Enantioselectivity of basic analytes in CZE enantioseparation under reversed-polarity mode using sulfated beta-cyclodextrins as chiral selectors: An unusual temperature effect.
Temperature effects on the enantioselectivity of basic analytes in CZE enantioseparation were studied under reversed-polarity mode using randomly sulfate-substituted beta-CDs (MI-S-beta-CD) as chiral seletors. Two catecholamines (epinephrine and isoproterenol) and two structurally related compounds (octopamine 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 degrees C are greater than those at 25 degrees C 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 phenomenon results from the inequality of the temperature effect on the mobility of the two enantiomers. In contrast, norephedrine 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 and 25 degrees C is greater than that of the (-)-enantiomer using MI-S-beta-CD at a concentration greater than about 0.7% w/v for enantioseparation of isoproterenol, 0.4% w/v for epinephrine, and 0.3% w/v for octopamine. This unusual temperature effect offers the advantages to enhance enantioselectivity, to improve enantioseparation, and to reduce migration times.
Lin
Chen-Hsing
CH
Department of Applied Chemistry, Fooyin University, Ta-Liao, Kao-Hsiung County, Taiwan.
Kuo
Chia-Ming
CM
Liu
Yu-Chih
YC
Cheng
Hsu-Tun
HT
Lin
Wann-Yin
WY
Wu
Jong-Chang
JC
Wang
Li-Fen
LF
Lin
Ching-Erh
CE
D002395:Catecholamines / Q000302:isolation & purification*; D019075:Electrophoresis, Capillary / Q000379:methods*; D013237:Stereoisomerism; D013431:Sulfates / Q000737:chemistry*; D013696:Temperature; D047392:beta-Cyclodextrins / Q000737:chemistry*
D002395:Catecholamines; D013431:Sulfates; D047392:beta-Cyclodextrins