Chiral Separation of Naproxen with Immobilized Liquid Phases

The use of solvent-impregnated resins (SIRs) as a hybrid technology between liquid extraction and adsorption was investigated for the enantioseparation of naproxen. A chiral recognition system from the enantioselective liquid–liquid extraction from the literature was taken as a starting point, comprising naproxen dissolved in an aqueous solution containing also the chiral selector hydroxypropyl-β-cyclodextrin (HP-β-CD) and an organic phase consisting of l-diisobutyl tartrate (l-IBT) dissolved in 1,2-dichloroethane. As a result of leaching of 1,2-dichloroethane, this solvent is unsuitable for use in a SIR and was replaced by 1-octanol. The effect of the concentrations of the chiral selectors on the equilibrium operational enantioselectivity was studied in the 1-octanol–water system. It was found that HP-β-CD strongly affected the operational selectivity but that l-IBT hardly affected the selectivity and could be omitted to reduce the complexity of the system. Enantioseparation of naproxen from aqueous systems using HP-β-CD as the selector with resin technology was investigated for both 1-octanol SIRs and nonimpregnated resins (NIRs) obtained using XAD4 resins. Both equilibrium capacities and uptake rates were studied, and it was found that the capacities were comparable in magnitude but that the uptake rates were remarkably much higher in the SIRs than in the NIRs. When applied in a packed bed, this will result in much shorter mass transfer zones and hence more effective use of the bed.