Reproducible measurements of the δH composition of non-exchangeable hydrogen in complex organic materials using the UniPrep2 online static vapour equilibration and sample drying system.

Non-exchangeable hydrogen-isotope ( H) measurements of complex organic samples are used in forensics to determine sample authenticity, traceability, and provenance. However, H assays of organics are usually complicated by uncontrolled "exchangeable hydrogen" and residual moisture contamination; hence, H assays are persistently incomparable amongst laboratories. We introduce a revised technical solution (UniPrep2) to control hydrogen-isotope exchange and for robust online sample drying and vapour equilibration.

An online temperature-controlled vacuum-equilibration preparation system for the measurement of δ2H values of non-exchangeable-H and of δ18O values in organic materials by isotope-ratio mass spectrometry.

Rationale: Measurement of δ(2) H values in non-exchangeable-H (δ(2) H(n)) and δ(18)O values in organic environmental samples are inconsistent among laboratories worldwide due to varied and lengthy approaches in controlling for H isotope exchange (for δ(2)H(n) values) and removal of trace moisture (δ(2)H(n) and δ(18)O values), which undermines the comparability of organic δ(2)H and δ(18)O data produced among different laboratories.

Methods: An online preparation system was developed for the measurement of the δ(2)H(n) and δ(18)O values of organic samples, coupled to isotope-ratio mass spectrometers. The system features a 50-position autosampler and isolation valve where (1) the samples are held isothermal between ambient to 40-120 ± 0.