PHOTO-TUNABLE STATIONARY PHASES FOR SEMI-MICRO HPLC

To develop photo-tunable chromatography, several azobenzene derivative s were immobilized or modified on silica gels or incorporated into pol ymers, The supports prepared were used as stationary phases in semi-mi cro HPLC, and the photo-dependence of their retention evaluated, On th ese stationary phases, the retention measured with 2-propanol in hexan e was increased by UV irradiation; in contrast, the retention was decr eased when methanol was used as mobile phase. It was assumed that the polarity of the stationary phase increases when the molecular structur e of the azobenzene moieties changes from the trans to the cis form. O n irradiation of the column with visible light after UV irradiation an d with methanol as mobile phase, the change of retention proved to be reversible. However, this reverse change was less dramatic than the in itial change. Such retention behavior is attributable to photo-isomeri zation of the azobenzene moieties, These findings will be exploited in our development of new photo-tunable stationary phases and new photo- controlled separation systems.