RU2276350C2 - Method of detecting asymmetric dimethyl hydrazine in water solutions - Google Patents

Abstract

FIELD: analytical chemistry.

SUBSTANCE: method comprises introducing 500-1000-fold excess of brown aldehyde to the sample of water solution to be analyzed up to the quantitative binding to produce dimethyl hydrazine, heating the mixture produced, extracting the dimethyl hydrazine by the chloroform, and taking a light reading of dimethyl hydrazine.

EFFECT: enhanced sensitivity.

5 dwg

Description

The invention relates to analytical chemistry, and in particular to methods for controlling harmful substances, one of which is asymmetric dimethylhydrazine, in the environment.

A known method for the determination of asymmetric dimethylhydrazine by gas chromatography, the sensitivity of which is 10 μg / ml (Savchuk S.A., Brodsky E.S. Application of capillary gas chromatography with selective detection to determine asymmetric dimethylhydrazine in soil // Journal of Chemistry. 1998. T.53. No. 7. S.759-763).

Low sensitivity, complex hardware design do not allow to widely use this method.

Known voltammetric method for determining asymmetric dimethylhydrazine (UDMH) using an electrochemical sensor (O. Kondratiev, Thermocatalytic and electrochemical sensors for determining asymmetric dimethylhydrazine. [Text]: dis. ... candidate of chemical sciences: 02.00.02: protected : 09/23/03 .approved: 11/26/03. / Kondratyev Oleg Tashpulatovich. - Krasnodar, 2003. - 175 p. - Bibliography: p. 170-175).

This method is very time-consuming and unsafe in the process of sampling and analysis, since UDMH is in a gaseous state.

The closest way to the claimed is a photocolorimetric method for determining asymmetric dimethylhydrazine in the form of dimethylhydrazone formed during the preliminary interaction of UDMH with para-nitrobenzaldehyde in aqueous solutions (RF patent No. 2111417, IPC (6) G 01 N 21/78).

Hydroxylamine hydrochloride and sodium hydroxide are introduced into the analyte sample, the resulting mixture is purged with an inert gas while boiling, the UDMH released during this is passed through a solution of para-nitrobenzaldehyde in ethylene glycol and acetic acid, followed by photometry of the resulting solution.

This method allows you to determine UDMH with a sensitivity of 0.02 mg / DM ³ . The method is expensive due to a large 10,000-fold excess of reagent and is also unsafe.

The technical task is to develop a sensitive, less time-consuming and safe method for determining UDMH.

To solve the technical problem, it is proposed to inject a 500-1000-fold excess of cinnamaldehyde into the analyte sample before quantitative binding of UDMH to dimethylhydrazone, heat the resulting mixture, extract the resulting dimethylhydrazone with chloroform and photometer it.

Distinctive features of the prototype is the use of cinnamaldehyde in a 500-1000-fold excess. The prototype uses an expensive reagent - para-nitrobenzaldehyde in a 10,000-fold excess.

In the inventive method, cinnamaldehyde is used, which was not previously used as a reagent for the analytical determination of UDMH, the conditions for its use are selected, which is a new and satisfying inventive step criterion.

In addition, instead of purging with an inert gas, chloroform extraction is suggested. When flushing with an inert gas, UDMH is in a gaseous state, which increases the risk of defeat by it and the complexity of the method. Replacing purge with extraction of UDMH creates safe working conditions.

Thus, the entire claimed combination of features is new and meets the criterion of inventive step.

Figure 1 shows the spectra of dimethylhydrazone depending on the heating time: a - 5 minutes, b - 10 minutes, c - 20 minutes, g - 30 minutes; figure 2 - absorption spectra of solutions of dimethylhydrazone with different water contents by volume: a - 40%, b - 30%, c - 20%, d - 15%, d - 5%; figure 3 - absorption spectrum of cinnamaldehyde (a) and its dimethylhydrazone (b); figure 4 is a graph of the dependence of the optical density on the excess of cinnamaldehyde; figure 5 - calibration dependence of the optical density on the concentration of UDMH.

Consider the definition of asymmetric dimethylhydrazine. A 25 ml volumetric flask was filled to the mark with a prepared sample containing asymmetric dimethylhydrazine. 1.4 ml of a working solution of cinnamaldehyde are added to the same flask. The contents of the flask are shaken and heated in a boiling water bath. It was experimentally determined that it is necessary to heat for at least 10 minutes (see figure 1).

Allow the resulting solution to cool, then transfer to a separatory funnel, add 10 ml of chloroform and extract for 30 minutes.

Experimentally, on the absorption spectra of dimethylhydrazone solutions containing 5, 15, 20, 30, 40% water by volume, it was found that the maximum absorption is observed when the water content is not more than 5% (see figure 2).

The extract obtained is transferred to a separate tube and its optical density at 400 nm is determined on a photoelectrocalorimeter in cuvettes with an absorbing layer thickness of 2 cm relative to the background solution extract.

The wavelength at which the optical density is determined was obtained from the absorption spectra of cinnamaldehyde and its dimethylhydrazone (see FIG. 3).

According to the calibration schedule, the concentration of UDMH in the extract is determined and the concentration of the analyte in the sample is calculated by the formula:

C _X = (C _E / 2.5) 0.96,

where C _X is the concentration of UDMH in the sample, μg / ml,

With _E - the concentration of UDMH in the extract, μg / ml,

2.5 - the degree of concentration of cinnamaldehyde dimethylhydrazone from the sample to chloroform,

0.96 is the degree of transition of cinnamaldehyde dimethylhydrazone from the sample to chloroform.

The calibration schedule (see figure 5) is constructed as follows. 0.005 is added to 10 ml volumetric tubes; 0.05; 0.1; 0.5 and 1.0 ml of a working solution of asymmetric dimethylhydrazine, 1.4 ml of a working solution of cinnamaldehyde are successively added to each, the volumes are adjusted to the mark with a mixture of ethylene glycol and acetic acid in a ratio of 4 to 1 by volume, stirred, heated and determined optical density, as in the case of the sample. Linearity is observed in the concentration range from 0.05 to 10 μg / ml, which indicates the possibility of finding UDMH. Taking into account concentration during extraction, the minimum level of detectable UDMH concentration is 0.02 μg / ml.

The UDMH working solution is prepared by diluting 2.5 ml of GSO in a 25 ml volumetric flask with distilled water.

A working solution of the reagent is prepared by diluting 1.3 ml of cinnamaldehyde in a 25 ml volumetric flask with a mixture of ethylene glycol and acetic acid.

The amount of excess reagent was determined from the experimental data of measuring the optical density at various ratios of cinnamaldehyde and UDMH in moles.

Table
Dependence of optical density on excess cinnamaldehyde No. p / p V _reagent V _UDMH , ml Ratio: reagent / UDMH Optical density one 25 μl 0.2 10 0.02 2 50 μl 0.2 twenty 0.02 3 125 μl 0.2 fifty 0.04 four 250 μl 0.2 one hundred 0.06 5 500 μl 0.2 200 0.06 6 1.25 ml 0.2 500 0.1 7 1.75 ml 0.2 700 0.1 8 2.5 ml 0.2 1000 0.1

As can be seen from the table and figure 4, cinnamaldehyde for the determination of UDMH through dimethylhydrazone must be taken in a 500-1000-fold excess. The most optimal is a 700-fold excess of cinnamaldehyde.

The inventive method of determination can be used with various methods of sample preparation, which expands the list of objects in which UDMH can be determined. It is safe and less time-consuming, since they work with solutions of dimethylhydrazone, and not with gaseous UDMH, as in the known methods.

Claims (1)

A method for determining asymmetric dimethylhydrazine in aqueous solutions, including photometry of the resulting dimethylhydrazone, characterized in that a 500-1000-fold excess of cinnamaldehyde is added to the analyte sample, the resulting solution is heated, dimethylhydrazone is extracted with chloroform, followed by photometry.

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