Bingyu Gao

Effect of K concentration mismatch up to 30% on δ⁴¹K value from RF Ref. of 1.05 V.

With single-column chemical purification, highly accurate δ ⁷ Li values for eight international reference materials are presented together with seventeen Chinese geological reference materials from NRCG using the Nu Sapphire.

Here we present an analytical method for Cu isotopic measurement using standard-sample bracketing on a Nu Sapphire multi-collector inductively coupled plasma mass spectrometer. The effects of Cu concentration and HNO₃ molarity mismatch between the standard and the sample, as well as the presence of matrix elements have been evaluated. Intermediate precision of better than ±0.030‰ for δ⁶⁵Cu (2SD) was routinely obtained on NIST SRM 3114 and NWU-Cu-A. Accurate measurements were achieved when C_Na/C_Cu < 0.5, C_Ti/C_Cu, C_Fe/C_Cu and C_Co/C_Cu < 1, C_Ni/C_Cu < 3 and C_Zn/C_Cu < 10. High-precision Cu isotopic data were determined for nineteen geological reference materials, including igneous rocks, sedimentary rocks, metamorphic rocks and chalcopyrite, with an overall range of ∼0.44‰ (−0.056‰ to 0.384‰), nearly 15 times the current analytical precision. The Cu isotopic data of these reference materials can be used for future interlaboratory comparisons.

This study presents high-precision analyses of calcium (Ca) isotope ratios using a collision-cell multi-collector inductively coupled plasma mass spectrometer (CC-MC-ICP-MS, Nu Sapphire). This instrument allows Ca isotope measurement in the low resolution mode, requiring much less sample compared with TIMS and conventional MC-ICP-MS, and has additional measurement capability of both radiogenic (ε⁴⁰Ca) and stable isotope ratios (δ^44/40Ca and δ^44/42Ca). The effects of several factors on the precision and accuracy of Ca isotopic data were evaluated, including the total Ca concentration, Ca intensity mismatch between the sample and standard, HNO₃ molarity mismatch between the sample and standard, and the presence of matrix elements. High precision was obtained on 100 ng g⁻¹ Ca samples (i.e., for 6 replicates ∼600 ng of Ca). Accurate measurements require the following conditions: (1) Ca intensities matched within 3% between the sample and standard, (2) low contents of Sr, Mg and Cr (Sr/Ca, Mg/Ca and Cr/Ca ratios need to be lower than 0.01%, and K/Ca, Al/Ca, Ti/Ca and Cr/Ca ratios δ^44/40Ca and higher than 0.05‰ (2 SD) for δ^44/42Ca. The slope of the fractionation line between δ^44/40Ca and δ^44/42Ca is 1.9616 ± 0.0794, within the error of the slope value from the exponential law.

Here we present an analytical method for Fe isotopic measurements in low resolution mode, using a Nu Sapphire collision cell-equipped multi-collector inductively coupled plasma mass spectrometer by standard-sample bracketing. High Fe sensitivity was obtained through reducing Ar based interference by over 9 orders of magnitude whilst other analytes remained unaffected. The effects of Fe concentration, Fe beam intensity and HNO₃ molarity mismatch between the standard and sample and the presence of matrix elements have been evaluated. The long-term analyses of JMC Fe and BCR-2 indicate that the obtained isotopic ratios are highly reproducible, with precisions of better than ±0.03‰ for δ⁵⁶Fe (2SD). Such accurate and precise data could be acquired via 3 to 6 repeat measurements consuming 50–100 ng Fe, which has improved by a factor 40 compared to those previously reported on other instruments. Accurate measurements were achieved by closely matching Fe intensities between the sample and standard (a 5% mismatch would create a 0.02‰ offset in the ⁵⁶Fe/⁵⁴Fe ratio). On the other hand, the ratio of the concentration between the matrix elements and Fe, such as C_Na/C_Fe, C_Mg/C_Fe, C_Ca/C_Fe, C_Ti/C_Fe and C_Ni/C_Fe, should be kept under 0.1, C_K/C_Fe under 0.3, C_Al/C_Fe and C_Cu/C_Fe under 1, and C_Co/C_Fe and C_Zn/C_Fe under 2 to avoid any matrix effect. In addition, high precision Fe isotopic data were obtained on twenty-one geological reference materials and were highly consistent with the literature values. Furthermore, we obtained δ⁵⁶Fe of standard chalcopyrite (XTC) for the first time: 0.127 ± 0.027‰ (2SD, n = 3).

In general, no more than 1 g of metal sulfide can be completely digested in 20 mL of inverse aqua regia using the Carius tube technique. In this study, the sample weight increased after adding HClO₄ to inverse aqua regia while the volume of acid concurrently decreased significantly. Three grams of metal sulfide were digested in 12 mL of acid (3 mL of HClO₄ and 9 mL of inverse aqua regia) via the HClO₄-inverse aqua regia method. The results using molybdenite reference materials JDC and HLP mixed with 3 g of pyrite were consistent with certified values. Compared to the traditional method, the HClO₄-inverse aqua regia method could dissolve a larger sample mass (3 g) with a smaller volume of acids (12 mL). We simultaneously found that the oxidation of digestion acids greatly affected the Os signal but had no influence on the equilibrium of isotope exchange between ¹⁸⁵Re and ¹⁹⁰Os spikes in Re and Os samples. Remarkably, the heating temperature was the most significant factor influencing the equilibrium of isotope exchange, and the Os in a sample was not equilibrated with the spike until the heating temperature reached 190 °C.