DETERMINATION OF PLASMA NONESTERIFIED FATTY-ACIDS AND TRIGLYCERIDE FATTY-ACIDS BY GAS-CHROMATOGRAPHY OF THEIR METHYL-ESTERS AFTER ISOLATIONBY COLUMN CHROMATOGRAPHY ON SILICA-GEL

Non-esterified fatty acids (NEFA) and triglycerides were isolated from human plasma by column chromatography on silica gel. Eight principal fatty acids of each of these lipid classes were determined by gas chro matography of their methyl ester derivatives and quantified relative t o multipoint standard curves. Within-day relative standard deviations for plasma non-esterified fatty acid and triglyceride fatty acid deter minations were 2.4 and 3.2%, respectively. Day-to-day relative standar d deviations for plasma non-esterified fatty acid and triglyceride fat ty acid determinations were 1.4 and 1.1%, respectively. The total plas ma concentration and the relative proportions of the eight non-esterif ied fatty acids determined by this method were significantly different from results obtained according to two generally accepted methods for direct plasma non-esterified fatty acid determination without a speci fic isolation step. These comparisons suggested that considerable fatt y acid ester lipid hydrolysis occurred during these direct determinati on procedures, and that this hydrolysis resulted in 3-fold overestimat ion of plasma NEFA content by those methods. Measured levels of arachi donic acid are substantially overestimated by these direct determinati on methods in which non-esterified fatty acids are not isolated before derivatization.