Electrochemical Study on Quantitative Structure‐activity Relationship (QSAR) Analysis under Steady‐state Conditions

The influence of the volume ratio of the aqueous to 1‐octanol phase on drug delivery under steady‐state conditions in a tubular electrolytic cell composed of an organic phase and two aqueous phases was elucidated. Electrochemical measurements on the transport of six quaternary ammonium chlorides were performed using three types of membrane filters of different thickness. The electric resistance of each system was evaluated, and the distribution coefficient of each chloride was estimated from the extraction experiments. The permeation process within the organic phase was the rate‐determining step for tetrapropylammonium, tetrabutylammonium, tetrapentylammonium and tetrahexylammonium chlorides. On the other hand, for tetraoctylammonium chloride, which was the most hydrophobic ion among the six tested, the salt was easily distributed into the organic phase. Therefore, the rate‐determining step changed to the permeation process within the aqueous phase. In addition, the influence of ion‐pair formation on drug delivery was evaluated.