REVERSED DETERMINATION OF THE FORMATION-CONSTANTS OF 1-ALLYL TERGURIDE WITH MANDELIC-ACID OPTICAL ISOMERS USING CAPILLARY ELECTROPHORESIS

A method is presented for the accurate determination of equilibrium co nstants of complex formation between mandelic acid enantiomers and 1-a llyl terguride. In earlier studies this ergot alkaloid has proven to b e a potential chiral selector for racemic acidic compounds. In these s tudies, the formation constant was determined by measuring the effecti ve mobility of some racemic acidic analytes at varying concentrations of ergot alkaloid. For these experiments, the assumption was made that the complex mobility was zero. In order to validate these data, the e xperimental set-up was reversed. In this new set-up, the cationic chir al selector is injected as sample, while the background electrolyte (B GE) contained either of the two optically pure mandelic acid enantiome rs, in varying concentrations. For accurate determination of the effec tive mobility, tetrabutylammonium was used as a mobility reference and the ionic strength of the BGE was kept constant. By performing these experiments at two different pH values, it was possible to determine c omplex-formation constants, and chiral selectivity towards both the di ssociated and the non-dissociated mandelic acid enantiomers. Results s how that only the dissociated acid interacts selectively with the ergo t alkaloid confirming our earlier results. In our earlier experiments we made the assumption that the non-dissociated acid does not interact with the ergot alkaloid. The experimental data obtained by the curren t method however, show that, although this interaction is not enantios elective, it cannot be neglected. Optically pure mandelic acid proved to be a suitable chiral selector for the separation of terguride enant iomers.