Pesticide confirmation by triple stage quadrupole mass spectrometry: etrimfos and dimethoate.

The production of a protonated molecular ion, MH+, for a pesticide under investigation is often preferred for primary identification purposes. However, the lack of fragment ions under such chemical ionization conditions can place the burden of proof on a single ion species for confirmation. Although a single ion representing the molecule at the correct retention time on a packed column or high-resolution capillary column might seem to have furnished sufficient evidence for unambiguous confirmation, in a number of cases additional specificity can improve the analytical result. With the introduction into commerce of triple stage quadrupole (TSQ) instruments, the possibility of improving the degree of specificity by chemical ionization has emerged for practical pesticide residue confirmation analysis. Use of collision-activated dissociation (CAD) experiments to form daughter ions from the protonated molecular ion of 2 representative organophosphorus pesticides has provided a second dimensional plane of characterization for confirmatory purposes at incurred residue levels.