This standard establishes a method to determine the partition coefficient (n-octanol/water). The partition coefficient of a substance, between water and a lipophilic solvent (n-octanol), can be very useful to know the possible transfer of this chemical species from an aqueous medium to a lipid constituent of an organism, and its possible bioaccumulation. in it. This method is based on Nerst's Partition Law, which is applicable only for constant temperature, pressure and pH and only for dilute solutions; therefore, it applies strictly to a pure substance dispersed between two pure solvents. Results can be influenced if several different solutes are present in one or both phases at the same time. The association or dissociation of dissolved molecules produces deviations in Nerst's Law and, as a consequence, the partition coefficient becomes dependent on the concentration of the solution. For this reason, and due to the multiple equilibria that may occur during the test, this method should not be used for ionizable compounds without applying the corresponding corrections. In these cases, it may be advisable to use buffer solutions instead of water. Difficulties may arise in the separation of the phases when determining the partition coefficient of surfactant substances, since these compounds favor the emulsion that is formed when stirring the n-octanol in the water.