Interlaboratory study of log P determination by shake-flask and potentiometric methods

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The pK(a) and log P values of 23 structurally diverse compounds, including well known drugs and two pharmacons under development, were determined by potentiometry. Also, the logP data were measured by the shake-flask method. Many of the samples were investigated at both of the participating laboratories in order to evaluate the reproducibility of the pH-metric log P technique. The interlaboratory evaluation of pK, and log P data obtained by potentiometry showed excellent agreement (average ΔpK(a) = + 0.02 and Δ log P = ± 0.07). The log P values obtained by the two different methods, ranging from - 1.84 to 5.80 (nearly eight orders of magnitude), were in very good concordance, as shown by the linear regression analysis: log P(pH-metric) = 0.9794 log P(shake-flask) - 0.0397 (r = 0.9987, s = ± 0.091, F= 8153). The advantages of potentiometric log P determination are discussed.

Original languageEnglish
Pages (from-to)1405-1413
Number of pages9
JournalJournal of Pharmaceutical and Biomedical Analysis
Issue number11
Publication statusPublished - Aug 1996


  • Dual-phase titration
  • Log P
  • Shake-flask method
  • Validation
  • pH-metric log P determination
  • pK(a)

ASJC Scopus subject areas

  • Analytical Chemistry
  • Pharmaceutical Science
  • Drug Discovery
  • Spectroscopy
  • Clinical Biochemistry

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