Evaluation of temperature-responsive open tubular capillary electrochromatographic column modified with poly(N-isopropylacrylamide)

We have recently reported the new concept of temperature-responsive capillary electrochromatography (CEC) using a poly(N-isopropylacrylamide)- grafted capillary column. In this study, temperature-responsive CEC separation of six clinical drugs including thymopentin and octreotide acetate (two peptides), homatropinum and oxazepam, benazepril hydrochloridec and amlodipine acetate was conducted to evaluate the separation efficiency of the CEC column. For comparison purposes, a bare capillary column was used for the control experiments. It was found that the resolutions and migration times of thymopentin and octreotide acetate, homatropinum and oxazepam on the modified column were much larger than those on the bare column. Enhanced resolving power mainly resulted from the interactions between analytes and PNIPAAm-grafted capillary surfaces. Therefore, the modification with temperature-responsive PNIPAAm was evaluated to achieve a better separation of the four analytes. The resolutions of benazepril hydrochloridec and amlodipine acetate on the modified column were smaller than those on the bare column because peak broadening and tailing were also obtained, although the differences in migration time between them were much larger. Furthermore, significant changes in the resolution and migration time were only observed on the modified column around the lower critical solution temperature of PNIPAAm, demonstrating its temperature- responsive property.