On-line high-precision stable hydrogen isotopic analyses on nanoliter water samples

We describe a new on-line chromium reduction technique for the measurement of stable hydrogen (deltaD) isotopes in waters using continuous-flow isotop e ratio mass spectrometry. The on-line Cr reduction method has low intersam ple memory effects (<1%) and excellent precision and accuracy for deltaD (/-0.5 parts per thousand and was used to analyze waters samples as smaLL as 50 nL. The on-line Cr method has a number of significant advantages over c onventional offline Zn and U reduction and on-line carbon-based pyrolysis t echniques. A single Cr reactor can be used to analyze similar to 1000 water samples using an injection volume of 0.5 muL, with an individual sample an alysis time of 4 min. Intersample memory effects are negligible. The Cr rea ctor temperature of 1050 degreesC is easily attainable on standard elementa l analyzers and so does not require the specialized and costly high-tempera ture furnaces of carbon-based pyrolysis reactors. Furthermore, hydrogen iso topes in extremely small water samples in the 100-nL range or less can be e asily measured; hence, this new method opens up a number of exciting applic ation areas in earth and environmental sciences, for example, natural abund ance deltaD measurements of individual fluid inclusions in geologic materia ls using a laser source and measurements of body fluids in physiological an d metabolic research.