Miniaturisation in Separation Science: Liquid-Liquid Separation on a Chip.

In recent years, the field for miniaturised analytical devices as well as micro-reactors and micro-mixers has grown rapidly. From this the need arose to also miniaturise and integrate sample preparation techniques such as extraction. Therefore, technologies to build new devices faster and cheaper have become increasingly important. The classic processing technique for glass or silicon is photolithography followed by wet etching. Major time and cost factors in this process are the production of lithography masks. A process to design masks based on printouts on office printers and photographic reduction was therefore developed. The process is capable of producing masks with features as small as 20μm. Furthermore a new process for bonding two glass slides with enclosed channels has been developed. The process was based on an intermediate polymer layer and allows the formation of a polymer coating inside the capillaries. The technique worked at low temperatures and allowed us to selectively coat capillaries etched in one slide but not to coat capillaries in the other slide. The ability to selectively coat capillaries allowed the construction of a miniaturised liquid-liquid separator. The separator was based on different contact angles of solvents on different surfaces. In general, polar solvents have a low contact angle on polar surfaces while non-polar solvents have low contact angles on non-polar surfaces. At a junction where one arm has a polar surface and one arm a non-polar surface the phases separate according to their polarity into the channels for which they have the greater affinity. Since the effect is not fully efficient at one junction, an array of multiple junctions was used to separate a two-phase mixture. The array consisted of five polar and five non-polar channels leading at a 90° angle to the other polarity, leading to two outlet channels. The separator achieved complete separation for isooctane and also achieved partial separation for more polar solvents such as octanol and ethylacetate