Tandem mass spectrometric study of the major fragmentation pathways of some non-ester pyrethroid insecticides having alkane, alkene and ether central linkages

Abstract

The non-ester pyrethroid MTI-800 which has an alkane central linkage has been studied using a tandem quadrupole mass spectrometer incorporating a hexapole collision cell under positive-ion electron ionization conditions. Other structurally related insecticides, NRDC 199 and NRDC 200, which have alkene central linkages and Flufen-prox which has an ether central linkage, have also been studied. Conventional mass spectrometry using the first quadrupole analyser only and tandem mass spectrometry have been used in this study. The positive-ion electron ionization mass spectrum of MTI-800 is dominated by an intense even electron (EE+) 1-(4-ethoxyphenyl)-1-methylethylium ion fragment which subsequently loses ethylene from the ethoxy side chain. The influence of other isosteric or isoelectronic substitutions at the geminal dimethyl position of MTI-800 and variations at the alkane linkage is shown by additional fragmentation pathways. The relative intensities of their respective molecule ions vary from 0% to 7%. The expulsion of difluorocarbene (:CF2) as a neutral species from the 1-(4-hydroxyphenyl)-2,2,2-trifluoroethylium fragment ion of Flufenprox has also been rationalized. © 1997 John Wiley & Sons, Ltd.