A Method for Measuring 1-Octanol−Water Partition Coefficients

Abstract

A new direct method for the determination of 1-octanol−water partition coefficients ( K ow, expressed as log K ow ) is presented. In the experimental setup, a dialysis tubing separates water from the octanol phase containing the analyte. This prevents the system from the frequently encountered problem of emulsions. Several tubings with molecular weight cutoffs between 2000 and 12 000 proved equally suitable. An added benefit is that ultrasonic agitation can be used to shorten the equilibrium time from days to hours. A time saving of over 90% is easily achieved. The concentrations of the analyte were determined by liquid chromatography, which allows the measurement of compounds that contain impurities. We report values for highly hydrophobic (log K ow > 6) to highly hydrophilic (log K ow = −2) substances. The results show high reproducibility when different dialysis tubings or ultrasonic agitation is used. The correlation coefficient of 0.998 for the comparison of log K ow data obtained by this method and literature data indicates an excellent agreement. Thus, the method described allows the fast determination of log K ow without great hardware expense.