Despite the variation in materials and procedures employed by the three laboratories, repeatable and reproducible ‘true’ 2H isotope values (δ2H hair,true) were determined by each laboratory for each of the four stock samples of human scalp hair. Although each laboratory employed varying means to comply with the generic features of the sample preparation protocol such as the 2H isotopic composition of exchange waters or drying down of samples prior to analysis, within each laboratory the Principle of Identical Treatment (P.I.T.) was applied for each individual experiment. This paper presents longitudinal 2H isotope data for four human hair samples of different provenance, measured by three different laboratories whose sample preparation was based on a two-stage H exchange equilibration method. However, to yield forensic data that are fit for purpose, analysis of the 2H isotopic composition of the same homogeneous human hair sample by any laboratory worldwide must yield the same isotopic composition within analytical uncertainty. 2H isotopic analysis can present a huge challenge, especially when dealing with exhibits comprising exchangeable hydrogen such as human scalp hair. Stable isotope analysis of organic materials for their hydrogen (2H), carbon (13C), nitrogen (15N) or oxygen (18O) isotopic composition using continuous flow isotope ratio mass spectrometry (CF-IRMS) is an increasingly used tool in forensic chemical analysis.
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