Quality control of rare earth compounds by multielement analysis without chemical separation

Abstract

The determination of impurities in the concentration range down to about 0.1 mg/kg in rare earth compounds without chemical separation or preconcentration has been investigated by application of various multielement methods suitable for routine analysis. Mass spectrometry with a plasma ion source (ICP-MS) is most favourable for the determination of foreign rare earth elements (REE) and provides very low detection limits. It is also suitable for measuring a great number of non-REE. Atomic emission spectrometry in inductively coupled plasma (ICP-AES) is also applicable for many non-REE in the range of low concentrations, in particular for elements of low volatility. Flame atomic absorption spectrometry (FAAS) is preferable for alkali and alkaline earth elements, and voltammetry is well suited for the determination of low concentrations of Cu, Zn and Cd. X-ray fluorescence analysis (XRF) is applicable only in the range of concentrations higher than 1 to 10 mg/kg; it is well suited to give a survey of the presence of foreign elements in concentrations >10 mg/kg. Analytical data for 15 commercial REE compounds are presented and detection limits, selection of suitable analytical lines, advantages and disadvantages of the methods are discussed. The analytical data are compared with the specifications given by the suppliers.