This Test Guideline describes a method to determine the fat solubility of solid and liquid substances. The fat solubility of a substance is one of the data for evaluating the storage of lipid soluble materials in biological tissue.

This test method can only be applied to pure substances, non-reactive with triglyceride, which are stable at 50°C for at least 24 hours and which also are not appreciably volatile under the same conditions. The substance is dissolved in a liquid "standard fat" by stirring, and the saturation mass fraction of the substance is achieved by continued addition until a constant value for the mass fraction dependent variable is achieved as determined by a suitable analytical method.The methods use eight samples; each should be twice the quantity necessary for saturation as determined in the preliminary test. After adding a weighed amount of approximately 25 g of liquified and mixed standard fat, four flasks are stirred at 30°C (group I) and the other four at approximately 50°C (group II), each for at least one hour. All the flasks are stirred at 37°C, for liquids during 3 hours for two flasks of each group and for at least 24 hours for the last two flasks. At the end a sample is taken, weighed and the mass fraction is determined with different methods (photometric methods, gas chromatography, and extraction).