Systematic evaluation of a strontium-specific extraction chromatographic resin for obtaining a purified Sr fraction with quantitative recovery from complex and Ca-rich matrices

This paper presents a systematic evaluation of a commercially available strontium-specific extraction chromatographic resin based on a crown ether (Sr spec™), for use in applications of Sr isotope ratio analysis dealing with samples displaying a complex and/or Ca-rich matrix composition. A protocol, consisting of (i) loading a sample digest in 7 M HNO₃ onto the resin, (ii) rinsing the resin with 7 M HNO₃ to remove concomitant matrix elements and (iii) rinsing the resin with 0.05 M HNO₃ to strip off the purified Sr fraction, was found to provide the best results. The performance in terms of (i) the purity of the Sr fraction obtained, (ii) the efficiency of Rb/Sr and Ca/Sr separation, (iii) the Sr recovery from samples with a complex and Ca-rich matrix composition and (iv) the Sr isotope ratios obtained using multi-collector ICP-MS, was evaluated for various amounts (250, 500, 750 and 2000 µL) of resin using digests of bone and soil certified reference materials, dental tissues, fluorite and glass samples. Further, it was investigated whether or not the isolation protocol introduces Sr isotopic fractionation. Also the possibility of regenerating the resin after use, allowing multiple use of the resin, was assessed. Finally, the Sr isotopic composition of 2 bone (NIST SRM 1400 Bone Ash and NIST SRM 1486 Bone Meal) and 2 soil (BCR CRM 141 Calcareous Loam Soil and BCR CRM 142 Light Sandy Soil) certified reference materials was determined. The method was shown to be fit-for-purpose for population migration studies and provenancing of archaeological artefacts, and is expected to be suited for a broad range of Sr isotope ratio applications.