The effect of mobile phase modifiers on the simultaneous LC elution of a gadolinium complex and free ligand.

A liquid chromatographic method was developed for simultaneous separation of a gadolinium complex and corresponding ligand using a reversed-phase anion-exchange column. The effect of mobile phase pH, EDTA and chloride ion concentration, added to the mobile phase as counter-ions, on the elution of a metal complex and ligand were investigated. Decreasing the mobile phase pH from 9.4 to 7.4 decreased the retention time of the free ligand but had little effect on changing the retention time of the complex. Increasing the EDTA concentration of the mobile phase from 0 to 0.5 mM decreased the retention of the free ligand but had little effect on changing the retention time of the metal complex. Both the retention times of the metal complex and free ligand decreased as the chloride ion concentration was increased from 0 to 0.2 M.