Rapid method for the determination of organochlorine pesticides in milk

Abstract

This method involved one step extraction of milk with acetate—acetone—methanol by ultrasonication. The supernatants were further cleaned-up and enriched by solid-phase extraction using octadecyl (C 18)-bonded silica catridges, then assayed by capillary gas—liquid chromatography with electron capture detection. The recoveries of eleven organochlorine pesticides (OCPs) from raw milks were quantitative, ranging from 90–110% at 10 times the limit of detection (LOD). The LOD ranged form 0.5 μ/l whole milk for α-hexachlorocyclohexane to 2.5 μg/l whole milk for 1,1,1-trichloro-2,2-bis( p-chlorophenyl)ethane. The day day-to-day variation of the method was evaluated over 7 days using 3 different pools of spiked cow miles (at the LOD, 5 and 10 times the LOD). The coefficient of variations (C.V.s) were 16±6, 10±2 and 9±3% (means S.D.), respectively. The method showed no emulsion problems common with conventional non-polar solvent extraction, and the use of solid-phase extraction considerably reduced the sample clean-up process compared with the existing method. The method also showed that OCPs in milk could be extracted quantitatively without extraction of total fat, and that OCPs spiked into cows milk could be used to construct calibration curves for human milk determinations.