The influence of an inert gas phase on liquid extraction using a microstructured device is analyzed. The gas phase establishes a modified flow pattern. The performance of the gas-liquid-liquid flow is compared to that of a segmented two phase flow, as regards mass transport as well as separation. The extraction of vanillin dissolved in water with toluene was chosen as an example and experiments at different residence times were conducted by varying the total volumetric flow rate. mu-PIV measurements were performed to reveal the influence of the inert gas phase on recirculation within the liquid slugs. Addition of the gas leads to an increase in mass transfer at flow velocities above 0.08 rn/s. However, no difference can be noted at lower flow velocities and longer residence times, respectively. The two liquid phases were separated within the microstructured device by using a capillary separator. Purity was always higher than 96%. For two phase segmented flow, the toluene phase was pure, whereas the water phase was free of toluene rests when applying the inert gas phase. Thus, the inert gas phase can be used to enhance mass transfer under certain circumstances and to tune the separation behavior of a capillary separator. (C) 2011 Elsevier B.V. All rights reserved.