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In this study, it is shown that calibration solutions prepared in control matrix extract can be used to compensate for matrix-induced chromatographic response enhancement observed for certain pesticides. This phenomenon is characterized by enhanced chromatographic response for certain pesticides in the presence of matrix due to reduced analyte loss during injection. Unacceptably high recoveries are seen for affected pesticides when matrix-free solutions are used for reference and calibration. The effects of matrix concentration on overall enhancement and linear response were determined. When used as reference standards for the determination of recovery, matrix-standard solutions were found to provide acceptable recoveries for pesticides subject to matrix-induced chromatographic response enhancement along with other pesticides. General guidelines are presented for using matrix-standard calibration solutions in pesticide residue analysis.

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A simplified rapid method is presented to determine organochlorine pesticides and polychlorinated biphenyls in fish. Samples are mixed with sodium sulfate and blended with petroleum ether. A portion of the blend is placed on a miniaturized Florisil column and compounds are eluted with mixtures containing 6 and 15% ethyl ether in petroleum ether. Gas-liquid chromatography with electron capture detection comparable to the official methods (29.018) is used for determination of residues. Each of 7 collaborators reported results in duplicate for 10 samples containing one or more of the following compounds: p,p’-DDD,p,p’-DDE, p,p’-DDT, dieldrin, heptachlor epoxide, Aroclor 1254, and Aroclor 1260. Recoveries ranged from 79.3 to 100.7%. The coefficients of variation between laboratories ranged from 6.3 to 20.6%. This method allows up to 80% reduction in reagents and up to 50% reduction in analytical time, and requires less laboratory space than current official methods. The method has been adopted official first action.

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%. Wholekhocolatehkim-milk and four infant formula products fortified at 0.02 ppm gave mean recoveries of 64103% with RSDs between 1.9 and 20.9% for 24 of 29 OPPs. Excluding skim milk, recoveries for Dichlowos, 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.