Potentiometric stripping analysis for simultaneous determination of copper and lead in lubricating oils after total digestion in a focused microwave-assisted oven

The determination of metals in lubricating oil has been used as an important means of preventing components failures, to provide environmental information, and to solve criminal issues. In this study derivative potentiometric stripping analysis (DPSA) was used for the simultaneous determination of copper and lead in lubricating oils of vehicular engines. The samples were completely digested in a focused microwave-assisted oven using a powerful oxidant mixture (HNO3, H2SO4, H2O2). The optimized heating program to digest about 1 mL of lubricating oil takes 45 minutes. The residual carbon content after digestion was below 0.3% m/m for all samples. Copper and lead were also determined by graphite furnace atomic absorption spectrometry (GFAAS), and the results obtained were in good agreement with those obtained by electrochemical measurements. Recoveries of 94-109 and 93-103%, for copper and lead, respectively, were obtained for new and used lubricating oil samples.