Table 1. Mass measurement accuracy of tentatively identified human plasma metabolites.

Metabolites were extracted from human plasma using cold (−20°C) methanol (4:1, v/v) with concomitant protein precipitation and removal via centrifugation. Extracts were dried in vacuo, reconstituted in water, and analyzed using capillary LC coupled with Orbitrap MS detection over a mass range of 100–1000 m/z. Metabolite masses were determined by averaging the mass spectra across the full-width at half-maximum for the corresponding LC peaks. Further validation of tentative identifications was made by comparison of theoretical and observed isotopic distributions (see Figure 6) and by using targeted MS/MS data and comparison to authentic standards, as applicable. Unpublished data.

Metabolite	Observed m/z	Predicted m/z	Mass error (ppm)
Tryptophan	205.0971	205.0977	2.9
Riboflavin	377.1456	377.1461	1.3
Tetradecanoylglycerophosphatidylcholine	468.3090	468.3090	0.0
Pentadecanoylglycerophosphatidylcholine	482.3245	482.3246	−0.3
Hexadecenoylglycerophosphatidylcholine	494.3255	494.3246	−1.7
Hexadecanoylglycerophosphatidylcholine	496.3394	496.3403	1.8
Heptadecenoylglycerophosphatidylcholine	508.3414	508.3403	−2.2
Heptadecanoylglycerophosphatidylcholine	510.3558	510.3559	0.3
Octadecatrienoylglycerophosphatidylcholine	518.3260	518.3246	−2.6
Octadecadienoylglycerophosphatidylcholine	520.3393	520.3403	1.9
Octadecenoylglycerophosphatidylcholine	522.3566	522.3559	−1.3
Octadecanoylglycerophosphatidylcholine	524.3711	524.3716	0.9
Eicosapentaenoylglycerophosphatidylcholine	542.3246	542.3246	0.0
Eicosatetraenoylglycerophosphatidylcholine	544.3387	544.3403	2.9
Eicosatrienoylglycerophosphatidylcholine	546.3549	546.3559	1.9
Docosahexaenoylglycerophosphatidylcholine	568.3396	568.3403	1.2
Docosapentaenoylglycerophosphatidylcholine	570.3574	570.3559	−2.5
Bilirubin	585.2701	585.2713	2