请教一个问题，看到一篇文献，做的同位素标记前体物饲喂，最后用GC-MS检测同位素标记的代谢物含量 这些化合物的分子量与他们标记的 target ion差别很大 比如第一个化合物分子量是
这些化合物的分子量与他们标记的 target ion差别很大
Supp. Table 3. Metabolites identified in RCH2 bacterial lysates and their corresponding 13C target ion used for recovery comparison, retention time (RT) and RT of authentic standards. Putative metabolite annotations are indicated by italics (retention time and/or spectra could not be confirmed with an authentic standard).
Compound 13C target ion Chemical Formula
alanine 221 C3H7NO2
valine 220 C5H11NO2
isoleucine 163 C6H13NO2
proline 146 C5H9NO2
glycine 249 C2H5NO2
uracil 245 C4H4N2O2
serine 206 C3H7NO3
Agilent 7890 gas chromatograph (Agilent Technologies, Santa Clara, CA)
Agilent 5977 single quadrupole mass spectrometer (MS)
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3.5. Microbial metabolite adsorption and recovery
To explore the types of microbial metabolites that adsorb to soil and therefore may represent those that are unavailable to microbes in situ, 13C-labeled RCH2 bacterial lysates were incubated with soil and extracted with water (Fig. 3). K2SO4 (10 mM) was compared to water to determine if this classical extractant was more efficient at metabolite recovery. The most intense peaks from the unlabeled RCH2 lysates (grown with 12C-acetate) were selected for further analysis in labeled samples (compound identification, 13C incorporation and recovery calculations). Spectra from unlabeled RCH2 were compared to labeled cultures, which resulted in the identification of 45 fully-labeled metabolites (Fig. 4, Supp. Table 3). The 13C target ion for each metabolite was quantified for all samples and recovery was calculated. Only 27% of the quantified metabolites showed >50% recovery in the WEOM, with the majority of those being neutral metabolites. All of the polyamine cations identified in this experiment (putrescine, cadaverine, lysine, spermine and spermidine) and most of the anionic metabolites were among those that adsorbed rapidly to soil (Fig. 4). The inclusion of 10 mM K2SO4 as a recovery extractant did not drastically improve or reduce recovery compared to water alone.