Well, I still have not found any 13C metabolites in my samples (analysed with GC-MS), but the composition of my samples is changing quite signifcantly due to microbiological activity. E.g. butanol, which I have detected in large quantities in the initial samples has disappeared and a range of other compounds (a lot of them aromtics) have appeared in my mass spectra. Among them are chlorobenzene, increased amounts of toluene and several others. So there is definitely something going on here.
Still, my goal is to find at least one 13C metabolite. Some of the spectra I could not assign to a compound despite a distinct MS signature. Maybe the NIST database and my own experience (or rather the lack thereof) misses the compound due to the changed isotopic composition. I guess that I have to keep on hunting.
Not much luck with the NMR measurements either. As feared, the concentration of labelled malonic acid is too low – so that means overnight runs (with fingers crossed) or increasing the amount of malonic acid and buffering the lowered pH with diluted NaOH, to keep the microbiology happy (and even more important: alive and productive).
