Acta Petrologica et Mineralogica

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, δ⁴⁴/⁴²Ca 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.

Ca isotopes; Cr; chemical separation; MC-ICPMS