Reproducible measurements of the δ2H composition of non-exchangeable hydrogen in complex organic materials using the UniPrep2 online static vapour equilibration and sample drying system

Leonard I Wassenaar; Leonardo Sisti; Matthias Pilecky; Martin Kainz

doi:10.1016/j.mex.2022.101984

Reproducible measurements of the δ²H composition of non-exchangeable hydrogen in complex organic materials using the UniPrep2 online static vapour equilibration and sample drying system

MethodsX. 2023 Jan 4:10:101984. doi: 10.1016/j.mex.2022.101984. eCollection 2023.

Authors

Leonard I Wassenaar¹, Leonardo Sisti², Matthias Pilecky^{1

3}, Martin Kainz^{1

3}

Affiliations

¹ WasserCluster Lunz - Biologische Station, Dr. Carl Kupelwieser Promenade 5, Lunz am See A-3293, Austria.
² Eurovector C/O Polo Tecnologico di Pavia, Via F.lli Cuzio, 42, Pavia 27100, Italy.
³ Department of Biomedical Research, Donau-Universität Krems, Dr.-Karl-Dorrek-Strasse 30, Krems an der Donau A-3500, Austria.

Abstract

Non-exchangeable hydrogen-isotope (δ ²H_n) measurements of complex organic samples are used in forensics to determine sample authenticity, traceability, and provenance. However, δ ²H_n assays of organics are usually complicated by uncontrolled "exchangeable hydrogen" and residual moisture contamination; hence, δ ²H_n 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:•Conduct reproducible controlled vapour equilibrations of complex organic samples and standards to determine the δ ²H_n values by controlling hydrogen-isotope exchange.•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 δ ²H_n 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 δ ²H_n for a complex organic environmental sample where matrix equivalent 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 δ ²H_n 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.

Keywords: Deuterium; Drying; Hydrogen isotopes; Non-exchangeable h; Organics; Reproducible and accurate determination of theδ2H of non-exchangeable hydrogen of complex environmental organic samples; Vapour equilibration.