Continuous flow pyrolysis techniques for the isotopic measurements of oxygen-deuterium in waters, organic and inorganic compounds

The technique of interfacing an elemental analyser (EA) with a stable isotope ratio mass spectrometer has, since its inception in 1983, proven to be a remarkably versatile analytical tool for the measurement of carbon and nitrogen isotopes across a wide application base. By 1994, sulphur isotopes had been added to the list and, more recently, those of oxygen and hydrogen. The analysis of oxygen and hydrogen involved a departure from the normal flash-combustion mode of operation to one of pyrolytic thermal decomposition of the sample. This paper describes a new EA technique for the measurement of hydrogen isotopes in water, in a continuous-flow carrier stream of helium. The system is totally carbon free and is based on the use of chromium (patented) as the active reactor material. Water injected into this system is reduced, resulting in the quantitative release of hydrogen gas, which is then carried by the helium to the mass spectrometer and analysed for deuterium concentration. This technique exhibits remarkably low memory effects, excellent precision and accuracy, and addresses sample sizes down to 50 nL. In addition, it allows a very high sample throughput with individual sample analysis time of 3 min