RU2698506C1 - Method for quantitative gas-chromatographic analysis of propionic acid vapour in contaminated air - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to analytical chemistry and specifically to gas chromatographic analysis of carboxylic acids. Method for quantitative gas-chromatographic analysis of propionic acid vapours in contaminated air, involving analysis of a sample of air contaminated with propionic acid vapour, on a gas chromatograph with a flame ionisation detector, is characterized by that in an absorbent device with a glass porous plate, an absorption solution is a mixture of ethyl alcohol and water in ratio of 1:1.

EFFECT: technical result is reduction of number of stages of analysis and simplification of sample preparation and sampling.

1 cl, 3 dwg, 2 tbl

Description

The invention relates to the field of gas chromatographic analysis of carboxylic acids.

Gas chromatographic analysis of such polar compounds as carboxylic acids, which include propionic acid, is associated with technical difficulties [1]. So, the method of sampling the air contaminated with vapors of carboxylic acids into alkaline solutions, followed by regeneration of phosphoric or hydrochloric acid and extraction with a volatile solvent, is complicated in hardware design and includes multi-stage sample preparation [2]. Concentration of acids from the air onto a film sorbent impregnated with tetraethylammonium hydroxide, followed by the conversion of acid salts to benzyl esters, also includes lengthy and laborious sample preparation [1].

Significant disadvantages of these methods:

multi-stage and complexity of sample preparation and sampling;

a large list of used reagents, including high hazard class.

The purpose of the present invention is to provide a method for the quantitative gas chromatographic analysis of propionic acid vapors in contaminated air with simplified sample preparation and sampling.

The objectives of the present invention are to choose:

- an absorption solution for propionic acid (available, low toxic and inexpensive);

- conditions for sample preparation and sampling;

- optimal gas chromatographic conditions for determining the concentration of propionic acid.

The essence of the method consists in a quantitative gas chromatographic analysis on a gas chromatograph with a flame ionization detector of air samples contaminated with propionic acid vapors taken in an absorption solution - a mixture of ethyl alcohol and water in a ratio of 1: 1 (by volume) in an absorption device with a glass porous plate.

The technical result achieved in the claimed invention is:

- the exception of multi-stage;

- simplification of sample preparation and sampling. The specified technical result is achieved by the fact that:

- the composition of the absorption solution is selected from the available components of a low hazard class;

- The conditions for sampling air have been determined;

- the optimal gas chromatographic conditions for determining the concentration of propionic acid vapor have been established;

- calibration dependencies are constructed.

The gas chromatograph was calibrated using the absolute calibration method [3].

Propionic acid calibration solutions were prepared in a mixture of ethyl alcohol and water (1: 1 by volume).

1 mm ³ samples of calibration solutions were introduced into the chromatograph with a concentration of 10 ⁵ to 10 ³ μg / cm ³ , then with a concentration of 10 ² μg / cm ³ , 4 mm ³ each, each solution at least 6 times. Using a standard ChemStation chromatographic information collection and processing program, the peak area with a retention time of 6.4 (± 0.2) minutes was measured on the chromatogram.

The measurements were carried out with the following operational parameters of the chromatograph:

column thermostat temperature 157 ° С plateau 9 minutes;

heating rate - 10 ° C / min to 210 ° C;

evaporator temperature 220 ° С;

flow division ratio 10: 1; detector temperature 240 ° С;

carrier gas flow rate 1.5 cm ³ / min;

air flow rate 300 cm ³ / min;

a hydrogen flow rate of 30 cm ³ / min;

HP-FFAP capillary column 50 m D-0.32 mm F-0.5 μm;

sample volume 1 mm ³ and 4 mm ³ ;

sorbing cotton wool was removed from the liner.

In the process, the optimal analysis conditions were selected:

1) the carrier gas flow was changed from 1.4 cm ³ / min to 2.0 cm ³ / min with a gradient of 0.1 cm ³ / min.

2) in peak shape, the optimal velocity of the carrier gas was 1.5 cm ³ / min;

3) the temperature of the thermostat was changed from 145 ° C to 160 ° C.

4) according to the shape of the peak and the area of the chromatographic peak, the optimal analysis temperature was 157 ° C.

Under these conditions, a chromatogram of propionic acid in an aqueous-alcoholic solution was obtained on an Agilent 6890N gas chromatograph with a flame ionization detector (Figure 1).

Based on the measurement data in table 1, the calibration dependence was obtained for concentrations from 10 ³ to 1 μg / cm ³ (figure 2).

Table 1 - Measurement data for concentrations from 10 ³ to 1 μg / cm ³ propionic acid

In order to obtain reliable quantitative results for low concentrations of propionic acid in air, a calibration dependence was constructed for concentrations from 7 to 1 μg / cm ³ (figure 3). The measurement data are presented in table 2.

Table 2 - Measurement data for concentrations from 7 to 1 μg / cm ³ propionic acid

To determine the concentration of propionic acid, the infected air is aspirated into 3 ml of an absorption solution of ethyl alcohol and water in a ratio of 1: 1 (by volume) in an absorption device with a glass porous plate.

Then the absorption solution from the device is transferred to the prepared vials and a quantitative gas chromatographic analysis is performed on an Agilent 6890N chromatograph with a flame ionization detector to determine the concentration of propionic acid in solution and in air using the calculated expressions presented below and the constructed calibration dependence.

According to the obtained calibration dependence of propionic acid for concentrations from 7 to 1 μg / cm ³ (figure 3), the concentration of propionic acid in the sample is calculated by the formula:

where x is the decimal logarithm of the concentration of propionic acid in the sample, μg / cm ³ ;

y is the decimal logarithm of the peak area s, conv. units

The concentration in sample b, μg / cm ³ is determined by the expression:

The concentration of propionic acid in air is calculated by the formula

where V _p-pa is the total volume of the sample solution, cm ³ ;

V _air - the volume of the investigated air sample, dm ³ .

The volume of the studied air sample (reduced to nu) is found as the product of the air flow in the aspirator and the sampling time:

where R _asp - air flow in the aspirator, DM ³ / min.

t _asp - sampling time, min.

Information sources

1. Peregud, EA Fast methods for determining harmful substances in the air / E.A. Peregud, M.S. Bykhovskaya, E.V. Gernet. - M .: Chemistry, 1970 .-- 360 p.

2. Kotsev, N. Handbook of gas chromatography: Handbook / N. Kotsev, N. Petsev. - M .: World. - 1987. - 260 p.

3. Drugov, Yu.S. Sample preparation in environmental analysis: a practical guide / Yu.S. Drugov, A.A. Rodin. - 4th ed. - M .: “Binom. Laboratory of Knowledge ”- 2013. - 855 p.

Claims (1)

A method for quantitative gas chromatographic analysis of propionic acid vapors in contaminated air, including analyzing a sample of air contaminated with propionic acid vapors on a gas chromatograph with a flame ionization detector, characterized in that a mixture of ethanol and ethanol is used in the absorption device with a glass porous plate water in a ratio by volume of 1: 1.

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