Amperometric determination of peroxides by glassy carbon electrodes modified with copper-phenantroline complexes

An amperometric sensor is described for the determination of peroxides in both aqueous and organic media. It consists of a rotating glassy carbon electrode modified by coating first with a thin film of a perfluorinated anionic exchanger (Tosflex) and then by immobilizing on this substrate the mixed-ligand copper complex [CuL(2)](2+) with 1,10-phenanthroline and bathophenanthroline (i.e., 1,10-phenanthroline containing two phenyl-sulfonic groups as substituents in the positions 4 and 7), thanks to the bonds formed between the -NR(3)(+) cationic groups of the Tosflex coating film and the -SO3- anionic groups present in the latter ligand. The modified electrode, which is rather stable with time and can be easily restored, permits detection of peroxides by their reduction at less cathodic potentials than at an unmodified electrode surface, It shows enhanced sensitivity in a variety of media (water, ethanol and ethanol-toluene 60/40 v./v.) which were investigated in view of their ability, on the whole, to dissolve peroxides originally present in different natural samples. Its satisfactory performance, which is unaffected by the presence of oxygen in the sample, in all the media studied is reported for hydrogen peroxide and tert-butyl hydroperoxide in terms of detection limits, dynamic ranges and response time. Its application to the direct determination of peroxides in some cereal oils was also attempted and the results found are compared with those obtained by conventional methods.