Study of trace element determination by ion chromatography with chemiluminescence detection
This thesis details the development of several highly sensitive liquid chromatography post-column reaction detectors based on chemiluminescence (CL) for the ion chromatography (IC) determination of metal species in a range of sample types. The first chapter describes a non-selective multi-element CL detector based on metal-ligand reactions involving cobalt (11) and EDTA. A complexation reaction was designed so that eluting metal species displaced or produced equivalent amount of free cobalt ions which then catalysed the CL oxidation of luminol. The effect of pH, temperature and reaction time was investigated and optimised. It was found that the detector responded to a wide range of metals capable of forming EDTA complexes, even the relatively weak complexes such as those of magnesium and calcium. However, problems with the high back-ground signal limited sensitivity to the low ug 1-1 range. The next chapter deals with the development of a highly sensitive IC method for the determination of two environmentally important chromium species, namely chromium (III) and chromium (VI). A rapid ion exchange separation was achieved using a single column with potassium chloride eluent. This was incorporated into a luminol-H2O2 CL detector, specific for chromium (III). On-line reduction was required in order to visualise the chromium (VI). Detection limits for chromium (III) and chromium (VI) wer 0.05 ug 1-1 and 0.1 /ug 1-1 respectively. Good results were obtained with a freshwater standard reference material and lyophilised samples as part of the author’s participation in a Bureau Communtaire de reference (BCR) certification exercise. Sample pH was found to have considerable influence on the stability of the species and this is described and discussed. The third and largest part of the study involved the development of an IC system for the ultra-trace determination of silver in pressurised water reactor (PWR) primary coolant, of particular concern to the nuclear power industry. A novel ion exchange separation was achieved on hydrophillic resins giving excellent separation from divalent cations. A CL post column reaction detector was designed based on the oxidation of luminol with persulphate. Good quantitative performance was accomplished based on the analysis of a certified reference material and simulated PWR coolant with detection limit for silver of 0.05 /ug 1-1. Finally, a CL detection system was developed for determining gold (III) after IC separation. A novel aspect was that no added co-oxidant was required for the luminol reaction. Results for a standard reference metal alloy sample was in good agreement with the certified value. Again, high sensitivity was achieved with a detection limit of 0.25 ug 1-1.