Determination of ascorbic acid in copper- ammonia buffer solution with GCE modified with rGO-Fe۲O۳ synthesis by Ferrate (VI)

Chemically modified electrodes have been widely used as sensitive and selective analytical devices for environmental and clinical analyses [۱]. Graphene or redused graphene oxide (rGO) and its nanocomposites were found to be an ideal two-dimensional catalyst because of its unique two-dimensional geometric structure, large surface area, and high mobility of charge carriers [۲]. In this research, glassy carbon electrode (GLE) modified with rGO-Fe۲O۳ was used to determination of ascorbic acid (AA) in the presence of ammonia copper. A simple and fast method was applied for the synthesis of rGO-Fe۲O۳ composite based on the reaction of ferrate (Fe (VI)) with graphene in alkaline medium, which was introduced in our previous work [۳]. This electrode showed a stronger voltammetric response for the measurement of AA in ammonia copper medium. Fig. ۱ shows the effect of copper on GCE without modifier and with GO and rGO-Fe۲O۳ modifier. As it is known, electron transfer is faster on the modified electrode surface.As can be seen, the electrode is stable in the ۵ scans taken. Cyclic voltammetry (CV) shows two cathodic peaks C۱ and C۲ at -۰.۱۲ and -۰.۷۴ V, respectively, and two anodic peaks A۱ and A۲ at -۰.۰۲ and -۰.۲۴ V. Peak current A۱ corresponds to a single-electron process, and the higher peak current A۲ is due to the re-dissolution of deposited copper during the potential scan. PeaksC۱ and A۱ may be due to the reversible reaction of equation:(...)۲NH۳ [۴]. In the second cathode peak, C۲, deposition of copper electrode occurs and, as can be seen, it is achieved by re-dissolution with peak A۲. The Cu(I)/Cu(۰) redox system is slow and its potential depends on the electrode/electrolyte surface Fig. ۲ shows the effect of AA on the CV of GCE alone and modified with GO and rGO- Fe۲O۳ in the presence of ammonia copper. As it is evident and clear, there is a considerable difference between the CV of the modified electrode with rGO-Fe۲O۳ and the other two electrodes. AA as a reducing agent increases the reduction reaction of Cu۲+ to Cu+ (C۱). Voltammetry was used to determine the linear range and detection limit of AA measurement on the surface of the modified electrode. The linear range was obtained with this method in the range of ۵-۳۰ mM and the detection limit using the formula C = ۳Sb/m equal to ۵۰ μM. The results also showed that this electrode, in addition to being simple to prepare, has good durability and shows good reproducibility in measurements.