Analysis of geological materials by inductively coupled plasma mass spectrometry with sample introduction by electrothermal vaporisation. Part 1. Determination of molybdenum and tungsten

Abstract

The determination of molybdenum and tungsten at low levels in geological materials by isotope dilution inductively coupled plasma mass spectrometry with sample introduction by electrothermal vaporisation is reported. This technique eliminates the need for the laborious, time-consuming separation steps associated with sample introduction by conventional nebulisation which not only impede productivity but also introduce analyte contamination. Analysis by isotope dilution is shown to be necessary in order to achieve precision values of less than 5% RSD (relative standard deviation) in the measurement step. Memory effects are evident in the determination of W due to carbide formation during ashing, in spite of the presence of Freon gas during vaporisation. Determination limits of 0.03 µg g^–1 for Mo and 0.06 µg g^–1 for W are obtained. Results for standard reference materials analysed by this procedure compare well with literature values.