Introduction Diesel fuel is a complex mixture of hydrocarbons including non-aromatic, mono-aromatic and polyaromatic hydrocarbons. It is well known that the composition of these compounds is closely related to the cetane number of fuel in the way that the cetane number becomes higher as the concentration of nonaromatics increases. The number becomes lower and the amount of particulate matter in exhaust gas increases as the concentration of aromatics increases. The analysis of diesel fuel is taking an important role in the automobile and fuel industries. ASTM (American Society for Testing and Materials) published the Standard Test Method for Determination of the Aromatic Content and Polynuclear Aromatic Content of Diesel Fuels and Aviation Turbine Fuels By Supercritical Fluid Chromatography (D 5186 03) using a Flame Ionization Detector (FID) in 2003 1). This application note demonstrates that SFC with supercritical CO2 can determine the non-aromatic and aromatic contents in commercially available diesel fuel in accordance with the ASTM method. JASCO SFC4000超臨界流體