Yankuang ceshi (Jul 2021)
Determination of Copper Isotope Composition of Soil Reference Materials by MC-ICP-MS
Abstract
BACKGROUND In recent years, copper isotopes have been widely applied in supergene environments and biogeochemical processes, acting as novel tracers for soil pollution and biogeochemical cycles during pedogenesis. To date, Cu isotope studies on natural soils have commonly analyzed basalt geostandards for monitoring data quality. However, the contents of copper, matrix ions, and organic matter in the soil and silicate rock are very different. For example, the copper content in silicate rock is >80μg/g, and the copper content in some soils is very low, that is, < 20μg/g. The use of silicate standard materials as reference samples to monitor the data quality of soil samples lacks representativeness. OBJECTIVES To provide new soil standards for high-precision Cu isotope analysis, this study reports high-precision copper isotope data for four soil reference materials (GBW07443, GBW07425, GBW07427, and GBW07389), expressed as δ65Cu relative to NIST SRM 976, which were measured using a multi-collector inductively coupled plasma-mass spectrometer (MC-ICP-MS). METHODS Soil samples were completely dissolved in high-pressure bombs in a muffle furnace. Complete separation of Cu from the matrices was obtained using a strong anion exchange resin (AG MP-1M). The instrument mass bias was corrected using the standard sample-standard method. RESULTS The long-term external reproducibility was higher than ±0.05‰ (n=306, 2SD). Cu isotopic compositions of the four soil reference materials, GBW07443, GBW07425, GBW07427, and GBW07389, from the China National Bureau of Standards were -0.04‰±0.04‰ (n=9, 2SD); -0.07‰±0.05‰ (n=12, 2SD); -0.06‰±0.04‰ (n=12, 2SD); and -0.02‰±0.06‰ (n=12, 2SD), respectively. CONCLUSIONS The δ65Cu values of these reference materials were close to zero and corresponded to the intermediate values of natural soils. Moreover, the sample was easy to obtain, and the experimental results showed uniformity in its chemical and copper isotopic compositions, making it suitable as a standard material for monitoring the reliability of the soil copper isotope chemistry and the mass spectrometry data.
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