Determination of the fragmentation mechanisms of organophosphorus ions by H₂O and D₂O atmospheric‐pressure ionization tandem mass spectrometry

Dimethylmethyl phosphonate (DMMP), dimethyl phosphite (DMPI), trimethyl phosphite (TMPI) and trimethyl phosphate (TMP) were investigated using H 2 O and D 2 O atmospheric‐pressure ionization (API) tandem mass Spectrometry. All daughter ions could be explained by losses of one or a successive number of stable molecules as opposed to losses of radicals such as the hydride, methyl and methoxy species. Losses of neutral methanol and dimethyl ether and of protonated methanol and formaldehyde ions from all four organophosphorus pseudo‐molecular ions were observed. The DMMP and DMPI MH + pseudomolecular ions produced the losses of neutral C 2 H 6 and water, respectively. Formaldehyde loss was not observed for the MH + ions, but it was well represented in the decomposition pathways of daughter ions. The D 2 O reagent gas highlighted the role of the ionizing proton/ deuteron in the various daughter ions, including m/z 95, 79, 65, 49, 33, 31 and 47. The last ion was found to be isobaric in that m/z 47 and 48 both appeared with similar abundances in the D 2 O‐API daughter ion mass spectra of TMPI and TMP.