Multistep pH-peak-focusing countercurrent chromatography with a polyethylene glycol-Na2SO4 aqueous two phase system for separation and enrichment of rare earth elements.

Multistep pH-peak-focusing countercurrent chromatography was developed for separation and enrichment of rare earth metal ions using a polyethylene glycol-Na(2)SO(4) aqueous two phase system (ATPS) and pH stepwise gradient elution. Metal ions in a sample solution are chromatographically extracted in a basic stationary phase (polymer-rich phase of the ATPS) containing a complexation ligand such as acetylacetone at the top of the countercurrent chromatography (CCC) column. After the sample solution is introduced, the mobile phases of which the pH values have been adjusted with buffer reagents are delivered into the column by stepwise gradient elution in order of decreasing pH.