Voltammetry of compounds confined at the hanging mercury drop electrode surface

With the introduction of PC-driven analytical voltammetric instrumentation, the investigation of several useful voltammetric characteristics of electroactive compounds has become much easier, increasing the possibilities of discrimination in analysis. In this work some suggestions are given for the development of strategies to apply in the systematic study of compounds adsorbed on a hanging mercury drop electrode (HMDE). This would establish their behaviour under different experimental conditions for analytical purposes. Although indications of reactant adsorption can be easily detected with normal-pulse voltammetry (NPV), this technique is not as appropriate as square-wave voltammetry (SWV) for analytical purposes. The different effects of SW frequency and amplitude on signals obtained with two quinoxalines were studied. Based on their different electrochemical reversibilities (dimethylquinoxaline (DMQ) reversible, and hydroxyquinoxaline (HOQ) irreversible), these two compounds could be determined simultaneously, in spite of their similar peak potentials. A marked effect of the surfactant tetraphenylphosphonium chloride (TPPC) on the peak potential of the azo colouring matter, azorubine, was also observed. A noticeable increase in peak height occurs at relatively low frequencies, in contrast to the (expected) reduced peak height at high frequencies. Finally the possibility of avoiding the time consuming need to remove oxygen is also considered. At high SW frequencies the interference of oxygen is drastically reduced. DMQ at concentrations as low as 10(-7) M could be determined without oxygen removal by using a SW frequency higher than 100 Hz. A direct application was made to the voltammetric determination of diacetyl in brandy: this involved prior derivatization of the compound with o-phenylenediamine to form DMQ. (C) 1999 Elsevier Science B.V. All rights reserved.