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

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 δ²H 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 R² (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 (R²≥0.999 7, n=35). It is suitable for the normalization method of hair δ²H and can be used as a recommended method for the construction of Chinese human hair δ²H 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.