Mass spectrometric studies of the path of carbon in photosynthesis: Positional isotopic analysis of 13C-labelled 2-octulose phosphates

The electron impact mass spectrometric fragmentation patterns of the per‐O‐trimethylsilyl (TMS) and alkoxime‐TMS derivatives of D‐glycerol‐D‐altro and D‐glycerol‐D‐ido‐octuloses were fully analysed using seven specifically labelled 13C analogues. Many of the more intense‐ ions in the spectra of the per‐O‐TMS furanose and pyranose derivatives have more than one origin. On the other hand, the mass spectra of the straight‐chain methoxime and ethoxime hepta‐O‐TMS derivatives contain ions each of which in general originares from a single cleavage process. This makes gas chromatography/mass spectrometry of the aikoxime‐TMS derivatives a suitable method for monitoring 13C incorporations at individual carbon atoms in the corresponding octulose phosphates during photosynthesis experiments with 13CO2.