Electroanalysis of aluminium
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The aim of this project was the development of new analytical methods for the measurement of reactive (toxic) aluminium in natural waters (i.e. soil solutions, rivers and lakes). Indirect electrochemical methods were used. These involve the formation of a complex between a metal and a redox-active ligand. The coordination chemistry of two redox-active ligands and aluminium was studied using the techniques of solution thermodynamics. After complex formation with aluminium a shift in the ligand's redox potential is observed. Three ligands were studied voltammetrically. A theoretical model taken from the literature describing the shifts in ligand redox potential was shown to be inappropriate and the shifts were shown to result from the direct electrode reaction of aluminium-coordinated ligand. The effect of variation in complex stoichiometry was also studied. Shifts in ligand redox potentials may be exploited in the development of analytical applications. A flow injection analysis (FIA) system was constructed which allowed the amperometric measurement of aluminium after formation of a complex with the reagent 4-nitrocatechol. Incorporation of a micro-column of oxine-derivatised gel into the manifold eliminated the effect of interfering cations and allowed the selective measurement of reactive aluminium in natural waters. A problem was encountered with electrode fouling in the amperometric system. Two novel FIA strategies were developed to overcome this. Screen printing technology was used to fabricate chemically modified electrodes for the analysis of aluminium. General advantages of the application of this technology were revealed. The particular electrodes made here were suitable for 'in-field' measurement of reactive aluminium in natural samples. The oxine micro-column was used in conjunction with the screen printed electrodes allowing selective measurement of reactive aluminium. This gives flexibility in the linear working range and eliminates the effect of interfering cations.