A liquid-liquid fractionation method based upon well-known chemical reactions has been developed. With the use of the fractionation method, a mixture of organic compounds can be separated into strong acid, weak acid, base, aldehyde, ketone, "polar," and "nonpolar" fractions. Organic compounds, representing several chemical classes, were used to determine how much material would be lost during the fractionation and to determine how well the various compound types could be separated from each other. Most of the compounds tested were recovered in yields which were sufficient to provide good qualitative and quantitative data;Problems relating to impurities introduced into samples by solvents and reagents were examined. In addition, some reactions which led to the formation of artifacts were investigated;The advantages of using the liquid-liquid fractionation method as a pre-separation method for GC/MS were shown for the analysis of real samples, including gasoline, diesel fuel, and exhaust from internal combustion engines using those fuels;('1)DOE Report IS-T-914. This work was performed under Contract W-7405-eng-82 with the Department of Energy.