Non-Aqueous Capillary Electrophoresis

Non-aqueous capillary electrophoresis and capillary electrochromatography are special variants of these techniques. Here, organic solvents or their mixtures with or without dissolved electrolytes are used as separation buffer or mobile phase, respectively

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Non-Aqueous Capillary Electrophoresis Michał Szumski and Bogusław Buszewski

Abstract Non-aqueous capillary electrophoresis and capillary electrochromatography are special variants of these techniques. Here, organic solvents or their mixtures with or without dissolved electrolytes are used as separation buffer or mobile phase, respectively. The most important features of non-aqueous systems are: better solubility of more hydrophobic ionic substances (many natural products) than in water, much less current and Joule heating allows for using highly concentrated buffers and/or larger capillary internal diameters, polar interactions are enhanced in organic solvents which is often highly advantageous in chiral separation systems. This chapter presents most frequently used solvents, their properties, as well as shows pH* scale which is often used in non-aqueous systems. In classical CEC and CEC aqueous or hydroorganic solvents are used but it is different in non-aqueous CE (NACE) and CEC (NACEC) which employ a wide range of organic solvents, without any addition of water. Despite non-aqueous approach was described as far as in the 1980s (Walbroehl and Jorgenson) [1, 2], a systematic increase in number of published papers has been dated since 1994 [3, 4]. There are several reasons for using NACE: • • • •

Improvement in selectivity. Electrophoresis in large bore capillaries—‘‘preparative’’ CE. Electrophoresis of compounds insoluble or slightly soluble in water. Employing during some separations (for example chiral compounds) polar interactions which are not present in water because of its ‘‘leveling effect’’. • In some cases an increase of fluorescence intensity may be observed when switching to NACE, which positively affects LOD.

M. Szumski (&)  B. Buszewski Faculty of Chemistry, Nicolaus Copernicus University, Torun´, Poland e-mail: [email protected]

B. Buszewski et al. (eds.), Electromigration Techniques, Springer Series in Chemical Physics 105, DOI: 10.1007/978-3-642-35043-6_11,  Springer-Verlag Berlin Heidelberg 2013

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M. Szumski and B. Buszewski

11.1 Solvents When compared to aqueous systems, application of a wide range of organic solvents and their mixtures, characterized by different properties opens new possibilities in controlling selectivity. For example, pKa values in organic solvents may differ significantly from those determined in water, which may allow for separation of analytes impossible to be separated in aqueous conditions. This is so, because the solvents used in NACE can belong to amphiprotic (like methanol) or typical proton acceptors (for example formamide) (Table 11.1). It may be quite important to pay attention to purity of the solvents used, particularly to possible water content. Sometimes when important data, not only analytical but also thermodynamic (for example dissociation constants), have to be obtained it might be necessary to determine water content, which may be done using Karl-Fischer method [5, 6]. In many pure solvents the electroosmotic flow may be observed during CE