Microscale separation of immiscible liquids using a porous capillary

We describe a simple method for the direct inline separation of two immiscible liquids based on the selective wetting and permeation of a porous polytetrafluoroethylene capillary by one of the liquids. Using water dispersed in fluorous carrier fluid as a test system, quantitative recovery of the water from the carrier fluid is achieved over a wide range of flow conditions, with no contamination by the fluorous component even when present in large (ten-fold) excess. The exiting water stream may be readily redispersed by injecting additional carrier fluid downstream, allowing for repeated switching between the segmented and continuous flow regimes - a critical requirement for multistep chemical processing. The separator is shown to simplify in-line sample analysis by allowing measurements to be carried out quasi-statically without the need for fast instrumentation synchronised to the segmented water flow.