Selectivity in normal-phase liquid chromatography with binary mobile phase
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Selectivity in normal-phase liquid chromatography with binary mobile phase Małgorzata Borówko · Barbara O´scik-Mendyk
Received: 26 February 2010 / Accepted: 13 May 2010 / Published online: 30 June 2010 © The Author(s) 2010. This article is published with open access at Springerlink.com
Abstract A simple theoretical approach to normal-phase liquid chromatography with binary mobile phase is presented. In the model used the driving force for the retention is competitive adsorption of solutes and both solvents. A new expression for the separation factor is proposed and discussed. An influence of different parameters on the selectivity is shown. The theoretical concepts are illustrated by the selected experimental data. Keywords Retention mechanism · Liquid–solid chromatography · Selectivity · Adsorption from solutions
1 Introduction Currently, liquid chromatography is the main method for separating compounds in solutions. A flow of the mobile phase along the stationary phase causes differentiated migration of solutes in chromatographic bed. The relative preference of the solute molecules for the two phases results in a solute distribution over the mobile and stationary phase. Knowledge of the mechanism of the retention is of the utmost importance for the control of separation and optimization of analysis time. In normal-phase liquid chromatography the driving force for the transfer of solute is its adsorption on the solid surface. It is generally acknowledged that the adsorption depends on parameters characterizing either the solute or the mobile phase and the adsorbent surface. The use mixed mobile phase allows the continuous change of the elution strength of the mobile phase and the M. Borówko () · B. O´scik-Mendyk Faculty of Chemistry, M. Curie–Skłodowska University, M. Curie–Skłodowska Sq. 3, 20-031 Lublin, Poland e-mail: [email protected]
selectivity of the chromatographic system. Such a manipulation of separation requires the functional relationships between retention factors and the mobile phase composition. Numerous models have been developed to describe the retention in liquid solid chromatography with mixed mobile phases, several reviews cover the results (Borówko 2002; Borówko and Jaroniec 1983a, 1983b; Jaroniec et al. 1985; Nurok 1989; Snyder 1969; Soczewi´nski 2002). These approaches involve various factors, namely, interactions with the surface (Glajch and Snyder 1981; Jandera et al. 2001; Jaroniec et al. 1978; Scott and Kucera 1975; Snyder and Glajch 1981), non-specific interactions in the liquid phase (Boehm and Martire 1980; Borówko 1984) association and solvation effects (Borówko and Jaroniec 1983a, 1983b; Jaroniec et al. 1985) differences in molecular sizes of components (Borówko 1986)), energetical heterogeneity of the adsorbent (Borówko 2002; Borówko and Jaroniec 1979; Jaroniec and O´scik-Mendyk 1981), orientation of solute molecules on the surface (Borówko 1988), etc. Nevertheless, theoretical aspects of liquid adsorption chromatography still remain a matter of the debate in the lit
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