APPLICATION OF ULTRASONIC NEBULIZATION FOR THE DETERMINATION OF RARE-EARTH ELEMENTS IN PHOSPHATES AND RELATED SEDIMENTARY-ROCKS USING INDUCTIVELY-COUPLED PLASMA-ATOMIC EMISSION-SPECTROMETRY WITH COMMENTS ON DISSOLUTION PROCEDURES

Low concentrations of all the rare earth elements (REE) can be determined in geological materials using ultrasonic nebulization and inductively coupled plasma atomic emission spectrometry (USN-ICP-AES). Using a matrix matched calibration procedure to compensate for an acid effect on REE spectral line intensities, caused by high concentrations of nitric acid, in-house and international geological reference materials were analysed. Provided that a total decomposition method was used, the data obtained compared well with those from the literature. Yttrium, La, Ce, Eu and Yb were also determined directly because of their superior limits of detection, relatively high abundance in geological samples, and freedom from spectral line interference as a result of the high resolution of the spectrometers. Various sample decomposition procedures were evaluated for the determination of REE in sedimentary rocks. The solutions obtained by decomposition with various acids (HCl, HNO3, HClO4 and HF) and sodium peroxide sintering and leaching were preconcentrated using a DOWEX 50 W x 8 ion-exchange column. Significant differences in Y, La and Ce concentrations occurred when the sediment samples were submitted to different methods of sample decomposition. Indeed, REE distributions between acid soluble and total samples differed significantly, having different Y:Ce, Y:La and La:Ce ratios.