Cr-Ca化学分离方法研究

A study on methods for chemical separation of Cr form Ca

多接收电感耦合等离子体质谱仪(MC-ICPMS)测定Ca同位素比值时,Cr元素产生的基质效应会使Ca同位素测试值偏离真实值。利用稀HCl介质和强酸性阳离子交换树脂的传统方法可实现绝大多数元素和Ca的高效分离,但Cr分离率约为90%,分离效果不理想。对于超基性岩等高Cr地质样品,Cr/Ca值可高达10。针对这类特殊地质样品的Ca同位素测试,我们研究了Cr-Ca在浓HCl介质中基于AG50W-X12(200-400 mesh)强酸性阳离子交换树脂的淋洗行为。研究结果表明,利用10 mol/L HCl可实现Cr-Ca的高效快速分离,Cr的分离率>99.9%,Ca元素回收率接近100%,同时该方法也可实现K、Mg、Al等元素与Ca的高效快速分离。应用该方法对过柱后Ca单元素溶液和高Cr橄榄岩标样进行Ca同位素测试,其Ca同位素组成(δ^(44/42)Ca)在测试误差范围内与参考值一致,表明该方法适用于高Cr样品的Ca元素分离提纯及同位素测试。

The determination of Ca isotope ratios by multi-collector inductively coupled plasma mass spectrometry(MC-ICPMS)is sensitive to the matrix effect,especially that is generated by Cr elements,which leads to a deviation in Ca isotope compositions.Traditional methods using dilute HCl medium and strong acid cation exchange resin can achieve high-efficiency separation of most matrix elements and Ca,except Cr,where nearly 10%of Cr cannot be removed from Ca elution.For geological samples with high Cr,such as ultramafic rocks,the Cr/Ca ratio can be as high as 10.To achieve Ca isotope analysis of these special geological samples,here we studied the elution of Cr-Ca in concentrated HCl medium based on AG50W-X12(200-400 mesh)strong acid cation exchange resin.The results showed that efficient and rapid separation of Cr-Ca can be achieved when using 10 mol/L HCl,with a Cr separation rate>99.9%.Moreover,this method can achieve efficient and rapid separation of elements such as K,Mg and Al from Ca.To test the validation of this method for Ca isotope analysis,δ^(44/42)Ca of the Ca single-element solution after column separation was determined using MC-ICPMS,with the results consistent with the theoretical value within the analytical error.This indicates that this method is efficient for Ca element purification and valid for Ca isotope analysis for those high Cr samples.