Determination of transition metals by high performance liquid chromatography.

A simple chromatographic analysis system was developed based on dynamic ion pairing using long chain anionic modifiers with a silica reversed phase based column. The aim was to carry out simultaneous multielement quantitative as well as qualitative analysis of samples containing mixtures of transition metal ions. Among the problems encountered and solved were: metalcontamination of the eluent,finding a suitable pump for the system, minimising the noise and reducing the elution times. Detection of the separated metal ions was enabled by post-column derivatisation prior to introduction to thespectrophotometric detector. This introduced many problems as the eluent and post-column reagent stream must beproperly mixed and reacted to ensure successful detection. The design and orientation of the device used for this purpose is also critical and this was studied in detail. The role played by the various constituents of the eluent in the chromatographic separation was investigated thoroughly to enable modifications to it to be made so that thechromatographic analysis could be optimised. It wasdiscovered that retention times were greatly affected byvariations in concentration and type of anionic modifier, concentration and composition of the complexing agent in the eluent and variations in the pH of the eluent. This enabled better understanding of the retention mechanism and a retention mechanism model for a dynamically coated column was proposed. Separation of copper, lead, zinc, nickel, cobalt, cadmiumand manganese in seven minutes was achieved using a mobile phase containing sodium hexanesulphate as anionic modifier, hydrogen tartrate as complexing agent at pH 3.1, with 4-(2-pyridylazo)resorcinol (PAR) detection monitored at 510 nm.Under these conditions, limits of detection in the range of 2 - 20 p.p.b. were achieved for 20 muL injections.