Optimization of surface imprinted layer attached poly(vinylidene fluoride) membrane for selective separation of salicylic acid from acetylsalicylic acid using central composite design

Highly selective molecularly imprinted membranes (MIM) for salicylic acid (SA) were synthesized with methacrylic acid (MAA), acrylamide (AM) or 4-vinylpyridine (4-VP) as the functional monomer, respectively based on the poly(vinylidene fluoride) microfiltration membrane. Fast kinetic equilibrium for the rebinding of SA was found on all the imprinted membranes. Comparing with MAA-MIM and AM-MIM, the 4-VP-MIM presented stronger adsorption capacity and higher permeation selectivity for SA due to the formation of ionic bond between SA and 4-VP. The separation effect on SA and acetylsalicylic acid (ASA) were strongly affected by the amount of polymer layers on the MIM. The experimental data were well fitted to a second-order polynomial equation using multiple regression analysis and also analyzed by analysis of variance (ANOVA). Response surface methodology was employed to investigate the best combination of separation conditions in the dynamic separation process. The optimal conditions for the separation of SA from ASA were as follows: the SA concentration of 10mgL^-1, the temperature of 10°C and the flow rate of 1mLmin^-1. Under these conditions, the experimental separation factor of SA and ASA was 10.24±1.06%, which was close to the predicted separation factor.