Closed-system automated microdistillation of small-volume water samples for tritium and stable isotope analysis.

Preparation of small-volume water samples for low-level tritium (³H) analysis commonly requires microdistillation to remove electrolytes and dissolved salts following electrolytic enrichment. This step must efficiently purify the sample, achieve quantitative water recovery, preserve hydrogen and oxygen isotope ratios, and avoid sample cross-contamination. Existing distillation approaches are often time and labor-intensive, require continuous operator supervision, and/or are poorly suited to batch processing of small volumes. This article documents a closed-system, automated microdistillation method for purifying small-volume (<20 mL) water samples prior to tritium and stable isotope analysis. The method is based on paired, chemically inert vessels connected in a sealed configuration and operated under controlled heating conditions. Validation data are presented demonstrating efficient gravimetric recovery of the water sample, quantitative removal of dissolved salts, accurate preservation of hydrogen and oxygen isotope ratios across a wide range of salinities and isotopic compositions, and negligible long-term memory effects for deuterium- and tritium-enriched samples. The method is intended for routine use in tritium laboratories processing electrolytically enriched samples and other stable isotope laboratories requiring reproducible microdistillation.•Automated closed-system microdistillation of small-volume water samples.•Batch processing under controlled thermal conditions.•Validation of recovery, isotopic integrity, and carryover performance.