Search

There has been a growing interest in using cadmium (Cd) isotopes to trace the source of Cd contamination and Cd cycling in the Earth surface. Yet it remains technically challenging to precisely and efficiently determine the Cd isotopic compositions of samples with extremely low Cd concentrations due to the imperfect separation of Cd from the matrix and the interference caused by resin-derived organics when TRU Spec resin was used. In this study, we present a two-stage column chromatography system (AG-MP-1M resin + UTEVA resin) for Cd purification. Here, a Prefilter resin combined with UTEVA resin effectively purifies Cd from Sn after the separation of Cd by AG-MP-1M column while keeping the phosphorous organic compounds to an acceptable level. In contrast to TRU Spec resin, which is prone to leaking through the Prefilter resin, we find that UTEVA resin is effectively retained by the Prefilter resin, thus avoiding the P-related anomalous shifts in the Cd isotope measurement (P/Cd < 1). UTEVA resin also exhibits a comparable capacity for purifying Cd from Sn and Mo when compared to TRU Spec resin. The recovery of the two-stage column system is generally higher than 99% and the procedural blank accounting for sample digestion and chemical purification is lower than 20 pg. The Cd isotopic compositions of several reference materials are determined using double spike MC-ICP-MS, with a 111Cd–113Cd double spike pair optimized for the 111Cd, 112Cd, 113Cd, and 114Cd inversion. The δ114/110Cd values of these reference materials relative to NIST SRM 3108 agree within analytical uncertainty with previous studies. The long-term external precision of δ114/110Cd determined based on replicated measurements of BCR-2 is 0.04‰ (n = 10, 2 SD) for a minimum sample size of 10 ng. Our study thus provides an efficient two-stage column system for determining the Cd isotopic compositions of geological samples with relatively low Cd concentrations. [ABSTRACT FROM AUTHOR]

Over the last decade, there has been a growing interest in using lithium (Li) isotopes in marine carbonates to trace chemical weathering and clay formation in the Earth's history. Yet it remains technically challenging to precisely and efficiently determine the Li isotope composition in carbonate samples due to the imperfect Li separation led by the matrix effect and the extremely low Li concentration in carbonates relative to the analytical threshold of sample size. For such high matrix and low-Li samples, here we present an efficient dual-column chromatography system for Li purification. The dual-column system has a large loading capacity, fixed Li elution range of merely 12 mL, complete Li recovery (>99.5%) and relatively efficient total elution time (7 hours). The procedural blank is 0.036 ± 0.002 ng accounting for sample dissolution and chemical purification, and the Na/Li mass ratio of the Li cut is below 0.5. High precision and accurate Li isotope measurement is performed efficiently with a small sample-sized protocol developed on a MC-ICP-MS (Neptune plus) connected with an APEX 2-IR desolvator. The whole procedure is validated by analyzing a series of certified reference materials. The long-term external precision of δ7Li determined based on L-SVEC and a high-purity Li solution is 0.6‰ (2SD) and 0.9‰ (2SD) for a minimum sample size of 7.5 ng. [ABSTRACT FROM AUTHOR]

The precise determination of Cd isotope ratios via multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has made the widespread application of Cd isotopes possible. However, previous studies are complicated by the chemical purification method and molecular interferences from Zn (e.g.70Zn36Ar+, 68Zn38Ar+, and 66Zn40Ar+ on 106Cd+, 70Zn38Ar+ and 68Zn40Ar+ on 108Cd+, 70Zn40Ar+ on 110Cd+). Separation of Zn from Cd requires the usage of a toxic reagent (HBr) and is also complicated by the relatively high procedural Zn blank especially when only a very small amount of Cd is available. Here we present a high-precision Cd isotope measurement method using double spike MC-ICP-MS, which avoids the molecular interferences from Zn introduced by both sample and chemical purification. A 111Cd–113Cd double spike pair optimized for the 111Cd, 112Cd, 113Cd, and 114Cd inversion was used to correct for the mass bias. Elemental doping experiments suggest that the measured Cd isotope data were not significantly affected when the measured solution has, Zn/Cd < 103, Pd/Cd < 102, Fe/Cd < 10−2, In/Cd < 10−3, Sn/Cd < 10−1, Zr/Cd < 10−2, Nb/Cd < 10−1, Mo/Cd < 10−2, Ru/Cd < 10−2, Ga/Cd < 10−2, Ge/Cd < 10−2, Se/Cd < 10−1, and As/Cd < 10−1. We thus modified the chemical purification method by removing the HBr step and eluting Zn and Cd together. The minimum requirement of sample size for precise measurement of stable Cd isotope ratios was tested to be as low as 10 ng. The measurements of pure Cd solutions (BAM I012 Cd and HPS Cd) give a long-term intermediate precision for δ114/110Cd relative to NIST SRM 3108 of 0.05‰. We further validated our method by measuring different reference materials covering a relatively wide range of Zn/Cd (∼9 to 1239), the results of which agree within uncertainty with previous studies. Our study thus provides an efficient and precise way to determine stable Cd isotope ratios of geological samples with relatively low Cd concentrations. [ABSTRACT FROM AUTHOR]