Investigation of Sr isotope ratios in prehistoric human bones and teeth using laser ablation ICP-MS and ICP-MS after Rb/Sr separation

Abstract

⁸⁷Sr/⁸⁶Sr isotope ratio measurements on bone and teeth tissue were used in order to assess prehistoric human migration. Microstructural changes of skeletal remains caused by post mortem influences (especially dissolving and re-crystallization), may lead to erratic results, if invasive techniques (e.g. digestion and liquid nebulization ICP-MS) are used. Therefore, Rb/Sr separation performed on digested sample solutions prior to ICP-MS measurements was optimized and we developed a procedure to separate Sr from Rb quantitatively to enable a fast and reliable interference free measurement of Sr isotope ratios. As main goal, we have applied LA-ICP-MS on transversal bone cross sections on diagenetically altered and non-altered areas making use of both high lateral resolution and isotope ratio capabilities. Sr isotope ratio measurements on bone material were performed with an instrumental precision between 0.1 and 0.2% RSD by LA-ICP-MS. We could reveal mineralized phases (Brushit) histomorphologically within the cross section of cortical femur samples. Those crystallites showed a significantly increased amount of Rb. The results indicate that these products are exogenous. In addition, human teeth were analyzed for their ⁸⁷Sr/⁸⁶Sr isotope ratio primarily to investigate possible differences in enamel and dentine. LA-ICP-MS led to excellent results and shows RSD of isotope ratio measurements of about 0.1–0.2% on both enamel and dentine. One specific individual (from Neolithic Asparn/Schletz) was investigated using the prior methods and showed homogeneous Sr isotope ratios in dentine and bone, while the Sr isotopic composition in enamel was significantly different. This result demonstrates a possible migration of this individual during early childhood.