DETERMINATION OF FREE MAGNESIUM-ION CONCENTRATION IN AQUEOUS-SOLUTION USING 8-HYDROXYQUINOLINE IMMOBILIZED ON A NONPOLAR ADSORBENT

The sorbent XAD-oxine was prepared by covalently attaching the ligand 8-hydroxyquinoline to the hydrophobic macroporous, styrene-divinylbenzene copolymer Amberlite XAD-2. The sorbent was used in the column equilibration/atomic absorption method to determine the concentration of the species Mg2+ in the presence of kinetically labile complexes of magnesium. With EDTA and oxalate ligands, which form hydrophilic complexes, the method is selective for Mg2+ (i.e., the complexes do not sorb). With picolinate ligand, which forms more hydrophobic complexes, the magnesium-picolinate complexes sorb along with Mg2+. Therefore, ligands bound to hydrophobic substrates are considered less useful for measuring free metal ion concentrations than are those bound to hydrophilic substrates.