The effect of viscosity index improvers on the determination of metal content in new and used multigrade oils

Abstract

Atomic absorption spectroscopy is widely used to determine the metal content, especially of zinc, calcium, iron, and copper, in new and used multigrade oils. Many methods involve dilution of the sample with kerosene followed by aspiration into the atomic absorption. However, results indicate that such methods are subject to matrix interferences, the factors most influencing such interferences being: the concentration of viscosity index improver incorporated into the multigrade oil formulations; chemical structure of the viscosity index improver; the molecular weight of the viscosity index improvers; and the viscosity of the solvent used. Regression equations for some commercial viscosity index improvers have been established, to permit correction of the concentrations of zinc, calcium, iron and copper measured in new and used multigrade oils.