Aqueous chromatography utilizing pH-/temperature responsive polymer stationary phases to separate ionic bioactive compounds

Cross-linked poly(N-isopropylacrylamide-co-acrylic acid) (poly(IPAAm-co-AAc))-grafted silica bead surfaces mere prepared and applied as new column matric; materials that exploit temperature-responsive anionic chromatography to separate basic bioactive compounds,specifically catecholamine derivatives,in aqueous mobile phases. Since poly(IPAAm-co-AAc); has a well-known temperature-responsive phase transition and apparent pK(a) shift, polymer-grafted silica bead surfaces are expected to exhibit simultaneous hydrophilic/hydrophobic and charge density alterations under thermal stimuli. Elution behavior of catecholamine derivatives from a copolymer-modified head packed column was monitored using aqueous mobile-phase HPLC under varying temperature and pH, Catecholamine derivatives had higher retention times on poly(IPAAm-co-AAc) columns at higher pH in comparison with those or, noncharged PIPAAm reference columns, suggesting an electrostatic interaction as a separation mode. Temperature also affected the retention behavior of catecholamine derivatives. Optimal separation of four catecholamine derivatives aas achieved at elevated temperature, 50 degreesC, and at pH 7.0. This is due to the increased hydrophobicity of the stationary phase as evidenced by the elution of a nonionic hydrophobic steroid. From these results, mutual influences of both electrostatic and hydrophobic interactions between basic catecholamine derivatives and pH-/temperature-responsive surfaces are noted. Consequently, elution of weakly charged bioactive compounds is readily regulated through the modulation of stationary-phase thermoresponsive hydrophilic/hydrophobic and charge density changes.