Anodic oxidation and amperometric sensing of hydrazine at a glassy carbon electrode modified with cobalt (II) phthalocyanine-cobalt (II) tetraphenylporphyrin (CoPc-(CoTPP)4) supramolecular complex

Abstract

This paper describes the electrocatalytic behaviour of a glassy carbon electrode (GCE) modified with cobalt(II)phthalocyanine (CoPc) complex peripherally tetrasubstituted with cobalt(II)tetraphenylporphyrin (CoTPP) complexes via ether linkages (i.e., CoPc-(CoTPP)4). The features of the immobilised pentamer were interrogated with cyclic voltammetry and electrochemical impedance spectroscopy (EIS) using [Fe(CN)6] 3-/4- as redox probe revealed enhanced electron transfer properties with kapp ≈ 18 × 10-6 cms-1 compared to that of the bare GCE (4.7 × 10-6 cms-1). The viability of this supramolecular complex as a redox mediator for the anodic oxidation and sensitive amperometric determination of hydrazine in alkaline conditions is described. The electrocatalytic oxidation of hydrazine by GCE-CoPc-(CoTPP)4 was characterised with satisfactory catalytic current response with low non-Faradaic current (ca. 30 times lower than the bare GCE) and at much lower oxidation potential (ca. 300 mV lower than the bare GCE). A mechanism for the studied electrocatalytic reaction was proposed based on the spectrophotometric evidence that revealed the major involvement of the Co(III)/Co(II) redox couple of the central CoPc species rather than the CoTPP component of the pentamer. Rate constant for the anodic oxidation of hydrazine was estimated from chronoamperometry as ∼ 3×103 M-1s-1. The proposed amperometric sensor displayed excellent charateristics towards the determination of hydrazine in 0.2 M NaOH; such as low overpotentials (+100 mV vs Ag|AgCl), very fast amperometric response time (1 s), linear concentration range of up to 230 μM, with micromolar detection limit, high sensitivity and stability. © 2006 by MDPI.