Comparison of methodological strategies to determine Sr concentrations in Ca-rich matrices

Over the last few decades, there has been a steady increase in available analytical techniques and protocols in geochemical and bioarchaeological research to determine elemental concentrations. However, the validity of acquired results greatly depends on multiple factors, such as the sample matrix, pre-treatment protocols, the used analytical technique, appropriate standardization, calibration strategies, and the adequacy of the selected reference materials. Samples such as excavated skeletal remains prove to be particularly challenging to characterize using mass spectrometric techniques, as these require extensive pre-treatment procedures, and display a phosphate-rich, calcium (Ca)-heavy matrix, leading to potential interference effects upon ionization within the plasma. In this study, strontium (Sr) concentration analyses of 98 calcined archaeological bone samples are determined relying on HR-ICP-MS and ICP-QQQ-MS, using well-established concentration determination protocols. The applied procedures and HR-ICP-MS and ICP-QQQ-MS measurement routines are considered fully suited for the concentration determination of Sr in a Ca-heavy matrix, provided that Ca-normalizations of the acquired Sr data are carried out. It was found that the Sr concentration data from MC-ICP-MS correlate well with the data obtained relying on HR-ICP-MS and ICP-QQQ-MS, implying that MC-ICP-MS is also suited for Sr concentration determination in given sample matrices with the described procedures, saving both resources and time. The acquired data is also fully comparable with HR-ICP-MS and ICP-QQQ-MS data for Sr-isolated solutions, where the sample matrix was removed. The findings of this study, tested on cremated bone material, open up novel method development perspectives on other Ca-heavy samples, such as shells, speleothems, phosphate minerals and limestones.