Identification of uncommon plant metabolites based on calculation of elemental compositions using gas chromatography and quadrupole mass spectrometry

Unknown compounds in polar fractions of Arabidopsis thaliana crude leaf ext racts were identified on the basis of calculations of elemental composition s obtained from gas chromatography/low-resolution quadrupole mass spectrome tric data. Plant metabolites were methoximated and silylated prior to analy sis. All known peaks were used as internal references to construct polynomi al recalibration curves of from raw mass spectrometric data. Mass accuracie s of 0.005 +/- 0.003 amu and isotope ratio errors of 0.5 +/- 0.3% (A + 1/A) , respectively, 0.3 +/- 0.2% (A + 2/A), could be achieved. Both masses and isotope ratios were combined when the elemental compositions of unknown pea ks were calculated. After calculation, compound identities were elucidated by searching metabolic databases, interpreting spectra, and, finally, by co mparison with reference compounds. Sum formulas of more than 70 peaks were determined throughout single GC/MS chromatograms, Exact masses were confirm ed by high-resolution mass spectrometric data. More than 15 uncommon plant metabolites were identified, some of which are novel in Arabidopsis, such a s tartronate semialdehyde, citramalic acid, allothreonine, or glycolic amid e.