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Stable isotope ratios are widely used to solve environmental, geological, medical, and forensic problems. The double spike technique is considered to be one of the most robust and efficient methods to correct for instrumental mass bias and isotopic fractionation that may occur during sample preparation. However, various hidden errors can arise from data processing and have been largely overlooked in previous studies. Several of these hidden errors were investigated in this work using measurement and synthetic data. Double spike inversion of chromium isotope raw data from 1116 natural samples demonstrated that averaging raw isotope ratios before double spike inversion can add significant errors to inverted isotope values, and such errors can be 1.5 times larger than the true analytical precision. Synthetic data were used to investigate the errors on inverted Cr isotope data caused by spike:analyte ratio and Fe-Ti-V interferences, and the following threshold values are recommended to minimize such errors: 54 Cr spike / 52 Cr sample ratio greater than 0.5, 56 Fe/ 52 Cr less than 0.2, 49 Ti/ 52 Cr less than 0.04, and 51 V/ 52 Cr less than 1. Sample preparation can potentially lead to large errors in inverted Cr isotope data if preparation-induced isotope fractionation deviates from the exponential law used in the double spike inversion, but such errors can be minimized by achieving >70% Cr yield. Our findings provide important insights for the double spike inversion procedure and assessing the reliability of inverted isotope data for not only the chromium isotope system but also other elements commonly analyzed using the double spike technique.

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]

Uranium isotopes (238U/235U) have been used widely over the last decade as a global proxy for marine redox conditions. The largest isotopic fractionations in the system occur during U reduction, removal, and burial. Applying this basic framework, global U isotope mass balance models have been used to predict the extent of ocean floor anoxia during key intervals throughout Earth's history. However, there are currently minimal constraints on the isotopic fractionation that occurs during reduction and burial in anoxic and iron‐rich (ferruginous) aquatic systems, despite the consensus that ferruginous conditions are thought to have been widespread through the majority of our planet's history. Here we provide the first exploration of δ238U values in natural ferruginous settings. We measured δ238U in sediments from two modern ferruginous lakes (Brownie Lake and Lake Pavin), the water column of Brownie Lake, and sedimentary rocks from the Silurian‐Devonian boundary that were deposited under ferruginous conditions. Additionally, we provide new δ238U data from core top sediments from anoxic but nonsulfidic settings in the Peru Margin oxygen minimum zone. We find that δ238U values from sediments deposited in all of these localities are highly variable but on average are indistinguishable from adjacent oxic sediments. This forces a reevaluation of the global U isotope mass balance and how U isotope values are used to reconstruct the evolution of the marine redox landscape. Key Points: δ238U values were measured in iron‐rich, anoxic (ferruginous) modern natural environments, and Paleozoic shales deposited under ferruginous conditionsδ238U fractionations in these environments are highly variable and generally indistinguishable from isotopic fractionations associated with oxic settingsδ238U fractionations in these environments are highly variable and generally indistinguishable from isotopic fractionations associated with oxic settings [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]

Stable molybdenum (Mo), thallium (Tl), and uranium (U) isotope ratios were determined in a suite of samples from the 1959 Kilauea eruption and from Kilauea Iki lava lake with the aim of understanding the effects of igneous differentiation on these isotope systems. The samples range from olivine cumulate with MgO up to 27% to internal differentiates with MgO less than 3%, representing a tholeiitic differentiation series. Molybdenum, Tl, and U behave incompatibly during differentiation, and Mo and U isotope ratios do not systematically vary amongst the different samples. δ98Mo values range from −0.17 to −0.31‰ and δ238U values range from −0.20 to −0.38‰. Most individual analyses for both isotope systems overlap within measurement uncertainty (± ~0.7 and ~ 0.6, respectively). Mean δ98Mo and δ238U values are −0.22 ± 0.08‰ (2σ) and − 0.29 ± 0.09‰ (2σ), respectively, which overlap with Pacific mid ocean ridge basalt (MORB). In contrast, Tl isotopes show small but resolvable variations, with ε205Tl ranging from +1.20 to −1.38. The most negative ε205Tl values are confined to some of the lowest [Tl] samples, but the ε205Tl values do not otherwise vary smoothly with MgO or [Tl]. Possible mechanisms for thallium isotope fractionation are considered (e.g., degassing, water leaching, sulfide fractionation) but none are found to be satisfactory. Overall, the lack of resolvable variation in the Mo and U isotope systems and the small magnitude of heterogeneity in the Tl isotope system indicate that differentiation in tholeiitic systems is unlikely to be a major contributor to global variation in these isotope systems. [ABSTRACT FROM AUTHOR]