Speaker
Description
Measuring the natural abundance of isotopes and the variations in their ratios in the archaeological hard tissues (such as bones and teeth) can provide important information about the evolution and migration of humans and animals and their origin. Strontium isotopes are among the most effective for characterizing the prehistoric mobility of humans and animals [1]. $^{87}$Sr/$^{86}$Sr isotope ratio incorporates into the surrounding biosphere from underlying bedrocks and is practically not fractionated by biological organisms. Since Sr can replace Ca in the hydroxyapatite crystal lattice of bones and teeth, $^{87}$Sr/$^{86}$Sr ratio can be directly attributed to the isotopic ratio of the geochemical province where humans and animals reside [1].
The work presents the method of $^{87}$Sr/$^{86}$Sr isotope ratio analysis in biogenic apatite by multi-collector (MC) ICP-MS using the standard-sample bracketing (SSB) technique with preliminary chromatographic separation of Sr.
All works were performed in cleanrooms (ISO 6, 7) of the Zavaritsky Institute of Geology and Geochemistry, UB RAS. Single-step chromatography technique modified from [2] and described in detail in [3] was applied for strontium isolation using SR resin (100–200 mesh, Triskem®). Sr isotope measurements were carried out using a MC ICP-MS Neptune Plus (Thermo Fisher Scientific, Germany) equipped by the ASX 110 FR sample introduction system (Teledyne CETAC, USA) fitted by PFA micro-flow nebulizer (50$\mu$L min$^{−1}$) connected to a quartz spray chamber.
Mass bias was corrected by the combination of exponential law normalization and standard-sample bracketing (SSB), the $^{87}$Sr/$^{86}$Sr ratio was normalized by the value of 88/86=8.375209 [4]. In addition, interference correction was provided by accounting of $^{86}$Kr and $^{87}$Rb by $^{83}$Kr/$^{86}$Kr=0.664162, $^{83}$Kr/$^{84}$Kr=0.201579 and $^{87}$Rb/$^{85}$Rb=0.386 ratios (also normalized). Subsequently, the normalized values were additionally corrected by the mean value variation of SRM-987 “bracketed” each two samples from the reference value of 0.710245 (GeoReM database, http://georem.mpch-mainz.gwdg.de/).
The analysis of Bone Meal SRM 1486 and Bone Ash SRM 1400 standard reference materials was carried out, and the expanded uncertainty was calculated. For NIST Bone Ash 1400, $^{87}$Sr/$^{86}$Sr = 0.71318 ± 0.00026, and for NIST Bone Meal 1486 $^{87}$Sr/$^{86}$Sr = 0.70933 ± 0.00022, which is in an excellent agreement with the GeoReM Database data (0.7131-0.7134) and (0.709269-0.70964), respectively. The method precision was estimated as the within-laboratory standard uncertainty (2σ) obtained for SRM-987 and was ± 0.003 %.
The developed method was applied to the strontium isotope analysis of animal and human teeth and bones from a number of archaeological sites in Russia.
The work was carried out at the “Geoanalitik” Center for Collective Use and supported by RFBR grant No. 20-09-00194.
References:
1. J.E. Ericson, Journal of Human Evolution 14, 503 (1985).
2. D. Muynck et al., Journal of Analytical Atomic Spectrometry 24, 1498 (2009).
3. A. Kasyanova et al., AIP Conference Proceedings 2174, 020028 (2019).
4. A.O. Nier, Physical Review 54, 275 (1938).
