Application of an argon-nitrogen inductively-coupled radiofrequency plasma (ICP) to the analysis of geological and related materials for their rare earth contents

Abstract

An account is given of the development of a procedure for the determination of the rare earth (RE) elements in a large variety of geological materials employing a medium power argon-nitrogen ICP coupled with a 3.4m Ebert spectrograph. The effects of the carrier and intermediate gas flow rates, height of observation and power on RE spectral line intensities have been studied. The line-to-background ratio of the RE analyte was found to increase with observation height and passed through a maximum at 12–14 mm above the top of the work coil. The method eventually developed allows the direct determination of the lanthanides and yttrium at the 50–200 μg g −1 levels using a single solution prepared by fusing 0.2–1 g samples with Na 2O 2 or LiBO 2 and dissolving the melt in 4–10% (v/v) HNO 3, or by treating the samples with HF-HClO 4-HNO 3 mixtures. For lower contents of the RE elements, they can be separated from matrix concomitants by ion exchange employing AG50W-X8 resin. A large variety of silicate and phosphate reference materials was analysed using scandium as the internal standard. The relative standard deviations vary from about 1.5–15%. No matrix effects were observed despite the large compositional variation of the samples analysed.