POSSIBLE ANALYTICAL APPLICATION OF LAPONITE CLAY-MODIFIED ELECTRODES

Laponite clay modified electrodes (LCME) have been used to detect trace amounts of neutral or cationic organometallic substances, including ferrocene (Fc) and cobaltocenium (Cc(+)), two molecules covalently attached to cobaltocenium, and a molecule labelled by ferrocene (N-amphetaminecarbonylferrocene) as an electroactive organic test species. During an ion-exchange preconcentration step, the cationic species (cobaltocenium derivatives) are collected in the laponite film from their dilute solutions under open-circuit conditions whereas the procationic species (ferrocene derivatives) are collected in their cationic form by applying a positive potential. Quantification of the surface bound cations is then carried out by applying a negative scan using voltammetry or square wave voltammetry. In the case of the two molecules labelled by Cc(+), a detection limit of 4 x 10(-8) mol l(-1) and a linear calibration range from 1 X 10(-7) to 2 X 10(-5) mol l(-1) are obtained reproducibly by using a new LCME for each measurement. Conversely with small redox molecules such as ferrocene and cobaltocenium, the same LCME can be used repeatedly because applying a negative potential leads to the exclusion of the resulting neutral molecule which can be rinsed efficiently from the film.