Effects of amine-pretreatment of silica gel on the TLC behaviour of rare earths

The TLC behaviour of all the rare earths except Pm has been examined on silica gel pretreated with aqueous solutions of four different amines iminodi-2-ethanol, tris(hydroxymethyl)aminomethane, nitrilotri-2-ethanol, and 1,3-diazole] in a 1 mol/l NH₄Cl solution. The Rf value of each metal decreased with increasing pKa value of the amines and also with increasing concentration and pH of the amine solution used for the pretreatment. The technique is simple and reproducible, and makes it possible to arbitrarily regulate the adsorbability of silica gel. Thus, the use of the amine-treated silica gels serves to develop many solvent systems for the separation of the rare earths.