Chiral separation of amino acids derivatized with fluoresceine-5-isothiocyanate by capillary electrophoresis and laser-induced fluorescence detection using mixed selectors of β-cyclodextrin and sodium taurocholate

Abstract

Chiral separation of 20 pairs of amino acids derivatized with fluoresceine-5-isothiocyanate (FITC) by capillary electrophoresis and laser-induced fluorescence detection was studied using the mixture of β-cyclodextrin (β-CD) and sodium taurocholate (STC) as selector. Resolution was considerably superior to that obtained by using either β-CD or STC alone. The molar ratio of β-CD to STC of about 2:3 was found to be critical to achieve maximum separation. At this β-CD-to-STC ratio, chiral separation occurred at really low total concentration of β-CD and STC (<0.1 m M). Other impacting factors were investigated including the total concentration of β-CD and STC, pH, and capillary conditioning procedure between two successive runs. Using a running buffer of 80 m M borate containing 20 m M β-CD and 30 m M STC at pH 9.3, all of the 20 pairs of FITC-amino acid enantiomers were baseline resolved. The resolutions of the most pairs of the amino acid enantiomers (17 of 20) were higher than 3.0, only three pairs gave a resolution lower than 3.0 but higher than 1.90 (β-phenylserine, pSer). The highest resolution reached 14.58 (Glu). Two derivatives of β-CD, 2-hydroxypropyl-β-CD (HP-β-CD) and heptakis(2,6-di- O-methyl)-β-CD (DM-β-CD) were also explored. HP-β-CD showed similar cooperative effect with STC, while DM-β-CD together with STC led to poorer chiral separation.