Carbon Paste Electrode Views

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Adsorptive stripping voltammetry (AdSV), involving the interfacial accumulation of surface-active complexes of uraniumon a hangingmercury drop electrode, has been found useful for the determination of subnanomolar levels of uranium in various natural water samples (18-22). Other approaches have also been reported recently for the determination of U[O.sub.2.sup.2+] by AdSV, for example, the bismuth-coated mercury electrode (23), the bismuth film electrode (24), the lead film electrode (25) on the basis of its cupferron complexation, the glassy carbon electrode (26) on the basis of 4-(2-hydroxyethyl)-1-piperazine ethane sulfonic acid complexations, and the hanging mercury drop electrode (27) on the basis of aluminon complexations. The carbon paste electrode modified with carbamoylphosphonic acid (28) has also been reported for the AdSV of uranium. All of these methods involve a long preconcentration time and a narrow working linear range.

In voltammetry, modification of the working electrode is of immense importance because it enhances sensitivity toward a specific analyte. In recent years, chemically modified electrodes (CMEs) have played an important role in various analyses because of their advantages, such as low background current, easy preparation, and regeneration (29). Modified carbon paste electrodes containing various modifiers, such as zeolite for the determination of copper, surfactant for the determination of chromium, clay for the determination of drugs and pollutants, and macrocyclic compounds for the determination of vitamin C and lead, have been described (30-34).

A carbon-paste electrode (CPE) is made from a mixture of conducting graphite powder and a pasting liquid.[1] These electrodes are simple to make and offer an easily renewable surface for electron exchange. Carbon paste electrodes belong to a special group of heterogeneous carbon electrodes. These electrodes are widely used mainly for voltammetric measurements; however, carbon paste-based sensors are also applicable in coulometry (both amperometry and potentiometry).

In general, CPEs are popular because carbon pastes are easily obtainable at minimal costs and are especially suitable for preparing an electrode material modified with admixtures of other compounds thus giving the electrode certain pre-determined properties. Electrodes made in this way are highly selective sensors for both inorganic and organic electrochemistry.