We developed an N-shaped partition cell to measure the logarithm of partiti
on coefficients between 1-octanol and water (log P-ow). The cell enabled us
to measure the concentrations of the solute in the two phases periodically
by HPLC without any tedious or time-consuming steps. The equilibrium time
in the cell was almost 4 hours, and the obtained log P-ow values were consi
stent with those by the conventional shake-flask method for neutral compoun
ds with 1.1 < log P-ow < 3.8. This approach was applied to a monovalent bas
ic drug, verapamil, and the dependence of log P-ow on the pH was measured u
sing six cells simultaneously. The obtained pK(a) and log P-ow values of ve
rapamil by the N-shaped cell method were in agreement with those by the sha
ke-flask method; the analysis time was alsomst 7 hours. The cell was used i
n an HPLC autosampler, and the whole operation for measuring log P-ow was p
erformed automatically in combination with HPLC.