ELECTROCHEMICAL SENSOR FOR HYDRAZINE BASED ON SILICA MODIFIED WITH NICKEL TETRASULFONATED PHTHALOCYANINE

Nickel tetrasulfonated phthalocyanine (NiTsPc) immobilized onto titani zed silica gel (ST) showed good stability and redox properties. The cy clic voltammograms obtained with a carbon paste electrode modified wit h ST-NiTsPc presented an enhanced peak current at 450 mV (vs. SCE) whi ch did not shift with solution pH. The redox process was attributed to Ni-II/Ni-III, which presented a good electrocatalytical activity for oxidizing hydrazine in neutral solution. The process is controlled by the electron transfer step and no diffusion limitation was observed. T he modified electrode was very sensitive for hydrazine, giving a detec tion limit of 1.0 x 10(-5) mol L-1, for an applied potential of 450 mV (vs. SCE). A linear response range was observed between 1.0 x 10(-4) and 6.0 x 10(-4) mol L-1, fit by the equation I = -0.1 (+/-0.1) + 7.9( +/-0.3) [Hydrazine], with a correlation coefficient of 0.998 for n = 6 . The repeatability for 11 measurements was excellent, with a relative standard deviation of 3.7 %. The active material, nickel tetrasulfona ted phthalocyanine modified silica, was stable for at least 6 months, losing only 10% of its signal over this period.