Evaluation of analytical methods for determining pesticides in baby foods and adult duplicate-diet samples

Determination of pesticides in food is often complicated by the presence of fats and requires multiple clean-up steps before analysis. Cost-effective methods are needed for analyzing the large number of samples generated in large-scale exposure studies. We examined two extraction methods, supercritical fluid extraction (SFE) and accelerated solvent extraction (ASE), coupled with various clean-up techniques for the analysis of pesticides in baby foods and exposure samples. The SFE-gas chromatogram/mass spectrometry (GC/MS) method did not provide quantitative recoveries (<50%) of the pesticides spiked into fatty baby foods. This led to the evaluation of ASE-enzyme-linked immunosorbent assay (ELISA) and ASEGC/MS. Two solvents (acetonitrile (ACN) and ethyl acetate), three extraction temperatures (80, 100, and 120°C), and several different sample clean-up procedures were evaluated. A set of ASE conditions was developed that consisted of extracting baby food with ACN at 80° C under 2000psi pressure. An ENVI-Carb solid phase extraction (SPE) condition was also developed to clean the ACN extract. The clean-up fraction was analyzed by ELISA for chlorpyrifos and by GC/MS for malathion, chlorpyrifos, and 4,4´-DDT. Duplicate-diet samples were analyzed for target pesticides by ASE-ELISA and by ASE-GC/MS. Concentrations of these compounds ranged from <0.3 to 110ppb.