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

Abstract

A number of RP–HPLC systems have been characterized by the linear free energy relationship: (i) log SP=c+r.R 2+s.π H 2+a.∑α H 2+b.∑β 2+v.V x 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 l00% water, and the solute descriptors are, R 2 an excess molar refraction, π 2 H the dipolarity/polarizability, ∑ α 2 H and ∑ β 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 Eq. (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. Eq. (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 Eq. (i)very similar to those for log P oct.