Extraction induced by emulsion breaking as a tool for simultaneous multi-element determination in used lubricating oils by ICP-MS

Abstract

This paper reports, for the first time, rapid simultaneous multi-element determination of Mg, Cr, Ni, Cu and Pb in used lubricating oils after their extraction/preconcentration from samples using the novel extraction induced by emulsion breaking. The quantification of the metals of interest in the extracts was performed by ICP-MS using rhodium as an internal standard. First, in order to make it possible to prepare the emulsion, 4 mL of each oil sample was mixed with 1 mL of toluene. Then the diluted oil sample was emulsified with 1 mL of Triton X-114 acid solution. Once the extraction of the metals was completed, the emulsion was broken by centrifugation for 10 min at 6000 rpm. After that, the lower aqueous phase, containing the analytes that were extracted from oil, was collected for the determination by ICP-MS. Several parameters affecting the extraction efficiency of the procedure were investigated including the nature and concentration of the solvent used for sample dilution, the type and concentration of the surfactant, the concentration of HNO₃, and the other operational conditions (extraction time, collection time and centrifugal speed). The limits of detection for Mg, Cr, Ni, Cu and Pb were 0.126, 0.058, 0.028, 0.078 and 0.009 μg L⁻¹, respectively. The accuracy of the method was checked by application of a recovery test, by an analysis of standard reference materials (SRM 1084a and 1085b) and by comparison with the microwave digestion method.