Multiresidue Method for Pesticides and Persistent Organic Pollutants (POPs) in Milk and Cream Using Comprehensive Two-Dimensional Capillary Gas Chromatography−Time-of-Flight Mass Spectrometry

Abstract

A method for the analysis of pesticides and their metabolites including most of the persistent organic pollutants (POPs) in milk and cream is described. The method was single-laboratory validated through milk fortification in quadruplicate with 34 pesticides, isomers, and metabolites including 12 of the insecticide POPs and their metabolites. Whole cow’s milk was fortified at 0.2, 0.4, 1, 2, 10, or 50 μg/kg wet weight and extracted with acetone/cyclohexane/ethyl acetate (2:1:1) with the addition of Mg₂SO₄ and NaCl. Fat recovered in the extract accurately reflected the fat content of the milk or cream. All test portions were purified on a gel permeation chromatograph (GPC) followed by solid phase extraction (SPE) cleanup on a mixed bed graphitized carbon black (GCB) and primary/secondary amine silica gel (PSA) column before determination using a comprehensive two-dimensional gas chromatograph interfaced to a time-of-flight mass spectrometer. Average recoveries were 77, 72, 73, 66, 77, and 84% for 0.2, 0.4, 1, 2, 10, and 50 μg/kg wet weight whole milk, respectively. The average relative standard deviations for 0.2, 0.4, 1, 2, 10, and 50 μg/kg were 10, 8, 7, 7, 3, and 3%, respectively. The limits of quantification (LOQs) for all pesticides were 0.2 or 0.4 μg/kg wet weight. An archived cream sample collected in 1982 on Oahu, Hawaii, was found to contain only hepatachlor epoxide (HE) and DDE-p,p′ at 380 ± 24 and 69 ± 17 μg/kg fat, significantly elevated over the current action level of 50 μg/kg fat for HE.