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ePaper created 2017-03-14, 10:25:37 | version 1.49.03
CHEMISTRY AND PROCESS INDUSTRY 2nd step 3rd fraction 2nd fraction 1st step mixture of substances 2 1st fraction 1 FREE FLOW ELECTROPHORESIS – DEVELOP- MENTS FOR INDUSTRIAL IMPLEMENTATION L e a Kö ni g, M a x imilian Kot zur, T h o ma s S ch e re r Separating substances in an electrical i eld Free l ow electrophoresis (FFE) is a continuous process that originally comes from the i eld of analytics. Its purpose is the selective separation or fractionation of a mixture of dissolved or suspended components that carry a charge. Numerous classes of substances can be addressed with FFE. These range from metal ions such as gold by way of organic substances and proteins to cell organelles and particulate matter. The application possibilities are therefore extremely varied. But FFE has other advantages such as excellent yields or extremely high selectivity and purity with a relatively low use of chemi- cals. Processes based on the previous technologies such as chromatography or extraction are often very complex and/or require numerous steps and the intensive use of chemicals to achieve a comparable product quality. Fraunhofer IGB is work- ing on developments that will make it possible to use the FFE process on an industrial scale. Operating principle In the FFE process the substances to be separated are fed di- rectly into a buffer l ow which continues through the process chamber as a laminar l ow. The electrical i eld perpendicular to the direction of l ow subjects the charged substances to a del ective force and these migrate along the i eld lines. The migration direction (to the anode or cathode) and speed of a substance depend on the substance-specii c, electrophoretic mobility (symbol µ). As a result, different substances undergo different del ections across their direction of l ow and can be separated into different fractions at a discharge grille. Challenges The electrophoretic mobility of a substance depends on a variety of parameters that cannot all be directly determined. The mobility can only be determined empirically in an FFE cell (Fig. 1) with considerable effort (Fig. 4, left). The follow- ing steps are necessary: operation of the FFE cell, analysis of numerous fractions, determining the migration distance of the product fraction and, on the basis of this distance, calculation of the electrophoretic mobility. For industrial implementa- tion, however, knowledge of the mobility is fundamental for process planning and dimensioning as well as for the design of systems. In addition to this, further decisive process param- eters such as dwell time or electric i eld strength have to be determined and optimized. Development strategy Among other things, the electrophoretic mobility largely de- pends on the charge and size of a substance. The lanthanoids are especially similar to one another as regards these charac- teristics. That is why Fraunhofer IGB uses them as a bench- mark to identify decisive parameters for the design of the pro- cess and the plant. In addition, a method for calculating the electrophoretic mobility on the basis of ex situ measurements of a sum parameter (outside the FFE cell) was developed at Fraunhofer IGB (Fig. 4, right). This method makes it possible to determine this crucial process parameter with very little effort and to use it for process planning and dimensioning, and also for the design of systems. 8 4