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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.
Vergel B. Casunuran is an environmental consultant with Booz Allen Hamilton at their San Antonio, Texas, location. Mr. Casunuran received his M.S. in chemistry from the University of Texas at San Antonio and has been working as a consultant environmental chemist since 1994. His interests are in the degradation of recalcitrant compounds and explosives and the application of mass spectrometry to environmental quality and remediation issues.Stephen Bach is an associate professor of chemistry and director of the Mass Spectrometry Facility at the University of Texas at San Antonio. Bach received his Ph.D. in physical chemistry from the University of Florida and did his postdoctoral training at the University of Florida and at the Naval Research Laboratory in Washington, DC. His interests are in the application of mass spectrometry to environmental quality and remediation issues.
Dibyendu Sarkar is an assistant professor and the director of the Environmental Geochemistry Laboratory at the University of Texas at San Antonio. Sarkar received his Ph.D. from the University of Tennessee and did his postdoctoral training at the University of Florida. His areas of expertise include soil chemistry, environmental quality and remediation, and risk assessment. Sarkar is also an associate editor of Environmental Geosciences.