Minor compounds and potential interferents in gas chromatographic analyses of human serum fatty acids

Fatty acids from 100 randomly selected human serum samples were esterified to fatty acid methyl esters and analyzed by gas chromatography with flame ionization detector. A subset of the 20 samples that spans the variation in the original set of 100 samples were thereafter analyzed by gas chromatography-mass spectrometry (GC-MS). The GC-MS data were acquired using capillary columns with two different stationary phases, BP20 (polyethylene glycol) and BPX70 (cyanopropyl polysilphenylene-siloxane). Equivalent chain lengths on the two columns are reported for 69 compounds that constituted more than 0.1% of the chromatographic area in at least one sample. Of these, 39 compounds were identified as regular fatty acid methyl esters. The remaining 30 compounds were decomposition products from cholesterol, dimethylacetals, three compounds that have been linked to poor kidney function, and 13 compounds that are currently unidentified. The retention index patterns showed that on both columns there were 16 compounds that were separated by less than 0.05 equivalent chain length units from the nearest neighbor, meaning that they were overlapping or poorly resolved. The relationship between the peak threshold level and the number of peaks found above the level predicts a dramatic increase in the number of peaks that have to be resolved if the threshold is lowered below 0.1%.