Adsorptive stripping voltammetry of derivatized biological molecules and metal complexes
Differential pulse stripping voltammetry preceded by a non-faradaic preconcentration step is a very powerful technique for the direct determination of metal complexes, drug compounds and proteins. Small molecules like the amino acids can play a very important role in the biochemistry of living organisms. Despite their importance, these substances (except for cystine and cysteine) are generally not strongly adsorbed on mercury and /or do not possess any electroactive group in their molecular structure making their determination by direct electroanalytical techniques difficult or even impossible. These difficulties can be overcome by reacting these compounds with derivatising reagents (1). Initially here, derivatisation techniques for the determination of amino acids were studied. Methods are presented for the determination of tyrosine and histidine after coupling with diazotised sulphanilic acid (chapter 3) and for amino acids in general, and glycine in particular, as methyl or phenylthiohydantoin derivatives (chapter 5). Nanomolar levels of histidine were determined by accumulating the amino acid in the presence of an excess of copper(II) using the reduction peak of its copper(II) complex (chapter 4) for detection. The uses of polyamino acids as electrode modifiers were also studied and a method for the determination of copper(II) based on its accumulation at a hanging mercury electrode modified by adsorption of a polyhistidine film (chapter 6) and of hexacyanoferrate(III) after preconcentration on a copper modified polylysine film electrode (chapter 7) are proposed. As an offshoot of the diazo coupling derivatization of tyrosine and histidine, a method for the determination of copper(ll) by reaction with diazo-1 H-tetrazole (DHT) and accumulation of its complex on the HMDE (chapter 8) is presented.