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 (δD) isotopes in waters using continuous-flow isotope ratio mass spectrometry. The on-line Cr reduction method has low intersample memory effects (<1%) and excellent precision and accuracy for δD (±0.5 ‰ and was used to analyze waters samples as small as 50 nL. The on-line Cr method has a number of significant advantages over conventional off-line Zn and U reduction and on-line carbon-based pyrolysis techniques. A single Cr reactor can be used to analyze ∼1000 water samples using an injection volume of 0.5 μL, with an individual sample analysis time of 4 min. Intersample memory effects are negligible. The Cr reactor temperature of 1050 °C is easily attainable on standard elemental analyzers and so does not require the specialized and costly high-temperature furnaces of carbon-based pyrolysis reactors. Furthermore, hydrogen isotopes in extremely small water samples in the100-nL range or less can be easily measured...