β-cyclodextrin and carboxymethylated β-cyclodextrin polymer film modified electrodes, hosting cobalt porphyrins, as sensors for electrocatalytic determination of oxygen dissolved in solution

New oxygen sensors, based on polymer film modified electrodes, were prepared and applied for electrocatalytic determination of dioxygen dissolved both in aqueous and aqueous-organic, mixed solvent solutions. The sensors were made of gold electrodes coated with thin polymer film matrices of either neutral beta-cyclodextrin polymer, beta-CDP, or cation-exchange carboxymethylated beta-cyclodextrin polymer, beta-CDPA, hosting electrocatalytically active centers of cobalt tetraphenylpolphyrin, (TPP)Co, cobalt tetrakis-(N-methylpyridyl)porphyrin, (TMPyP)Co, or cobalt tetrakis-(4-sulfonatophenyl)porphyrin, (TPPS)Co. Films were cast from aqueous solutions of the respective beta-cyclodextrin prepolymer, cobalt porphyrin and glutaric dialdehyde used as the polycondensation crosslinking reagent. Catalytic dioxygen electroreduction at the electrode coated with polymer film hosting the cobalt porphyrin catalyst involves two electrons and two protons resulting in the formation of hydrogen peroxide. The sensitivity of dioxygen determination largely increases in the order (TPPS)Co<(TPP)Co<(TMPyP)Co for the beta-CDPA film electrodes, being governed by ion-exchange equilibria with respect to the cobalt porphyrin catalyst, while it depends only slightly on the nature of the cobalt porphyrin catalyst for the beta-CDP film. The catalytic rate constant of the dioxygen reaction with the cobalt porphyrin catalyst in the film was estimated as k approximate to 2 x 10(4) M(-1)s(-1) being larger than those for either adsorbed or electropolymerized catalyst at the electrode and close to that for the catalyst present in solution. The performance of the sensors is presented with respect to the detection signal linearity, reproducibility, long-term stability, reversibility regarding dioxygen binding and response time.