Quantitative determination of plasma C8-C26 total fatty acids for the biochemical diagnosis of nutritional and metabolic disorders

We have developed a capillary gas chromatography-electron-capture negative- ion mass spectrometry (GC/MS) method for the quantitative determination of C8-C26 total fatty acids in plasma. Following hydrolysis, hexane extraction , and derivatization with pentafluorobenzyl bromide, fatty acid esters are analyzed in two steps: a splitless injection and a second, split injection (1:100) far the quantitation of the more abundant long-chain species, Fourt een saturated and 25 unsaturated fatty acids are quantified by selected ion monitoring in ratio to 13 stable-isotope-labeled internal standards. Calib rations exhibit consistent linearity and reproducibility, Intraassay (n = 1 7) and interassay (n = 12) CVs ranged from 2.5 to 13.2% and from 4.6 to 22. 9%, respectively. Recoveries ranged from 76 to 106%. Reference ranges were established for four age groups (<1 month, 1 month to 1 year, 1-17 years, > 18 years) and compared to specimens from patients with nutritional deficien cy of omega -3 and omega -6 polyunsaturated fatty acids, inborn errors of m itochondrial fatty acid oxidation, and peroxisomal disorders. Retrospective evaluation of the concentration of linoleic acid in 35 cases with a diagno sis of essential fatty acid deficiency previously made by gas chromatograph ic analysis with flame ionization detection (GC/FID) found a specificity an d sensitivity of only 55 and 50%, respectively, for the GC/FID method when compared to GC/MS. (C) 2001 Academic Press.