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The double spike-standard addition (DSSA) is a powerful method proposed for isotope measurement of ultra-trace elements in samples. Here, we test the method's practicality and robustness for obtaining high-precision δ114/110Cd data in samples with complex matrices and ultra-trace cadmium (Cd) concentrations as low as 0.004 μg g−1. Through a DS data reduction routine and isotope binary mixing model, the δ114/110Cd values obtained for numeral geological and biological reference materials (GRMs/BRMs) agree well with certified or previous measurements, even for ∼2.1 ng Cd of BCR-2. The overall precision of both single- and multi-standard addition depends on the sample fraction (fspl) owing to the error propagation. And 0.041 ± 0.022‰ (2SD, n = 46) of precision for δ114/110Cd can be achieved when the sample fraction (fspl) is ≥20%, comparable to 0.056 ± 0.039‰ (2SD, n = 23) obtained by the traditional DS method. However, it becomes greater than 0.110‰ when fspl is <20%, indicating that 20% (1/5) −50% (1/2) of fspl is the optimal mixing range to obtain high-precision data if the minimal sample sizes are required. These further confirm that accurate and precise Cd isotope ratios can be determined by DSSA. Correspondingly, the purification scheme can be simplified to a single column due to the added standard solution boosting analyte and diluting ratios of matrix/Cd. Animal organs, with 0.004–0.106 μg g−1 Cd, yield large variations of δ114/110Cd (−0.054 ± 0.030‰ (2SD, n = 4) and 0.681 ± 0.022‰ (2SD, n = 4) for ovine liver and kidney, respectively), suggesting that Cd isotopes can be fractionated significantly during biological metabolic processes and may be a potential use in medical diagnosis. Robust measurement of Cd isotope composition in ultra-trace Cd samples with complex matrices by DSSA broadens the scope of measurable samples by the traditional DS method, thus potentially opening a range of new opportunities in life, agricultural, environmental, and earth/planetary sciences. [ABSTRACT FROM AUTHOR]

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 δ114/110Cd relative to NIST 3108) during column separation and instrument mass bias was corrected for by a 111Cd–113Cd double spike. NIST 3108 was determined at a concentration of 5–25 ng mL−1 on a Neptune Plus (112Cd signal intensity: ∼640 V ppm−1) and 25–50 ng mL−1 on a Nu plasma III (112Cd 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 δ114/110Cd 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 δ114/110Cd in basalt and stream sediments is relatively homogeneous and overlaps with that of the bulk silicate earth (BSE). The δ114/110Cd 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. [ABSTRACT FROM AUTHOR]

Correction for 'High-precision measurement of Cd isotopes in ultra-trace Cd samples using double spike-standard addition MC-ICP-MS' by Hui Chang et al., J. Anal. At. Spectrom., 2023, 38, 950–962, https://doi.org/10.1039/D3JA00047H. [ABSTRACT FROM AUTHOR]

Nickel (Ni) isotopes have been developed as a potential biosignature and proxy for tracing the occurrence of the Great Oxidation Event. However, the precise measurement of Ni isotopes is still hindered by the costly operation, complicated procedures and/or high procedural blanks of the chemical purification schemes. Here, a novel purification scheme, utilizing only dimethylglyoxime (DMG) and acetone as organic reagents, is proposed to separate Ni from samples through a four-step procedure with five chromatographic columns. Steps I, II and III are designed to effectively eliminate major matrix elements, including 99% Fe, Ca, Ti, and Al, 85% Mn, 55% K, even for samples with [Ca]/[Ni] ≈ 4600 and [Mg]/[Ni] ≈ 1900. Step IV utilizes the formation of Ni(DMG)2 complexes in an aqueous medium containing 0.5 M HCl, 95% acetone and 0.1 M DMG, which can remove residual elements such as 45% K; this step avoids the use of Ni-specific resin, which requires careful pH tuning. Steps III and I can be repeated to obtain high-purity Ni. The Ni yield through these four steps is greater than 92%, with a maximum loss of ∼8% occurring in Step II for low-Ni samples. The total procedural blank is 0.4 to 1.2 ng. When double spiking (61Ni–60Ni) is used to correct for instrument mass bias and purification-related isotope fractionation, small sample sizes (600–800 ng) are sufficient for achieving high-precision Ni isotope determination. Nickel isotopes for standards such as SRM 986 and geological reference materials (GRMs) such as BHVO-2, NOD-P-1, and NOD-A were determined on a Nu Plasma III MC-ICP-MS. The long-term reproducibility is 0.05‰ (2SD, n = 134) for pure solution and 0.06‰ (2SD, n = 18) for GRMs, and the average δ60Ni values are in excellent agreement with previous studies. These results show that our new purification method can be applied to various samples. Using this new method, we measured a set of granite, sediment, diamictite and loess samples and preliminarily constrained the δ60Ni of the upper continental crust to be 0.11 ± 0.14‰ (2SD, n = 17). [ABSTRACT FROM AUTHOR]

Chromium (Cr) isotopes have been used to trace pollution processes and reconstruct paleo-redox conditions. However, the precise determination of Cr isotopes is still challenged by difficulties in purifying Cr from samples with low Cr and high matrix content. Here, we developed an improved, flexible and easily operated three-step chromatographic procedure to separate Cr from high-matrix samples. A continuous, two-stage column (Step I) filled with 2 mL cation resin AG50W-X8 (200–400 m) and 2 mL anion resin AG1-X8 resin (100–200 m), followed by Step II, with 1 mL of AG1-X8 resin (200–400 m), was used to remove at least 99% of Ca, Fe, and Ti, and ＞90% of V and most other matrix elements, even for samples with Fe/Cr ≈ 6000 and Ti/Cr ≈ 1000. The recovery of Cr in both Step I and Step II can reach nearly 100%. Step III utilizes 2 mL AG1-X8 (100–200 m) combined with an (NH4)2S2O8 oxidant to remove residual matrix elements and achieve high-purity Cr. The total yield of Cr through our three-step procedure is greater than 80% even for low-Cr (2.6 μg kg−1) samples. A relatively small sample amount (300–600 ng Cr) is enough to achieve high precision Cr isotope measurement due to a low procedural blank (＜1 ng). Chromium isotopes in geological reference materials (BHVO-2, JDo-1, JP-1, etc.) were measured on a Neptune Plus MC-ICP-MS. The long-term external precision is 0.06‰ (2SD), and the δ53Cr values are in great agreement with previously reported values. The δ53Cr of the upper continental crust is estimated to be −0.10 ± 0.10‰ using a suite of granite, diamictite, sediment and loess samples. Both plants and human hair are ∼0.1‰ heavier than the upper continental crust. Tests show that our improved purification procedure is applicable to various geological and environmental samples. [ABSTRACT FROM AUTHOR]