Peak currents iP vs. CV scan rate square root √𝜈 depicted in Fig. for three independent samples demonstrate a linear behaviour, characteristic of the Randles-Sevcik formula and its approximation for irreversible redox processes . Following the observed reaction irreversibility, the ESA estimated for [Fe(CN)6] 4-oxidation was 12% higher compared to [Fe(CN)6] Finally, the 3DPECs were studied for electrochemical detection of nimesulide in diluted industrial sewage, employing DPV. These studies were performed on 3DPEC with identical geometry as previously used but with a closed flow-through cell (volume 1.6 cm 3 ) overprinted at the top of the electrodes, see Fig. . 3DPEC allows for an effective mixing and 1:10 (v/v) dilution (0.01 M PBS, pH 7.01: sewage). The electrolytic window of the 3DPEC in industrial sewage spans over 1.4 V, as is presented in Fig. . This value is lower compared to the analogous experiment in the PBS (~ 1.9 V); nevertheless only small changes in the background currents between both supporting electrolytes were recognized at low and moderate overpotentials. When the LOD is studied without dilution, the calibration curve linearity is broken, which indicates the sample matrix effect. Moreover, a linear range cannot be determined, and it is noticed that peak potential is shifted as long as the concentration is increased, which is also due to an interference of the sample matrix (see SI file, Fig. ). The discontinuous function of the calibration curve in undiluted industrial sewage is likely caused by the kinetic limitation of the charge transfer process due to the adsorption of interferents from the sample matrix .