Fructose electrochemical oxidation

The presence of glucose, fructose, galactose, arabinose and citric, malic and tartaric acid did not produce interference on the quantification of gluconic acid. Only ascorbic acid yielded an amperometric response under the working conditions, due to the electrochemical oxidation of this compound at the applied potential. Nevertheless, the content of gluconic acid in honey samples is remarkably higher than the possible content of ascorbic acid. Consequently, no significant interference should be expected in the analysis of the proposed real samples. 

Q.29.9 You are asked to experimentally evaluate a new multi-stage microfluidic fuel cell in which a crude solution of cane sugar (sucrose) is first hydrolyzed by and acidic stage and then glucose and fructose diffuse into a second stage where electrochemical oxidation produces power. Propose a microscopic method to measure the rate of sucrose hydrolysis in the first stage. 

The electrocatal3rtic oxidation of sucrose has only been the subject of a few investigations. The chemical oxidation of sucrose was firstly mentioned in the works of Bresler (1) and Usch (2). Karabinos (3) analysed the oxidation products of fructose, glucose, glucono-y-lactone and sucrose in 0.5 M NaHCOa. The author concluded that the main reaction products were CO2 and H2O. Bockris et al. (4), investigated the electrochemical oxidation of different carbohydrates at platinum electrodes for their possible use in fuel cells. They noticed that the electroactivity was better in alkaline medium than in acidic medium, and that the reactivity of the molecule decreased with increasing molecular weights. 

Fabre and co-workers have investigated the electrochemical sensing properties of boronic acid substituted bipyridine iron(II) complex 72 [140]. On addition of 10 mM D-fructose the oxidation peak was shifted by 50 mV towards more positive values. 

This paper will discuss the characteristics of this detector with respect to the above applications. Stable oxides are formed at potentials in excess of 200 mV vs. SUE. A chrono-coulorometric experiment has been used to follow the formation of the oxide layer, loss of silver due to the formation of soluble hydroxy species, and reduction of the oxide to metallic silver. With respect to carbohydrate oxidation, several factors are important including hydroxide concentration, temperature and potential. The long term stability has been considered and is analyte dependent. Many carbohydrates (i.e. glucose, fructose, galactose) do not cause any observable dimunition while some analytes (cytidine, glycerol) cause a noticable loss of sensitivity. In all cases the sensitivity can be restored by electrochemical treatment in which the oxide is reduced and regenerated. 

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