Electrochemical behavior of riboflavin immobilized on different matrices

The electrochemical behavior of riboflavin (RF) adsorbed on different surfaces of inorganic matrices was investigated using modified carbon paste electrodes. Silica gel and sol-gel silica modified with niobium oxide were denominated as (SN) and (SNsol-gel), respectively. These materials were treated with a H3PO4 solution to graft phosphate groups and were denominated as (SNP) and (SNPsol-gel). The immobilization of RF on these materials indicated a high electrode stability, avoiding leaching out of the electroactive species (RF) from the electrode surface. The values of formal potential (E-0') of the adsorbed RF on the different matrices changed from -283 (SNRF) up to -165 mV (SNPRFsol-gel) vs SCE in 0.1 mol l(-1) NaNO3 solution at pH 7.0. Compared to the E-0' for soluble RF, the values are shifted 183 up to 305 mV toward more positive potentials. The stability of the electrodes and the formal potential of the adsorbed RF on different matrices remained constant upon changing the solution pH from 3 to 8. Some kinetic parameters were estimated; indicating that all systems studied presented a good electron transfer rate. (C) 2003 Elsevier Inc. All rights reserved.