GC/CI/MS studies of aldicarb and butocarboxime, two isomeric oxime carbamates

Abstract

A direct GC/MS determination of aldicarb[2-methyl-2-(methylthio) propionaldehyde O-(-N-methylcarbamoyl) oxime] and its structural isomer butocarboxime[2-methylthio-O-(-N-methylcarbamoyl) butanone-3-oxime] is reported. Mild GC conditions, using 2% OV-17 as liquid phase provide the lowest extent of degradation. Butocarboxime is analyzed intact as its[M+H] + ion whereas aldicarb undergoes an on column dehydration, leading to an [M-18] + fragment with an intact carbon skeleton in the isobutane - Cl mass spectra. The GC/CI of these molecules shows characteristic fragmentation patterns which allow the mass spectrometric distinction between the two isomers.