Ion chromatographic separation of rare earth elements (REE) was studied using isocratic elution from Dionex Ion Pac CS3+CG3 column with sulfonic acid functional groups and buffered solutions of tartaric (HTart), citric (HCit) and nitrilotriacetic (NTA) acids, respectively, at temperatures 25-70 degrees C. Apparent atomic numbers (App. At. No.) of Y and Sc with respect to lanthanide series were established and found to vary widely both with the ion exchange system and with temperature. A novel method for the separation of Dy-Y-Tb triad was proposed using 68mmol L(-1) HCit, pH 3.18 at T = 60 degrees C and its capability to be used for analytical determinations was demonstrated. The significance of contribution of longitudinal diffusion in the stationary phase to total zone spreading in the systems studied was emphasized.