Monitoring of engine oil degradation by voltammetric methods utilizing disposable solid wire microelectrodes

Gold wire microelectrode assemblies were used to perform cyclic and pulsed voltammetry directly in oil. The unmodified microelectrode behaviour was characterized by measuring ferrocene in mineral oil and a linear calibration was obtained over the concentration range 1-5 mM. The voltammograms remain sigmoidal with scan rates up to 200 mV s(-1), An antioxidant, phenothiazine, was studied as a typical marker of engine oil degradation and a linear calibration was obtained over the normal additive concentration range for phenothiazine (0-10 mM). For the phenothiazine system, the voltammetric response remained sigmoidal although hysteresis was observed in the scan, which is thought to be due to the difficulty in deprotonation of the system for phenothiazine oxidation, The observations demonstrated that the sensor assembly allows voltammetry in previously inaccessible systems, the resistivity of mineral oil being five orders of magnitude greater than that of water.