Capillary electrophoretic separation of mono- and dimaltosyl-β-cyclodextrins and determination of the stability constants of their benzoate complexes

Capillary electrophoretic analysis of the derivatives and isomers of benzoate and phthalate

A capillary electrophoretic method for the analysis of 12 commonly found derivatives and isomers of benzoate and phthalate, including p-toluic acid, p-acetamido and p-hydroxy derivatives of benzoic acid, salicylic acid and its acetyl ester, 2- and 4-isomers of carboxybenzaldehyde, meta-, para-, and ortho-isomers of phthalic acid, and monomethyl terephthalic acid was developed. Capillary electrophoresis (CE) was performed in the free zone electrophoresis mode. Performing CE in 10 mM phosphate buffer, pH 7.0 could separate most of the benzoic acid derivatives except the structural or positional isomers. The positional isomers of phthalic acids could be completely separated with co-addition of alpha- and beta-cyclodextrins. Addition of poly(ethylene glycol) 600 (4%) could further resolve some structural isomers. The CE method developed here is rapid, i.e. complete separation could be achieved in less than 8 min for the nine monoanionic benzoate derivatives and in less than 14 min for the three dianionic phthalate isomers. The new method has good precision and linearity and can be readily applied to real samples for quantitative analysis. It is sensitive and can detect sub-ppm (w/w) level of impurity in real terephthalic samples.

Nonlinear analysis of dynamic binding in affinity capillary electrophoresis demonstrated for inclusion complexes of beta-cyclodextrin

The stability of the molecular host-guest inclusion complexes of beta-cyclodextrin with benzoate and four different hydroxybenzoates is investigated. For the measurement of the binding constants an experimental method is devised that is based on affinity capillary electrophoresis (ACE) with indirect UV absorbance detection. We derive an explicit equation for effective mobilities in ACE experiments without violation of rigorous mass balance. This equation is employed in the nonlinear least-squares analyses of the experimental data yielding binding constants of 48+/-2 M(-1) for benzoate, 299+/-38 M(-1) for 2-hydroxybenzoate, 37+/-1 M(-1) for 3-hydroxybenzoate, 228+/-9 M(-1) for 4-hydroxybenzoate, and 895+/-110 M(-1) in the case of 2,4-dihydroxybenzoate.