Historical Background

In a series of papers (1952-1957) on solvent extraction of metal complexes, Dyrssen and coworkers [1,11-14] and Rydberg [15] appear to be the first to have applied the dual-phase potentiometric titration to determining log P. Not only that, but they considered ion-pair log P, studied dimerization reactions of dialkylphosphates in aqueous as well as chloroform solutions, and used log D vs pH plots. Brandstrom [16] and Seiler [17] were also among the earliest users of the pH-metric log P technique. Brandstrom performed constant pH titrations (using a pH-stat) to determine log P, while Seiler proposed the determination of pKa and log P from a single titration, where octanol is added half way through the assay, near the half-ionization point. Kaufman et al. [18] introduced the use of difference plots to the interpretation of log P titration data. There were other significant early studies which contributed to the development of the pH-metric technique [19-26].

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