Determination of scandium, yttrium and eight rare earth elements in silicate rocks and six new geological reference materials by simultaneous multi-element electrothermal atomic absorption spectrometry with Zeeman-effect background correction

Abstract

A method was developed for the simultaneous determination of a group of four rare earth elements (REE) in one firing using a multi-element graphite furnace atomic absorption spectrometer. The instrument can be programmed for automatic determination of an additional four REE elements in a second group by two firings. The sensitivities with a pyrolytic graphite coated graphite tube furnace are sufficiently high to permit the determination of low-µg g^–1 amounts of Y, Nd and Sm and ng g^–1 amounts of Sc, Eu, Dy, Ho, Er, Tm and Yb in silicate rocks from as little as 0.1 g or less of sample concentrate in a 1 ml final volume. After dissolution of the sample in acids, Sc, Y and the REE were preconcentrated by cation-exchange chromatography or coprecipitation with calcium oxalate and hydrated iron oxide carriers and determined by the proposed method. The interferences due to the presence of trace amounts of common metals in the ion-exchange concentrates were corrected for with Zeeman-effect background correction. Inter-method correlation plots for electrothermal atomic absorption spectrometry (ETAAS)versus inductively-coupled plasma mass spectrometry (ICP-MS) values and for oxalate versus ion-exchange recovery results for REE showed good agreement. Satisfactory results were obtained for Sc, Y and eight REE in three international reference rocks, MRG-1, SY-2 and NIM-G. The method was applied to the determination of these elements in six new candidate reference rocks of the Canadian Certified Reference Materials Project. In most instances the ETAAS results compared satisfactorily with those obtained independently by inductively coupled plasma atomic emission spectrometry (ICP-AES) and ICP-MS.