An analytical methodology for directly analyzing organophosphorus pesticides (OPPs) in solid matrices was devised around a multigram capacity direct insertion probe (DIP) interfaced to a quadrupole mass spectrometer (MS). The DIP-MS system was used to analyze acephate [O,S-dimethyl acetylphosphoramidothioate] and diazinon [O,O-diethyl-O-(2-isopropyl-6-methyl-4-pyrimidinyl)phosphorothioate] in a “clean” sand matrix, namely, Ottawa sand. Diazinon was also analyzed in a Florida spodosol, Immokalee soil. Instrument detection limit studies demonstrate that the DIP-MS system is capable of detecting 5 μg of acephate in the absence of an interfering matrix. The method detection limit for diazinon was calculated at 2.5 μg. DIP-MS analysis of diazinon in the Immokalee soil showed as much as a 50% reduction in instrument response compared to the relatively pure Ottawa sand. This was attributable to the “dilution effect” of codesorbing soil organic matter. Results from the performance evaluation studies using Immokalee soil demonstrate the potential of the DIP-MS technique to directly analyze OPPs and other thermally extractable chemicals in soils and other solid matrices without the need for solvent extraction, sample pretreatment, or confirmation by other analytical methods.

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