ASSAY OF LOW DEUTERIUM ENRICHMENT OF WATER BY ISOTOPIC EXCHANGE WITH [U-C-13(3)]ACETONE AND GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

A sensitive assay of the H-2-enrichment of water based on the isotopic exchange between the hydrogens of water and of acetone in alkaline me dium is described and validated. For low H-2-enrichments (0.008 to 0.5 %), the sample is spiked with [U-C-13(3)]acetone and NaOH. After excha nge, H-2-enriched [U-C-13(3)]acetone is extracted with chloroform and assayed by gas chromatography-mass spectrometry. With some instruments , ion-molecule reactions, resulting in increased baseline enrichment, are minimized by lowering the electron ionization energy from the usua l 70 to 10 eV. The H-2-enrichment of water is amplified nearly sixfold in the M4/M3 ratio of [U-C-13(3)]acetone. For high H-2-enrichments (0 .25 to 100%), the use of unlabeled acetone suffices. After exchange, t he mass isotopomer distribution of acetone is analyzed, yielding the H -2 enrichment of water. The assay with [U-C-13(3)]acetone allows measu ring the H-2-enrichment of water even in biological samples containing acetone. This technique is more rapid and economical than the classic al isotope ratio mass spectrometric assay of the enrichment of hydroge n gas derived from the reduction of water. (C) 1998 Academic Press.