Microelectrochemical measurements expanding droplets

The ET reaction between aqueous Fe(CN)g and the neutral species, TCNQ, has been investigated extensively with SECM, in parallel with microelectrochemical measurements at expanding droplets (MEMED) [84], which are discussed in Chapter 13. In the SECM studies, a Pt UME in the aqueous phase generated Fe(CN)g by reduction of Fe(CN)g. TCNQ was selected as the organic electron acceptor, because the half-wave potential for TCNQ ion transfer from DCE to water is 0.2 V more positive than that for ET from Fe(CN)g to TCNQ [85]. This meant that the measured kinetics were not compromised by TCNQ transfer from DCE to the aqueous phase within the potential window of these experiments. 

A recent development, termed by the inventors microelectrochemical measurements at expanding droplets (MEMED) [29], is a technique based on forming small droplets of a phase containing a reactant in a second immiscible liquid phase (Fig. 5.24). An ultramicroelectrode (UME, see Section 5.3.2.8 and Chapter 6) measures an electrochemical response as the droplet expands towards it, from which a concentration profile can be derived and, hence, the kinetics of related processes. Because the surface is continuously refreshed, it avoids... 

Liquid/liquid interfaces have been discussed in Chapter 8. A related approach involves using an expanding droplet of a nonaqueous solvent positioned above a stationary microelectrode (microelectrochemical measurements at expanding droplets, or MEMED) (18,19). More recent work has probed bilayer lipid membranes (BLMs). A BLM is produced by placing a small amount of a lipid, such as lecithin, on a small orifice ( 600 /xin... 

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