Electrodialytic Reagent Introduction in Flow Systems

We report on electrodialytic introduction of ionizable molecules of significant size (e.g., 4-(2-pyridyl(azo) resorcinol, PAR)) in capillary scale flow systems. Such reagent introduction can be conducted without volumetric dilution, easily programmed through current control and with excellent mixing characteristics. Electrodialytic transport of large hydrophobic aromatic ions through conventional aromatic ion exchangers is inefficient. Such ions are strongly retained by hydrophobic and pi-pi interactions. An external electric field cannot modulate this retention. We show that the electrodialytic introduction of aromatic dye anions is readily possible through both unmodified cellulose dialysis membranes and through cellulose membranes modified with methacrylate skeleton anion exchangers. The applied electrodialysis current conveniently controls the reagent flux. Although the applied voltage is sufficient to cause electrolytic production of hydrogen and oxygen; the gases are generated outside the flowstream of interest. The present device was constructed with a sub-microliter internal volume. We show capillary scale trace analysis of transition metals. A limit of detection of 0.5 fmol Zn (S/N = 3) is demonstrated with a capillary scale flow injection system with a simple light emitting diode based detector.