Reproducible measurements of the 62 H composition of non-exchangeable hydrogen in complex organic materials using the UniPrep2 online static vapour equilibration and sample drying system

Non-exchangeable hydrogen-isotope ( 62Hn) measurements of complex organic samples are used in forensics to determine sample authenticity, traceability, and provenance. However, 62Hn as-says of organics are usually complicated by uncontrolled exchangeable hydrogen and residual moisture contamination; hence, 62Hn 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. The UniPrep2 device is coupled to a high-temperature thermochemical elemental analyser and continuous-flow isotope-ratio mass spectrometer. This technical solution empowers isotope analysts to:center dot Conduct reproducible controlled vapour equilibrations of complex organic samples and standards to determine the 62Hn values by controlling hydrogen-isotope exchange.center dot Conduct online vacuum-oven evacuation with extensive helium drying without exposure to air to reabsorb or exchange hydrogen with ambient water vapour.The protocol describes the operation of the UniPrep2 device and the step-by-step procedures needed to obtain accurate and precise 62Hn values for a wide range of organic sample types. Two analytical approaches are described in detail; the Dual-Vapour Equilibration (DVE) approach, intended for determining 62Hn for a complex organic environmental sample where matrix equiv-alent H isotope reference materials are not available, and the Comparative Equilibration (CE) approach, which is intended for routine high-throughput analyses of complex organic samples where at least two matrix-equivalent organic isotope reference materials with consensus 62Hn values are being used. These standard operating procedures are envisioned to be a sound basis for advancing hydrogen-isotope analysis for different organic environmental matrices and studies.

Automated summary

Non-exchangeable hydrogen-isotope (62Hn) measurements are important in forensics for sample authenticity, traceability, and provenance determination. However, the measurements are often complicated due to uncontrolled exchangeable hydrogen and moisture contamination, leading to incomparability among laboratories. A revised technical solution (UniPrep2) is introduced to control hydrogen-isotope exchange and enable robust online sample drying and vapor equilibration. This solution empowers isotope analysts to conduct reproducible controlled vapor equilibrations and vacuum-oven evacuation with helium drying, providing accurate and precise 62Hn values for various organic sample types.