Chemical separation and mass spectrometry of Cr, Fe, Ni, Zn, and Cu in terrestrial and extraterrestrial materials using thermal ionization mass spectrometry

A sequential chemical separation technique for Cr, Fe, Ni, Zn, and Cu in terrestrial and extraterrestrial silicate rocks was developed for precise and accurate determination of elemental concentration by the isotope dilution method (ID). The technique uses a combination of cation-anion exchange chromatography and Eichrom nickel specific resin. The method was tested using a variety of matrixes including bulk meteorite (Allende), terrestrial peridotite (JP-1), and basalt (JB-1b). Concentrations of each element was determined by thermal ionization mass spectrometry (TIMS) using W filaments and a Si-B-Al type activator for Cr, Fe, Ni, and Zn and a Re filament and silicic acid-H ₃PO₄ activator for Cu. The method can be used to precisely determine the concentrations of these elements in very small silicate samples, including meteorites, geochemical reference samples, and mineral standards for microprobe analysis. Furthermore, the Cr mass spectrometry procedure developed in this study can be extended to determine the isotopic ratios of ⁵³Cr/⁵²Cr and ⁵⁴Cr/⁵²Cr with precision of ∼0.05ε and ∼0.10ε (1ε ) 0.01%), respectively, enabling cosmochemical applications such as high precision Mn-Cr chronology and investigation of nucleosynthetic isotopic anomalies in meteorites.