Enantiomer separations of phenylephrine and synephrine by capillary electrochromatography on bare silica stationary phase using hydroxypropyl-?-cyclodextrin as a mobile phase additive

The feasibility of enantiomer separation by capillary electrochromatography (CEC) was shown on 75-μm (i.d.) capillary columns packed with 3-μm bare silica packings. Racemic phenylephrine [3-hydroxy-α-(methylaminomethyl) benzyl alconhol] and synephrine [4-hydroxy-α-(methylaminomethyl) benzyl alconhol] were resolved on bare silica stationary phase using hydroxypropyl-β-cyclodextrin (HPβCD) as a chiral mobile phase additive. The effects of HPβCD concentration, pH of mobile phase, electrolyte concentration, and separation temperature have been investigated. Optimum separations were achieved for phenylephrine using 10 mM Tris–H3PO4 buffer (pH 3.12) containing 14 mM HPβCD and those of synephrine with HPβCD concentration 18 mM at 25°C. The chiral recognition mechanisms in these systems were also discussed.