Precise determination of Rb, Sr, Ba, and Pb in geological materials by isotope dilution and ICP-quadrupole mass spectrometry following selective separation of the analytes

Abstract

A new method was developed for the high precision measurement of Rb, Sr, Ba, and Pb concentrations in silicate rocks. This method is based on the combined use of isotope dilution and ICP quadrupole mass spectrometry, with matrix element removal. The concomitant separation of the analytes is achieved by extraction chromatography (Ba, Sr, Pb) and inorganic cation exchange chromatography (Rb), on two small tandem columns filled with 0.1 ml of “Sr resin” and 1 ml of zirconium (or titanium) phosphate, respectively. Compared to previous separation schemes based on cation- and anion-exchange, this method allows the rapid, concomitant isolation of four trace elements of great interest in geochemistry, with a greatly reduced volume of reagents. The capabilities of the method in terms of precision (equal to or better than 1% RSD) and accuracy are demonstrated by duplicate analyses of four international reference materials (BIR-1, BHVO-1, AGV-1 and RGM-1, from the US Geological Survey) representative of various silicate rock bulk compositions and spanning a large range (0.2–1000 µg g⁻¹) of analyte concentrations.