IMAGING OF ELECTROPHORETIC FLOW ACROSS A CAPILLARY JUNCTION

We have designed a simple system to allow visualization of electroosmotic flow across a capillary junction. Two capillaries are placed in close proximity by careful micropositioning, and the distance between the capillaries is controlled with submicron resolution. The junction thus produced is placed at the focal point of a stereomicroscope, where the image collected by the microscope is imaged onto a CCD camera. Illumination of the junction (immersed in a buffer solution) allows visualization of the electroosmosis of a dye across the liquid junction. This has allowed the determination of the dimensional characteristics of the junction and the optimization of the composition of the buffer bathing the junction, thereby allowing efficient transfer of a sample across a 50-200-mum gap.