MONITORING OF ENGINE OIL DEGRADATION BY VOLTAMMETRIC METHODS UTILIZING DISPOSABLE SOLID WIRE MICROELECTRODES

Gold wire microelectrode assemblies were used to perform cyclic and pu lsed voltammetry directly in oil. The unmodified microelectrode behavi our was characterized by measuring ferrocene in mineral oil and a line ar calibration was obtained over the concentration range 1-5 mM. The v oltammograms remain sigmoidal with scan rates up to 200 mV s(-1), An a ntioxidant, phenothiazine, was studied as a typical marker of engine o il degradation and a linear calibration was obtained over the normal a dditive concentration range for phenothiazine (0-10 mM). For the pheno thiazine system, the voltammetric response remained sigmoidal although hysteresis was observed in the scan, which is thought to be due to th e difficulty in deprotonation of the system for phenothiazine oxidatio n, The observations demonstrated that the sensor assembly allows volta mmetry in previously inaccessible systems, the resistivity of mineral oil being five orders of magnitude greater than that of water.