Integrated Microfluidic Device for Continuous Separation and Preconcentration of Surface Active Solutes

Foam fractionation is extensively used for the separation and purification of surface active solutes from a low concentration mixture at room temperature. In this work we present the design of a novel microfluidic device to concentrate a solute by adsorbing it on a gas–liquid interface. The device is integrated with a downstream separator where the foam is separated from the residual liquid. Both gas and liquid streams flow continuously into the device. The device has a diverging and converging cross section to facilitate the formation of a foam-like structure. The device is demonstrated on the enrichment of bovine serum albumin (BSA) using cetyltrimethylammonium bromide (CTAB) as a surfactant. The effect of various parameters, i.e., gas flow rate, aqueous phase flow rate, and salt concentration, on the enrichment of the solute is investigated. We show how we can infer diffusiophoresis in the system at low gas flow rates by measuring macroscopic parameters like mean residence time.