Influence of thermal annealing on the thermodynamic and mass transfer kinetic properties of D- and L-phenylalanine anilide on imprinted polymeric stationary phases

An investigation of the material, chromatographic, thermodynamic, and kinet ic properties of thermally treated (i.e., annealed) polymeric stationary ph ases imprinted with L-phenylalanine anilide (L-PA) was carried out. The imp rinting procedure of the solid phase used in this study was the same as for the untreated imprinted stationary phase studied previously. However, afte r polymerization, these new stationary phases were treated at elevated temp eratures (50, 120, 140, and 160 degrees C) for 24 h, The treatment at 120 a nd 140 degrees C led to a larger decrease in the retention of L-PA than tha t of D-PA. The polymer treated at 160 degrees C could no longer resolve the D,L-PA racemate. The heat treatments were accompanied by a decrease in swe lling and an increase in density causing an increase in the density of the remaining active sites. The polymer treated at 120 degrees C was chosen for classical frontal analysis. The adsorption isotherms and the mass-transfer rate coefficients of D- and L-PA were derived from the experimental breakt hrough curves. This study was carried out in the same temperature and conce ntration ranges as the previous one. A comparative discussion of the proper ties of the two polymeric molecular imprinted stationary phases is presente d. The thermal treatment increases the saturation capacity of the packing m aterial by one-third to one-half, reduces markedly the separation factor of the two enantiomers, and slightly accelerates their mass-transfer kinetics . There seems to be no interactions on the annealed polymer between the sel ective L-PA imprinted sites and the D-PA molecules.