SIMULTANEOUS DETERMINATION OF PLASMA-LEVELS OF ALPHA-KETOISOCAPROIC ACID AND LEUCINE AND EVALUATION OF ALPHA-[1-C-13]KETOISOCAPROIC ACID AND [I-C-13]LEUCINE ENRICHMENT BY GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

A sensitive method for the simultaneous analysis of plasma alpha-ketoi socaproic acid (KIC) and leucine using GC-MS is described. Plasma was deproteinized after addition of both alpha-ketovaleric acid and norleu cine as internal standards. Derivatization of the compounds involved p rotection of the keto groups with methoxyamine and tert-butyldimethyls ilylation under optimized conditions. Mass spectral analyses were carr ied out in electron impact ionization mode and the gas chromatographic conditions selected prevented interference by other keto acids and am ino acids normally present in plasma or by the biological matrix. Dete rmination of both plasma levels and isotopic enrichment of KIC and leu cine required a single injection and was easily accomplished in 7-9 mi n. The good reproducibility of the method, in addition to rapidity and simplicity, permits several samples to be accurately analyzed daily. Therefore, the method is particularly useful for studies on the metabo lism of amino acids. (C) 1994 Academic Press, Inc.