An automated system for hydrogen isotope analysis of water

An automated inlet system has been developed for deuterium/hydrogen isotope analysis of water using on-line reduction to hydrogen. A modified HPLC autosampler introduces precise aliquots of water (0.5 to 5 μl) into a heated expansion chamber which is connected via a capillary to hot uranium where the water is reduced to uranium oxide, and hydrogen for analysis. The 600°C uranium reduction furnace is kept at analyzer pressure in the mass spectrometer, which maximizes the lifetime of the reductant to handle more than 4000 injections per 0.5 g of depleted uranium. This is a flow-through system, and unlike zinc or catalyst methods, some `memoryʹ effects are encountered, requiring two injections to obtain a δD precision of less than ±1‰, and four injections for a precision of less than ±0.5‰. Sample preparation is limited to pipetting water into an autosampler vial. The computer-controlled system provides extended unattended operation allowing, for instance, large runs of samples that can occupy the instrument over entire weekends.