Sulphonated azoligand for metal ion determination in ion interaction chromatography

An azosulphonated ligand, namely cyclo-tris-7-(1-azo-8-hydroxynaphthalene-3 ,6-disulphonic acid), Calcion, which is generally used as a metallochromic indicator for metal ion titrations, has been studied in order to verify its suitability as a new ligand for metal ion separation in a liquid chromatog raphy technique based on the ion interaction mechanism. Before chromatograp hic method development, studies on the complexation capabilities of Calcion with Ni2+, CU2+, Fe3+ and Al3+ metal ions were performed, determining the stability constants of the complexes between such metal ions and the ligand . The procedure is based on ion-exchange chromatography and involves the re tention of the negatively charged complexes on an anion-exchange resin and the determination of free and complexed metal by inductively coupled plasma atomic emission spectrometry. Chromatographic separation of Ni2+-Cu2+ and Fe3+-Al3+ was reached, using a silica-based octyl stationary phase, through pre-complexation with Calcion, and UV-visible detection of the resulting a nionic complexes. The effect of the main mobile phase parameters (concentra tion of the ion interaction reagent tetrabutylammonium chloride, organic mo difier methanol and pH) on k' of analytes was studied and optimization of t he metal ion separation was achieved. In order to obtain the simultaneous d etermination of metal ions, the concentration of CH3OH and pH gradient elut ion were also considered. The method developed has been applied to tap wate r analysis. (C) 1999 Elsevier Science B.V. All rights reserved.