Determination of Spinosad and Its Metabolites in Food and Environmental Matrices. 2. Liquid Chomatography−Mass Spectrometry

A selective and sensitive method utilizing liquid chromatography−mass spectrometry (LC-MS) has been developed for determining residues of the natural insect control agent spinosad in several crop matrices that are difficult to analyze by HPLC with UV detection. The method determines the active ingredients (spinosyns A and D) and three minor metabolites (spinosyns B and K and N-demethylspinosyn D) in alfalfa hay, wheat hay, wheat straw, sorghum fodder, and corn stover. The analytes are extracted from the samples with an acetonitrile/water solution, and the extracts are purified by solid phase extraction with a C18 disk and a silica cartridge. All five analytes are determined simultaneously in a single injection using positive atmospheric pressure chemical ionization LC-MS with selected ion monitoring. The average recoveries ranged from 69 to 96% with standard deviations ranging from 4 to 15%. The method has a validated limit of quantitation of 0.01 μg/g and a limit of detection of 0.003 μg/g. The LC-MS method can also provide residue confirmation in addition to quantitation. Keywords: Spinosad; spinosyn A; spinosyn D; spinosyn B; spinosyn K; N-demethylspinosyn D; residues; alfalfa; wheat; sorghum; corn; LC-MS