High-sensitivity determination of Cd isotopes in low-Cd geological samples by double spike MC-ICP-MS. Issue 4 (28th February 2020)

• Record Type: Journal Article
• Authors: Tan, Decan; Zhu, Jian-Ming; Wang, Xiangli; Han, Guilin; Lu, Zhuo; Xu, Wenpo
• Is Part Of: Journal of analytical atomic spectrometry. Volume 35:Issue 4(2020)
• Page Start: 713
• Page End: 727
• Publication Date: 2020-02-28
• Subjects: Atomic spectra -- Periodicals; Atomic absorption spectroscopy -- Periodicals; 543.0858
• DOI: 10.1039/c9ja00397e
• Languages: English
• ISSNs: 0267-9477

Abstract

Abstract : The accuracy and precision of Cd isotope measurement at different injecting sample sizes. Abstract : With new advancements in MC-ICP-MS technology, small Cd isotope fractionations in geological processes have attracted more interest in recent years. However, challenges remain in obtaining high-precision Cd isotope data for geological samples with low Cd concentrations and complex matrices. By an improved Cd purification and cleaning resin scheme for low-Cd samples using AGMP-1M resin with >90% Cd recovery, the ratios of trace elements Sn, Mo, Zr, etc. to Cd in the samples, which could potentially jeopardize the accuracy and precision of Cd isotope analysis under a high-sensitivity setup, were less than 0.001 after purification, and the total procedure blank is ≤0.1 ng. Hence, a sample containing 20–30 ng Cd can be employed for purification and subsequent isotope measurement. Cadmium isotope fractionation (expressed in δ 114/110 Cd relative to NIST 3108) during column separation and instrument mass bias was corrected for by a 111 Cd– 113 Cd double spike. NIST 3108 was determined at a concentration of 5–25 ng mL −1 on a Neptune Plus ( 112 Cd signal intensity: ∼640 V ppm −1 ) and 25–50 ng mL −1 on a Nu plasma III ( 112 Cd signal intensity:∼280 V ppm −1 ) MC-ICP-MS equipped with an Aridus II/III desolvator for more than one year, with a total external analytical precision of 0.034‰ (2SD, n = 181). NIST SRM 2711a, NOD-P-1 and GSS-1 were measured at 5, 10, 20, 25 and 50 ng mL −1 levels to be 0.532 ± 0.038‰, 0.133 ± 0.038‰ and 0.098 ± 0.027‰, respectively, indicating that good accuracy and precision of Cd isotope analysis can be achieved with an injecting sample size as low as 5 ng Cd. Our method can be reliably applied to various geological reference materials (GRMs). The δ 114/110 Cd values of GRMs with relatively high and low Cd concentrations are consistent with previous studies: NOD-A-1 (0.124 ± 0.067‰), GSD-11 (−0.274 ± 0.037‰) and BCR-2 (−0.030 ± 0.063‰). SGR-1b (0.069 ± 0.049‰), GSH-1 (−0.337 ± 0.077‰) and others are reported for the first time in this paper. The δ 114/110 Cd in basalt and stream sediments is relatively homogeneous and overlaps with that of the bulk silicate earth (BSE). The δ 114/110 Cd in shale and soils varies greatly from −0.694 to 0.532‰. Human hair and other animal organs are enriched in light isotopes relative to BSE, whereas terrestrial plants are enriched in heavy isotopes.