Temperature-Controlled High-Performance Liquid Chromatography Using a Uniformly Sized Temperature-Responsive Polymer-Based Packing Material

Uniformly sized polymer-based packing materials modified with a temperature-responsive polymeric selector, poly(N-isopropylacrylamide), on either the internal or the external surface were prepared by an in situ surfaceselective modification method. These packing materials were utilized as stationary phases in reversed-phase highperformance liquid chromatography to evaluate their ability to thermally control chromatographic separation selectivity. A packing material having a modified internal surface showed temperature-dependent separation selectivity in drug separation. Drugs that could not be separated below the phase transition temperature of the poly(N-isopropylacrylamide) selector were separated faster and with much better resolution above the phase transition temperature, while the unmodified base packing material afforded worse resolution of the drugs above the phase transition temperature due to the peak overlapping resulting from faster elution of all the solutes employed. In addition, a packing material modified on the external surface showed a temperature-responsive shift of the elution region for a polypeptide such as BSA, which was thought to be useful in direct injection of a serum sample.