A STUDY OF IRREVERSIBLE ELECTRODE PROCESSES UNDER STEADY-STATE FLOWING SOLUTION CONDITIONS WITH A MICROELECTRODE BASED SCANNING ELECTROCHEMICAL DETECTOR

A study of the irreversible oxidation of L-tyrosine and a series of ca techolamines has been undertaken at a microelectrode under both flow a nalysis and reversed-phase liquid chromatography (LC) conditions. Expe rimental parameters (electrode radius 5 mu m, flow rate 1.0 ml min(-1) , scan rate in the range 1-2 V s(-1)) were chosen so that the complete current-voltage curve could be obtained via the use of fast potential scan rates, but still under steady-state or near steady-state conditi ons. This feature means that unlike peak currents associated with tran sient techniques, the limiting current achieves the ideal analytical c haracteristic of being relatively insensitive to kinetic terms. The in dividual voltammograms obtained from flow analysis or LC experiments e xhibit the characteristics of the non-reversible response expected for L-tyrosine and the catecholamines with the expected changes to both t he half-wave potential and the shape of the voltammograms being observ ed as the eluant pH was adjusted from 2.0 to 7.0. Interestingly, it is shown that the irreversibly oxidised catecholamines, l-adrenaline and 6-hydroxy-L-dopa which are poorly resolved chromatographically may be resolved in the electrochemical domain under fast scan rate, but near steady-state conditions achievable at microelectrodes in flowing solu tion.