Optimization of sample preparation for sensitive determination of DDT metabolites in food by gas chromatography – mass spectrometry

Detecti on of trace amounts of organochlorine pesticides in food (ng/kg) is very complex and expensive. Therefore, development of highly sensitive and inexpensive methods is of a high importance . The current study is devoted to the development of inexpensive method for sample preparation and highly sensitive determination of organochlorine pesticides using gas chromatography with mass spectrometric detection. Optimized sample preparation includs an organic solvent extraction, clean-up step by extract passing through a multilayer column on the basis of modified silica gel and pre-concentration to a small volume. It was established that 100 ml of n-hexane eluant volume is optimal for maximum extraction of metabolites of DDT from the column. Analytes losses on the clean up step were 20%, on pre-concentration step - 30%. Optimization of the method allowed to decrease limit of detection of organochlorine pesticides up to 12 ng/kg. Limits of reproducibility of DDE and DDD did not exceed 25 and 27%, respectively. Screening of food of animal and plant origin from Almaty was carry out using optimized sample preparation method. Results showed that 55 out of 70 samples were contaminated by DDE and DDD. The highest concentrations were found in milk sample (DDE 1.07 ng/g, DDD 2.46 ng/g) and in fish sample (DDD 88.6 ng/kg).