Behavior of riboflavin on plain carbon paste and aza macrocycles based chemically modified electrodes

The electrochemical behavior of riboflavin at a carbon paste electrode and electrodes modified with aza crown ethers have been studied using voltammetric techniques. The macrocycles used as modifiers were 1,4,8,11-tetraazacyclooctadecane; 7,16-dibenzyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane; 1,4,7,10-tetraoxa-13-azacyclopentadecane and 1,4,7,10-tetratosyl-1,4,7,10-tetraazacyclooctadecane, out of which 1,4,8,11-tetraazacyclooctadecane showed better response for riboflavin. The interaction of riboflavin with 1,4,8,11-tetraazacyclooctadecane was confirmed by complexation study in 20% DMSO + water (log K 5.58) using differential pulse polarography. The kinetic parameters viz. electron transfer coefficient and rate constant of electron transfer across the modified electrode were found to be 0.708 and 5.5 s−1, respectively. The surface coverage of the 1,4,8,11-tetraazacyclooctadecane modified electrode was calculated to be 5 × 10−10 mol cm−2 by cyclic voltammetry and chronocoulometry. A linear working range of 0.5 ng cm−3 to 70 μg cm−3 with a detection limit of 0.2 ng cm−3 has been obtained using 1,4,8,11-tetraazacyclooctadecane modified electrode by square wave anodic stripping voltammetry. It was possible to determine riboflavin in presence of some organic molecules like thiamine hydrochloride, nicotinamide, pyridoxine hydrochloride, ascorbic acid, para-aminobenzoic acid and l-tryptophan. Also simultaneous and quantitative determinations were achieved for combination of some of these. The electrode could be used for estimation of riboflavin in pharmaceutical and food samples.