Fragmentations and reactions of three isotopically labelled dimethyl methylphosphonate ions produced by electrospray ionisation in an ion trap mass spectrometer

In an initial investigation into the electrospray ionisation ion trap mass spectrometry (ESI/ITMS) of simple organophosphate esters we reported that in one of the collision induced fragmentation steps of protonated dimethyl methylphosphonate ( DMMP), formaldehyde was eliminated with a concomitant partial scrambling of the methyl group attached to the phosphorus and a methoxy group. The present paper describes a further investigation of this reaction. Three novel isotopomers of DMMP were used for this study and their synthesis and properties are reported. A mechanism for the formaldehyde elimination and scrambling of the methyl groups is proposed and supported by a kinetic analysis of a limiting case. During this study black holes were found to occur in one of the ITMS instruments used and it is shown that these could lead to severe distortions in the amounts of product ions observed. A brief analysis of this observation is presented.