic potentiometric titrator with automatic fixation of the equivalence point from the potential jump on the titration curve. 2. The method according to claim 1, characterized in that, in order to reduce the mass of the analyte and the number of reagents used, the time for one analysis, the exclusion of indicators and routine manual labor and overall automation of the process, a direct determination of O-alkylmethylphosphonates is carried out, in 100 ml conical flask weighed 0.03-0.05 g of the corresponding O-alkylmethylphosphonate depending on the molecular weight of the analyte, dissolved in 25 ml of distilled water, placed in a solution of combined eleme the electrode and the tip of the dispenser of the automatic potentiometric titrator, where a 0.1 N sodium hydroxide solution acts as a titrant, turn on the magnetic stirrer and start the O-alkylmethylphosphonates titration subroutine; upon completion of titration, the device gives out the titrant volume corresponding to the potential jump on the titration curve, mass fraction the main substance is calculated from the ratio:

where V is the volume of a 0.1 n sodium hydroxide solution, which went to the titration of a sample of a standard sample of O-alkyl methylphosphonate, ml;
T - titer of 0.1 n sodium hydroxide solution for O-alkylmethylphosphonate, g / ml;
K is the correction factor for the solution concentration of 0.1 n sodium hydroxide;
m is the mass of a sample of a standard sample of O-alkylmethylphosphonate taken for measurements, g.