多接收电感耦合等离子体质谱(MC-ICP-MS)法测定土壤的铁同位素组成

ZENG Zhen,SUN Yufang,GONG Hua,TANG Haoye(Soil and Environment Analysis Center,Institute of Soil Science,Chinese Academy of Sciences,Nanjing,Jiangsu 210008,China)

铁(Fe)同位素(δ^(56/54)Fe)在土壤科学中可以用来研究铁在土壤圈中的迁移、转化等过程。为了确保不同类型样品中的铁同位素测量的准确性,需要标定一系列标准物质的铁同位素组成。通过使用硝酸-氢氟酸-高氯酸混酸对土壤样品中的硅酸盐和有机质进行消解,利用阴离子交换树脂(AG1-X8,0.038~0.074 mm)对土壤样品中的铁与基质元素进行分离,同时为了获得可靠的纯化流程,考察了不同浓度的盐酸对基质的淋洗效果。结果表明,当盐酸浓度4.0~7.0 mol/L时,基质元素都能有效地被分离干净,综合考虑选择5.0 mol/L的盐酸将基质元素从阴离子树脂中淋洗出来,再用0.3 mol/L的盐酸将铁元素收集起来。利用多接收电感耦合等离子体质谱仪测定铁同位素组成。通过对实验室标准铁溶液(ISS-Fe和USTC-Fe)的长期监测,测定δ^(56/54)Fe的外精度好于±0.05‰(2SD)。测定的两个玄武岩标样(BCR-2和BHVO-2)中铁同位素组成,其δ^(56/54)Fe值分别为0.08‰±0.05‰和0.09‰±0.05‰,均在文献值误差范围内。此外,测量了六个土壤标样的Fe同位素组成,其δ^(56/54)Fe值从-0.11‰变化到+0.15‰,研究结果为土壤铁同位素研究提供了有力的数据支撑。

Iron(Fe)isotope(δ^(56/54)Fe)can be used to study the migration and transformation of iron in the soil circle.In order to ensure the accuracy of iron isotope measurement in different types of samples,it is necessary to calibrate the iron isotope composition of a series of standard materials.Silicate and organic matter in soil samples were digested by mixed acid of nitric acid-hydrofluoric acid-perchloric acid,and iron in soil samples was separated from matrix elements by anion exchange resin(AG1-X8,0.038-0.074 mm).At the same time,in order to obtain a reliable purification process,the leaching effect of hydrochloric acid with different concentrations on matrix was investigated.The results showed that when the concentration of hydrochloric acid was 4.0-7.0 mol/L,the matrix elements were effectively separated.5.0 mol/L hydrochloric acid was selected to elute the matrix elements from the anionic resin,and then 0.3 mol/L hydrochloric acid was used to collect the iron elements.The iron isotope composition was determinated by multi-collector inductively coupled plasma mass spectrometry.Through the long-term monitoring of laboratory standard iron solutions(ISS-Fe and USTC-Fe),the external accuracy of δ^(56/54)Fe was better than±0.05‰(2 SD).The iron isotopic compositions of two basalt standard samples(BCR-2 and BHVO-2)were determined,and their δ^(56/54)Fe values were 0.08‰±0.05‰and 0.09‰±0.05‰respectively,which was within the error range of literature values.In addition,the iron isotopic composition of six soil standard samples were measured,and the δ^(56/54)Fe values varied from-0.11‰to+0.15‰.This research will provide strong data support for the study of iron isotopes in soil.