Retention of small molecules on polymethacrylate monolithic capillary columns

Abstract

In this paper, the concentration of N-isopropylacrylamide in the polymerization mixture has been variedto prepare several polymethacrylate monolithic capillary columns. Polymer monoliths combining N-isopropylacrylamide with zwitterion monomer, as well as various dimethacrylate crosslinking monomershave been prepared and characterized. Uracil, thiourea, phenol, toluene, ethylbenzene, propylbenzene,and butylbenzene have been used to characterize retention of prepared capillary columns in the mobilephases with 40–95% of acetonitrile and at working temperatures ranging from 25 to 60◦C. By an optimiza-tion of six-parameter polynomial models we have found that the retention of small molecules is affectedmainly by the concentration of the acetonitrile in the mobile phase with very low contribution of work-ing temperature and combined effect of acetonitrile concentration and temperature. Concentration ofthe mobile phase controlled also enthalpy of the retention. On the other hand, entropic contribution wasalmost insensitive to the change of the mobile phase composition, especially for mobile phases containingmore than 60% of acetonitrile.