Strontium isotope ratio measurements in prehistoric human bone samples by means of high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS)

Abstract

This paper explores the suitability and application range of a commercially available high-resolution ICP-mass spectrometer (Finnigan MAT Element) in determining strontium isotope ratios of human bone samples. Any paleoanthropological interpretation of such samples requires a highly accurate isotopic ratio determination with a precision of at least 0.1% relative standard deviation (RSD). Thus, optimum instrument operating parameters such as sampling time, scan duration, and instrumental bias factors including mass bias and deadtime, were investigated in an initial step. The instrument itself was used without modification but equipped with a commercial microconcentric nebulizer. All experiments were performed under clean room conditions with filtered (class 10.000), temperature controlled, and excess pressured air. Complementary mathematical correction methods like deadtime and mass bias corrections, allowed the achievement of a87Sr/86Sr isotope ratio precision below 0.03% (RSD for n=5). Compared with the certified NIST SRM 987 Strontium Carbonate (Isotopic) value (0.71034±0.00026), our 87Sr/86Sr isotopic ratio revealed a 0.7103±0.0002 match. This optimized procedure was performed on 7000-year-old human skeleton samples from a Neolithic settlement in Asparn/Schletz, Lower Austria, to determine their stable strontium isotope ratio. Specific isotope patterns thereby shed light on the provenance of single individuals.