Investigation of the dissociation pathways of metolachlor, acetochlor and alachlor under electron ionization - application to the identification of ozonation products.

With the future aim of using gas chromatography coupled with mass spectrometry to characterize the transformation products of ozonated herbicides: metolachlor, acetochlor and alachlor, an interpretation of their electron ionization mass spectra is presented. Fragmentation mechanisms are proposed on the basis of isotopic labelling and multiple-stage mass spectrometry experiments carried out on an ion trap mass spectrometer. We also give examples in order to demonstrate how the elucidation of such fragmentation mechanisms for herbicides may simplify the characterization of their ozonation products.