Chelation ion chromatography of metal ions using an ODS reversed-phase column and a mobile phase containing methylthymol blue

An ODS reversed-phase column has been used in conjunction with an aqueous mobile phase containing methylthymol blue for the separation and visible detection of metal ions. Retention is due to the formation of a dynamically coated chelating stationary phase and is dependent upon mobile phase pH and ligand concentration. Post-column addition of a buffer solution enables the sensitive visible detection of the metal ions as methylthymol blue complexes at 600 nm. The developed method resulted in improved peak efficiencies and a differing selectivity for certain metal ions, when compared to a pre-coated methylthymol blue chelating column (where the ligand was first used to modify the stationary phase, but was not included as a component of the mobile phase). The isocratic separation and visible detection of 12 metal ions was possible, including a number of the lanthanide series metals