Principles for microscale separations based on redox-active surfactants and electrochemical methods

We report principles for microscale separations based on selective solubili zation and deposition of sparingly water-soluble compounds by an aqueous so lution of a redox-active surfactant. The surfactant, (11-ferrocenylundecyl) -trimethylammonium bromide, undergoes a reversible change in micellization upon oxidation or reduction. This change in aggregation is exploited in a g eneral scheme in which micelles of reduced surfactant are formed and then p ut hi contact with a mixture of hydrophobic compounds leading to selective solubilization of the compounds. The micelles are then electrochemically di srupted, leading to the selective deposition of their contents. We measured the selectivity of the solubilization and deposition processes using mixtu res of two model drug-like compounds, o-tolueneazo-beta -naphthol (I) and 1 -phenylazo-2-naphthylamine (II). By repeatedly solubilizing and depositing a mixture that initially contained equal mole fractions of each compound, w e demonstrate formation of a product that contains 98.4% of I after six cyc les. Because the aggregation states of redox-active surfactants are easily controlled within simple microfabricated structures, including structures t hat define small stationary volumes (e.g., wells of a microtiter plate) or flowing volumes of liquids (e.g., microfabricated channels), we believe the se principles may be useful for the purification or analysis of compounds i n microscale chemical process systems. When used for purification, these pr inciples provide separation of surfactant and product.