Identities of significant features, observed values and measures of statistical support.

aThe observed mass to charge ratio.bThe observed retention time.cWhether the m/z-RT pair was observed in position (+) or negative (−) ion mode.dThe basis for the identification of the compound. Standard: Comparison of MS/MS spectrum and RT to a commercial standard. LM MS/MS: Comparison of MS/MS spectrum to spectra published in LIPID MAPS. MassTRIX: Identified by MassTRIX based upon exact mass. LM Mass: Compound identity based upon exact mass matches in LIPID MAPS. Murphy: The compound was compared to mass data in Murphy, 2002 [30].eThe median abundance value observed in the individual (non-pooled) samples.fThe area under the curve (AUC) of the receiver operating characteristic (ROC) curve with a 95% confidence interval denoted as a ± value.gCompounds which fragmented in MS/MS. See Figures 2, 3, 4 and Supplement S2 for MS/MS spectra of samples and commercial standards. See Supplement S3 for additional spectra.hConfidence levels for compound identifications as per Sumner et al, 2007 [31]. Lower values indicate a more confident identification.