On-line Quantitative Determination of 2H/1H Isotope Ratios in Organic and Water Samples Using an Elemental Analyser Coupled to an Isotope Ratio Mass Spectrometer

A rapid continuous-Ñow technique for the quantitative determination of hydrogen isotope ratios in organic materials and water, at natural abundance levels, is described. Samples are pyrolysed in a helium stream at 1080 ÄC over an inert form of carbon. Hydrogen is separated from the other pyrolysis gases by gas chromatography and enters the ion source of the isotope ratio mass spectrometer (IRMS) via a crimp. The 2H/1H ratio of the gas was determined by the simultaneous integration of the m/z 2 (1H1H) and m/z 3 ion beams over time. (2H&1H) d2H& values of organic and water samples were determined by comparison with organic and water standards, respectively. The precision of the on-line measurement is The accuracy of the method was demonstrated d2H& Æ3.3& . by the analysis of a laboratory standard water (NTW), a European Community Bureau Reference material, N,N-tetramethylurea (TMU) and an International Atomic Energy Association polyethylene reference material (IAEA-CH-7). The measured values were NTW TMU and IAEA-CH-7 (reference Ô39.4& , Ô144.1& Ô100.7& values are NTW TMU and IAEA-CH-7 No apparent memory e†ect was Ô38.5& , Ô147.4& Ô100.3&). observed when measuring samples at the natural abundance level. Calibration of organic measurements with water reference materials did not give satisfactory results, probably owing to di†erences in their respective pyrolysis pathways. The potential of the technique for food analysis was demonstrated by measuring the values of d2H& vanillin samples derived from natural and synthetic sources and by the analyses of hexamethylenetetramine synthesized from beet, cane and apple juice sugars. Crown copyright 1998. Reproduced with the permission of the ( Controller of Her MajestyÏs Stationery Office.