Stable Isotope Unit, The James Hutton Institute, Invergowrie, Dundee DD2 5DA, UK.
Rapid Commun Mass Spectrom. 2011 Nov 15;25(21):3331-8. doi: 10.1002/rcm.5235.
Stable isotope analysis of organic materials for their hydrogen ((2)H), carbon ((13)C), nitrogen ((15)N) or oxygen ((18)O) isotopic composition using continuous flow isotope ratio mass spectrometry (CF-IRMS) is an increasingly used tool in forensic chemical analysis. (2)H isotopic analysis can present a huge challenge, especially when dealing with exhibits comprising exchangeable hydrogen such as human scalp hair. However, to yield forensic data that are fit for purpose, analysis of the (2)H isotopic composition of the same homogeneous human hair sample by any laboratory worldwide must yield the same isotopic composition within analytical uncertainty. This paper presents longitudinal (2)H 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. Although each laboratory employed varying means to comply with the generic features of the sample preparation protocol such as the (2)H 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. Despite the variation in materials and procedures employed by the three laboratories, repeatable and reproducible 'true' (2)H isotope values (δ(2)H(hair,true)) were determined by each laboratory for each of the four stock samples of human scalp hair. The between-laboratory differences for obtained δ(2)H(hair,true) values ranged from 0.1 to 2.5 ‰. With an overall 95% confidence interval of ±2.8 ‰, these differences were not significantly different, which suggests that the general method of two-stage exchange equilibration carried out at ambient temperature is suitable for accurately and reproducibly determining 'true' δ(2)H-values for hair and other proteins provided that certain key conditions are met.
利用连续流动同位素比质谱仪（CF-IRMS）对有机材料的氢（(2)H）、碳（(13)C）、氮（(15)N）或氧（(18)O）同位素组成进行稳定同位素分析，是法医化学分析中越来越常用的工具。(2)H 同位素分析可能具有很大的挑战性，特别是在处理包含可交换氢的标本时，如人头皮毛发。然而，为了获得适合目的的法医数据，全球任何实验室对同一均质人发样本进行的(2)H 同位素组成分析，必须在分析不确定度范围内得出相同的同位素组成。本文提供了四个不同来源的人发样本的纵向（2)H 同位素数据，这些样本由三个不同的实验室进行测量，这些实验室的样本制备基于两步 H 交换平衡方法。尽管每个实验室都采用不同的方法来符合样品制备方案的一般特征，如交换水的(2)H 同位素组成或在分析前将样品干燥至恒重，但在每个实验室中，每个单独的实验都应用了相同处理原则（P.I.T.）。尽管三个实验室使用的材料和程序存在差异，但每个实验室都为四个人头皮毛发库存样本中的每一个重复且可重现的“真实”(2)H 同位素值（δ(2)H(hair,true)）。获得的δ(2)H(hair,true)值的实验室间差异范围为 0.1 至 2.5‰。在 95%置信区间总体为±2.8‰的情况下，这些差异没有显著差异，这表明在环境温度下进行的两步交换平衡的一般方法适用于准确且可重现地确定毛发和其他蛋白质的“真实”δ(2)H 值，前提是满足某些关键条件。
