Automation and miniaturization of an on-line flow injection Sr/matrix separation method for accurate, high throughput determination of Sr isotope ratios by MC-ICP-MS

Abstract

In this work we present a fully automated Sr/matrix separation method, based on flow injection (FI) hyphenated to a multiple collector-inductively coupled plasma-mass spectrometer (MC-ICP-MS). Our method compares favourably to the common, manual, batch Sr/matrix separation procedure, with respect to labour and reagent investment. We validated the system analyzing NIST SRM 987 Sr isotope reference material and digests of Asparagus officinalis at Sr concentrations of approximately 30–40 ng g⁻¹ total Sr using separation columns containing approximately 40 μL of Sr specific resin. 33 consecutive runs of the NIST SRM 987 Sr isotope reference material could be repeated with 0.03% (2 RSD), yielding an average ⁸⁷Sr/⁸⁶Sr isotope ratio of 0.71030 which is well within the certified range. 5 Hungarian and 5 Austrian samples were determined to have ⁸⁷Sr/⁸⁶Sr isotope ratios ranging from 0.70504–0.70746 and 0.70884–0.70923 respectively. ⁸⁷Sr/⁸⁶Sr isotope ratios of single elutions could be measured with typical precisions of 0.02–0.1% (2 RSD) depending on signal intensities. 6 successive measurements could be repeated with 0.006–0.04% (2 RSD). Results presented in this work are in agreement with results previously obtained via off-line Sr/matrix separation and subsequent measurement of ⁸⁷Sr/⁸⁶Sr isotope ratios by MC-ICP-MS. We were able to use a single 40 μL column for Sr/matrix separation of 66 samples.