Solid-phase extraction in segmented flow.

Two-phase flow systems are increasingly popular for miniaturized, high-throughput performance of analytical or chemical reactions. In this contribution, we extend a previously described method that allows to increase the range of applications of heterogeneous reactions in two-phase flow, i.e., reactions that rely on isolation and purification of the compound of interest for downstream analysis. Our concept is based on liquid plugs, which serve as miniaturized compartments for the analytical reactions. Purification of the target compound is achieved by extracting the analyte from the aqueous compartments using magnetic beads as solid carriers. In the present paper, we elucidate the influence of parameters such as the polarity of the liquid/liquid and solid/liquid interfaces, the magnetic forces and the fluidic conditions onto the extraction performance. The conditions for reliable extraction and purification of the target compounds are determined. Furthermore, we investigate how to facilitate breaking of the plugs through reduction of the surface tension of the solid/liquid interface. When a lower surface tension is employed, a smaller number of beads is required for the extraction process, which implies a higher sensitivity of the device. In addition, we generate channels with different surface chemistries, which are able to manipulate the flow of the two immiscible liquids. We describe a very simple way to generate such devices and show that we can achieve a transition from segmented flow of plugs to a side-by side flow of the two immiscible liquids, a key requirement for the purification of the compounds.