Separation of fatty alcohol polyethoxylates by capillary electrophoresis through easy electroosmotic flow control with a quaternary diammonium salt

An optimised protocol for the fast and reliable analysis of fatty alcohol polyethoxylates (FAEs), with resolution between the alkyl chain and ethylene oxide (EO) oligomers, is reported. Phthalic and maleic anhydrides were used to quickly form the hemiesters, which were separated by capillary electrophoresis. Effective reduction of the electroosmotic flow to very low values was achieved by previously rinsing the capillary with a quaternary diammonium salt, which remains strongly adsorbed to the silica wall. The phthalic hemiesters of a FAE mixture with 10 carbon atoms in the alkyl chain, and an average EO number of 6, were separated in a background electrolyte (BGE) containing 25 mM borate buffer of pH 9.0 in water. The same capillary pre-treatment was used to separate mixtures of the maleic hemiesters of hydrophobic FAEs, having 12–16 carbon atoms in the alkyl chain and an average EO number of 3. Full resolution of all the oligomers was achieved by using a finely tuned BGE in which a 35% borate buffer was mixed with 65% acetonitrile