The method described here is routinely applied to establish complete fatty acid profiles in
cultured and primary cells, tissues and blood plasma samples [40,41]. Figure 5 shows a
representative chromatogram of free (non-esterified) fatty acids isolated from human
plasma. As can be seen, not all fatty acids are fully baseline resolved, but they are
distinguished by MS due to differences in m/z. This illustrates the importance of careful SIM
group assignments of analytes and appropriate adjustments of SIM parameters to achieve
complete discrimination from other fatty acids with similar retention times. It also illustrates
the power of MS detection over FID. A complete list of all free fatty acids found in normal
fasting human plasma is shown in Table 2. To estimate extraction recoveries, plasma was
spiked with known amounts of fatty acids prior to extraction. Recoveries were calculated by
comparison of the fatty acid content of the spiked plasma with the basal fatty acid content of
the untreated plasma.