OECD 107/117: Partition Coefficient

OECD 107: Partition Coefficient (n-octanol/water), Shake Flask Method

This method can not be used with surface-active materials. The partition coefficient is defined as the ratio of the equilibrium concentrations of a dissolved substance in a two-phase system consisting of two largely immiscible solvents. The test should be done at a temperature in the range 20 to 25°C, kept constant at ± 1°. There are three runs with different volumes ratio of n-octanol to water. Duplicate vessels containing accurately measured amounts of the two solvents and stock solution are used in all three runs. After agitation the separation of the two phases, in general, is achieved by centrifugation. It is necessary to determine the concentrations of the test substance in both phases. Analytical methods which may be appropriate are: photometry, gas chromatography and high performance liquid chromatography. The total quantity of substance present in both phases should be calculated and compared with the quantity originally introduced. A Pow value is calculated from the data of each run. The six log Pow values should fall within a range of ± 0.3 units.


OECD 117: Partition Coefficient (n-octanol/water), HPLC Method

Reverse phase HPLC is performed on analytical columns packed with a solid phase containing long hydrocarbon chains chemically bound onto silica. The chemicals are retained in the column in proportion to their hydrocarbon-water partition coefficient, with hydrophilic chemicals eluted first and lipophilic chemicals last. The HPLC method covers log Pow in the range of 0 to 6, but it can be expanded to cover the log Pow range between 6 and 10 in exceptional cases. The HPLC operation mode is isocratic. The test substance is injected in the smallest detectable quantities in the column. The retention time is determined in duplicate. The partition coefficient of the test substance is obtained by interpolation of the calculated capacity factor on the calibration graph. For very low and very high partition coefficients extrapolation is necessary.