| Summary: | 碩士 === 國立臺灣大學 === 化學研究所 === 95 === Temperature effects on the enantioselectivity of basic analytes in CZE enantioseparation were studied under reversed-polarity mode using randomly sulfate-substituted beta-cyclodextrins (MI-S-beta-CD) as chiral seletors. Two catecholamines (epinephrine and isoproterenol) and two structurally related compounds (octapamine and norephedrine) were selected as test compounds in an electrophoretic system at low pH. The mobility differences between the (+)-enantiomers and the (-)-enantiomers of the two catecholamines and dopamine at 40 oC are greater than those at 25 oC with MI-S-beta-CD even at a concentration as low as 0.3 % (w/v). Thus the enantioselectivity of these three basic analytes increases with increasing temperature. This is resulted from the inequality of the temperature effect on the mobility of the two enantiomers. On the contrary, ephedrine behaves differently. The (+)-enantiomers of these basic analytes were found to migrate faster than the (-)-enantiomers. Consequently, the unusual temperature effect on the enantioselectivity can be observed when the mobility difference of the (+)-enantiomer between 40 oC and 25 oC is greater than that of the (-)-enantiomer using MI-S-beta-CD at a concentration greater than about 0.7 %, 0.4 % and 0.3 % (w/v) for enantioseparation of isoproterenol, epinephrine and octopamine, respectively. This unusual temperature effect offers the advantages to enhance enantioselectivity, to improve enantioseparation, and to reduce migration times.
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