Electrochemical preparation of over-oxidized polypyrrole/multi-walled carbon nanotube composite on glassy carbon electrode and its application in epinephrine determination

摘要

A composite film constructed of surfactant doped over-oxidized polypyrrole and multi-walled carbon nanotube was prepared on the surface of glassy carbon electrode by the electro-polymerization method. Surface characterization of the modified electrode was performed by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectrometry. The investigations have been proved that the over-oxidation of the modifier film resulted in a porous thin layer that improves the interlayer diffusion mechanism for the electroactive species. On the other hand, the negative charge density on the surface of the electrode excludes the negative analytes (e.g. ascorbate and Fe(CN)_6~(3-/4-)) and attracts the positive ones (e.g. dopamine and epinephrine). A remarkable enhancement in the microscopic area of the electrode resulted in a considerable increase of the peak current of epinephrine (EN) oxidation (～35 times). Differential pulse voltammetry has been applied as a very sensitive analytical method for the determination of sub-micromolar amounts of EN. Two linear ranges have been obtained for the EN concentration within the ranges of 0.1-8.0 and 10-100 μM. The voltammetric detection limit of the modified electrode for EN (based on 3σ) was 40nM. On the other hand, this sensor has an excellent selectivity and sensitivity for the EN determination in the presence of clinical interferences (e.g. uric acid, ascorbic acid, and the human serum contents). The recovery for the EN determination in pharmaceutical injections was obtained as 96.4% with a RSD of 4.8%, based on 5 replicate determinations. These excellent properties make the prepared sensor suitable for the analysis of the trace amounts of EN in pharmaceutical and clinical preparations.