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A novel sample loading method and protocol for monitoring sample fractionation for high precision Ca stable isotope ratio measurements using double-spike TIMS

Abstract

The external reproducibility (2σSD) of Ca stable isotope ratio measurements (δ44/40Ca) using double spike - Thermal ionization mass spectrometry (TIMS) shows a large range from < 0.1 ‰ to 0.5 ‰. We demonstrate that using a 43Ca-48Ca double spike, which allows simultaneous measurements of δ44/40Ca and δ44/42Ca, and analyses at moderate signal strengths (40Ca ranging from 6 to 10 V), high precision δ44/40Ca (external reproducibility better than ± 0.08 ‰, 2σSD) as well as δ44/42Ca can be obtained if samples and standards are analyzed under similar fractionation conditions. To monitor the fractionation condition, the usage of a parameter β is proposed, which measures the deviation of the 43Ca/48Ca ratio of the sample-double spike mixture from that of the pure double spike. A novel, low-cost sample loading technique using combination of Re and Ta filaments and a Ta2O5 activator is presented which results in a steady signal. We report the δ44/40Ca and δ44/42Ca values, calculated w.r.t. NIST SRM 915a and reported as deviations in parts per mil (‰), of NIST standards SRM 915a (0.01, -0.02) and SRM 915b (0.73, 0.32), NASS 6 (seawater, 1.80, 0.89), USGS silicate rock standards BHVO-2 (0.86, 0.47) and BCR-2 (0.89, 0.48), Geological Survey of Japan carbonate standards JCp-1 (coral, 0.85, 0.45) and JCt-1 (clam shell, 0.83, 0.46) and ECRM 752-1 (alternative name BCS-CRM 393) (0.83, 0.46) from the Bureau of Analyzed Samples Ltd. UK. The Ca stable isotopic compositions of JCt-1 and ECRM 752-1 are being reported for the first time.

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Publication details

The article was received on 26 Sep 2017, accepted on 04 Dec 2017 and first published on 05 Dec 2017


Article type: Paper
DOI: 10.1039/C7JA00322F
Citation: J. Anal. At. Spectrom., 2017, Accepted Manuscript
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    A novel sample loading method and protocol for monitoring sample fractionation for high precision Ca stable isotope ratio measurements using double-spike TIMS

    S. Mondal and R. Chakrabarti, J. Anal. At. Spectrom., 2017, Accepted Manuscript , DOI: 10.1039/C7JA00322F

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