ENERGY-RESOLVED MASS-SPECTROMETRY OF DIALKYL METHYLPHOSPHONATES WITH AN ATMOSPHERIC-PRESSURE IONIZATION TANDEM MASS-SPECTROMETER

The dialkyl methylphosphonates: dimethyl methylphosphonate (DMMP), die thyl methylphosphonate (DEMP), diisopropyl methylphosphonate (DIMP), a nd isopropyl methyl methylphosphonate (IMMP) were characterized using atmospheric pressure chemical ionization energy resolved mass spectrom etry (API-ERMS). API, a very soft ionization technique, is required fo r these compounds since they undergo very low energy rearrangements, a nd even methane-chemical ionization results in significant fragmentati on. API-ERMS was used to characterize the above homologous series of c ompounds. This work shows that ERMS can supply much more information t han conventional fixed energy tandem mass spectrometry (MS/MS), by pro viding the energy at which product ions are formed in addition to the mass-to-charge ratio and intensity data provided by MS/MS. From these results, dissociation pathways were proposed and compared with those p roduced by other workers. In addition, it was shown that the dissociat ion pathways of IMMP could be predicted solely based on energetic cons iderations and the knowledge of the dissociation pathways of DIMP and DEMP. This is the first work to provide the dissociation pathways of I MMP.