Determination of solute lipophilicity, as log P(octanol) and log P(alkane) using poly(styrene-divinylbenzene) and immobilised artificial membrane stationary phases in reversed-phase high-performance liquid chromatography

A number of RP-HPLC systems have been characterized by the linear free energy relationship: log SP = c + r.R-2 + s.pi(2)(H) + a.Sigma alpha(2)(H) + b.Sigma beta(2) + upsilon V-x (1) Here, SP is either log k' or log k(w) for a series of solutes in a given system, where k' is the capacity factor and k(w) is the capacity factor extrapolated to 100% water, and the solute descriptors are, R-2 an excess molar refraction, pi(2)(H) the dipolarity/polarizability, Sigma alpha(2)(H) and Sigma beta(2) the overall or effective hydrogen-bond acidity and basicity, and V-x the McGowan characteristic volume. Comparison of the coefficients in Eq. (1) with those for water-solvent partitions confirms that the modified electrostatically coated C-18 phase of Pagliara et al. (J. Liq. Chromatogr, 18 (1995) 1721) can be used to obtain solute lipophilicities, as log P-oct. For RP-HPLC systems based on poly(styrene- divinylbenzene), the coefficients in Eqs. (i) are nearer those for the correlation of water-alkane partition coefficients, as log P-alk, than for the correlation of log P-oct, suggesting that the RP-HPLC systems with poly(styrene-divinylbenzene) phases could be used as a rapid method for determination of solute lipophilicity, as log P-alk or as log P-cyc, where the latter is the water-cyclohexane partition coefficient. Eqs. (i) has also been applied to RP-HPLC log k' values obtained with an immobilized artificial membrane (IAM) phase. A good regression equation was obtained, but the coefficients in this equation are substantially different to those for regressions with log P-oct, log P-alk, or log P-cyc as the dependent variable. On the other hand, log k' values from the RP-HPLC system of Miyake al. [J. Chromatogr., 389 (1987) 47], consisting of silica gel coated with dipalmitoyl phosphatidyl choline as a stationary phase, with aqueous acetonitrile mobile phases, yielded coefficients in Eqs. (i) very similar to those for log P-oct.