A critical analysis of the voltammetry of fenamic acids: Evidence of diclofenac and mefenamic acid electroactive film formation

The voltammetric behaviour of diclofenac and mefenamic acid at a screen printed carbon electrode is very similar and both compounds share a similar molecular structure to that of diphenylamine. In each case on repeated scanning, an electroactive film is deposited due to the polymerisation of either of the molecules. The resultant film adheres to the electrode and is stable in aqueous solution for both diclofenac and mefenamic acid. This film formation is unique to a carbon electrode as no layers were found to form on Pt or Au. The formal potential of the confined layer shifts with pH, with a slope of about -59 mV/pH unit. Such layers will prevent the multiple use of the electrode in quantitative analysis unless it is cleaned between runs. A model based on the polymer formation from a diphenylamine backbone is proposed.