Page 150 - Analytical Electrochemistry 2d Ed - Jospeh Wang

4-5 WORKING ELECTRODES 135

smaller dimensions are preferred. Chronoamperometric experiments, such as the one
shown in Figure 4-29, can be used to estimate the transition between these time
regimes, and the fraction of the conductive surface in accordance with the theoretical
model (93). In addition to their large collective current, enhanced signal-to-noise
ratios, and ¯ow-rate independence (in the ¯ow detection), composite electrodes hold
great promise for incorporating appropriate modi®ers within the bulk of the
composite matrix.
Closely spaced band electrodes (pairs or triples), with each electrode within the
diffusion layer of the other, can be used for studying reactions in a manner analogous
to ring-disk generation±collection and redox recycling experiments (94,95). Unlike
with rotating ring-disk electrodes, the product of the reaction at the collector
electrode can diffuse back across the narrow gap to the generator electrode to
give higher collection ef®ciencies (and hence sensitivity). A typical generation±
collection experiment at such an array is illustrated in Figure 4-30. The covering of
such closely spaced microelectrodes with conducting polymers can form the basis
for novel microelectronic (transistor-like) sensing devices (see Chapter 6). The
properties and applications of interdigitated arrays of microband electrodes have
been reviewed (96).

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