RU2009471C1 - Method for benzidine and 3,3-dimethoxibenzidine presence amount determining - Google Patents

Abstract

FIELD: chemical technology. SUBSTANCE: sampling under investigating is treated by solution of 4,56: 10M-4,56: 10M n-dimethyl aminocinnamic aldehyde in presence of sodium dodecylsulfate with concentration 4,0: 10M-4,0: 10M in medium of citrate buffer solution with pH factor equal to 2,0-5,0. EFFECT: quite sufficient method for cited in title agents determining.

Description

The invention relates to analytical chemistry, namely to the photometric determination of benzidine and dianisidine. Benzidine is used in the manufacture of azo dyes and is a reagent for the determination of sulfates, tungstates, discovery and calorimetric determination of Cr (II), Cu (II), Al (III), Pb (IV), Hg (II) Fe (CN) ₆ ^3- , Ce (IV), NO ₂ , Pt, OS, Ag, and also as a redox indicator in volume analysis. Dianisidine is used in the production of high-strength synthetic dyes, ion-exchange resins.

 A known method for the determination of benzidine and 3,3-dimethoxybenzidine, which consists in the fact that in the first stage, benzidine and dianisidine are diazotized with sodium nitrite. In the second stage, the resulting product is combined with a solution of 11-ethyl-1-naphthylamine hydrochloride in ethyl alcohol (1).

 The closest in technical essence is the photometric method for the determination of benzidine and dianisidine, which is based on a reaction using p-dimethylaminobenzaldehyde as an organic reagent. The essence of the method lies in the fact that they mix 1.5 ml of a solution in 2% hydrochloric acid containing 1-10 μg of benzidine or dianisidine with 0.3 ml of a 3% solution of p-dimethylaminobenzaldehyde in 2% hydrochloric acid . After 5 minutes, absorbance was measured. The detection limit is 0.5 μg / ml (2).

The disadvantages of this method are:
low detection limit;
the use of hydrochloric acid, which must be stored under special conditions.

 The purpose of the invention is to lower the detection limit of benzidine and 3,3-dimethoxybenzidine.

This goal is achieved in that the determination of benzidine and 3,3-dimethoxybenzidine is carried out using p-dimethyl-aminocinnamic aldehyde (p-DMAKA) as an organic reagent with a concentration in the reaction mixture of 4.56 ˙ 10 ^-5 - 4.56 ˙ 10 ^-4 M, in the presence of sodium dodecyl sulfate in an amount 4,0˙10 ^-3 - 4,0˙10 ^-2 M in the medium citrate buffer at pH 2.0-5.0.

 Adding to the test solutions containing benzidine or dianisidine the organic reagent p-DMAKA in the medium of citrate buffer solutions leads to the formation of a bright yellow color, when a solution of sodium dodecyl sulfate (DS11a) is introduced into the same mixture, the color changes from bright yellow to violet.

It is spectrophotometrically fixed in a binary system containing benzidine (dianisidine) and p-dimethylaminocinnamic aldehyde - 2 absorption bands in a medium of citrate buffer solutions with λ _max ^I = 280 nm, λ _max ^II = 400 nm. When benzidine (dianisidine) - p-DMAC solution DSNa is introduced into the system, the appearance of a third absorption band with λ _max ^III = 585 nm is observed.

 The optimal conditions for the determination of benzidine and its methoxy derivative with p-DMAC in the presence of DS11a were established. It was shown that the analytical signals of the benzidine (dianisidine) + p-DMAKA + DS11a system are quite large and allow determination of benzidine and dianisidine in the pH range 2.0–5.0 (Table 1).

 When going beyond the indicated interval, i.e., at pH 5.0 and pH 2.0, the value of analytical signals drops sharply and reaches pH 0.02 at pH 6.0.

It was established that for the determination of the studied substances, the optimal use of p-DMAC solution in the concentration range of 0.1-1.0 0.2% solution, which in terms of C _working is 4.56˙10 ^-5 - 4.56˙ 10 ^-4 M. The data given in table. 2 suggest that the errors in the determination of benzidine and dianisidine in the range of these concentrations are minimal. Errors increase with C _slave <4.56˙ 10 ^-5 M and C _slave > 4.56˙10 ^-4 M.

The concentration of sodium dodecyl sulfate in the reaction mixture should be 4,0˙10 ^-5 - 4,0˙10 ^-2 M, this is achieved by adding a solution of an anionic surfactant (DSNa) in an amount of 10 ^-1 - 1 ml of a 1 M solution. When concentration C DSNa <4,0˙10 ^-3 and Ni> 4,0˙10 ^-2 M error determination benzidine and its methoxy increases (Table. 2).

All further studies were carried out with solutions of the following concentrations: p-DMAKA 1.14 × 10 ^-2 M (0.2% solution) was injected with 0.1 ml of sodium dodecyl sulfonate 10 ^-1 M, 1 ml was introduced into the reaction mixture.

 We studied the subordination of the benzidine (dianisidine) + p-DMACA + DSN system according to the Bouger-Lambert-Behr law, the range of concentration variation was 0.2-0.8 mg / ml. It was found that by the described method it is possible to determine large and small concentrations of benzidine and dianoisidine.

a) Benzidine
1) 0.1-3.0 μg / ml, l = 1cm
2) 0.04-0.3 μg / ml, l = 5 cm
b) dianisidine
1) 0.3-3.0 μg / ml, l = 1 cm
2) 0.04-1.0 μg / ml, l = 5 cm.

The analytical signals of the system are recorded at KFK-2, λ _max 590 nm, in cuvettes with an absorbing layer thickness l = 1 cm, l = 5 cm.

 The proof of the range of the determined contents is shown in table. 3.

 Analysis of the data presented in table. 3, it can be stated that it is possible to determine concentrations for different intervals, when using cuvettes with different thicknesses of the absorbing layer l = 1 cm, the range of determined concentrations (for large quantities) is 0.1-3.0 μg / ml, it is in this concentration range that the error determination is minimal and does not exceed 5%. When going beyond the indicated range of concentrations, i.e., at C = 0.05 μg / ml and C = 4.0 μg / ml, the error in determining large quantities of the investigated substances increases to 12%.

 When using a cuvette with an absorbing layer thickness l = 5 cm in experimental work, for the determination of small amounts of benzidine, the range of determined contents is 0.04-0.3 μg / ml. The determination error is minimal, not exceeding 8.5%. When going beyond the indicated concentration range, the error of determination increases to 20%.

 Determining the detection limit of the investigated substances, we proceed from the concept that the detection limit is the smallest content at which, using this technique, you can detect the presence of the detected component with a given confidence probability.

 As already shown, the lower limit of the range of the determined contents of benzidine and dianisidine is 0.04 μg / ml, therefore, this is the confidently determined detection limit at λ = 590 nm, l = 5 cm on a KFK-2 device. A relationship was established between the values of the detection limit of the studied substances, the concentrations of p-DMACA (Table 4), the concentration of DSNa (Table) and the pH of the medium (Table 6).

 PRI me R 1. The construction of the calibration characteristics for the photometric determination of large quantities of benzidine and dianisidine (for example, dianisidine).

An exact portion of dianisidine (0.025 g) was placed in a 25 ml volumetric flask and dissolved in distilled water. The standard solution contains 1 μg / ml. The working solution contains 10 μg / ml dianisidine. To construct the calibration characteristic, 6 ml flasks with a capacity of 25 ml are placed 10 ml of citrate buffer solution pH 4.0, 7.5 ml (3 μg / ml), 5 ml (2 μg / ml), 2.5 ml (1 μg / ml), 1.25 ml (0.5 ml), 0.5 ml (0.2 μg / ml), 0.25 μg / ml. To each of the flasks was added 0.1 ml of 0.2% (1,14x x10 ^-2 M) solution of p-DMAC and 1 mL of 10 M ^-1 DSNa solution and then brought to volume with citrate buffer solution of pH 4.0. The optical density of the resulting solutions was measured on KFK-2 in cuvettes with an absorbing layer thickness of l = 1 cm at λ = 590 nm relative to a comparison solution containing 0.1 ml of a 0.2% solution of p-DMAKA, 1 ml 10 ^-1 M a solution of DSNa and a citrate buffer solution with a pH of 4. Based on the obtained values of optical density, the dependence A = f (C) is built. The Bouguer-Lambert-Beer law holds at a dianisidine concentration of 0.1-3 μg / ml.

 PRI me R 2. The construction of the calibration characteristics for the photometric determination of small amounts of benzidine and dianisidine (for example, benzidine).

To build the calibration characteristics using a working solution of benzidine 1 μg / ml In 6 volumetric flasks with a capacity of 25 ml, 10 ml of citrate buffer solution is added with a pH of 4.0, 7.5 ml (0.3 μg / ml), 5.0 ml (2 μg / ml), 2.5 ml (1 μg / ml), 2.0 ml (0.08 μg / ml), 1.0 ml (0.04 μg / ml), 0.5 ml (0.02 μg / ml) of benzidine working solution, then into each flask add 0.1 ml of a 0.2% solution of p-dimethylaminocinnamic aldehyde, 1 ml of a 10 ^-1 M sodium dodecyl sulfate solution and adjust the volume to the mark with citrate buffer solution at pH 4.0. The optical density of the resulting solutions was measured on KFK-2 in cuvettes with an absorbing layer thickness of l = 5 cm at λ = 590 nm relative to a comparison solution containing 0.1 ml of a 0.2% solution of p-DMAC, 1 ml 10 ^-1 M DSNa solution and citrate buffer solution with a pH of 4.0. According to the obtained optical density, the dependence A = f (C) is built. The Bouguer-Lambert-Beer law is satisfied at a benzidine concentration of 0.04-0.3 μg / ml.

 The proof of the significant differences of the described method is presented in table. 7.

 The positive effect of the claimed method for the determination of benzidine and 3,3-dimethoxybenzidine is that the detection limit of the test substances is reduced by 3 orders of magnitude compared with the base method and 12 times with the prototype; the experimental technique has been changed, the use of reagents is not required, which require compliance with special safety standards and requirements, and it allows the determination of both small and large contents of substances. The advantages of the claimed method allow us to offer it for the analysis of technological environments and environmental objects for the content of trace amounts of benzidine and dianisidine.

 (56) I. Korenman, Photometric Analysis. Methods for the determination of organic compounds, M.: Chemistry, 1970, p. 343.

 Peregud E.A. et al. Fast methods for determining harmful substances, M.: Chemistry, 1970, p. 358.

Claims (1)

METHOD FOR QUANTITATIVE DETERMINATION OF BENZIDINE AND 3,3-DIMETHOXYBENZIDINE, including processing the analyzed sample with an organic reagent in a buffer solution followed by photometric analysis of the resulting solution, characterized in that, in order to reduce the detection limit, a solution of p-dimethylaminocinnamide 4 is used as an organic reagent 56 · 10 ^-5 - 4.56 · 10 ^-4 mol and the treatment is carried out in the presence of sodium dodecyl sulfate with a concentration in the reaction mixture of 4.0 · 10 ^-3 - 4.0 · 10 ^-2 mol in a citrate buffer solution with pH 2.0 - 5.0.

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