The accumulation of polycyclic aromatic hydrocarbons in lubricating oil over time--a comparison of supercritical fluid and liquid-liquid extraction methods.

Optimal extraction conditions including extraction temperature, fluid density of carbon dioxide and concentration of modifier for supercritical fluid extraction (SFE) to extract of 16 2-6-ring polycyclic aromatic hydrocarbons (PAHs) spiked into used lubricating oil collected from a gasoline-driven automobile were determined. A comparison of extraction efficiency 2-6-ring PAHs spiked into the used lubricating oil extracted by SFE and liquid-liquid extraction (LLE) methods was made. Results indicated that recoveries of PAHs extracted by SFE from the used lubricating oil were higher than those by LLE. PAH profiles of lubricating oil samples collected at various driving distances from an old and a new gasoline-driven automobiles were determined by combining SFE, gel permeation chromatography clean up and gas chromatography-mass spectrometry analysis. Results showed that the concentrations of total PAH in lubricating oils collected from both automobiles increased rapidly after oil change. Two- and three-ring PAHs dominated the PAH profiles of oil samples collected from both automobiles. High concentrations of the more toxic 4-6-ring PAHs, were found in the oil samples collected from both automobiles even at a short driving distance after oil change. The concentrations of total PAH in lubricating oil collected from two automobiles driven for a longer distance after oil change were very similar.