Electrooxidation of nitrite mediated by Cu-x-tetraaminophenylporphyrin (x = 2, 3, and 4) glassy carbon-modified electrodes: Effect of substituent position

A study of glassy carbon electrodes modified with poly-Cu-x- tetraaminophenylporphyrin (TAPP) (x = 2, 3, and 4) toward the electrooxidation of nitrite is reported. The position of the amino group influences the degree of electropolymerization and the response toward the electrooxidation of nitrite. The influence of pH on the electrocatalytic oxidation of nitrite was also studied, finding that the activity is strongly pH-dependent. For each system (polymeric porphyrins, poly-Cu-2-TAPP, poly-Cu-3-TAPP, and poly-Cu-4-TAPP), the behavior of the modified electrode as amperometric nitrite sensor was studied at the best pH response, finding a linear correlation over a wide range of concentrations for poly-Cu-3-TAPP. With poly-Cu-2-TAPP, the range is smaller, and there is no linear relationship for poly-Cu-4-TAPP. The plot of I _p vs. the square root of the scan rate shows a linear relationship for all the polymer systems, indicating that the electrooxidation of nitrite in the modified electrodes is a process controlled by diffusion. The Tafel slope was calculated, indicating that the determining step in the electrooxidation of nitrite varies depending on the position of the substituent, showing a dramatic change in the nature of the active sites.