Optimisation methodology in the chiral and achiral separation in electrokinetic chromatography in the case of a multicomponent sample of dansyl amino acids

Chiral separation of terbutaline and non-steroidal anti-inflammatory drugs by using a new lysine-bridged hemispherodextrin in capillary electrophoresis

A method for the separation of a mixture of terbutaline and non-steroidal anti-inflammatory drugs was developed using capillary electrophoresis with a new hemispherodextrin, ad hoc designed, the lysine - bridged hemispherodextrin (THLYSH). The use of lysine residues to bridge the trehalose capping unit moiety to the cyclodextrin cavity gives rise to a receptor with two long chains with amine nitrogen atoms, whose charge can be easily tuned as a function of the solution pH. The new hemispherodextrin was accurately characterised by ESI-MS and NMR spectroscopy, also highlighting its protonation behaviour. Circular dichroism and ESR spectroscopy measurements were also carried out to test its inclusion ability towards anthraquinone-3-sulfonate and its metal coordination ability towards copper(II) ion, respectively. Analogously to the other hemispherodextrins, the main skill of this new derivative lies in its chiral selector properties, as shown by the separation of the enantiomeric pairs of terbutaline and ibuprofen, flurbiprofen, suprofen and tiaprofenic acid by capillary electrophoresis. The focused use of the solution equilibria involved in the separations made it possible to understand the phenomena occurring in solution, and to finely tune the charge status of the receptor. In this way the chiral separation of the racemic mixture was successfully obtained, even if the receptor was individually used, differently by the other hemispherodextrins previously studied whose chiral separation capabilities are present only if used as binary mixtures.

Derivatization in Capillary Electrophoresis

Capillary electrophoresis is a well-established separation technique in analytical research laboratories worldwide. Its interesting advantages make CE an efficient and potent alternative to other chromatographic techniques. However, it is also recognized that its main drawback is the relatively poor sensitivity when using optical detection. One way to overcome this limitation is to perform a derivatization reaction which is intended to provide the analyte more suitable analytical characteristics enabling a high sensitive detection. Based on the analytical step where the CE derivatization takes place, it can be classified as precapillary (before separation), in-capillary (during separation), or postcapillary (after separation). This chapter describes the application of four different derivatization protocols (in-capillary and precapillary modes) to carry out the achiral and chiral analysis of different compounds in food and biological samples with three different detection modes (UV, LIF, and MS).

Improving the sensitivity in chiral capillary electrophoresis

CE is known for being one of the most powerful analytical techniques when performing enantioseparations due to its numerous advantages such as excellent separation efficiency and extremely low solvents and reagents consumption, all of them derived from the capillary small dimensions. Moreover, it is worth highlighting that unlike in chromatographic techniques, in CE the chiral selector is generally within the separation medium instead of being attached to the separation column which makes the method optimization a more versatile task. Despite its numerous advantages, when using UV-Vis detection, CE lacks of sensitivity detection due to its short optical path length derived from the narrow separation capillary. This issue can be overcome by means of different approaches, either by sample treatment procedures or by in-capillary preconcentration techniques or even by employing detection systems more sensitive than UV-Vis, such as LIF or MS. The present review assembles the latest contributions regarding improvements of sensitivity in chiral CE published from June 2013 until May 2015, which follows the works included in a previous review reported by Sánchez-Hernández et al. [Electrophoresis 2014, 35, 12-27].