Sorption of magnesium–picolinate complexes on a macroporous styrene–divinylbenzene copolymer containing immobilized 8-hydroxyquinoline and on the copolymer itself

Abstract

The sorbent XAD-OXINE was prepared by covalently binding 8-hydroxyquinoline onto the surface of the macroporous copolymer Amberlite XAD-2 to give about 20% surface coverage. Sorption, onto both XAD-2 and XAD-OXINE, of the magnesium-containing species that are present in solutions of magnesium ion and picolinic acid was studied by the column equilibration/atomic absorption technique at solution pH of 6.00 and 7.50 and ionic strength of 0.25. By using solutions containing various amounts of added magnesium and picolinic acid, in which the ratio of the two metal–ligand complex species, MgP+/MgP2, varied greatly (P− is the ligand picolinate), it was shown that neither the species Mg2+ nor the species MgP+ sorb to an appreciable extent onto the parent polymer XAD-2, but the neutral species MgP2 sorbs strongly and exhibits a linear isotherm. Then, by measuring the sorption isotherm of the species Mg2+ on XAD-OXINE in the absence of picolinic acid, by measuring the overall sorption of magnesium-containing species on XAD-OXINE in the presence of picolinic acid, and by assuming that the sorption of the species MgP2 onto XAD-OXINE was about the same as it was on XAD-2, it was possible to show that the species MgP+ sorbs strongly onto XAD-OXINE, and exhibits linear sorption isotherms. Thus, XAD-OXINE sorbs all three species Mg2+, MgP+, and MgP2. Keywords: Amberlite XAD-2, immobilized oxine, magnesium ion.