Accurate determination of Zn in geological and cosmochemical rock samples by isotope dilution inductively coupled plasma mass spectrometry

Abstract

Inductively coupled plasma mass spectrometry (ICP-MS) procedures with isotope dilution were established for the accurate determination of trace Zn (in the level of 10⁻⁴ to 10⁻⁵ g g⁻¹) in several tens of mg of geological and cosmochemical rock samples. Zinc was determined by ⁶⁶Zn/⁶⁷Zn and ⁶⁸Zn/⁶⁷Zn ratios with the use of an enriched isotope, i.e.⁶⁷Zn. Among possible interferences for Zn isotopes (⁶⁶Zn, ⁶⁷Zn and ⁶⁸Zn), molecular ions from ambient gases and sample solutions were found to be negligibly small, whereas doubly charged Ba ions (¹³²Ba²⁺, ¹³⁴Ba²⁺ and ¹³⁶Ba²⁺) potentially interfered with the three Zn isotopes concerned. Either such interferences were eliminated by chemical separation in the matrix-separation ICP-MS procedure or they were mathematically corrected in the ICP-MS procedure without matrix separation. The three analytical procedure studies were evaluated in terms of analytical capability and data quality.