Electrochemical study of Fe[Fe(CN)5NO] in graphite paste electrode

Iron nitroprusside (FeNP) was syntetised and characterized by IR and atomic absorption. The FeNP was incorporated into a carbon paste electrode and the electrochemical studies were perfomated with cyclic voltammetry. The cyclic voltammogram of FeNP into carbon paste exhibit two redox couple with following midpoint potentials (E-m); (E-m)(1) = 0.24 V and (E-m)2 = 0.85 V vs SCE (KCl =1.0 M,- v = 20 mVs(-1)) assigned to the Fe-(II)/Fe-(III) and Fe-(II)(CN)(5)NO / Fe((III))(CN)(5)NO respectively. At sweep rates between 10 and 100 mVs(-1) the peaks currents intensity increase linearly with sweep rate. The FeNP incorporated into a graphite paste electrode is very stable for several days. The electrochemical behavior of the FeNP was examined in solution of various supporting electrolytes. For two processes the nature of the cation affect the E, as current intensity, shifting the E, for more positive potentials, in following order: Li+>K>Na+. The nature of the anion (Cl-,NO3-, SO42- did not affect both redox couples. The voltammograms obtained with different KCl concentrations (0.05 - 2.5M) exhibit a shift in the (E-m)(1) to more positive potentials, this change is linear with the supporting electrolyte concentrations change. The slop of the strainght line is 66 mV for decade of the potassium concentration, which indicate a subnernstian process. It was verified that the mid-point potential (E-m) remained practically constant at pH between 8 and 3. However, a new process with (E-m)(3) (0.47 V) appears at pH < 3 and was ascribed to formation of intermediary species.