Consecutive reactions in the vitamin D series. A New insight into the mechanism of vitamin D and provitamin D isomerizations in the mass spectrometer

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AbstractThe individual steps of the consecutive reactions equation image arising from metastable molecular ions, derived from vitamin D3, vitamin D2 and their respective provitamins (7‐dehydrocholesterol, ergosterol), were examined in different field‐free regions of a triple‐sector mass spectrometer of B/E/E geometry. The comparison of the translational energy release (T) and the metastable peak shapes corresponding to these reactions, as well as unimolecular and collision‐induced dissociation mass‐analysed ion kinetic energy spectra, showed that there are probably two structures of the [M – H2O]+˙ and [M – CH3˙]+ ions depending upon whether the respective ions are formed in the ion source through high‐energy reactions, or from the fragmentation of metastable molecular ions through slow, low‐energy processes which occur in the first field‐free region.