Improvements in Cu-Zn isotope analysis with MC-ICP-MS: A revisit of chemical purification, mass spectrometry measurement and mechanism of Cu/Zn mass bias decoupling effect

A revised chemical purification procedure for Cu-Zn isotopes is proposed in this study. The handing time and amounts of chemicals, such as H2O2 and HCl are largely saved with this modification. The ionization efficiencies of Cu and Zn are investigated in detail in wet and dry plasma with two kinds of skimmer cones. The ionization efficiency of Zn is depressed by HNO3 in the matrix, while HCl affects Cu and Zn ionization efficiency similarly. Potential polyatomic interferences with Zn-68(+) and Zn-70(+) are (ArN2+)-Ar-40-N-14 and (ArNO+)-Ar-40-N-14-O-16 respectively, which are highly dependent on the amount of N-2 in dry plasma and on the HNO3 concentration in wet plasma. Use of the DNS sample introduction device without N-2 gas provides the best conditions for Cu-Zn isotope measurement. A Cu/Zn mass bias decoupling effect has been revealed in this study, and this effect appears to be dependent on the presence of HNO3 and N-2 in ionizing plasma. (C) 2015 Elsevier B.V. All rights reserved.