Abstract
The potential effects of deep eutectic solvents (DESs) based on eutectic mixtures of amino acids (AAs) and tetrabutylammonium bromide (TBABr) in combination with beta-cyclodextrin (β-CD) were first evaluated as chiral systems in capillary electrophoresis (CE). Three DESs: tetrabutylammonium bromide/l-arginine (TBABr/l-Arg), tetrabutylammonium bromide/l-alanine (TBABr/l-Ala) and tetrabutylammonium bromide/l-proline (TBABr/l-Pro)) were used. Markedly improved chiral discrimination for four native amino acids (dl-methionine, dl-valine, dl-serine and dl-threonine) were obtained with high resolutions ranging from 4.78 to 9.84 in the presence of TBABr/l-Arg/β-CD chiral selector. Optimal CE conditions were a BGE containing 15 mmol L−1 β-CD and 10% (v/v) TBABr/l-Arg mixed with 50 mmol L−1 borate at pH 9.5, 20 kV applied voltage and 25 °C capillary temperature. The relative standard deviations (RSDs) of intra- and inter-day variations of migration times were less than 2.2% and 3.5%, respectively. l-Arg has the highest isoelectric point (pI = 10.7 at 25 °C) among protein amino acids which is appropriate for formation of stable DES at an alkaline separation medium. Moreover, TBABr/l-Arg/β-CD possessed the lowest electroosmotic flow velocity (0.018 cm2 min−1 V−1) among the investigated chiral systems providing more opportunities for chiral recognition of analytes within 14 min. Analytical characteristics of the CE/UV developed method were evaluated and demonstrated to be adequate to apply the methodology to enantiomeric analysis of methionine in commercial dietary supplements including enantiomeric impurity of d-methionine at 0.03% level (m/m). Therefore, the proposed TBABr/l-Arg/β-CD could be used as a versatile, simple and effective selector for baseline chiral recognition in CE.
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Alshitari, W., Abd El-Hady, D. Use of Tetrabutylammonium Bromide and l-Arginine-Based Deep Eutectic Mixture in Combination with Beta-Cyclodextrin for Chiral Discrimination of Amino Acids in Capillary Electrophoresis. Chromatographia 84, 1151–1162 (2021). https://doi.org/10.1007/s10337-021-04100-4
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DOI: https://doi.org/10.1007/s10337-021-04100-4