Voltammetric Determination of Zinc in Lubricating Oils

Anodic stripping voltammetry with a hanging mercury drop electrode was used to determine zinc in automotive lubricating oils. An experiment design was carried out in order to optimize the experimental conditions of ultrasonic extraction (20 mg of sample for 60 min), with the aid of heating (90 degrees C), HCl (2.0 mL), and H2O2 (2.0 mL). The procedure provided stripping waves with good repeatability and relatively small errors, with a determination limit of 6 mg kg(-1), for only 30 s of deposition time, and results comparable to the ASTM D4951 method. Furthermore, the method dispenses with the use of toxic solvents, high purity reagents, or a sophisticated apparatus and is suitable for routine analyses of additives, as well as for used and unused lubricating oils (synthetic or mineral ones).