In this study the unique properties of microfluidic flow have been exploited to generate efficient mass-transfer in continuous segmented flow to investigate an alternative approach for performing chemical extractions. The concept of extraction-enhancement, by incorporation of a solid absorbent in the extracting phase, was explored. Proof-of-principle studies focused on the use of molecularly imprinted polymers (MIPs) to increase the effectiveness of conventional approaches. Laser machining and micro-milling were used to prepare PTFE microfluidic separation devices. Importantly, this included the design and integration of a continuous-flow microfluidic liquid phase separator. Propranolol selective molecularly imprinted polymer microspheres (3.6 µm) were prepared by precipitation polymerisation. MIP performance was assessed using conventional (equilibrium batch rebinding) and segmented-flow liquid-liquid systems. Interfacial mass transfer processes that occur during segmented flow were characterised with respect to flow variables, fluid properties and channel geometries. Segment aspect ratio and flow velocity, together with channel diameter and curvature, were shown to be important. The MIP was shown to possess high affinity and selectivity for the template (propranolol). Incorporation of the MIP into a segmented flow extraction regime was shown to significantly enhance the extent of analyte extraction. Mathematical optimisation approaches showed good correlation with experimental data. On-chip phase separation was demonstrated to be 100% efficient for particle-containing and particle-free immiscible flows. The discovery of soluble MIP species possessing similar binding characteristics to their insoluble counterparts may further improve the kinetics of the reported solid-liquid-liquid extractions. It was successfully demonstrated that a solid phase material can be incorporated into an organic phase to enhance extraction from an aqueous sample either in continuous segmented flow or under equilibrium conditions. The integration of the segmented flow approach with an on-chip liquid phase separator provides a novel platform for the development of unique and highly-efficient continuous flow devices for molecular enrichments, separations and manipulations.
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