A modified liquid-liquid extraction scheme has been developed which is applicable to complex mixtures of organic compounds. Fractionation into strong and weak acids, bases, polar and non-polar compounds, aldehydes and ketones provides chemical information useful in GC/MS identifications of components in mixtures. Advantages and problems attending fractionation of mixtures have been elucidated by the use of standards and mixtures containing trace amounts (1-10 ppm) of a variety of classes of organic compounds. Examples of possible artifacts occurring during a fractionation are described. -- AATA