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Low Frequency Impedance Studies on Covalently Modified Glassy Carbon Paste
Author(s) -
Varma Shailly,
Mitra Chanchal K.
Publication year - 2002
Publication title -
electroanalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 128
eISSN - 1521-4109
pISSN - 1040-0397
DOI - 10.1002/1521-4109(200211)14:22<1587::aid-elan1587>3.0.co;2-w
Subject(s) - dielectric spectroscopy , chemistry , electron transfer , cyclic voltammetry , horseradish peroxidase , redox , glassy carbon , analytical chemistry (journal) , electrode , substrate (aquarium) , hemin , electrochemistry , inorganic chemistry , photochemistry , organic chemistry , heme , enzyme , oceanography , geology
Cyclic voltammetry and impedance studies have been carried out on covalently coupled horseradish peroxidase, hemin, reconstituted horseradish peroxidase and blank glassy carbon paste electrodes. The cyclic voltammogram of native enzyme paste showed a clear oxidation peak at −50 mV and an increase in the oxidation currents in presence of the substrate was observed. In order to increase the electron transfer kinetics the redox center (hemin) of the enzyme was directly bound onto the electrode followed by reconstitution with apoperoxidase. Hemin bound paste showed a reduction peak at −275 mV and an oxidation peak at ca. −50 mV. Upon reconstitution with apoperoxidase a shift of 175 mV in the reduction peak and ca. 100 mV in the oxidation peak was observed. We have also studied the effect of electron donors like hydroquinone and p ‐aminobenzoic acid on the modified electrodes. It was observed that the native enzyme showed a clear increase in the electron transfer in the presence of electron donor whereas with the reconstituted enzyme paste the effect of the electron donor was not evident. Low frequency electrochemical impedance spectroscopy was carried out in the frequency range of 10 mHz to 1 kHz in order to study the kinetics of slow processes occurring at the electrode surface. The impedance data of the system in the supporting electrolyte was simulated to an equivalent circuit model, the modified Randles cell circuit for an irreversibly adsorbed species. The data in the presence of substrate was modeled to modified Randles cell circuit with Warburg impedance. The models show a reasonably good fit in the frequency region studied. The unmodified blank paste electrode showed more or less a constant phase angle behavior. From the simulated data the parameters values of the circuit used were obtained which were used to calculate the kinetic parameters.