POSSIBLE ANALYTICAL APPLICATION OF LAPONITE CLAY-MODIFIED ELECTRODES

Laponite clay modified electrodes (LCME) have been used to detect trac e amounts of neutral or cationic organometallic substances, including ferrocene (Fc) and cobaltocenium (Cc(+)), two molecules covalently att ached to cobaltocenium, and a molecule labelled by ferrocene (N-amphet aminecarbonylferrocene) as an electroactive organic test species. Duri ng an ion-exchange preconcentration step, the cationic species (cobalt ocenium derivatives) are collected in the laponite film from their dil ute solutions under open-circuit conditions whereas the procationic sp ecies (ferrocene derivatives) are collected in their cationic form by applying a positive potential. Quantification of the surface bound cat ions 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 cali bration range from 1 X 10(-7) to 2 X 10(-5) mol l(-1) are obtained rep roducibly by using a new LCME for each measurement. Conversely with sm all 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 e fficiently from the film.