RETENTION MODEL FOR THE SEPARATION OF ANIONIC METAL - EDTA COMPLEXES IN ION CHROMATOGRAPHY

A retention model is derived for complex anions eluted from an anion-e xchange column with multiple ionic eluents containing hydrogencarbonat e, carbonate, and hydroxyl species and the sample solution, containing transition metals, anions and complexing ligand. The theory is based on the generalized ion-exchange equilibrium, protonation and complex-f ormation equilibria. The unknown parameters of chromatographic ion-exc hange equilibrium constants for sample and eluent species are determin ed from the experimental retention data by iterative minimization, usi ng a non-linear regression algorithm. The model was utilized to predic t the retention behaviour of CdEDTA2-, CoEDTA2-, MnEDTA2- and NiEDTA2- ions. The capacity factors of complex ions were determined for wide r anges of pH values and eluent concentrations. Good agreement was obtai ned between the observed and predicted retentions.