Comparative study of electrothermal atomic absorption spectrometric methods for the determination of silver in used lubricating oils

Three methods for the determination of trace amounts of silver in used lubricating oils by electrothermal atomic absorption spectrometry (ETAAS) were developed and evaluated in terms of their analytical performance. The first method involved direct sampling in the furnace (using either platform or filter furnace technique) after dilution with an organic solvent mixture. In the second method, silver was determined after a previous microwave digestion of the oil samples. Finally, oil samples were introduced in the furnace in the form of oil-in-water micro-emulsion. The three procedures have similar detection limits but the emulsification method allows a higher sampling throughput. By using a calibration curve, good accuracy was obtained in the analysis of certified reference lubricating oil samples, except for the dilution method, which required the analyte addition calibration.