The widely used separation process of liquid - liquid extraction is performed in a variety of contactors. The interfacial area in these conventional contactors is often poorly defined, because of the complex hydrodynamics involved, and the intensity of mass transfer is limited by the constraints imposed by the underlying buoyancy or gravitational effects being exploited. Similar shortcomings are apparent in most of the laboratory equipment presently used for investigating extraction and biphasic reactions. In the present work, a new contactor concept, liquid - liquid slug flow in a capillary, is presented as an alternative to conventional equipment. Experiments were performed to investigate the effect of operating conditions on mass-transfer coefficients for different nonreacting systems. In addition, a flow splitter was developed for downstream separation of two liquid phases. The combination of this flow splitter with the capillary provides miniature mixer-settler modules, which can be networked in a wide variety of configurations. Finally, the results obtained were compared with the literature data, and it was determined that such a microextractor - reactor offers superior performance and greater efficiency, in comparison to conventional equipment for liquid-liquid extraction. The results also show that such equipment can be exploited to enhance mass-transfer- and heat-transfer-limited liquid-phase reactions.