Untersuchungen zur Anwendbarkeit der online-Kopplung IC-ICP-AES/-MS zur Ermittlung thermodynamischer und kinetischer Daten des Zerfalls von Metall-Ligand-Komplexen

This work investigates how far the online coupling IC-ICP-(OES, MS) can be applied for the determination of 1-1-complexes of trivalent metal ions. The chelating agents F–, Ox2–, NTA3– and EDTA4–, differing in their denticity, and the M3+-ions of Cr, Al, Fe, Ga, In and lanthanoids were used. Only the EDTA-complexes of the lanthanoids, which show an extremely high aqua-ligand-exchange-rate, are sufficiently inert to be detected after the IC seperation. For Fe, Ga und In with slower ligand-exchange-rates, the NTA-complexes are also determinable. Chromium and aluminum show such a low exchange rate that all complexes can be chromatographically characterized. It becomes apparent that the stability of the complex as well as the ligand-exchange-rate of the metal ion and the denticity of the chelating agents are important. In order to predict the inertness/lability of a 1-1-complex, an equation was derived using the complex stability constant KK and the aqualigand- exchange-rate kH2O of the metal ion. The not detected complexes decompose so fast, that only the M3+-ion is observed. [GaOx]+ represents an exception. Its decomposition is on a similar timescale as the chromatographic separation. Therefore the obtained chromatogram is an overlay of the separation process and the decomposition. Those chromatograms were used to gain kinetic and thermodynamic data by simulating the decomposition process. The data is in good agreement with theoretically calculated species distributions. The decomposition rate is dependend of the flowrate, the metal to ligand ratio and the exchange capacity of the column. A simulated chromatogram for the case of inert complexes can also be derived from measurement and simualtion. This simulation shows a possibility to relocate the limitations of the coupling technique for less inert complexes by subsequent back calculation.