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Optimizing Band Width and Resolution in Micro-Free Flow Electrophoresis

Bryan Fonslow and Michael Bowser have recently described the sources of band broadening in micro-free flow electrophoresis (μ-FFE) devices. This allows important variables such as flow rate and separation voltage to be optimized to minimize band width and maximize resolution. This work will be published in the Dec. 15 issue of Analytical Chemistry [Anal. Chem. 78, 8236-8244 (2006).

μ-FFE is a continuous separation technique that holds great promise for microscale preparative separations and continuous monitoring applications. The mechanism of separation is shown in the figure below. A continuous stream of sample is introduced into a planar flow channel. Analytes are deflected laterally in the electric field based on their size and charge. The mechanisms of band broadening in μ-FFE are fundamentally different than most other separation techniques because flow and separation do not occur in the same direction. The absence of rigorous theories describing band broadening and resolution has hampered μ-FFE method development. We have shown that band broadening is determined by diffusion at low flow rates. At higher flow rates and electric fields a migration distance related, hydrodynamic broadening source dominates. We have developed equations that describe the effect of flow rate, voltage and mobility on these sources of band broadening. Combined with equations for predicting the positions of analyte streams in the separation channel these equations are powerful tools that can be used to predict band width and resolution over a wide range of experimental conditions.

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