SU1427256A1 - Method of analyzing methylmercaptan and dimethylsuleide in air - Google Patents

Description

(21) 4166324 / 28-04

(22) 12/24/86

(46) 09/30/88. Bgap K 36

(71) Leningrad Scientific and Research Institute of Occupational Hygiene and Occupational Diseases

(72) V.P. Yakimova, A. B. Rodionov and L.I. Brodsk

(53) 543.42.062 (088.8)

(56) Maksimov V.F., Namestnikov I.V. , Yakovleva O.I. Methods of monitoring working conditions in the pulp and paper industry. L., 1982, p. 71-72.

Vlnov V.M. The method of separate determination of hydrogen sulfide, mercaptans and dimethyl disulfide in the air. - Hygiene and Sanitation, 1974, No. 4, p. 63-65.

(54) METHOD FOR DETERMINING METHILMERCAPTANE AND DIMETHIPDISULFIDE IN AIR

(57) The invention relates to analytical chemistry, in particular to the determination of methyl mercaptan and dimethyl disulfide in the air. The goal is to increase the selectivity and accuracy of the method. The determination is carried out by aspiration of air through the absorption solution. As the latter, use a mixture containing, wt.%: Cadmium acetate 1.00-2.00, water 4.00-10.00, acetic acid 0.02-0.20, ethyl alcohol or propyl alcohol - the rest. Two equal aliquot parts of the sample are selected, one of which is processed by a chromogenic reagent — a hydrochloric acid solution of H, H-dimethle-p-pheny — lendiamine and ferric chloride (III) is treated with mercury acetate or nitrate. The resulting colored solution is measured. The method provides for the determination of these compounds with a minimum concentration with a relative error of no more than 12%. 4 tab.

(Ls

This invention relates to analytical chemistry, in particular, to methods for the separate determination of methyl mercaptan (MM) and dimethyl disulfide (DMDS) in the presence of air in the air.

The purpose of the invention is to increase the selectivity and accuracy of the method.

The method is carried out as follows.

Example. 15 l of air is aspirated at a rate of 1.0 l / min through two successively connected absorption devices with a porous plate containing 10 ml of an absorption solution (5 g of cadmium acetate are dissolved in 20 ml of distilled water, acidified with 0.1 ml of acetic acid). acids and volume of the solution is made up to 500 ml with propanol. During sampling, the absorbers are cooled in a mixture of ice and water. The contents of the absorption devices are analyzed separately, the results are summarized.

Equal aliquots of the 4 ml sample solution are taken into two test tubes with ground plugs

5.0 ml of water, 0.5 MP of the chromogenic reagent (a mixture of a 0.2% solution of K, N-dimethyl-p-phenylenediamine in concentrated hydrochloric acid, and an A% solution of iron ( Iii) in a 1 M solution of hydrochloric acid, taken in a ratio of 3: 1) and stir the solution.

0.5 ml of a 5% mercury acetate solution is added to the second tube and the contents are gently mixed. After 0.5-1.0 min, 4.5 ml of water and 0.5 ml of chromogen reagent are poured.

After 15 min, the 11 1 1P1 solutions are photometrized at a wavelength of 500 nm in cuvettes with a layer thickness of 2 cm relative to a control solution prepared similarly to an aliquot portion of a K 1 sample.

The content of methyl mercaptan (III) and dimetry disulfide (D1SHS) is determined by the equation of the calibration graph of the dependence of optical density on the content of methyl mercaptan in the photometric volume of the solution (µg). The main standard solution is obtained by dissolving the exact weighed DSPC in propanol in a 25 ml volumetric flask. Working standard solution with concentration / ESCH 49 µg / i-m, corresponding to the concentration of methyl mercap

25 µg / ml is prepared by diluting the stock solution with an absorption solution.

To build a calibration graph in a series of tubes containing 0.5 ml of a 5% aqueous solution of mercury acetate, add from 0 to 2.0 ml of the working standard solution, bring the volume of solutions to 4.0 ml with an absorption solution, pour in 4.5 ml of water, 0.5 ml of chromogenic reagent, and then photometric solutions similar to the sample.

The concentration of MI.1 and DMDS in (C) is calculated by the formulas:

the air

SJ.Y ° 2.41.

v.v

mg / m

20

lj, 96 (b-a) - VOBUI / 3

Sd.-y--, mg / m,

 al

five

0

five

0

five

0

five

where a

OL

No. 1 amount found in the sample volume of the sample solution in the test tube ti I, µg; b is the amount of JCl found in the sample volume of the sample solution in tube I-2 (in the presence of mercury), µg; V.,. - total volume of sample solution, ml;

volume of solution taken for analysis, ml; V - air volume selected

 for analysis, ml;

1.96 is the conversion factor of the mass content of fOI to DGHS. In tab. Figures 1 and 2 show the results of a separate determination of No. 1 and / RSChS in air at aspiration rates of 0.5-1.0 l / min and aspirated air volumes of 0.5-15.0 l.

As follows from the table. 1, the average percentage of determination of my substances is 99%. From} 1st definitions of determination error at si. 0.95 and p 12} ie 12%.

In tab. 3 shows the degree of absorption No. 1 and DAS with a different ratio of components in the absorption solution.

The degree of absorption of flfl and GHS in two successively connected absorbing devices is 100%, with at least 80% of the detected substances being trapped in the first absorber.

As can be seen from the table. 3, except for propyl alcohol, you can take ethyl

alcohol, and besides mercury acetate, use mercury nitrate.

The criterion for choosing the optimal composition of the absorption solution is the degree of absorption of the substance from the air by the first absorption device & 80%.

The main component of the absorption solution, which is responsible for removing the substance from the air, is for 101 cadmium acetate, which binds the mercaptan to a non-volatile cadmium mercaptide, and for SchS, an alcohol. Small amounts of acetic acid are added to prevent the hydrolysis of cadmium acetate during storage of the absorption solution, while No. 1 and DMDS are well absorbed by alcohol-water solutions of cadmium acetate that do not contain acetic acid. The addition of 0.02-0.2% acetic acid does not affect the absorption of the components, but prevents the hydrolysis of cadmium acetate. An increase in the concentration of acetic acid of 0.2% does not lead to a decrease in the degree of absorption of the test substances from the air; however, it is impractical because the main function of acetic acid does not exceed the specified concentration range.

As follows from the table. 3, MM is trapped from air with a degree of absorption in the 1st absorption device greater than 80% in solutions containing at least 1 wt.% Cadmium acetate. An increase in cadmium acetate concentration above 2% does not improve the absorption of methyl mercaptan, therefore it is not advisable.

DMDS is well captured (with a degree of absorption in the 1st absorption device 80%) in ethanol or propanol, as well as in alcohol-water solutions containing not more than 10% water. The preparation of cadmium acetate solutions containing less than 4% water is difficult because of the limited solubility Q r 0 5 Q

five

Q

bridges of this salt in propanol (ethanol) water mixtures.

In tab. 4 shows the comparative data for the determination of MM and DMDS by the known and proposed method.

As can be seen from the table. 4, the known method yields lowered compared with the given values the results of the determination of DMDS and curled results of determining the concentration of MM, as in the first pair of absorbing devices intended in the known method for trapping MM, not only this substance, but also DMDS is delayed (on average 63%), forming a mercaptan during reactions with mercury ions and a chromogenic reagent.

The proposed method allows the selective determination of methyl mercaptan at a minimum concentration of 0.2 mg / m (with MPC in the working area air 0.8 mg / m) and dimethyl disulfide with a minimum concentration of 0.34 mg / m (with MPC 1.5 mg / m) with a relative error of not more than 12%.

Claims (1)

Invention Formula The method of determining methyl mercaptan and dimethyl disulfide in the air by aspirating air through the absorption solution, processing the sample with a solution of H, N-dimethyl-p-phenylenediamine and iron (III) chloride followed by photometry of the resulting solution, which differs from that, in order to increase the selectivity and accuracy of the method, a mixture containing, in wt.%, is used as the absorption solution: Cadmium Acetate 1.00 - 2.00 Water4.00 - 10.00 Acetic acid 0.02 - 0.20 Ethyl or propyl alcohol The rest is taken two equal aliquot parts of the sample, one of which is treated with mercury acetate or nitrate before treatment with the chromogenic reagent. Table 1 in vD vOo ooo -O CSl n a s h YU a 00 in ON 00 about vO CM (M 00 1L " oo Ti- WHG -. fO -. M ui m "" in ff 4b vO -fM  # 0000 -m Oco "" "H CM- -cs  r - in m vO r O - vO CNC CM n GO - m cs  CO r - en in CM in -Cm CO 1427256 Methyl mercapt a absorption (air bleed rate l / min) 10 Table 3