Tritium (3H) in natural waters is a powerful tracer of hydrological processes, but its low concentrations require electrolytic enrichment before precise measurements can be made with a liquid scintillation counter. Here, we describe a newly developed, compact tritium enrichment unit which can be used to enrich up to 2 L of a water sample. This allows a high enrichment factor (>100) for measuring low 3H contents of <0.05 TU. The TEU uses a small cell (250 mL) with automated re-filling and a CO2 bubbling technique to neutralize the high alkalinity of enriched samples. The enriched residual sample is retrieved from the cell under vacuum by cryogenic distillation at −20 °C and the tritium enrichment factor for each sample is accurately determined by measuring pre- and post- enrichment 2H concentrations with laser spectrometry.

Several improvements are described for the existing tritium enrichment system at the Isotope Hydrology Laboratory of the International Atomic Energy Agency for processing natural water samples. The improvements include a simple method for pretreatment of electrolytic cells to ensure a high tritium separation factor, an improved design of the exhaust system for explosive gases, and a vacuum distillation line for faster initial preparation of water samples for electrolytic enrichment and for tritium analysis. Achievements included the reduction of variation of individual enrichment parameters of all cells to less than 1% and an improvement of 50% of the stability of the background mean. It resulted in an improved detection limit of less than 0.4 TU (at 2s), important for application of tritium measurements in the future at low concentration levels, and resulted in measurement precisions of +/- 0.2 TU and +/- 0.15 TU for liquid scintillation counting and for gas proportional counting, respectively.