We have developed a new method of chromatography, temperature-responsive chromatography, using packing materials modified with poly(N-isopropylacrylamide) (PNIPAAm). The temperature-responsive polymer, PNIPAAm, shows a reversible and sharp phase transition in an aqueous solution. The PNIPAAm-modified stationary phase alters the properties of the surface from hydrophilic to hydrophobic in response to temperature changes at the phase-transition temperature. In this study, we examined the separation of five catechins (epigallocatechin, epicatechin, catechin, epigallocatechin gallate and epicatechin gallate) using a PNIPAAm-modified column without changing the composition of the mobile phase. In this method, interactions between catechins and the stationary phases were controlled by the temperature. The retention times of all catechins were retarded, because the interaction increased at elevated temperature. We achieved the separation of catechins using only an aqueous solution as a mobile phase by temperature-responsive chromatography.
