Therefore, a stock solution of 25 g L−1 glucose was prepared.This solution was left for mutarotation for 24 h and then stored at 4 °C.A solution containing 0.1 M NaOH (Panreac, Barcelona, Spain) was used as background electrolyte solution for all the determinations. This alkaline medium favors the oxidation of organic molecules on the surface of metallic oxides.