Correlation between hydrophobicity and retention data of several antihistamines in reversed-phase liquid chromatography with aqueous-organic and micellar-organic mobile phases Original Research Article

The correlation between the retention of 12 antihistamines (carbinoxamine, chlorpheniramine, cyclizine, cyproheptadine, dexbrompheniramine, dexchlorpheniramine, diphenhydramine, doxylamine, pheniramine, phenyltoloxamine, pyrilamine and tripelennamine), in reversed-phase liquid chromatography (RPLC) with aqueous-organic (methanol-water) and micellar-organic (sodium dodecyl sulphate (SDS)-pentanol) mobile phases of varying composition, and their octanol-water partition coefficients expressed as log Po/w (ranging between 2.02 for pheniramine and 4.92 for cyproheptadine), was examined. For this study, the retention of the drugs was measured in six mobile phases of methanol-water, and seven mobile phases of SDS-pentanol, which permitted to obtain the coefficients of model equations that described the retention for any mobile phase composition inside the considered factor space (0.40–0.70 (v/v) methanol, or 0.05–0.15 M SDS and 0.02–0.06 (v/v) pentanol). Log k versus log Po/w plots gave better correlations than k versus log Po/w plots, and the maximal regression coefficients were the same for both aqueous-organic and micellar-organic RPLC. In both techniques, there was a range of mobile phase compositions where the correlations were similar (r=0.96–97): 0.55–0.70 (v/v) methanol and 0.05–0.09 M SDS/0.05–0.06 (v/v) pentanol. Good correlations were found in micellar-organic RPLC between the extrapolated retention factor at zero micelle and organic modifier concentrations (r=0.964), and log Po/w, and between the inverse of the solute-micelle association constant and log Po/w (r=0.986).