A VARIETY OF SOLUTIONS FOR MEASURING HYDROGEN ISOTOPES ON WATERS AND ORGANIC COMPOUNDS

Hydrogen has been a tracer of great interest even from the very early days of stable isotope analyses. At this time, D/H ratios were predominantly measured on water samples; either pure waters or waters extracted from soils, body fluids, fruit juices and wines, etc.

For many years the only way to measure Hydrogen was using IRMS in dual inlet mode, with the most widely used technique involving metal reduction, where water is reacted with a metal, forming Hydrogen and a metal oxide. This method can be carried out using uranium either off-line or through on-line automated systems comprising a uranium furnace, however uranium metal has become more and more difficult to obtain. Zinc reduction has subsequently evolved as the most common way to measure hydrogen, the difficulty being that the water samples need to be clean to optimise the reaction with the zinc. More recently, Hydrogen equilibration systems have become available, allowing D/H analyses of a wider range of non-pure water samples.

Now, with the development of analytical techniques, it is possible to measure hydrogen in continuous flow mode. This has enabled the use of EA-IRMS or GC-IRMS in pyrolysis mode for the measurement of D/H in organic samples or water samples. In this paper we will describe the various techniques used in Hydrogen analysis and review the advantages of the different methods. The latest development in hydrogen isotopic analysis is a new pyrolysis technique for EA-IRMS using ChromeHDTM technology, allowing D/H determination on very small water samples (below 1 microlitre) with extremely good specifications. The performance of this new system for the analysis of enriched waters, brines and chlorinated hydrocarbons will be discussed in order to demonstrate the advantage of the new technique over existing methods.