Determination of Pesticides in Composite Dietary Samples by Gas Chromatography/Mass Spectrometry in the Selected Ion Monitoring Mode by Using a Temperature-Programmable Large Volume Injector with Preseparation Column

Abstract

Use of a temperature-programmable preseparation column in the gas chromatographic (GC) injection port permits determination of a wide range of semi-volatile pesticides including organochlorines, organophosphates, triazines, and anilines in fatty composite dietary samples while reducing sample preparation time and solvent consumption. Dietary samples are mixed with diatomaceous earth and are Soxhlet-extracted with an azeotropic solution of hexane and acetone. Sample preparation uses liquid-liquid partitioning over diatomaceous earth followed by normal phase chromatography over partially deactivated alumina. The final cleanup step occurs in a preseparation column in the GC injector, which is able to perform splitless transfer of the analytes to the analytical column and purge 99% of the high molecular weight residue. Detection is performed by GC/mass spectrometry (MS) in the selected ion monitoring mode. Method detection limits were at or below 2 ng/g for 24 of 35 pesticides studied, with recovery between 70 and 125% for 27 pesticides in samples fortified at 10 ng/g. Recovery was not dependent on fat content when measured in laboratory fortified samples containing 1, 5, and 10% fat by weight. Precision over multiple injections was acceptable, with a relative standard deviation of 2.6-15% for 25 analytes.