The determination of rubidium and strontium in silicates by flameless atomic-absorption spectroscopy

A new method is described for the determination of Rb and Sr concentrations in silicate minerals and rocks by flameless (heated-graphite furnace) atomic-absorption spectrometry. Matrix effects, notably perchlorate interference with Rb, Ca with Sr and ionization of Rb0 to Rb+, are completely avoided by the addition of sulphuric acid to standards and unknowns of both Rb and Sr and by adding KC1 to the Rb solutions before analysis. Absolute amounts down to 1.10-10g Sr and 5.10-11g Rb, can be measured with a reproducibility within +- 2% (for duplicates). The results obtained on standard silicate rocks are in good agreement with the values recommended by the U.S. Geological Survey (Flanagan, 1973). The method is suitable for Rb and Sr analysis of almost any silicate rock or mineral. It should find important application in Rb-Sr geochronology, where it can be used both for total Rb determination and for calibration of the Sr separation columns