The experiments were carried out in Eppendorf-type polypropylene microtubes in triplicates. A 2.5-μL aliquot of 20 mM DMSO stock solution of a test compound was added into a preliminarily mutually saturated mixture containing 500 μL of H2O and 500 μL of 1-octanol. The solution was allowed to mix in a rotator at 30 rpm for 1 h. Phase separation was assured by centrifugation for 2 min at 6000 rpm. The octanol phase was diluted 100-fold with 40% aqueous acetonitrile, and the aqueous phase was diluted 10-fold with the same solvent. The samples of both phases were analyzed using an HPLC system coupled with a tandem mass spectrometer.