Devices and Equipment. For batch measurements, the electrochemical cell included one of the composite sensors as
working electrode, a Pt commercial counter electrode and a Ag/AgCl/10% (w/v) KNO reference electrode . For in flow measurements, a gold thin-film twoelectrode device defined on a 3 × 3.5 cm silicon substrate and also fabricated by a standard microfabrication process was implemented. The device included a 2.77 mm counter electrode and a 1.62 mm pseudoreference electrode. Before its use, 5 μL of the Nafion commercial solution was cast on the gold electrodes. After solvent evaporation at room temperature, a Nafion film was generated over the two electrodes that acted as a protection barrier and prevented them from adsorption/ desorption and contamination processes of organic species presented in the water samples, while keeping the required electrical contact between the electrodes and the solution.Aμ-Autolab potentiostat/galvanostat (Eco Chemie B.V., Uthecht, The Netherlands), controlled by a GPES 4.7 software package was used for all voltammetric and amperometric measurements. A poly(methyl methacrylate) (PMMA) flow cell made inhouse
was also utilized that integrated both the COD sensor and the Nafion-modified gold transducer. The fabrication and
operational modes of the flow system were thoroughly explained elsewhere. Briefly, the system also integrated two
micropumps and five microvalves , all of them electrically actuated. A homemade power supply and multiplexor was used to control these liquid actuators. This controller was connected to a data-acquisition card and the instrumentation was completed with a PC. The communication between the PC and the data-acquisition card was performed through a
USB board and employing software programmed with LabViewgraphic language.