多接收器电感耦合等离子体质谱法测定土壤标准物质铜同位素组成

刘婉; 李丹丹; 刘盛遨

doi:10.15898/j.cnki.11-2131/td.202012130163

多接收器电感耦合等离子体质谱法测定土壤标准物质铜同位素组成

Determination of Copper Isotope Composition of Soil Reference Materials by MC-ICP-MS

摘要

摘要: 近年来，铜同位素在表生环境和生物地球化学中的应用越来越广泛，尤其是土壤的铜同位素组成可以示踪环境污染物来源及生物地球化学过程。目前，对土壤铜同位素进行研究时，主要以硅酸岩标准物质为标样来衡量土壤样品铜同位素测定的准确性和精确性。但土壤与硅酸岩中铜、基质离子及有机质的含量等存在很大差异（如：硅酸岩中的铜含量>80μg/g，一些土壤中的铜含量很低， < 20μg/g），将硅酸岩标准物质作为标样来监测土壤样品的数据质量缺乏代表性。为了弥补这一缺陷，本文精确测定4个国家土壤标准物质（GBW07443、GBW07425、GBW07427、GBW07389）的铜同位素组成，并将其作为检验土壤样品铜同位素测定过程中的标准。实验中采用高温高压反应釜消解样品，利用AG MP-1M树脂进行纯化，全流程空白 < 2ng，回收率≥ 98%，通过多接收器电感耦合等离子体质谱仪（MC-ICP-MS）采用标样-样品-标样间插法进行仪器分馏校正，δ⁶⁵Cu的长期测试外精度优于0.05‰（n=306，2SD）。GBW07443、GBW07425、GBW07427和GBW07389的铜同位素组成分别为-0.04‰±0.04‰（n=9，2SD）、-0.07‰±0.05‰（n=12，2SD）、-0.06‰±0.04‰（n=12，2SD）、-0.02‰±0.06‰（n=12，2SD）。这些土壤标准物质的铜同位素组成均位于0附近，大致为自然界土壤铜同位素比值变化范围（-0.5‰~+0.5‰）的中间值，且样品容易获得，其化学和铜同位素组成均一，适合作为监控土壤铜同位素化学及质谱分析数据可靠性的标准物质。

Abstract:
BACKGROUNDIn 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.
OBJECTIVESTo 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).
METHODSSoil 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.
RESULTSThe 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.
CONCLUSIONSThe 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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