The application of two-phase slug flows for extraction processes in micro capillaries was investigated and the mass transfer performance under different conditions was analysed. As contacting capillaries PTFE or FEP tubes were used with internal diameters ranging from 0.5 mm to 1 mm. Two extraction systems were experimentally tested for the evaluation and the extraction efficiencies were measured for various flow rates and slug lengths. In the experiments the slug length was manipulated at a constant flow rate by means of a specially developed slug valve and a complete separation was ensured by a newly designed robust phase separator. Besides single-step experiments, a counter-current microfluidic flow was realised by connecting co-current flow modules in a counter-current arrangement and performance results for a two-stage counter-current operation were also obtained. (C) 2016 Elsevier B.V. All rights reserved.