Foam-based electrophoretic separation of charged dyes

Electrophoretic separation of a fluorescent dye mixture, containing rhodamine B and fluoresceine, in liquid foams stabilised by either anionic, cationic or non-ionic surfactants in water-glycerol mixtures was studied in a custom-designed foam separation device. The effects of the external electric field applied across the foam and the initial pH of the solution on the effectiveness of separation was also studied. The fluid motion due to electroosmosis and resulting back pressure within the foam and local pH changes was found to be complex and affected the separation. Fluorescein dye molecules, which have a positive or negative charge depending on the solution pH, aggregated in the vicinity of an electrode leaving a pure band of neutral dye rhodamine B. The effectiveness of the separation was quantified by the percentage width of the pure rhodamine B band, which was found to be between 29% and 42%. This study demonstrates the potential of liquid foam as a platform for electrophoretic separation.