Modelling electrochemical processes at the three phase junction between electrode–aqueous electrolyte–oil droplet presents a considerable challenge due to the complexity of simultaneous electron transfer between electrode and droplet, ion uptake or expulsion between droplet and aqueous phase, the interaction of redox centers at high concentration, and transport processes accompanying the electrochemical process. For the case of oxidation of para‐tetrahexylphenylenediamine (THPD) microdroplet deposits on basal plane pyrolytic graphite electrodes or random arrrays of microelectrodes (RAM) three models may be envisaged which proceed via A) exchange of ions between droplet and aqueous electrolyte with the electrochemical process commencing at the electrode–oil interface, B) rapid electron transport over the oil–aqueous electrolyte interface and the electrochemical process commencing from the oil–aqueous electrolyte interface inwards, and C) slow electron transport across the oil–aqueous electrolyte interface and the electrochemical process commencing solely from the triple interface. Numerical simulation procedures for these three models, which allow for interaction of redox centers via a regular solution theory approach, are compared with experimental data. A positive interaction parameter, Z=1.4, consistent with a dominant ionic liquid–ionic liquid and neutral oil–neutral oil type interaction is determined from experimental data recorded at sufficiently slow scan rates. The overall mechanism, which governs the voltammetric characteristics at higher scan rates, is shown to be apparently consistent with the triple interface model C). However, the rate of diffusional transport determined by comparison of experimental with simulation data is orders of magnitudes too high. Additional convection processes, possibly of the Marangoni type, appear to be responsible for the fast rate observed for the redox process. The significance of the models presented in the context of microdroplet deposits for other related electrochemical systems is discussed.

Electroanalytical sulfide detection via oxidation of N 1 -[4-(dihexylamino)phenyl]-N 1 ,N 4 ,N 4 -trihexyl-1,4-phenylene diamine (DPTPD) deposited in form of microdroplets onto basal plane pyrolytic graphite electrodes immersed in aqueous 0.1 M NaClO 4 containing sulfide is proposed to be associated with two consecutive reversible one electron processes accompanied by ClO 4 2 uptake, sulfide accumulation, and formation of a methylene blue derivative.

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The quantitative detection of lead in petrol is shown to be possible by anodic stripping voltammetry in aqueous media under conditions of insonation‐induced emulsification. An immersion horn probe is introduced into a thermostatted conventional three‐electrode cell opposite a mercury plated platinum disk working electrode. Under ultrasonic emulsification of the sample, lead is preconcentrated as an amalgam on the Hg/Pt electrode surface via reduction at –1.0 V (vs. SCE). The large mass transport associated with power ultrasound makes this step highly efficient. Subsequently the lead is quantified by applying an anodic linear sweep of the potential from –1.0 V to –0.15 V (vs. SCE) so as to oxidize the Pb(0) to Pb(II). The area under the stripping peak gives a measure of the lead formed during the initial step. By use of standard microaddition of lead to the solution the system can be calibrated to give the total amount of lead present in the petrol sample. Experiments using samples of 4 star leaded petrol gave a total lead content of 380±40 mgL–1. This value was in quantitative agreement with that obtained by an independent laboratory using atomic absorption spectroscopy (AAS). In addition to the high mass transport and emulsification insonation offers the crucial benefits of first surface activation and cleaning, helping to prevent electrode fouling by the organic components of petrol and second the complete extraction of lead from the water‐insoluble target phase.

The quantitative detection of lead in petrol is shown to be possible by anodic stripping voltammetry in aqueous media under conditions of insonation-induced emulsi®cation. An immersion horn probe is introduced into a thermostatted conventional three-electrode cell opposite a mercury plated platinum disk working electrode. Under ultrasonic emulsi®cation of the sample, lead is preconcentrated as an amalgam on the Hg/Pt electrode surface via reduction at À1.0 V (vs. SCE). The large mass transport associated with power ultrasound makes this step highly ef®cient. Subsequently the lead is quanti®ed by applying an anodic linear sweep of the potential from À1.0 V to À0.15 V (vs. SCE) so as to oxidize the Pb(0) to Pb(II). The area under the stripping peak gives a measure of the lead formed during the initial step. By use of standard microaddition of lead to the solution the system can be calibrated to give the total amount of lead present in the petrol sample. Experiments using samples of 4 star leaded petrol gave a total lead content of 380 + 40 mgL 71. This value was in quantitative agreement with that obtained by an independent laboratory using atomic absorption spectroscopy (AAS). In addition to the high mass transport and emulsi®cation insonation offers the crucial bene®ts of ®rst surface activation and cleaning, helping to prevent electrode fouling by the organic components of petrol and second the complete extraction of lead from the water-insoluble target phase.