[Separation of norephedrine enantiomers by high performance liquid chromatography (HPLC) with urea derivative as chiral stationary phase].
By using normal-phase HPLC with urea derivative as chiral stationary phase(CSP), the direct separation of racemic norephedrine has been investigated. The resolution was optimized by varying the concentration of iso-propanol in a ternary mobile phase which consists of two other components: hexane and 1,2-dichloroethane. The lower the percent of iso-propanol, the better the resolution is. But the retention time is longer as the percent of iso-propanol decreases. In an attempt to reduce the retention time without reducing the stereoselectivity, we chose the mixture of hexane, 1,2-dichloroethane and iso-propanol as the mobile phase with a proportion of 73.5:25:1.5 in vol. We also altered the organic modifier by substituting ethanol, acetonitrile and tetrahydrofuran (THF) for iso-propanol. The addition of ethanol appears to increase the hydrogen bond interactions between the solute and solvent, which results in lower k' values and an increase in alpha and Ra. Acetonitrile is only a kind of proton-accepter and the interactions of hydrogen bonding between the solute and solvent are weaker than iso-propanol, which results in higher k' values and a reduction in alpha and Ra. These separations are in agreement with the three-point rule. When THF is used as organic modifier, a reversed elution order and a more favorable separation can be obtained. The specific behavior of THF in HPLC has not been explained satisfactorily yet.
Wang
Z
Z
Department of Chemistry, Beijing Normal University, Beijing, 100875.
Yun
Z
Z
D002851:Chromatography, High Pressure Liquid; D010665:Phenylpropanolamine / Q000302:isolation & purification*; D013237:Stereoisomerism; D014508:Urea / Q000737:chemistry*
D010665:Phenylpropanolamine; D014508:Urea