Ion-Pair Chromatography of Metal Complexes of Unithiol in the Presence of Quaternary Phosphonium Salts

The chromatographic behavior of heavy-metal (Pb, Cd, Cu, Hg, and Ni) complexes of unithiol was studied by ion-pair reversed-phase chromatography using new ion-pair reagents: tetrabutylphosphonium and tributylhexadecylphosphonium bromides. The dependence of the retention of metal unithiolates on the nature and concentration of ion-pair reagents, concentrations of an organic solvent and inorganic salts in the mobile phase, and the pH of the mobile phase was studied. It was found that the retention of complexes increases upon increasing the hydrophobicity and concentration of the ion-pair reagent and upon decreasing the concentrations of acetonitrile and inorganic salts (NaClO₄ and NaNO₃). Optimal conditions of the separation of Pb, Cd, Cu, Hg, and Ni unithiolates were selected, and the possibility of their separate determination in a mixture was demonstrated. Concentrations of metals in process water were determined.