Institute for Analytical Chemistry, University of Vienna, A 1090 Vienna Währingerstr. 38, A 1090 Vienna, Austria.
J Chromatogr A. 2014 Mar 28;1335:16-30. doi: 10.1016/j.chroma.2014.01.010. Epub 2014 Jan 13.
This two-part review critically gives an overview on the theoretical and practical advances in non-aqueous capillary electrophoresis (NACE) achieved over the recent five years. Part I starts out by reviewing the aspects relevant to electromigration in organic solvents and evaluates potential advantages of the latter in comparison to aqueous solvent systems. The crucial role of solubility for the species involved in CE - analytes and back ground electrolyte constituents - is discussed both for ionic and neutral compounds. The impact of organic solvents on the electrophoretic and electroosmotic mobility and on the ionization (pKa values) of weak acids and bases is highlighted. Special emphasis is placed on methanol, acetonitrile and mixtures of these solvents, being the most frequent employed media for NACE applications. In addition, also solvents less commonly used in NACE will be covered, including other alcohols, amides (formamide, N-methylformamide, N,N-dimethylformamide, N,N-dimethylacetamide), propylene carbonate, dimethylsulphoxide, and nitromethane. The discussions address the consequences of dramatic pKa shifts frequently seen for weak acids and bases, and the important contributions of medium-specific electroosmotic flow (EOF) to electromigration in nonaqueous media. Important for NACE, the role of the water content on pKa and mobility is analyzed. Finally, association phenomena rather specific to nonaqueous solvents (ion pairing, homo- and heteroconjugation) will be addressed, along with their potential advantages for the development of NACE separation protocols. It is pointed out that this review is not intended as a listing of all papers that have been published on NACE in the period mentioned above. It rather deals with general aspects of migration and selectivity in organic solvent systems, and discusses - critically - examples from the literature with particular interest to the topic. An analog discussion about the role of the solvent on efficiency will be presented in Part II.
这篇由两部分组成的综述批判性地概述了过去五年中非水相毛细管电泳（NACE）在理论和实践上的进展。第一部分首先回顾了有机溶剂中电泳迁移的相关方面，并评估了后者相对于水溶剂体系的潜在优势。讨论了涉及 CE 的物种（分析物和背景电解质成分）的溶解度，包括离子和中性化合物。强调了有机溶剂对电泳和电渗流迁移以及对弱酸和弱碱的离解（pKa 值）的影响。特别强调了甲醇、乙腈以及这些溶剂的混合物，它们是最常用于 NACE 应用的介质。此外，还将涵盖在 NACE 中较少使用的溶剂，包括其他醇、酰胺（甲酰胺、N-甲基甲酰胺、N,N-二甲基甲酰胺、N,N-二甲基乙酰胺）、碳酸丙烯酯、二甲基亚砜和硝基甲烷。讨论涉及到弱酸碱经常出现的剧烈 pKa 位移的后果，以及介质特异性电渗流（EOF）对非水介质中电泳迁移的重要贡献。对于 NACE 来说，分析了水含量对 pKa 和迁移率的重要作用。最后，将讨论非水溶剂中特定的缔合现象（离子对形成、同共轭和异共轭），以及它们对 NACE 分离方法发展的潜在优势。需要指出的是，本综述并非旨在列出上述期间发表的所有关于 NACE 的论文。而是处理有机溶剂系统中迁移和选择性的一般方面，并批判性地讨论文献中与主题特别相关的示例。在第二部分中，将对溶剂对效率的作用进行类似的讨论。
