The suitability of three different retention models to predict the retention times of poly(ethylene glycol)s (PEGs) in gradient and isocratic chromatography was investigated. The models investigated were the linear (LSSM) and the quadratic solvent strength model (QSSM). In addition, a model describing the retention behaviour of polymers was extended to account for gradient elution (PM). It was found that all models are suited to properly predict gradient retention volumes provided the extraction of the analyte specific parameters is performed from gradient experiments as well. The LSSM and QSSM on principle cannot describe retention behaviour under critical or SEC conditions. Since the PM is designed to cover all three modes of polymer chromatography, it is therefore superior to the other models. However, the determination of the analyte specific parameters, which are needed to calibrate the retention behaviour, strongly depend on the suitable selection of initial experiments. A useful strategy for a purposeful selection of these calibration experiments is proposed.

Attempts to theoretically address the problems involved in transferring linear gradient elution methods have been somewhat ad hoc due to the simplifying assumptions usually made in conventional gradient elution theory. Until now, all equations based on the k* parameter of linear gradient elution theory used as the basis for predicting the separation selectivity have not explicitly included the effect of the dwell volume (VD). Using an exact equation for predicting k*, that is, one which fully accounts in an a priori fashion for VD, we find a set of simple yet exact equations which unequivocally must be satisfied to transfer an optimized linear gradient elution method from one system (column or instrument or both) to another. 

This paper is written to honor Csaba Horváth and to remember his work on Reversed Phase Chromatography, (RPC) a theoretical fundament of the mechanism of retention on nonpolar stationary phases, called the "Solvophobic Theory" from the subjective point of view of the author. The paper is trying to compile a few stations in the development of this important theory, which is valid more than ever and look out for its consequences in developing robust methods for routine work, especially in the daily applications of RPC in industrial settings worldwide. It was Horváth, who laid the fundaments of this valuable technique, which makes the application of RPC to a still growing use in scientific research and in pharmaceutical and chemical production. Although the Solvophobic Theory of RPC was reflecting only a part of Horváth's scientific work, the impact of RPC in life science is tremendous and the technique RPC is today one of the most popular, most widely used tools in analytical chemistry and will remain for long time in use due to its stability and to its robustness.

The separation of anionic, cationic, and neutral drugs in microemulsion electrokinetic chromatography (MEEKC) was studied. The concentration of sodium dodecyl sulfate (SDS, surfactant) and 2-propanol (organic solvent) was varied in a three-level full factorial design. 29 different model substances were chosen with different hydrophobicities and charges (neutral, positive, and negative).

DryLab is used for the optimization of a model drug candidate and its degradation products. Accuracy of DryLab predicted retention times and resolution is compared with experimental values.

Multi-linear gradients have not been widely used in general-purpose HPLC in part because of experimental inconvenience in method development. Even with the use of computer modeling, identifying an optimum set of breakpoints has been done primarily by trial and error. Combining a spreadsheet with controllable chromatography modeling software has allowed to implement a systematic approach to bi- and tri-linear gradient optimization.