Application of the CuO/AgO Sensor in a Flow System. With the aim of performing these measurements online and in
continuous mode, the CuO/AgO sensor was inserted in a flow system fabricated in our group, together with a Nafionmodified gold transducer. This transducer incorporated the counter and the pseudoreference electrodes. The micropumps and microvalves integrated in the fluidic platform allowed an automatic management of the liquids, either sample, calibration stock, or background solution. As before, the calibration curve was constructed by chronoamperometry using glucose standard solutions. According to the voltammetric response (data not shown), a set potential of +750 mV vs gold pseudoreference was chosen, which was 150 mV more positive than that used when the sensor was calibrated in batch using a standard Ag/ AgCl reference electrode. The pretreatment with NaOH to fix the pH and the protection of the Nafion layer ensure a stable potential from the gold pseudoreference, in spite of the different composition of the WWTP influents and the calibration solutions. The overall time for one analysis was set to 30 s. The COD values found in the real samples were considered, and the concentration range was adjusted from 0 to 496 mg L−1 of O , as can be seen in the chronoamperograms depicted in Figure 5A.