Electroactive speciation studies for metal ion sensing

Abstract

Chemical speciation is an important factor in understanding the role of metals in the environment. Bioavailability of trace metals is influenced by the degree of the labile fraction of the metal that is readily available for interaction with a cell surface of an organism. Voltammetric methods are capable of measuring this labile fraction, and are able to achieve limits of detection in the biologically relevant range. In this study, voltammetric methods were used to examine a set of trffluoromethyl and tolyl pyridylsulfonamide metal-ligand systems during the formation of ML„ complexes at a fixed [M]:[T] ratio and varied pH, to investigate speciation and the potential use of these ligands in surface modified sensors. Formation constants with cobalt(II), nickel(II), copper(II), zmc(II), and the varied pyndykulfonamide moieties, were fully evaluated by potentiometry. A method for simultaneous voltammetric-spectral pH titrations was developed and used to correlate formation constant findings. Voltammetric investigations at a bare glassy carbon electrode had varying electroactive response from the metal-ligand systems. The labile and electroactive systems, e.g. [CuL(^1)(_2)] and [CuL(^4)(_2) were used in formation constant mass-balance refinements derived from voltammetric pH titration data. It is believed that under optimised conditions, formation constant measurement by voltammetry at a glassy carbon electrode is feasible, and this method would be applicable for voltammetric speciation of metal ions in the environment.