CHARACTERIZATION OF BAND BROADENING IN CAPILLARY ELECTROPHORESIS DUE TO NONUNIFORM CAPILLARY GEOMETRIES

A simple procedure for creating a region of expanded diameter os a capillary column is described. This bubble-shaped on-column flow cell provides an extended path length for absorption detection in capillary electrophoresis (CE) or capillary chromatography. To properly probe the compressed analyte zone in this region, a laser beam with a noise-cancellation circuit was used. Up to 8X enhancement in signal was achieved. Characterization of CE flow profiles in the bubble-shaped region shows that distortions in flow lead to band broadening, especially when a rapid change in diameter over a short column length is present. The electric field lines are, however, still oriented axially throughout the bubble region. Similar disturbances are expected in any coupling schemes in CE that involve a geometry change, in addition to multipath effects and distortions in the electric field.