ONLINE QUANTITATIVE-DETERMINATION OF H-2 H-1 ISOTOPE RATIOS IN ORGANIC AND WATER SAMPLES USING AN ELEMENTAL ANALYZER COUPLED TO AN ISOTOPE RATIO MASS-SPECTROMETER/

A rapid continuous-flow technique for the quantitative determination o f hydrogen isotope ratios in organic materials and water, at natural a bundance levels, is described. Samples are pyrolysed in a helium strea m at 1080 degrees C over an inert form of carbon. Hydrogen is separate d from the other pyrolysis gases by gas chromatography and enters the ion source of the isotope ratio mass spectrometer (IRMS) via a crimp. The H-2/H-1 ratio of the gas was determined by the simultaneous integr ation of the m/z 2 ((HH)-H-1-H-1) and m/z 3 (H-2 parts per thousand H- 1) ion beams over time. delta(2)H parts per thousand values of organic and water samples were determined by comparison with organic and wate r standards, respectively. The precision of the on-line delta(2)H part s per thousand measurement is < 3.3 parts per thousand. The accuracy o f the method was demonstrated by the analysis of a laboratory standard water (NTW), a European Community Bureau Reference material, N,N-tetr amethylurea (TMU) and an International Atomic Energy Association polye thylene reference material (IAEA-CH-7). The measured values were NTW - 39.4 parts per thousand, TMU -144.1 parts per thousand and IAEA-CH-7 - 100.7 parts per thousand (reference values are NTW -38.5 parts per tho usand, TMU -147.4 parts per thousand and IAEA-CH-7 -100.3 parts per th ousand). No apparent memory effect was observed when measuring samples at the natural abundance level. Calibration of organic measurements w ith water reference materials did not give satisfactory results, proba bly owing to differences in their respective pyrolysis pathways. The p otential of the technique for food analysis was demonstrated by measur ing the delta(2)H parts per thousand, values of vanillin samples deriv ed from natural and synthetic sources and by the analyses of hexamethy lenetetramine synthesized from beet, cane and apple juice sugars. (C) Crown copyright 1998. Reproduced with the permission of the Controller of Her Majesty's Stationery Office.