INFLUENCE OF THE CONCENTRATION OF ADSORBATE AND MODIFIER IN THE MOBILE-PHASE ON RETENTION IN HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A method for the determination of the monomolecular adsorption constan ts from binary (adsorbate-eluent) solution directly from chromatograph y data (retention volume and concentration) is suggested. The constant s of the adsorption equation are calculated from an anisole chromatogr am measured on hydroxylated silica using n-hexane in the low concentra tion region. The adsorption isotherm of anisole is constructed. Good a greement between isotherms calculated by the suggested and by Glueckau f's methods is shown. The influence of the modifier concentration on r etention of benzene derivatives is studied for the chromatographic sys tem: n-hexane-tetrahydrofuran-aminopropyl silica. The deviation from l inear dependence of the reciprocal of the retention volume on mole fra ction of the polar modifier is explained by molecular modifier-modifie r interaction in eluent. Taking into account this interaction and usin g the quasi-chemical model of retention allows one to describe the dep endence of chromatographic data of benzene derivatives on the modifier concentration in the eluent. (C) 1998 Published by Elsevier Science B .V.