Separation selectivity of some phenolic acids in RP HPLC systems with binary mobile phase comprised various modifiers
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Separation selectivity of some phenolic acids in RP HPLC systems with binary mobile phase comprised various modifiers Anna Klimek-Turek · Tadeusz H. Dzido
Received: 5 March 2010 / Accepted: 31 May 2010 / Published online: 30 June 2010 © The Author(s) 2010. This article is published with open access at Springerlink.com
Abstract Retention of phenolic acid has been correlated for reversed-phase high-performance liquid chromatography systems with different binary mobile phases containing methanol, acetonitrile or tetrahydrofuran as modifiers and buffer at pH 3.0, 4.6 and 5.0. The changes of separation selectivity of solutes, when one modifier is replaced by another in the eluent, has been explained taking into consideration molecular interactions of the solutes with components of the stationary phase region, i.e. extracted modifier, and ordering of the stationary phase by the modifier. Keywords Modifier selectivity · Mechanism of separation selectivity in reversed phase liquid chromatography · Phenolic acids
1 Introduction Liquid chromatography is the most popular mode for analytical separations of chemical compounds in pharmaceutical, biomedical and environmental pollution samples. Optimization of chromatographic conditions is the most important task of performing separation of mixture components. Typical values of retention factor of the solutes should be in the range 1–10 and values of resolution greater than 1.5 when quantitative analysis to be performed. Separation selectivity can be varied with type of the stationary and the mobile phases (Szepesy 2002; Lavine et al. 2002; Sandi and Szepesy 1999). However, the simplest way leading very often to a variation of separation selectivity of A. Klimek-Turek · T.H. Dzido () Department of Physical Chemistry, Medical University of Lublin, ul. Staszica 6, 20-081 Lublin, Poland e-mail: [email protected]
solutes is based on alteration of composition of the mobile phase including concentration and type of a modifier (organic component of the mobile phase) and pH of buffer. The last variable is especially valuable when solutes are weak electrolytes. If solutes do not undergo dissociation then, in general, pH variation does not lead to selectivity change. However, with the possible exception of the solutes, which demonstrate proton acceptor properties because proton donor property of silanol groups of the stationary phase is altered with pH change of the mobile phase. Replacement of the modifier type in the mobile phase can lead to an alteration of separation selectivity. A choice of the appropriate solvent is often an real challenge, especially if one takes into account many possible molecular interactions of separated solutes with components of the mobile and stationary phases. In our previous paper we proposed the approach in which separation selectivity changes can be explained by molecular interactions of solute molecules and components of the stationary phase. This approach was presented in the paper (Dzido 2000). Basing on the data of partition constants of benzen
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