Temperature-responsive interpenetrating network hydrogel coated silica used for multi-mode stationary phases

In this work, a novel type of liquid chromatography stationary phase (Sil-NH₂@CMC/PNIPAM) with a multi-mode separation capability was obtained by coating a hydrogel onto the surface of amino silica (Sil-NH₂). The hydrogel comprises an interpenetrating network of carboxymethyl chitosan (CMC) and poly(<i>N</i>-isopropyl acrylamide) (PNIPAM). The modification process was successfully verified using Fourier Transform Infrared (FI-IR) spectroscopy, Scanning Electron Microscopy (SEM) and Thermogravimetric Analysis (TGA). This stationary phase effectively enables the separation and analysis of various compounds in three distinct modes: hydrophilic interaction chromatography (HILIC), reversed-phase liquid chromatography (RPLC), and ion exchange chromatography (IEC). Notably, PNIPAM exhibits a pronounced temperature-responsive characteristic in the stationary phase. Our experimental results suggest that this responsiveness is mainly attributed to the weakening of hydrogen bonds within PNIPAM as the temperature rises. Such weakening prompts the contraction of molecular chains, making the interpenetrating network more compact. As a result, there is a significant change in the retention behavior of the analyte. Additionally, the Sil-NH₂@CMC/PNIPAM column has demonstrated its efficacy in the separation and analysis of the ethanol extract from <i>Codonopsis pilosula</i>. Overall, this temperature-responsive and multi-mode stationary phase offers promising avenues for future innovations in High-performance Liquid Chromatography (HPLC).