A hydrophobicity scale based on the migration index from microemulsion electrokinetic chromatography of anionic solutes

A migration index (MI) concept, previously introduced as a novel scale for measuring the hydrophobicity of neutral solutes, was applied to anionic solutes, The required parameters for determining the MI were measured by both microemulsion electrokinetic chromatography with a sodium dodecyl sulfate/1-butanol/heptane/buffer solution and capillary zone electrophoresis with 1-butanol added to the buffer, The obtained MI values of anionic solutes correlated very well with the logarithm of the partition coefficients between 1-octanol and water (log P), whereas the reversed-phase chromatographic retention parameter (log k'(w)), which is also used as a hydrophobicity scale, correlated very little with log P for the tested anionic solutes, Moreover, the Linear relationship between the MT and log P of the anionic solutes was consistent with that of neutral solutes, Although the relationship between the MI and log P of solutes having carboxylic groups deviated from those of others, the MI provided better regression to bioactivities such as human skin permeability than log P in quantitative structure-activity relationship studies, Therefore, this system would be an appropriate biochemical model, In addition, because measurement of the MI is easy, rapid, and reproducible, and the required sample amount is nanogram size, the MI is expected to be a useful and universal hydrophobicity scale.