Determination of organophosphorus pesticides in whole/chocolate/skim-milk and infant formula using solid-phase extraction with capillary gas chromatography/flame photometric detection

Twenty nine organophosphorus pesticides (OPPs) are identified on a DB‐17 capillary column using gas chromatography‐flame photometric detection (GC‐FPD). An acetone‐acetonitrile mixture is used to initially extract OPPs from milk and infant formula samples, followed by partition of the analytes into dichloromethane (DCM). Dichloromethane is removed on a rotary evaporator and the residue taken up in acetonitrile (ACN) for cleanup on a C‐18 (octadecylsiloxane bonded silica) (SPE) cartridge. ACN eluate is evaporated under nitrogen and the residue taken up in acetone for GC‐FPD determination. Initial studies showed mean recoveries for 28 of 29 OPPs in whole milk fortified at 0.10 ppm ranged between 69 and 99% with a relative standard deviation (RSD) of 1.0–9.7%. Whole/chocolate/skim‐milk and four infant formula products fortified at 0.02 ppm gave mean recoveries of 64–103% with RSDs between 1.9 and 20.9% for 24 of 29 OPPs. Excluding skim milk, recoveries for Dichlorvos, Methamidophos, Mevinphos E, and Acephate ranged between 47 and 89%. Sample extracts were extremely clean and posed no difficulty to the GC system. The procedure is faster and less costly than Association of Official Analytical Chemists (AOAC) procedures and allows for determination of a broad spectrum of OPPs.