The simultaneous analysis of metal-EDTA complexes and inorganic anions by suppressed ion chromatography

Abstract

This work extends a multiple species retention model to the retention behavior of EDTA complexes of Cu, Zn, and Pb together with inorganic anions (Cl-, NO2-, Br-, NO3-). The study incorporates an ion-exchange system with a carbonate eluent at various concentrations and pH levels. A theoretical framework is developed when complexation effects are present in the sample. The unknown values for the ion-exchange equilibrium constants, which are required in the model, are determined by repetitive minimization using a nonlinear regression algorithm and are then used to compare observed and predicted retention data. The results are in good agreement for all metal-EDTA complexes and simple anions studied. Practical application of the retention model to the determination of the elution behavior of the species proves successful and demonstrates the reliability of the model. Furthermore, the new method for simultaneous analysis is successfully applied in a quantitative manner using a mixed carbonate eluent and EDTA as a complexing agent in the sample. The detection limit with this method is about 1 order of magnitude better than in a nonsuppressed system that uses EDTA as the eluent.