Surfactant analysis by capillary electrophoresis

Surfactants are widely used in industrial and consumer formulations as comp lex mixtures of homologues and isomers. Efficient separation methods are th erefore required for selective analysis In the past few years, capillary el ectrophoresis (CE) has been successfully used to separate anionic, cationic and neutral surfactants in "real-world" samples. Linear alkylbenzenesulfon ates (LAS) are the most important surfactants. They have been determined as total LAS and separated into homologues and isomers in industrial and hous ehold formulations. The low detection pow,er of CE limits its applicability for environmental analysis but after preconcentration it was also possible to detect concentrations in the mu g/l range in water samples. For anionic surfactants without chromophores, indirect UV detection has been used in b uffers with electrophoretic mobilities close to the analyte mobility. Separ ations in pure organic solvents offer the possibility of high peak resoluti on of homologues, e.g. in cosmetics. Cationic surfactants sorb strongly onto the capillary, surface and form mic elles easily, leading to peak tailing and insufficient resolution. The addi tion of organic solvents to the buffer or performing rite separation in a n on-aqueous medium resulted in high resolution and good peak shape. For indi rect UV detection, the use of absorbing cationic surfactants as buffer addi tives is a most promising way to achieve high sensitivity. The separation m ethods were applied to cosmetics and pharmaceuticals. Nonionics of the alkylphenol polyethoxylate type were separated according t o their degree of ethoxylation, using association with sodium dodecylsulfat e in buffers containing high amounts of acetonitrile. In this case, micelle formation of SDS is inhibited. The strength of the association complex and therefore the migration behavior depends oil the degree of ethoxylation, a llowing sufficient characterization of technical products. Determination of Triton X-100 in vaccines was also possible. Alcohol ethoxylates were deriv atized with phthalic anhydride to obtain W-absorbing anions, which could be efficiently separated in detergents using buffers with high organic conten ts.