Quantitation of 1,3-butanediol and its acidic metabolites by gas chromatography-mass spectrometry.

A number of problems present themselves during the gas chromatographic-mass spectrometric assay of R,S-1,3-butanediol as its bis-tert-butyldimethylsilyl ether. To circumvent these problems, three labeled internal standards were synthesized: (i) R,S-1,3-[3,4-13C2]-butanediol, (ii) R,S-1,3-[1,1,3-2H3]butanediol, and (iii) R,S-1,3-[1,1,3-2H3,3,4-13C2]butanediol. The availability of internal standards with different degrees of labeling allows (i) assaying of either unlabeled or 13C-labeled R,S-1,3-butanediol and (ii) analysis of 1,3-butanediol in either blood or urine samples. Reproducible standard curves were obtained using both electron impact and ammonia chemical ionization modes. The latter provides greater sensitivity and a lower limit of detection (5 microM). We have also designed an indirect assay of S-3-hydroxybutyrate, a catabolite of R,S-1,3-butanediol, which is difficult to analyze by conventional methods. This assay relies on the difference between (i) the concentration of R,S-3-hydroxybutyrate assayed by gas chromatography-mass spectrometry and (ii) the concentration of R-3-hydroxybutyrate assayed enzymatically.