Determination of cyclodextrins and their derivatives by capillary electrophoresis with indirect UV and conductivity detection.

A fast and simple capillary electrophoretic method suitable for the determination of native alpha-, beta-, gamma-cyclodextrins, their randomly substituted tert-butyl derivatives (average degree of substitution 3.8-4.4), heptakis (2,6-di-O-methyl)- and heptakis (2,3,6-tri-O-methyl)-beta-cyclodextrin was developed. Naphthyl-2-sulfonic acid (2-NSA), 3-iodobenzoic acid (3-IBA) and (1S)-1-phenylethylamine (PHEA) were tested as selective complex forming and UV absorbing background electrolyte additives. The composition of optimized background electrolyte for the separation of uncharged cyclodextrins and their derivatives was: 15 mM 3-iodobenzoic acid titrated with tris[hydroxymethyl]aminomethane to pH 8.0, 5% (v/v) of acetonitrile. A complete resolution of mono-2-O-, mono-3-O- and mono-6-O-carboxymethyl-beta-cyclodextrin regioisomers was achieved in the optimized background electrolyte system: 40 mM PHEA titrated with 2-[N-morpholino]ethanesulfonic acid to pH 5.6. In addition to indirect UV detection a contactless conductometric detector was successfully utilized.