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 d ioxide and titanium phosphate were used in carbon paste mixtures to pr epare electrodes. The electrochemical properties of methylene blue wer e investigated by cyclic voltammetry. The electron mediator property o f the dye was optimized using a factorial design, consisting of two le vels and three factors. The factorial analysis was carried out by sear ching for better reversibility of the redox process, i.e. the lowest s eparation between anodic and cathodic peak potentials and a current ra tio near unity. The supporting electrolyte concentration has a small e ffect. The interaction between pH and the silica support was very sign ificant for the peak separation. The solution pH has a significant eff ect on the current ratio. Lower values for peak separation were observ ed at pH 4.0 for STM and pH 7.0 for STPM. However, the current ratio w as closer to unity for pH 4.0 in both cases. (C) 1997 Elsevier Science S.A.