A simple electrochemical approach to evaluate oxygen reduction catalysts using an inexpensive screen-printed ring disk carbon electrode system, consisting of a ring electrode deposited with MnO(2) and a disk electrode modified with the catalysts for study, is developed in this study. The as-prepared MnO(2) is selective and sensitive for H(2)O(2) oxidation in the presence of O(2) and is crucial to the proposed approach. By coupling with a wall-jet electrochemical cell, the product generated from the reduction reaction at the disk electrode can effectively be monitored at the MnO(2)- deposited ring electrode. Model catalysts of nano-Au and nano-Pd representing 2e(-) reduction of O(2) to H(2)O(2) and 4e(-) reduction to H(2)O, respectively, were evaluated as electrode materials in oxygen reduction reaction to demonstrate the applicability of the proposed method

A preanodized screen-printed ring disk carbon electrode was applied to the determination of chloramphenicol (PhÀNO 2 , CAP) by flow injection analysis (FIA). By setting up the first irreversible reduction reaction of PhÀNO 2 to PhÀNHOH at the disk electrode, the following reversible oxidation of hydroxylamine (PhÀNHOH) to the nitroso (PhÀNO) derivative can be monitored/collected at the ring electrode for CAP analysis. The interference from dissolved oxygen and others can thus be avoided by using this approach and precise CAP determination can be easily performed by FIA under aerobic conditions. Preanodization treatment helps to lower the overpotential of the electrochemical reaction of CAP and favors the selective detection in aqueous medium. Under the optimum conditions, ten repetitive determinations at 1 mM and 10 mM CAP resulted in relative standard deviations of less than 4%, indicating good reproducibility of the system. A linear calibration range of 0.1 -20 mM with a detection limit of 0.074 mM (S/N ¼ 3) was obtained. Veterinary pharmaceutics were finally analyzed by this sensor to validate its practical applicability.

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