124 Current Analytical Chemistry, 2012, 8, 124-132 1573-4110/12 $58.00+.00 © 2012 Bentham Science Publishers Improvement of Separation in Non-Aqueous Capillary Electrophoresis using Surfactants and Calixarenes as Additives Hashem Hisham a,c , Kaeßler Andre b and Jira Thomas b,* a Faculty of Pharmacy, Analytical Chemistry Department, Zagazig University, Egypt b Institute of Pharmacy, Pharmaceutical/Medicinal Chemistry, Ernst-Moritz-Arndt-University Greifswald, F.-L.-Jahn- Str. 17, D-17487 Greifswald, Germany c Faculty of Pharmacy, Pharmaceutical Chemistry Department, Jazan University, Saudi Arabia Abstract: In this study the effect of the presence of some different additives on non-aqueous capillary electrophoresis (NACE) separations of some structurally related compounds belonging to beta-blockers, antidepressants or neuroleptics were examined. Presence of surfactant was found to have a strong effect on separations. The anionic surfactant sodium dodecyl sulfate (SDS) enhanced separation of neuroleptics and beta-blockers. Upon combination between SDS and t- octyl-calix [4] arene-tetra-ethylester (TOCXTEE) separation of beta-blockers could be optimized. Use of cyanomethyl- calix [4] arene (CMCX [4] ) with buffer including SDS for separation of neuroleptics elongated the separation time and had some positive and negative effects on separation. The cationic surfactant tetrabutylammonium-bromide (TBAB) was found to be better than that of SDS for the separation of antidepressants. Structure of analytes and calixarenes played an effective role in separation. Keywords: Antidepressants, Beta-blockers, Calixarenes, NACE, Neuroleptics, Surfactants. 1. INTRODUCTION Capillary electrophoresis (CE) has experienced a rapid advancement since its introduction in 1981 [1]. The technique possesses both high resolving power and efficiencies. These features have attracted researchers to the technique, resulting in several contributions in this field [2]. Micelles were introduced to the CE to overcome the problem of the absence of charge on neutral analytes and to increase the solubility of hydrophobic analytes and additives [3]. This technique, termed micellar electrokinetic chromatography (MEKC), has experienced a rapid growth and popularity, especially for compounds with minimal solubility in aqueous, non-micellar media. MEKC was not used only for neutral but also for charged analytes. Organic solvents as modifiers have been shown to significantly affect both CE and MEKC separations [2, 4- 11]. The first report of 100% NACE separation appeared in 1984 [12]. In addition to the enhanced solubility of hydrophobic analytes and additives, organic solvents offer a greater flexibility in selectivity adjustment and permit a wider range of acid/base strength than in water, leading to extending the range of compounds that can be ionized. Chemical and physical properties of organic solvents are much different from those of water and can be exploited in optimization of the CE separations. Geiser and Veuthey [13, 14] mentioned that NACE does not always lead to better solubility or selectivity than aqueous CE, but the *Address correspondence to this author at the Institute of Pharmacy, Pharmaceutical/Medicinal Chemistry, Ernst-Moritz-Arndt-University Greifswald, F.-L.-Jahnstr. 17, D-17487 Greifswald, Germany; Tel: +49(0)3834/864850; Fax: +49(0)3834/864843; E-mail: jira@uni-greifswald.de large choice of solvents and solvent mixtures makes it very likely to achieve its intended purpose. Other advantages include the reduced interaction of hydrophobic compounds with capillary wall, ion pairing capabilities and ability to invoke various forms of chemical equilibriums in order to place a charge on compounds and thereby allow electrophoretic separation [14, 15]. Use of micelles in NACE is limited, due to the instability of micelles structure in the presence of non-aqueous media; however use of surfactants in non-aqueous media sometimes enhanced selectivity [16-21]. Walbroehl and Jorgenson [18] and Ahuja and Foley [19] used solvophobic interactions and hydrophobic interaction electrokinetic chromatography (HI-EKC), respectively, to describe an interaction between the individual surfactant molecules and analytes in the presence of high content of organic modifier, excluding a formation of micelle. After that HI-EKC was used for separation of neutral and charged compounds [19-22]. Addition of calixarenes [23-25] can be an alternative method to enhance the selectivity in NACE. Karbaum [23] was the first to examine addition of calixarenes to NACE for separation of structurally related compounds. This was followed by examinations by Sokoließ et al. [24] to separate the geometric isomers of neuroleptics using calixarenes as additives in NACE. Hashem et al. [25] found that the addition of calixarenes to AgNO 3 leads to an enhancement of sulfa- drugs separation. Although calixarenes are widely used in CE and HPLC, examination of their use in NACE was described only in the three previously mentioned works [23-25]. It was found that the combination of sodium dodecyl sulfate (SDS) and calixarenes enhanced separation of geometric isomers of neuroleptics [24]. Calixarenes can interact with analytes through hydrophobic interactions, hydrogen bond formation, charge-transfer-complex formation and/or inclusion complex formation [26-30].