Group separation of trace rare-earth elements by countercurrent chromatography for their determination in high-purity calcium chloride

A method has been developed for the separation of the entire group of rare-earth elements from high-purity calcium chloride by countercurrent chromatography, and subsequent determination of the elements by ICP– MS. A solution of diphenyl[dibutylcarbamoylmethyl]phosphine oxide in chloroform (0.5 mol L –1 ) has been chosen as reagent for the extraction and preconcentration of trace rare-earth elements from aqueous 5% CaCl2 solution, 3 mol L –1 in HNO3 and 0.1 mol L –1 in HClO4. The analytes are back-extracted into a small volume of water and the aqueous eluate is subjected to ICP–MS measurements. The performance characteristics of the procedure developed have been checked by use of the standard addition technique and a real CaCl2 sample (Merck product) has been analyzed. The results obtained demonstrate the applicability of countercurrent chromatography to the determination of ultratrace elements.