STABLE-ISOTOPE METHOD FOR DETERMINING THE GASTROINTESTINAL HANDLING OF [1-C-13]PALMITIC ACID

The C-13 enrichment in individual fatty acids extracted from human fec es following the oral administration of [1-C-13]palmitic acid has been determined using a novel approach based upon gas chromatography-isoto pe ratio mass spectrometry. The method was established and tested for precision and repeatability. Analytical precision was determined from 10 repeated injections of a sample containing 16:0 and 18.0 with level s of delta(13)C abundance measured at -34.01 +/- 0.60 and -23.62 +/- 0 .95 delta per mil (parts per thousand) (parts per thousand), respectiv ely (mean +/- SD). For the repeatability study, measurement of enrichm ent of the same mixture of unlabeled fatty acid methyl ester (FAME) st andards (13:0, 14:0, 16:0, and 18:0) was found to have standard deviat ions (0.45, 0.56, 1.46 and 1.54 parts per thousand, respectively). Whe n labeled [1-C-13]palmitic acid was serially diluted with naturally en riched palmitic acid, a linear relationship was obtained to a dilution of 10% enriched compound (530 parts per thousand). FAME were prepared from two fecal samples from a normal healthy adult; the first, a base line specimen, containing no added label and the second, followed a si ngle oral dose of [1-C-13]palmitic acid and was enriched. Enrichment i n C-13 was confined to the solvent-soluble fraction following lipid ex traction, and was only identified with prior acidification. The enrich ments were measured in triplicate, baseline sample -32.66 +/- 0.5 part s per thousand, enriched sample +268.61 +/- 8.0 parts per thousand. En richment was restricted to the labeled species consumed, 16:0. The met hodology described here allows for the separation of compounds prior t o the determination of enrichment and can be utilized to contribute to a more complete description of the gastrointestinal handling of label ed substrates than previously obtained.