Mass spectrometric fragmentation of cyclophosphamide (CP) has been studied in detail using linked field scanning, isotope labelling, low energy ionization and accurate mass measurements. The molecular ion is of low abundance and it favours loss of HCl and .CH,CI to form the base peak at m / z 211. All the other ions are formed by sequential fragmentation processes. The direct bond rupture between phosphorus and the N-chloroethyl group produces two ions m/z 120 and m / z 92. The ion m / z 56 is a triplet. Many of the ions in the spectrum are produced by several competing pathways. Several of the rearrangement mechanisms involve a single hydrogen transfer.
Quantitative differences between two commercial C P preparations were observed in the linked field scanning spectra. Differences in the abundances of the metastable ions strongly suggest that there is an intense isomeric competition in the decomposition pathways. The experimental evidence supports the conclusion that the two CP preparations differ in their isomeric composition and these differences are related to their stereoisomers. The rates of the individual fragmentation pathways are dependent upon the isomeric structure of the parent molecule and might also be reflected by different rates of metabolism of the isomers of the drug in uiuo.