Journal of Chromatography A, 1201 (2008) 27–34 Contents lists available at ScienceDirect Journal of Chromatography A journal homepage: www.elsevier.com/locate/chroma Modeling the combined effect of temperature and organic modifier content on reversed-phase chromatographic retention Effectiveness of derived models in isocratic and isothermal mode retention prediction A. Pappa-Louisi ∗ , P. Nikitas, K. Papachristos, C. Zisi Laboratory of Physical Chemistry, Department of Chemistry, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece article info Article history: Received 29 February 2008 Received in revised form 27 May 2008 Accepted 29 May 2008 Available online 3 June 2008 Keywords: Reversed-phase liquid chromatography Isocratic-isothermal retention prediction Combined temperature-mobile phase composition effect abstract Models considering simultaneously mobile phase organic content and column temperature were devel- oped in this study by an extension of different equations describing the influence of temperature on solute retention. This extension was achieved by two methods: a semi-thermodynamic and a direct combination of equations expressed separately the dependence of the retention upon each of these factors. The above approaches gave a great number of expressions for the logarithm of the solute retention factor in terms of both temperature and organic content in the mobile phase, ln k(T,ϕ), determined from the dependence of the standard enthalpy of the retention process on T. From the final expressions of ln k(T,ϕ) we tested only those with the minimum number of adjustable parameters, i.e. those that correspond to a constant stan- dard enthalpy of the retention process. For this test we examined the retention behaviour of a sample of alkylbenzenes in aqueous acetonitrile eluents. These compounds exhibit ln k versus 1/T plots with a very small curvature. We found that a new equation for ln k(T,ϕ) based on the adsorption model for retention performs better than all the others. The average percentage prediction error ranges from 0.7 to 1.4%. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Most of the last decade and more recently theoretical stud- ies reported on the effects of temperature in reversed-phase liquid chromatography (RPLC) mainly focused on elucidating reten- tion mechanism during the chromatographic process by obtaining thermodynamic parameters from van’t Hoff plots [1–8]. How- ever, although nearly all the physical parameters that play a role in liquid chromatographic separation are a function of temper- ature, temperature has not yet been adequately explored as a parameter to improve separations. Nowadays, column tempera- ture is recognized as an important variable in controlling retention and/or selectivity in RPLC [9,10]. Even in cases where the impact of temperature on selectivity is minor, the reduction in analy- sis time is still an interesting reason to consider it. Thus, since the main factor in RPLC separations is the organic solvent con- tent due to its significant effect on selectivity and retention of any kind of solute, the column temperature can be selected ∗ Corresponding author. Tel.: +30 2310 997765; fax: +30 2310 997709. E-mail address: apappa@chem.auth.gr (A. Pappa-Louisi). simultaneously with this parameter in optimizing separations. However, it is known that a reliable way of any univariate or multivariate optimization is an accurate computer prediction of the chromatographic behavior of solutes approached by models [11–15]. Up to now, according to our knowledge, there is no report of any systematic theoretical study for the combined effect of the organic modifier concentration, ϕ, and column temperature, T, on the reten- tion. In previous work, optimized separations were developed by using either DryLab software based on an empirical linear relation- ship between the retention time, at a given isocratic or gradient mode, and T [16–21], or simple mathematical models describing the variation of retention with simultaneous change of T and ϕ [22–23], which, however, are not adapted to all compounds types especially when non-linear van’t Hoff plots are observed on solute retention under isocratic conditions or a non-linear dependence of ln k upon ϕ describes the isothermal behavior of solutes. Thus, having in mind that generally retention prediction for optimiza- tion purpose suffer from the inaccuracy of models, this study was focused on developing and testing a variety of models considering the combined effect of the mobile phase composition and tempera- ture on solute retention to some extent that they enable an accurate prediction. 0021-9673/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.chroma.2008.05.083