MICROCHEMICAL DETERMINATION OF 9 RARE-EARTH ELEMENTS IN SILICATE ROCKS BY CATION-EXCHANGE PRECONCENTRATION ION-INTERACTION CHROMATOGRAPHY

A method of applying ion-interaction chromatography to the determination of the rare earth elements in silicate rocks on a 100 to 200 mg sample basis has been developed. The rare earths are first separated as a group from matrices by cation-exchange chromatography in hydrochloric acid-thiocyanate media and isolated in a small, defined volume (3.00 ml). Using fractions of this, on-column concentration of the rare earths on a C-18 bonded phase silica coated with 1-octanesulfonate and a subsequent concentration gradient elution with.glycolate (0.05 to 0.35 M) at pH 3.5 allows the respective separation of La, Ce, Pr, Nd, and Y (100 mul aliquot used) and of -Er, Tm, Yb, and Lu (2.00 ml aliquot used). Sm, Eu, Gd, Th, and Dy elute together, and Ho is not sufficiently well resolved from these middle rare earth elements. The eluted rare earth elements are detected and quantified by post-column reaction with Arsenazo III photometrically, using a UV-VIS spectrophotometer at a wavelength of 650 nm. The method is. shown to be capable of determining nine of the rare earth elements in a variety of international reference rock samples with good precision and accuracy.