Stable hydrogen isotopic analysis of nanomolar molecular hydrogen by automatic multi-step gas chromatographic separation

We have developed a new automated analytical system that employs a continuous flow isotope ratio mass spectrometer to determine the stable hydrogen isotopic composition (δD) of nanomolar quantities of molecular hydrogen (H₂) in an air sample. This method improves previous methods to attain simpler and lower‐cost analyses, especially by avoiding the use of expensive or special devices, such as a Toepler pump, a cryogenic refrigerator, and a special evacuation system to keep the temperature of a coolant under reduced pressure. Instead, the system allows H₂ purification from the air matrix via automatic multi‐step gas chromatographic separation using the coolants of both liquid nitrogen (77 K) and liquid nitrogen + ethanol (158 K) under 1 atm pressure. The analytical precision of the δD determination using the developed method was better than 4‰ for >5 nmol injections (250 mL STP for 500 ppbv air sample) and better than 15‰ for 1 nmol injections, regardless of the δD value, within 1 h for one sample analysis. Using the developed system, the δD values of H₂ can be quantified for atmospheric samples as well as samples of representative sources and sinks including those containing small quantities of H₂, such as H₂ in soil pores or aqueous environments, for which there is currently little δD data available. As an example of such trace H₂ analyses, we report here the isotope fractionations during H₂ uptake by soils in a static chamber. The δD values of H₂ in these H₂‐depleted environments can be useful in constraining the budgets of atmospheric H₂ by applying an isotope mass balance model. Copyright © 2011 John Wiley & Sons, Ltd.