Factorial design optimization of redox properties of methylene blue adsorbed on a modified silica gel surface

Methylene blue immobilized on silica surfaces modified with titanium dioxide and titanium phosphate were used in carbon paste mixtures to prepare electrodes. The electrochemical properties of methylene blue were investigated by cyclic voltammetry. The electron mediator property of the dye was optimized using a factorial design, consisting of two levels and three factors. The factorial analysis was carried out by searching for better reversibility of the redox process, i.e. the lowest separation between anodic and cathodic peak potentials and a current ratio near unity. The supporting electrolyte concentration has a small effect. The interaction between pH and the silica support was very significant for the peak separation. The solution pH has a significant effect on the current ratio. Lower values for peak separation were observed at pH 4.0 for STM and pH 7.0 for STPM. However, the current ratio was closer to unity for pH 4.0 in both cases. (C) 1997 Elsevier Science S.A.