Fig. 1. Overview of a GC-MS chromatogram from an Arabidopsis leaf extract (here, ecotype Cvi-0). (a) total ion current chromatogram, showing annotation of typical peaks (in red). The observed mass spectrum at 15.05 min is shown in (b), with characteristic ions of 6-phosphogluconate 3TMS annotated in red. Note the contribution of ion m/z = 387.14254 Da (fragment C13H32O7PSi2+). Note that a close, but easily distinguishable mass (387.32912 Da, fragment C22H47O3Si+) can be observed at 15.25 min, from arachidic acid 1TMS; nominal mass analysis would have generated the same apparent mass at 387 (or 388) Da.