Electrokinetic separations juxtaposed by flow fields represent a valuable tool for separating complex mixtures. A novel separations technique that can dynamically capture specific species in bulk solution from a complex mixture without molecular recognition elements is presented here. The basic premise of the new device is based on electrophoretic principles and exploits differential transport near the capillary entrance by employing a large contraction ratio and setting flow and electric field gradients opposite one another.

Initial experiments examine the interface where potential is initiated near a channel by examining the fundamental parameters of flow dynamics, applied potential, and electrophoretic mobility. Published results demonstrate the successful exclusion, concentration, and differentiation of small dye molecules in solution. Using a first-generation flow injection-like strategy, Methyl Violet (MW 393.9) was concentrated up to 40 times in 30 s. Additionally, positively-charged Neutral Red (MW 288.8) was isolated from an aspartic acid buffer (pH 2.8) containing cationic Methyl Green dye (MW 458.5). The Neutral Red dye was successfully concentrated while allowing the Methyl Green to evacuate the main chamber at 2.5 kV. The critical parameter for exclusion is the threshold voltage of a species, or the potential at which an analyte will be excluded from the capillary. The results from these experiments enabled the study of proteins using the electrophoretic exclusion method. Several parameters were altered in order to examine proteins, including buffer, capillary, and pH. The concentration enhancement and exclusion profile of myoglobin (16.9 kDA) is investigated. Preliminary results indicate over 1200 times concentration of myoglobin in 60 s. Furthermore, the differentiation of two negatively-charged proteins (myoglobin and allophycocyanin, 105 kDA) and two proteins of opposite charge (allophycocyanin and cytochrome c) is demonstrated. This simple approach of countering electric field and hydrodynamic flow to exclude species has the potential to improve upon electrophoretic separations and the analysis of complex biological solutions.