Seven FDA pesticide laboratories collaborated to develop and validate an LC-MS/MS method to determine 173 pesticides in <20 min. The average determination coefficient (r²) was >0.99 for all but two compounds tested. The limits of detection were <20 ng/mL for all compounds and <10 ng/mL for 363 of the 368 transitions reported. The method was used to determine pesticides in two AOAC sponsored proficiency samples. The LC-MS/MS determination was used for the analysis of oranges, carrots and spinach using the QuEChERS (Quick, Easy, Cheap, Effective, Rugged, Safe) method. Each matrix was fortified at 20, 100, 400, and 1000 ng/g. No false positive responses were detected in controls of the three matrices. 165 pesticides had recoveries between 70 and 130%, and 161 had minimum detection levels less than 10 ng/g. Recoveries of 169 compounds for the 1000 ng/g spikes were within 50-150%. A matrix effect study indicated all three matrices caused a small net suppressing effect, the most pronounced attributable to the citrus matrix. The procedure proved to be accurate, precise, linear, sensitive and rugged, and adds 100 pesticides to the scope of the FDA pesticide program.
An existing method for chloramphenicol (CAP) determination in shrimp using a gas chromatograph with electron capture detector was adapted for confirmation of CAP with a liquid chromatograph interfaced to a triple quadrupole mass spectrometer. CAP residues are extracted from tissue with ethyl acetate, isolated via liquid–liquid extraction, and concentrated by evaporation. Extracts are chromatographed by using a reversed-phased column and analyzed by electrospray negative mode tandem mass spectrometry. Four product ions (m/z 152, 176, 194, and 257) of precursor m/z 321 were monitored. Moving from gas chromatography to liquid chromatography–tandem mass spectrometry improved the sensitivity of the method greatly, enabling reliable confirmation of CAP residues at 0.3 μg/kg (ppb). The method meets confirmation criteria recommended by the U.S. Food and Drug Administration and 4-point identification criteria established by the European Union. With slight modifications to accommodate different equipment, the method was validated in 3 laboratories.
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