SU1720013A1 - Method of determination of diphenyloxide-3,4,3ъ,4ъ- tetracarbonic acid in air in the presence of its anhydride - Google Patents

Abstract

The invention relates to analytical chemistry, in particular the determination of diphenyloxide-3,4,3,4-tetracarboxylic acid in the presence of its anhydride in air. The goal is to increase the sensitivity of the analysis. It is conducted by passing air through a filter, removing the precipitate from the filter with acetone, treating it with a mixture of acetone and triethylamine and photometric it. The sensitivity of the determination is 0.125 mg / m3.1 table.

Description

This invention relates to analytical chemistry and relates to methods for determining carboxylic acids in air in the presence of their anhydrides.

The method can be used for sanitary-chemical analysis of air to determine diphenyl oxide-3,4,3, 4-tetracarboxylic acid (DFOTC) in the presence of its anhydride.

A known method for the determination of carboxylic acids in the presence of their anhydrides is based on the possibility of titrating primary and secondary amines in the form of the corresponding dithiocarboxylic acids. In this process, a sample containing anhydride and acid is added to a precisely known excess of the morpholinz solution and the free acid present in the sample is titrated and the acid formed by the reaction of the anhydride with morpholine. By adding carbon disulfide near the equivalence point of acid titration, morpholine is converted

in dithiocarboxylic acid and it is titrated with a solution of alkali. The difference between the results of the blank titration and the second titration of the sample is a measure of the amount of anhydride contained in the sample. The difference between the results of both titrations of the sample corresponds to the content of the free acid.

| The disadvantage of this method is its laboriousness, complexity in execution, low sensitivity of the determination of acid, limited by the possibilities of titrimetric analysis.

Closest to the proposed method for the determination of DFOTC is a method for the determination of free acids in some anhydrides by direct titration with a tertiary amine. This method allows the determination of free acid in maleic and phthalic anhydrides directly. Tertiary amines, tripropylamine and N-ethylpiperidine, have been used successfully for this purpose. They do not react with anhydrog

WITH

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In addition, with quite strong bases, they neutralize acids, which is determined by potentiometry. Ketones are used as solvents, which best enhance the basicity and acidity of the substances under study.

The disadvantage of this method is the inadequate sensitivity of the determination of acids, which makes it impossible to measure the concentrations of acids at the level of their maximum allowable in air.

The purpose of the invention is to determine DFOTC in the presence of its anhydride at a concentration of DFOTC in the air at the level of its maximum allowable value.

The goal is achieved by the fact that according to the method of determining DFOTC in the presence of its anhydride in air, including treating with a tertiary amine, the analyzed air is passed through a filter, filter residue is removed with acetone, the resulting solution is treated with a mixture of a solution of bromophenol blue in acetone and a solution of triethylamine in acetone followed by photometry the resulting solution. Moreover, a solution of 0.1 g of bromophenol blue in 100 ml of acetone and a solution of 0.1 ml of triethylamine in 20 ml of acetone are used, and a mixture of a solution of bromophenol blue in acetone and a solution of triethylamine in acetone is prepared at a volume ratio of -. Nii of the above solutions 12: 1.

The lower limit for measuring the content of DFOTK in the analyzed solution is 4 µg. The lower limit for measuring the concentration of DFOTC in the air is 0.125 mg / m3 (when sampling 64 liters of air). The range of measured concentrations in air is from 0.125 to 1.56 mg / m3.

Primer p. Instruments, apparatus, dishes:

spectrophotometer, aspiration device, FSVA filters, Bunsen flask, funnel with a porous plate, test tubes with a capacity of 20 ml with stoppers, volumetric flasks with a capacity of 100 ml, pipettes with a capacity of 1.5, 10 ml, cylinders with a capacity of 25.100 ml. ...,

Reagents, solutions, materials: acetone, bromophenol blue, 0.1 g dissolved in 100 ml of acetone, triethylamine, 0.1 ml dissolved in 20 ml of acetone.

Composite reagent: To 12 ml of a solution of bromophenol blue in acetone, add 1 ml of a solution of triethylamine in acetone and mix thoroughly.

Standard solutions DFOTK in acetone No. 1 with a concentration of 100 μg / ml and No. 2 with concentrations of TO μg / ml.

Preparation of a scale of calibration solutions. Calibration solutions are prepared by mixing a standard DFOTK solution and acetone in accordance with the table.

0.3 ml of the compound reagent is added to the prepared calibration solutions, the solutions are thoroughly mixed and the optical density is measured at

a wavelength of 450 nm. Measurements are carried out in cuvettes with an absorbing layer thickness of 10 mm with respect to a comparison solution that does not contain DFOTC (solution no. 1).

Build a calibration graph in the coordinates: the content of DFOTK in the calibration solutions (µg) is the optical density.

Sample analysis. Air at a rate of 4 l / min is aspirated through an FSVA filter.

Sampling time 16 min. The filter with the sample taken is placed on a funnel with a porous filter and the DFOTC is removed with acetone while the latter is gradually added in 2 ml portions and the liquid is sucked out when the water jet pump is diluted. DFOTC requires 6 ml of acetone for complete recovery.

For the analysis, 3 ml of the resulting solution is added to the tube, 0.3 ml of the compound reagent is added, the solution is thoroughly mixed, and the optical density is measured at a wavelength of 450 nm. The measurements are carried out in a cuvette with an absorbing layer thickness of 10 mm with respect to the solution.

comparison, not containing DFOTK.

The optical density of the analyzed solution is 0.102. According to the previously constructed calibration curve, the content of DFOTC in the sample is determined, which is 8 mcc.

The concentration of DFOTC s (mg / m3) in the air is calculated by the known formula “a” in

where a is the content DFOTK in the analyzed volume of the sample solution, found on the calibration curve, mcg;

B is the total volume of the sample solution, taken for analysis, ml;

b — volume of sample solution, taken for analysis, ml;

V is the air volume selected for analysis and reduced to standard conditions, l.

For the case in question

 0-25 mg / m3.

The technical and economic advantages of the proposed method consist in the possibility of determining diphenyloxide-3,4,3

5 17200136

4-tetracarboxylic acid in the presence of detection, analyzing its anhydride in the air. Air is passed through the filter, from the formula of the invention involve the precipitate with filter acetone,

The method of determining the diphenyloxide-resulting solution is treated with a mixture

3,4,3;, 4-tetracarboxylic acid in the presence of 5-solution of bromophenol blue in acetone

its anhydride in air, including a solution of triethylamine in acetone with a tertiary amine aftertreatment, which differs by photometry of the

u and with the fact that, in order to increase its solution.

Claims (1)

Claim Method for determination of diphenyl oxide ZAZ'X-tetracarboxylic acid in the presence of its anhydride in air, including tertiary amine treatment, characterized in that, in order to increase its detection sensitivity, the analyzed air is passed through a filter, the precipitate with the filter is removed with acetone, the resulting solution is treated a mixture of a solution of bromphenol blue in acetone and a solution of triethylamine in acetone, followed by photometry of the resulting solution. Standard Number Standard solution, ml Acetone, ml The content of DFOTK in graduated solutions, mcg Standard solution number 2 1 0 3.0 0 2 0.4 • 2.6 4 3 0.6 2,4 6 Standard solution number 1 4 0.1 2.9 10 5 0.2 2,8 20 6 0.3 2.7 thirty Ί 0.4 2.6 40 8 0.5 2,5 fifty