Matrix separation of Sr and Pb for isotopic ratio analysis of Ca-rich samples via an automated simultaneous separation procedure


This paper presents a systematic investigation of the effects of Ca on the matrix separation of Sr and Pb and subsequent isotope-amount ratio measurements using a variety of synthetic solutions and reference materials with varying Ca content during the application of an automated analyte/matrix separation approach. The separation method based on the DGA resin was optimized by using increased column bed volumes, comparing two different column sizes (1-mL and 3-mL-bed volume). Certified reference materials (synthetic calcium carbonate – MACS-3, basalt – BCR-2, saggital otolith – FEBS-1, bone meal – NIST SRM 1486, bone ash – NIST SRM 1400, and skim milk powder – BCR-063R) with varying Ca content, Ca/Sr and Ca/Pb mass fraction ratios were separated using the optimized method and analyzed for the Sr and Pb isotopic composition by multi collector inductively coupled plasma mass spectrometry (MC ICP-MS). The developed separation method based on the 3-mL-bed volume column provides quantitative recoveries (84% to 105% for Sr, 77 % to 96% for Pb), while maintaining a quantitative separation of Sr and Pb. Procedural blank levels were <0.04 ng g−1 for Sr and <0.05 ng g−1 for Pb, respectively. The method allows for the automated extraction of Sr in Ca-rich matrices with Ca/Sr mass fraction ratios of up to 4051 corresponding to an absolute Ca load of 965 µg ± 86 µg (BCR-063R, milk powder). Furthermore, the method allows for the simultaneous extraction of Pb from these matrices showing Ca/Pb mass fraction ratios of up to 42095 corresponding to an absolute Ca load of 761 µg ± 122 µg on column (NIST SRM 1400, bone tissue), respectively.
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