RU2386130C2 - Method for catalytic spectrophotometric determination of cyanide anion - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method for catalytic spectrophotometric determination of the cyanide anion in organic extracts involves treatment of the solution of a sample with solutions of para-nitrobenzaldehyde in methyl cellosolve, chromogenic oxidising agent in form of benzofuroxan in methyl cellosolve and potassium hydroxide in ethanol at temperature of 293 K and volume ratio of 1:1:1:1 respectively, with subsequent measurement of optical density and determination of content of the cyanide ion from a calibration curve.

EFFECT: increased sensitivity and reliability of analysis.

1 tbl, 1 dwg

Description

The invention relates to the field of analysis of inorganic and organic compounds and can be used to solve environmental control problems.

A number of catalytic colorimetric determination methods are known in which the cyanide anion is a catalyst for the condensation of organic compounds and redox reactions.

1. The cyanide anion catalyzes the benzoin condensation of benzaldehyde, the product of which is benzoin, which reduces orthodinitrobenzene to blue-colored products [Feigl F., Caldis A. Catalytic Detection of Cyanide Through the Benzoin Condensation, Mikrochim. Acta, 1955, p. 992; Franke S. u.a., Lehrbuch der Militarchemie, Bad 2, Berlin, 1967, s. 616]. The opening minimum of the cyanide anion in this method is 0.01 μg.

2. The cyanide anion can catalyze the condensation of paranitrobenzaldehyde into colored products [US Patent 2753248. Paper for detection of HCN (Johnson JE, Poor ER) - CA, 1956, 50, 15352b.]. This reaction was used to create an indicator tube for hydrocyanic acid, the detection sensitivity of which is 1.0 · 10 ^-3 mg / l [US Pat. Chekhosl. 112190, 1964, CA, 62, 8308, 1-965; Bobkov S.S., Smirnov S.K. Hydrocyanic acid. M .: Chemistry, 1970, p.174].

3. The highest sensitivity level for determining the cyanide anion was achieved using the redox reaction of orthodinitrobenzene - paranitrobenzaldehyde with a detection limit of 1.0 · 10 ^-6 mg / ml [Guilbault GG, Kramer DN Ultra Sensitive, Specific Method for Cyanide Using p-Nitro -benzaldehide and o-Dinitrobenzene. Anal. Chem., 1966, 38, No. 2, 7, p. 834].

The disadvantage of the method for the catalytic determination of cyanide anion based on the reaction of orthodinitrobenzene and paranitrobenzaldehyde, taken as a prototype of the invention, is the color instability of the reduced form of orthodinitrobenzene, which complicates the quantitative study of the content of cyanide anion.

The aim of the invention is to increase the stability of the color of the reduction product used in the catalytic reaction for the determination of the cyanide anion of the oxidizing agent, and to achieve a higher level of sensitivity for the determination of the cyanide anion.

This goal is achieved in that in the method for the catalytic colorimetric determination of cyanide anion based on the reaction of orthodinitrobenzene with paranitrobenzaldehyde instead of orthodinitrobenzene, benzofuroxane or a derivative of this series of compounds is used as a chromogenic oxidizing agent. A solution of the selected benzofuroxan is mixed with a solution of paranitrobenzaldehyde in methylcellosolve and potassium hydroxide in ethyl alcohol. A test solution of an alkali metal salt of hydrocyanic acid in ethanol is added to the resulting mixture of reagents. The mixture is mixed and poured into a cuvette for measuring optical density after a period of 30 minutes selected for analysis.

The optical density is measured at a wavelength of maximum absorption of the reduction product of the oxidizing agent selected for analysis: the benzofuroxane reduction product, λ _max = 435 nm, ε ₄₃₅ = 1.9 · 10 ³ M ^-1 · l · cm ^-1 ; the recovery product of bis-benzofuroxan, λ _max = 400 nm, ε ₄₀₀ = 9.5 · 10 ³ M ^-l · l · cm ^-l ; reduction product of 6-chloro-7-methoxy-benzofuroxane, λ _max = 425 nm, ε ₄₂₅ = 6.3 · 10 ³ M ^-1 · l · cm ^-1 .

The lower limit of the determined concentrations of the cyanide anion using benzofuroxanes is for benzofuroxan - (2.0 ± 0.3) · 10 ^-8 mg / ml; for bis-benzofuroxan - (1.3 ± 0.2) · 10 ^-8 mg / ml; for 6-chloro-7-methoxybenzo-furoxan - (1.0 ± 0.1) · 10 ^-8 mg / ml.

The process diagram for the catalytic determination of cyanide anion:

The basis of the catalytic determination of the cyanide anion is the reversibility of the electronic transfers of paranitrobenzianhydrin between the chromogenic oxidizing agents of the benzofuroxan group and paranitrobenzaldehyde in an alkaline medium of methylcellosolve - ethyl alcohol.

Example. Catalytic spectrophotometric determination of cyanide anion

Reagents and equipment used

Paranitrobenzaldehyde, GOST 14049-68, twice recrystallized from a 40% aqueous-alcoholic solution.

Benzofuroxan "h", TU 6-09-07-1498-85, twice recrystallized from alcohol.

Potassium hydroxide "hch", GOST 4203-65.

Methyl cellosolve MRTU 6-09-6347-69. It is purified from technical impurities and peroxide compounds by vacuum distillation over calcium or magnesium oxide in a stream of nitrogen. Distilled solvent is stored in a yellow glass container under nitrogen.

Ethyl alcohol, GOST-4197-74, distilled. It is purified by distillation over calcium or magnesium oxide.

Analytical balance VLR-200 - 1 pc.

SF-46 spectrophotometer - 1 pc.

Dispenser DP-1-1000, set - 1 set.

10 ml tubes - 15 pcs.

Conical flasks per 100 ml - 3 pcs.

Stopwatch - 1 pc.

To obtain a basic solution, a sample of potassium cyanide taken on an analytical balance (± 0.00005 g) is dissolved in ethanol to obtain 10 ml of a solution with a concentration of 0.1 mg / ml. Working solutions of potassium cyanide are prepared by serial dilution. The working solution is prepared on the day of the analysis.

Potassium hydroxide is prepared in the form of 0.2 M in ethyl alcohol in a volume of 20 ... 30 ml per day of analysis. Paranitrobenzaldehyde is prepared in the form of 0.35 M in methylcellosolve in a volume of 20 ... 30 ml per day of analysis. Benzofuroxan (or its derivatives) is prepared in the form of 0.084 M in methylcellosolve in a volume of 20 ... 30 ml per day of analysis.

Method for constructing a calibration dependence

, который представлен на чертеже. Экспериментальные данные для его построения представлены в таблице.Potassium cyanide working solutions are prepared in the concentration range (1.0 · 10 ^-5 -2.0 · 10 ^-8 ) mg / ml. To 1.0 ml of the studied concentration of potassium cyanide in ethanol is added 1.0 ml of 0.35 M paranitrobenzaldehyde in methylcellosolve, 1.0 ml of a 0.084 M solution of benzofuroxan in methylcellosolve and 1.0 ml of a 0.2 M solution of potassium hydroxide in ethyl alcohol . The mixture is mixed, poured into a cuvette with an optical path length of 1 cm and installed in the working chamber of a spectrophotometer. At the same time, a control experiment is being prepared in which, instead of a solution of potassium cyanide, only its solvent, ethyl alcohol, is used. Measurement of optical density both in the experiment and in the control is carried out at a wavelength of 435 nm at 30 minutes of the experiment. An analysis of four to five concentrations of potassium cyanide in the concentration range from 2.0 · 10 ^-8 to 1.0 · 10 ^-5 mg / ml. The calibration graph is plotted in coordinates

which is presented in the drawing. The experimental data for its construction are presented in the table.

Quantitative catalytic determination of cyanide anion is carried out using the obtained calibration dependence.

Inorganic anions do not interfere with determination. Organic compounds capable of reversible oxidation and reduction in an alkaline medium interfere with determination: aromatic ketones, alpha-diketones, quinones, chalcones with acceptor groups.

Claims (1)

A method for the catalytic spectrophotometric determination of cyanide anion in organic extracts, comprising processing a sample solution with solutions of para-nitrobenzaldehyde in methyl cellosolve, a chromogenic oxidizing agent in the form of benzofuroxan in methyl cellosolve and potassium hydroxide in ethyl alcohol at a temperature of 293 K at a volume ratio of 1: 1: 1, respectively: 1, followed by measuring the optical density and determining the content of cyanide ion according to the calibration graph.

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