Capillary electrophoretic separation of positional isomers of hydroxynaphthalenecarboxylic acids through the formation of inclusion complexes with β-cyclodextrin Original Research Article

Capillary electrophoresis for 1,2-, 2,1-, 2,3-, and 6,2-hydroxynaphthalenecarboxylic acids (HNs) has been examined. At pH 8.0, where all of the HN positional isomers are in a monoanionic form, three peaks have been observed for a mixture of the four HNs, suggesting different molecular volumes including a hydration shell. There have also been three peaks for the four HNs at pH 10.1 where the mono- and dianions of the HNs coexist, except for 2,3-HN which is exclusively in a monoanionic form. The effects of β-cyclodextrin (β-CD) on the migration times of the HNs have been examined at pH 10.1. In addition, the apparent equilibrium constants for the formation of inclusion complexes of β-CD with the HNs have been estimated. The four HN isomers have been baseline separated in pH 10.1 buffers containing β-CD of 5.0 × 10−4–1.0 × 10−3 mol dm−3.