The present study describes the optimization of an analytical procedure for the determination of 14 rare earth elements (REE) in geological samples. The proposed method involves sodium peroxide (Na2O2) sintering of sample material after addition of a Tm spike, the cation exchange separation of the REE from matrix elements, and the determination of individual REE by means of HPIC-ICP-MS coupling system. The Dowex 50W-X8 cation exchange resin is used for the study of the REE group separation and the elimination of matrix elements. The REE are separated from the bulk matrix in order to avoid the spectral interference from polyatomic ions (in particular BaO+) in the determination by ICP-MS and to minimize signal suppression. The most efficient separation consisted in a nitric acid media gradient elution, where the matrix elements are removed using 2 mol l-1 HNO3 containing a small amount of oxalic acid and the REE are eluted using 6 mol l-1 HNO3. Furthermore, High Performance Ion Chromatography (HPIC), using oxalic acid and diglycolic acid as mobile phase, was investigated for the separation and the quantitative determination of rare earth elements (REE). In this matter, the influence of different gradient elution on the retention and hence the separation efficiency of the individual REE was studied. The separation was carried out using an IonPac CS5A (2 x 250 mm) analytical column. The optimum gradient elution enables the separation and determination of the 14 naturally occurring REE in less than 17 minutes. The validity of the proposed analytical procedure is assessed by analysis of two well characterized Reference Materials, BIR-1 and BRP-1. REE concentration data obtained for these reference materials are generally in good agreement with published and certified values. Satisfactory results were obtained in the analysis of samples (OU-1, OPC-1, OKUM and MUH-1), including materials with low REE abundances. Relative standard deviation (RSD) ranging from 0,2 to less than 9% were obtained after raw data correction using Tm. Smooth REE normalized pattern were obtained for all the reference materials and samples analyzed by the proposed analytical procedure. This work is the basis for further REE concentration studies. In combination with isotope dilution mass spectrometry (ID-MS), the lowest measurement uncertainties of all currently available analytical procedures can be achieved.