MINIATURIZED LIQUID-LIQUID EXTRACTION SYSTEM BASED ON CONTROLLED AQUEOUS AND ORGANIC DROPLETS V. Jokinen 1* , T. Sikanen 2 , R. Kostiainen 2 and S. Franssila 1 1 Aalto University, Department of Materials Science and Engineering, FINLAND and 2 University of Helsinki, Faculty of Pharmacy, FINLAND ABSTRACT Liquid-liquid extraction is studied on surfaces with patterned hydrophilic and hydrophobic domains. These domains are used to shape and stabilize aqueous and organic droplets, between which the extraction takes place. Both two-phase and three-phase extraction are possible using this method. As a proof of concept, we study the extraction of fluorescein, fluo- rescein diacetatate and fluorescein dibutyrate from an acidic donor droplet, through an organic droplet to a basic acceptor droplet. The experimental results and theoretical considerations of the partitioning tendencies of the three compounds are in good agreement, demonstrating the feasibility of the system. KEYWORDS: Liquid Extraction, Droplets, Hydrophilic, Hydrophobic INTRODUCTION Liquid-liquid extraction (LLE) [1] is a widely used sample pretreatment method. In two phase LLE, the sample is ex- tracted from an aqueous donor phase to an organic acceptor phase, which can then be transferred for further analysis steps. In three phase LLE, the sample is extracted from an aqueous donor phase to an aqueous acceptor phase through an intermediary organic phase i.e. a supported liquid membrane (SLM) wetted with immiscible solvent phase. The latter approach is better suited for coupling to separation systems, but construction of such three phase compartments requires rather complex experi- mental setups, for example the use of porous polymer membranes to act as supports for the SLM [1-3]. Our concept, performing LLE on open surfaces with controlled droplets, is built on a previous work [4], which showed how chemically modified silicon nanograss can be used to control the shapes of droplets in the millimeter and micrometer scales. The aqueous phases are confined to hydrophilic areas, while the organic phases are confined to the hydrophobic areas surrounded by the aqueous phases. THEORY An aqueous droplet that comes into contact with a hydrophilic/hydrophobic patterned surface will tend to assume the 2- dimensional shape of the hydrophilic area [4], as long as the wettability contrast between the domains is high enough and the hysteresis of the hydrophobic domain is low enough. On the other hand, controlling the shapes of oil droplets is trickier, as re- entrant geometries need to be introduced [5], and even then controlling the shapes of oils with very low surface tensions re- mains to be demonstrated based purely on surface patterning. However, in the present case, it is possible to get around this problem by confining the oil droplets inside aqueous droplets that act as barriers that prevent unwanted spreading of the oil. Based on this, we utilized a ring shaped hydrophilic area with a circular hydrophobic center for 2-phase LLE, and a circular hydrophilic center, surrounded by a hydrophobic ring, which in turn is surrounded by a hydrophilic ring for 3-phase LLE. These geometries are shown in Figure 1. Figure 1. a) Two phase droplet LLE geometry consisting of a 1 mm wide hydrophobic central circle (donor, empty in the fig- ure) and a 1 mm wide hydrophilic ring (acceptor, containing 2 μl water). b) Three phase liquid-liquid extraction geometry, consisting of a 1 mm wide hydrophilic central circle (acceptor, 0.5 μl water), a 400 μm wide hydrophobic middle ring (or- ganic, 0.5 μl hexadecane) and a 1 mm wide hydrophilic outer ring (donor, 3 μl water). 978-0-9798064-4-5/μTAS 2011/$20©11CBMS-0001 897 15th International Conference on Miniaturized Systems for Chemistry and Life Sciences October 2-6, 2011, Seattle, Washington, USA