Experimental observation of light-induced solitary waves of analyte bands in capillary electrophoresis

The phenomenon of electrophoresis in free solution has been studied theoret ically down to the molecular level for decades. In addition, intermolecular photo-induced proton transfer reactions, which occur in a wide class of mo lecules (phenols and aminoarenes) as well as proteins (green fluorescent pr otein), were also studied extensively. However, the study of the effect of light-induced electrophoretic mobility changes of the analytes in electroph oresis was begun only recently. In the present work, capillary zone electro phoresis was chosen as the environment to measure the magnitude of these el ectrophoretic mobility shifts induced by light. Background electrolytes (ru nning electrolytes) with high refractive indices were developed, allowing t he capillary to work like an optical fiber. The experimental conditions for obtaining stable coupling and guided laser light along the liquid core are discussed. Experimental evidence of band compression is observed, leading to a solitary wave behavior of the analyte band (2-naphthol). These solitar y waves result from competition between thermal diffusion (dispersion mecha nism) and a nonlinear (band compression) effect due to the combined electro phoresis phenomenon and absorption of guided light by the molecules of the band (which are subjected to a "reversible intermolecular proton transfer r eaction" as one of their decay routes). The possibilities of applying this effect to different methods and techniques are also discussed.