Steady-State Continuous-Flow Purification by Free-Flow Electrophoresis
Agostino, Fletcher John
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Synthesis, purification, and analysis are fundamental in chemical processing, and can be achieved by continuous-flow or batch strategies. Continuous-flow technology facilitates chemical syntheses and can improve production efficiency. For product isolation and analysis, continuous-flow systems can be used to facilitate high-throughput purification as well as real-time monitoring. The combination of synthesis, purification, and analysis (in-flow) is a challenging feat due to the scarce number of continuous-flow purification techniques that exist. A potential continuous-flow purification candidate to integrate with continuous-flow chemistry is Free-Flow Electrophoresis (FFE). FFE devices are available at the macro-scale, milli-scale (mFFE), and micro-scale (µFFE). In FFE, samples are carried by a pressure-driven hydrodynamic flow through a high aspect ratio channel, in which a voltage is applied perpendicular to the flow. The electric field forces the individual components of the sample to separate based on differences in their charge-to-size ratios, also called electrophoretic mobilities. Separation, however, can be easily compromised by the generated electric current. Typical currents in FFE result in Joule heating and electrolysis; which produces bubbles along with by-products that can alter pH. Over time, steady-state purification is compromised and can rapidly deteriorate separation quality. Macro-scale FFE devices are capable of overcoming issues that destroy steady-state purification; however, their implemented strategies are not easily transferrable to small-scale devices (mFFE and µFFE). Both mFFE and µFFE devices are attractive purification techniques because they use less reagent and sample material than macro-scale FFE, and have already been combined with real-time continuous-flow analysis. Therefore, establishing steady-state continuous-flow purification in small-scale devices can have significant advantages for streamlining, especially continuous-flow synthesis. In this dissertation, I introduce novel geometric modifications that ultimately provide steady-state purification over a wide range of mFFE separation conditions. These modifications include i) chimneys, which are used to evacuate bubbles completely from mFFE devices, and ii) sacrificial channels, which maintain flow uniformity and reduce pH gradients. Both chimney and sacrificial channel geometries were thoroughly optimized to allow consistent separation conditions over long periods of time. The combination of chimneys and sacrificial channels allows at least 12 hours of continuous-flow purification; thus, facilitating its integration with other continuous-flow techniques.