Non-aqueous capillary electrophoretic separation of Bronsted acids as heteroconjugated anions

Capillary electrophoretic separation of phenols, carboxylic acids, and alcohols has been studied in acetonitrile. Under the condition where these compounds are not dissociated, they interact with an inorganic anion added to a running solution to form heteroconjugated anions, and migrate toward the anode. Though small anions with high charge densities (e.g. chloride) form more stable heteroconjugated anions, even perchlorate ions are involved in heteroconjugation with phenols and carboxylic acids, and allows them to behave as anionic species. The extent of heteroconjugation is dependent on the charge density in the oxygen atoms of the carboxyl group in a carboxylic acid and the hydroxyl group in a phenol or an alcohol, and thus the order of migration correlates well with various electron induction factors (e.g. Hammet sigma or pK(a) values). Quantitative evaluation and determination of heteroconjugated anion formation constants are also feasible.