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

Mondal, Surajit and Chakrabarti, Ramananda (2018) A novel sample loading method and protocol for monitoring sample fractionation for high precision Ca stable isotope ratio measurements using double-spike TIMS. In: JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, 33 (1). pp. 141-150.

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Abstract

The external reproducibility (2 sigma(SD)) of Ca stable isotope ratio measurements (delta Ca-44/40) using double-spike thermal ionization mass spectrometry (TIMS) shows a large range from <0.1 parts per thousand to 0.5 parts per thousand. We demonstrate that using a Ca-43-Ca-48 double spike, which allows simultaneous measurements of delta Ca-44/40 and delta Ca-44/42, and analyses at moderate signal strengths (Ca-40 ranging from 6 to 10 V), high precision delta Ca-44/40 (external reproducibility better than +/- 0.08 parts per thousand, 2 sigma(SD)) as well as delta Ca-44/42 can be obtained if samples and standards are analyzed under similar fractionation conditions. To monitor the fractionation conditions, the usage of a parameter beta is proposed, which measures the deviation of the Ca-43/Ca-48 ratio of the sample-double spike mixture from that of the pure double spike. A novel, low-cost sample loading technique using a combination of Re and Ta filaments and a Ta2O5 activator is presented which results in a steady signal. We report the delta Ca-44/40 and delta Ca-44/42 values, calculated w.r.t. NIST SRM 915a and reported as deviations in parts per mil (parts per thousand), 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 (limestone, 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 reported for the first time.

Item Type:	Journal Article
Publication:	JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY
Publisher:	10.1039/c7ja00322f
Additional Information:	Copy right for this article belongs to the ROYAL SOC CHEMISTRY, THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND
Department/Centre:	Division of Mechanical Sciences > Centre for Earth Sciences
Date Deposited:	25 Jan 2018 06:09
Last Modified:	25 Jan 2018 06:09
URI:	http://eprints.iisc.ac.in/id/eprint/58861

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