Linear free energy relationship analysis of microemulsion electrokinetic chromatographic determination of lipophilicity

Log k' values for microemulsion electrokinetic chromatography (MEEKC) with a microemulsion of 1.44% (w/w) SDS, 6.49% (w/w) butan-l-ol and 0.82% (w/w) heptane are well correlated through the linear free energy relationship equation, (i) log k' = - 1.133 + 0.279 R(2) - 0.692 pi(2)(H) - 0.060 Sigma alpha(2)(H) - 2.805 Sigma beta(2)(O) + 3.048V(x) n = 53, p = 0.9941, S.D. = 0.090, F = 791 The solute descriptors are R(2), an excess molar refraction; pi(2)(H) the dipolarity/polarizability; Sigma alpha(2)(H) and Sigma beta(2)(O), the overall or effective hydrogen-bond acidity and basicity and V-x, the McGowan characteristic volume. The coefficients in Eq. i are almost exactly the same as those in the correlation of water-octanol partition coefficients, as log P-oct, confirming that the particular microemulsion system used is an exact model for water-octanol partition. The 53 solutes in Eq. i include phenols and heterocyclic bases (pyrimidines, pyrazines, pyrroles, indoles and furans) with no outliers at all, so that the microemulsion system can be used generally for the determination of solute lipophilicity.