A New Method for the Study of Processes at the Liquid–Liquid Interface Using an Array of Microdroplets on a Au Electrode

Abstract

We report the fabrication of partially blocked gold electrodes, with regularly and hexagonally spaced inert hydrophobic blocks on their surface. The hydrophobic blocks, with diameters of 5 mum, are used to support liquid 5-nonyl-salicylaldoxime (Acorga-P50) droplets on the surface. By voltametrically monitoring the transport-controlled reduction rate of Cu(II) (in pH 5 solution) at the unblocked part of the gold surface it is possible to deduce, via simulation, the parameters controlling the rate of uptake of Cu(II) at the droplet-aqueous solution interface as the droplet "fills up" with Cu(II). Experimentally, it is recorded that the reduction current increases until the droplet is filled completely; after this, there is no further noticeable effect of the droplet coating. A rigorous theoretical analysis of the transients permits the deduction of partition coefficients between the aqueous solution and the organic-droplet phase and of diffusion coefficients within the droplet. The partition coefficient for Cu(II) between water and 5-nonyl-salicylaldoxime was found to be 200 at 25 degrees C and the diffusion coefficient of Cu(II) inside the organic phase was determined to be 5 x 10(-11) cm2 s(-1).

Microelectrode Arrays for Electrochemistry: Approaches to Fabrication

“…This is of particular relevance in real sample analysis where a wide variety of metals may be present in significant concentrations 133. A new concept for the preferential removal of these contamination signals is “diffusional protection” using liquid–liquid interfaces as suggested by Compton and coworkers 133–136. The 5‐nonyl‐salicylaldoxime,133, 134 N,N ‐didodecyl‐ N,N ‐ diethylphenylenediamine (DDPD),135 and dodecane136 microdroplets were found to immobilize onto the relatively hydrophobic silicon oxinitride blocks rather than the arrayed gold surface to form a partially blocked electrode (Figure 7A and B).…”

“…A new concept for the preferential removal of these contamination signals is “diffusional protection” using liquid–liquid interfaces as suggested by Compton and coworkers 133–136. The 5‐nonyl‐salicylaldoxime,133, 134 N,N ‐didodecyl‐ N,N ‐ diethylphenylenediamine (DDPD),135 and dodecane136 microdroplets were found to immobilize onto the relatively hydrophobic silicon oxinitride blocks rather than the arrayed gold surface to form a partially blocked electrode (Figure 7A and B). 136 Using this partially blocked electrode, the interferant is preferentially absorbed by the regularly spaced droplets on the electrode surface before it reaches the electrode surface, whereas the species of interest is allowed to diffuse unhindered towards the bare electrode surface.…”

Probing carboxylate Gibbs transfer energies via liquid|liquid transfer at triple phase boundary electrodes: ion-transfer voltammetry versus COSMO-RS predictions

“…The microdroplet phase forms a triple phase boundary [15] which allows ion transfer processes to be studied for anions [16] as well as for cations [17]. Over the recent years several studies addressed the need for inert redox systems [18], the quantitative data analysis [19], new mechanistic insights [20], novel electrode designs based on array surface patterning [21], wireintersected liquid|liquid interfaces [22], or mesoporous films to host the organic microdroplet phase [23,24], and microfluidic methodologies [25] for monitoring triple phase boundary processes.…”

Ion Transport Across Liquid|Liquid Interfacial Boundaries Monitored at Generator‐Collector Electrodes

“…The redox system employed in the organic phase is often a water-insoluble metal complex such as Co(II)tetra-phenylporphyrin [28], N-butyl-N-decamethylferrocenylamine [29], or n-butylferrocene [30]. When oxidation occurs in the triple phase boundary reaction zone, associated anion transfer processes at the liquid j liquid j solid interface occur in order to maintain electro-neutrality within the organic phase [31][32][33]. The ability of anions to transfer from the aqueous into the organic phase is correlated to the hydrophobicity [34] or more generally to the Gibbs energy of transfer [35][36][37][38].…”