OPTIMISATION AND ASSESSMENT OF A METHOD FOR DETERMINATION OF TRACE METALS IN USED INDUSTRIAL OILS

The selection of a method for the determination of trace metals in used industrial oils led to the use of graphite furnace atomic absorption spectrometry (GF-AAS) as the best technique for sample decomposition/atomisation/detection. After this step, the instrumental variables were studied with special emphasis on optimising the type of diluent used as function of both the physical characteristics of the sample and the concentration of the analytes to the GF-AAS instrument. A key aspect of the method was the type of standard (organic or inorganic solutions) used for calibration which yielded very different metal concentrations for the same samples. The use of a certified reference material (NIST CRM 1084a) enabled to assess organic solutions of metal as the best for calibration. Then, the method thus validated was applied to different used industrial oils.