GC/CI/MS Analysis of Aldicarb, Butocarboxime, and Their Metabolites

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Abstract
A direct GC/MS determination of aldicarb [2-methyl-2-(methylthio)propionaldehyde o-(methyl carbamoyl) oxime], of its structural isomer butocarboxime [2-methylthio-o-(N-methyl carbamoyl) butanone-3-oxime], and of their toxic sulfoxide and sulfone metabolites is developed. Mild GC conditions using a 2% OV-17 (phenyl-methyl silicone polymer) liquid phase column provide the lowest extent of degradation. The CI/MS of the directly introduced molecules is compared to their GC/CI/MS. Butocarboxime is analyzed intact whereas its metabolites, as well as aldicarb and its sulfone derivative, undergo an on-column dehydration. The intact carbon skeleton is maintained in this process, as evidenced by the [M-18]+ fragment observed in the isobutane-CI mass spectra. Aldicarb sulfoxide, the more labile molecule in these series, degrades on-column to the corresponding nitrile. Typical fragmentation patterns are observed in the GC/MS analysis which allow distinction between the two series of isomers.

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