Fragmentation of a Non-Ester Pyrethroid Insecticide by Atmospheric Pressure Chemical Ionization

We elucidated the mechanism of fragmentation of ethophenprox (Mw = 376), a non-ester pyrethroid insecticide, in the presence of a proton, by using tandem mass spectrometry in combination with an atmospheric pressure chemical ionization technique in positive-ion mode. When methanol or acetonitrile was used as a solvent, no protonated ethophenprox ion was observed in the mass spectra even at low cone voltage (10V), at which solvent cluster ions can exist. Instead of the protonated ion, an unexpected m/z 359 ion was strongly observed under all conditions examined. The product ion spectrum of the m/z 359 ion obtained under low collision energy (20 eV) showed that this ion can be formed through structural rearrangement involving water loss mainly via the six-centered pathway in this system, although two pathways (five-centered and six-centered) to form the m/z 359 ion are suggested in the literature.