Rapid method for trace determination of organochlorine pesticides and polychlorinated biphenyls in yogurt

A new multiresidue method was developed for the analysis of 19 organochlorine pesticides and 6 polychlorinated biphenyls in yogurt. The sample was extracted twice with acetone by homogenization with an Ultra-Turrax dispersing unit, and the combined extracts were filtered. The extract was then purified by reversed-phase C-18 columns and subjected to further cleanup with neutral alumina columns. The residues were determined by gas chromatography with electron capture detection. After the method was optimized, it was validated by determination of recovery percentages, precision (repeatability and reproducibility), and sensitivity (detection and quantitation limits) with yogurt samples fortified at 10 and 1 mug/kg concentration levels. The recovery of 23 organochlorine residues ranged from 77 to 95 % at a level of 10 mug/kg, from 74 to 102% at a level of 1 mug/kg, and between 54 and 61 % for dieldrin and alpha-endosulfan. The method is repeatable and reproducible, with relative standard deviation values <19% for all residues except dieldrin. Detection and quantitation limits were between 0.02 and 0.62 mug/kg. The analytical method proposed was quick, accurate, repeatable, and reproducible for the determination of organochlorine residues in yogurt samples.