头发氢稳定同位素比值检测的标准品选择研究

Selection of Reference Materials for Hydrogen Stable Isotope Detection of Human Hair

人头发中稳定同位素比值可追溯人的生活时空信息,构建可供比对的中国人头发稳定同位素比值数据库,对法庭科学研究和公安侦查意义重大。稳定同位素比值检测常因各实验室对样本的预处理和测量值校正方法不同等原因,影响其精确度和真实性,以致数据重现性较低而难以建库比对。本研究利用元素分析-同位素质谱技术(EA-IRMS),以中国人头发氢稳定同位素比值(δ~2H)检测方法为例,系统论证了其标准品选择和真值校正算法。首先,选择具有固体氢同位素真值的6种国际标准品(USGS42、USGS43、CBS、KHS、EMAP1和EMAP2)进行适合性评估;依据现有所测和文献报道的中国人头发的δ~2H值范围(-55‰^-80‰),选取3种真值囊括待测样品极负值、极正值和中间值的标准品进行组合,比较不同组合的标准曲线系数和拟合度R^2;经对比6种标准品组合,论证可得USGS42、USGS43和CBS组合的标准校正曲线拟合度R^2和标准曲线系数最适合且稳定。同时,选择北京和上海的两家实验室,历时4个月,共进行35次重复验证。结果表明,该标准品组合的校正曲线拟合度高、稳定性好(R^2≥0.999 7),适合作为头发δ~2H的标准校正方法,可作为中国人头发δ~2H数据库构建的推荐方法。本实验甄选标准品和真值校正曲线的思路亦可为其他稳定同位素标准库的建立提供参考。

The stable isotope ratio in human hair can be used to trace back the spatial and temporal information of human life. The construction of a comparable database of stable isotope ratio in Chinese human hair has a great significance for forensic science research and public security investigation. However, the interference of sample pretreatment and the difference of normalization methods affected the accuracy and reproducibility of hydrogen isotope ratio measurement and made it difficult to make comparison between laboratories. This research were based on the elemental analysis-isotope ratio mass spectrometer technic(EA-IRMS), and it systematically demonstrate the selection of hydrogen isotopic reference materials and the normalization method of hydrogen isotopic compositions to isotope reference scales. Firstly, six international reference materials(USGS42, USGS43, CBS, KHS, EMAP1 and EMAP2) were selected to evaluate their suitability. Then, according to the range of δ~2H values(-55‰^-80‰) of Chinese human hair measured and reported in the literatures, three of them were selected, including the minimum, maximum and middle values of the samples. Finally, by comparing the six reference materials combinations(CBS/USGS42/USGS43, CBS/USGS42/EMA-P1, CBS/USGS42/KHS, EMA-P2/USGS42/USGS43, EMA-P2/USGS42/EMA-P1 and EMA-P2/USGS42/KHS), it is proved that the standard calibration curves fitting R^2(1.000 0±0.000 0, n=4) of USGS42, USGS43 and CBS combinations are the highest, and the coefficients(1.061 8±0.006 6, n=4) of them are the most stability than other combinations by utilizing linear regression of multiple-point normalization method. At the same time, two laboratories in Beijing and Shanghai were selected to carry out 35 repeated validations. The results show that the multiple-point normalization method of the standard combination has the highest fitting degree and good stability(R^2≥0.999 7, n=35). It is suitable for the normalization method of hair δ~2H and can be used as a recommended method for the construction of Chinese human hair δ~2H database. The idea of selecting isotopic reference materials and the normalization method of hydrogen isotopic compositions to isotope reference scales can also provide reference for the establishment of other stable isotope ratio database.