Electrochemical characterization of liquid-liquid micro-interfaces modified with mesoporous silica

In this work, the array of miniaturized interfaces between two immiscible electrolyte solutions was modified with a mesoporous silica material. The electrochemical behavior of such silica deposits was evaluated with six analytes: 3 tetraalkylammonium cations of different sizes, the anionic 4-octylbenzenesulfonate and two poly(aminoamide) dendrimers (generation 0 and 1). Presence of silica deposits affects the ion transfer across the liquid/liquid interface for all six probes with the effect greater for species possessing higher hydrodynamic radius. Analytical parameters (sensitivity and detection limit) were extracted from the calibration curves plotted in the presence and in the absence of silica deposits. Results indicate that silica constitutes an obstacle for interfacial transfer reaction and becomes limiting factor for interfacial mass transfer. Three main conclusions can be drawn from the experimental observations: (i) for tetraalkylammonium species, the larger species (tetrabutylammonium) is more affected by the presence of silica deposits than the smaller species (tetramethylammonium); (ii) due to the negative charge of silica walls, anions are more affected than cations of the same size; (iii) multiply charged cationic dendrimers are less affected by the presence of silica deposits than smaller single charge cations. Apparent diffusion coefficients for all species were also extracted from calibration curves plotted after modification.