Continuous purification of reaction products by micro free-flow electrophoresis enabled by large area deep-UV fluorescence imaging

Simon A. Pfeiffer, Benjamin M. Rudisch, Petra Glaeser, Matthias Spanka, Felix Nitschke, Andrea A. Robitzki, Christoph Schneider, Stefan Nagl, Detlev Belder

Microreactors have gained increasing attention in their application toward continuous micro flow synthesis. An unsolved problem of continuous flow synthesis is the lack of techniques for continuous product purification. Herein, we present a micro free-flow electrophoresis device and accompanying setup that enables the continuous separation and purification of unlabeled organic synthesis products. The system is applied to the separation and purification of triarylmethanes. For imaging of the unlabeled analytes on-chip a novel setup for large area (3.6 cm(2)) deep ultra violet excitation fluorescence detection was developed. Suitable separation conditions based on low conductivity electrophoresis buffers were devised to purify the product. With the optimized conditions, starting materials and product of the synthesis were well separated (R > 1.2). The separation was found to be very stable with relative standard deviations of the peak positions smaller than 3.5% over 15 min. The stable conditions enabled collection of the separated compounds, and purity of the product fraction was confirmed using capillary electrophoresis and mass spectrometry. This result demonstrates the great potential of free-flow electrophoresis as a technique for product purification or continuous clean-up in flow synthesis. Graphical Abstract Micro free-flow electrophoresis (μFFE) allows continuous separation and purification of small organic synthesis products. Enabled by a novel deep-UV imaging setup starting materials and product of a recently developed synthesis for triarylmethanes could be purified. Thereby demonstrating the potential of μFFE as continuous purification technique for micro flow synthesis.