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In aqueous capillary electrophoresis selectivity between different alkyl chain lengths within one anionic surfactant-group markedly exceeds selectivity between different functionalities at a given chain length. Peak identification and quantitative analysis in complex mixtures is almost impossible, especially, if the sample contains ethoxylated surfactants as well. Applying nonaqueous capillary electrophoresis (NACE), significant differences in the mobilities of the various functionalities can be generated to exceed at satisfying separation. In this paper, method development of NACE systems is described and the application of these systems to anionic surfactant analysis in real sample matrices is documented.

Nonaqueous capillary electrophoresis (NACE) is a powerful tool for the analysis of surface-active substances, which represent a broad class of analytes containing cationic and anionic species, such as surfactants, phosphoric acid esters, and amines. In order to conduct an efficient method development in NACE, the influence of the electrolyte composition on the electroosmotic flow (EOF) of organic separation systems was systematically investigated. Background electrolytes and background chromophores appropriate for direct and indirect UV-detection were considered, as the majority of surface-active substances do not absorb UV-light. It was found that theoretical models developed to describe the EOF in aqueous electrolyte systems are insufficient for organic electrolyte systems. Experimental data on electroosmosis in a variety of organic solvents and mixtures of methanol and acetonitrile applying different background chromophores and basic or acidic additives are given. Differences between them are discussed with relation to the physicochemical properties of the organic solvents.

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