An evaluation of emulsions in wear-metal-in-oil analyses

The emulsification of used lubricating oil as a method of sample preparation, preceding the determination of wear-metals in the oil using ICP-OES, was compared to the preparatory methods of ashing and dilution. The oil samples were treated with acid and emulsified in water (1% w/w) using tetralin as a solvent and Triton X-100 as a surfactant. The performance characteristics (detection limits, accuracy, precision and spike recovery) of the emulsion methodology were evaluated. The calibration for the emulsion method compared favourably with the traditional methods of sample preparation. The detection limits for the emulsion method were lower in certain cases than those for ashing and dilution. The precision was on average approximately 2% RSD or less, except where the sample's concentration value was close to the detection limit.