Use of Di(n-butyl) and Di(iso-butyl)dithiophosphoric Acids as Complexing Agents in the TLC Separation of Some d and f Transition Metal Ions

The thin layer chromatographic behavior of U(VI), Th(IV), lanthanides(III), Co(II), Ni(II), and Cu(II) on silica gel H with di(n-butyl) and di(iso-butyl)dithiophosphoric acids as complexing agents in the organic mobile phase has been investigated. The results obtained show that the dithiophosphate anion has a substantial effect on the migration of these metal ions. The presence of electron-donor solvents in the mobile phase increases retention, especially for U(VI), Th(IV), and lanthanides(III). The effect is explained on the basis of greater solubility of the metal chelates of the dithiophosphoric anions in the organic mobile phase, because of a solvation process. Separation was investigated for three groups of metal ions — actinides, lanthanides, and d transition metals. By choice of an appropriate organic mobile phase, separation of the pairs Th(IV)-U(VI), Pr(III)-Sm(III), Sm(III)-Gd(III), and Gd(III)-Er(III) was achieved, as was separation of Co(II), Ni(II), and Cu(II) from each other. A complex separation mechanism based on adsorption-desorption, cation exchange, and extraction is suggested.