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

Abstract

The phenomenon of electrophoresis in free solution has been studied theoretically down to the molecular level for decades. In addition, intermolecular photo-induced proton transfer reactions, which occur in a wide class of molecules (phenols and aminoarenes) as well as proteins (green fluorescent protein), were also studied extensively. However, the study of the effect of light-induced electrophoretic mobility changes of the analytes in electrophoresis was begun only recently. In the present work, capillary zone electrophoresis was chosen as the environment to measure the magnitude of these electrophoretic mobility shifts induced by light. Background electrolytes (running electrolytes) with high refractive indices were developed, allowing the 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 solitary waves result from competition between thermal diffusion (dispersion mechanism) and a nonlinear (band compression) effect due to the combined electrophoresis phenomenon and absorption of guided light by the molecules of the band (which are subjected to a "reversible intermolecular proton transfer reaction" as one of their decay routes). The possibilities of applying this effect to different methods and techniques are also discussed.

Cyclic band compression in toroidal capillary electrophoresis delivers an unlimited number of theoretical plates with a quadratic growth in time and a constant peak capacity

“…In one procedure, a segment of the capillary is illuminated with light, and this in turn modulates the pH of some buffers or the p K a of some analytes. Originally, it was used to generate solitary waves , but this could also be used to compress the analyte bands, decreasing their widths and SDs ( σ ). Nevertheless, this is slightly limited because there are only a few classes of compounds that exhibit both a light‐sensitive p K a and the required photorobustness for such an application.…”