Journal of Chromatography A, 838 (1999) 89–99 Polyethylene glycol as a separation medium for capillary zone electrophoretic analysis of pyridine derivatives * ´ˇ ˇ ´ ´ ´ ´ Petr Bednar , Zdenek Stransky, Petr Bartak, Pavel Adamovsky ´ Department of Analytical Chemistry, Palacky University, Svobody 8, 77146 Olomouc, Czech Republic Abstract The influence of the addition of polyethylene glycol (PEG) to the background electrolyte on the capillary zone electrophoretic (CZE) separation of alkylpyridines was studied. It was found out that interactions between polyethylene glycol chains and protonized pyridine bases cause the increasing of the resolution. The separation of a model mixture of pyridine, all isomers of methylpyridine, and some other alkyl and aryl derivatives was performed. The separation was complete except for some dimethylpyridines. The influence of the co-ion was discussed, too. Polyethylene glycol solution as a separation medium was used for the capillary zone electrophoretic determination of pyridine bases in an industrial mixture.  1999 Elsevier Science B.V. All rights reserved. Keywords: Background electrolyte composition; Pyridines; Alkylpyridines; Polyethylene glycol 1. Introduction PEG 2000 and alkylpyridines for CZE separations of their mixtures is investigated. It has been known a long time, that inorganic The studied alkylpyridine mixtures contained cations cationize oxyethylene chains and create homologues and positional isomers, so the main ternary complexes with anions (ionic association) problem was, in contrast to the inorganic samples, [1]. This phenomenon was used for the determi- the separation of ions with the same molecular mass nation of oxyethylated products by creating these and charge. Pyridines are protonized in acid buffers, complexes. Cationization has been used later in so the cationization reactions can be considered. chromatography and recently some electromigration Moreover, hydrophobic interactions can occur. So applications have appeared in the literature. The the main discrimination factors are differences in complete isotachophoretic (ITP) [2] and capillary friction, cationization reactions and hydrophobic zone electrophoretic (CZE) [3] separation of alkali interactions. and alkaline earth metal cations was achieved. The effect has been used for the separation of some other inorganic cations, too [4,5]. 2. Experimental No proper attention has been given to the fact that the polyethylene glycol (PEG) chain can be cat- 2.1. Chemicals ionized also by organic cations-protonized bases. In this paper the application of interactions between Phosphoric acid (analytical-reagent grade, E. Merck, Darmstadt, Germany), sodium hydroxide, * Corresponding author. potassium hydroxide (both analytical-reagent grade, 0021-9673 / 99 / $ – see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S0021-9673(98)00973-X