Effect of separation conditions on chromatographic determination of hydrophobicity of acidic xenobiotics.

Problems encountered in the chromatographic determination of hydrophobicity of acidic xenobiotics are discussed. First, the definition and meaning of hydrophobicity is briefly presented. Next, the methods of determination of the hydrophobicity parameter by reversed-phase high-performance liquid chromatography are described. The methods of determination of the dead volume are analyzed with regard to calculation of the thermodynamically valid retention parameters. Relationships between retention factors and pH of mobile phase which have been reported in the literature are presented. The effects of ionic strength and buffer composition on the apparent retention parameters are discussed. The reversed-phase stationary phase materials presently employed for hydrophobicity determinations are reviewed. Application of micellar electrokinetic chromatography in the determination of hydrophobicity of ionizable analytes is presented. The ability of chromatography to provide the measures of hydrophobicity of xenobiotics best modelling their biological activity is underlined.