Optimization of the sample preparation procedure in the determination of y-hexachlorocyclohexane in water by gas chromatography

Abstract

A high toxicity of organochlorine compounds, even present in trace amounts in food products, leads to increased requirements for the accuracy of chemical analysis in food safety control. The interstate standard GOST 31858-2012 was taken as a basis for this study. We have improved the method of sample preparation of drinking water for the determination of residual amounts of y-hexachlorocyclohexane (y-HCCH) by gas chromatography with an electron capture detector. Strictly following the instructions of the standard, we failed to obtain the value of the recovery factor of 94% prescribed by GOST for y-HCCH. In this regard, we proposed to use higher-boiling re-heptane instead of re-hexane as an extractant to reduce losses at the stage of sample preparation, and to use sodium chloride instead of ethyl alcohol prescribed by GOST to break the emulsion formed during the extraction of water with hexane. The volume of the analyzed sample, the mass of sodium chloride, the volume of the extragent, and the extraction time were optimized. The use of sodium chloride is shown to provide total emulsion breakage in 100% of experiments and to increase the recovery of pesticides with a concentration of 22 pg/liter from 77 to 96% with a relative standard deviation of 2%. Replacing the extragent with re-heptane led to an increase in the recovery of Y-HCCH to 98% with a relative standard deviation of 1%. It is shown that at a lower concentration of the pesticide, the recovery rate is 98 - 100 %. An increase in the concentration of y-HCCH to 45 pg/liter leads to a sharp decrease in the recovery degree. The proposed method can be considered as an improved method of liquid-liquid extraction with excellent extraction of the pesticide from the aqueous matrix.