Free-flow electrophoresis

Free-flow electrophoresis (FFE), also known as carrier-free electrophoresis, is a matrix-free electrophoretic separation technique. FFE is an analogous technique to capillary electrophoresis, with a comparable resolution, that can used for scientific questions, where semi-preparative and preparative amounts of samples are needed. It is used to quantitatively separate samples according to differences in charge or isoelectric point. Because of the versatility of the technique, a wide range of protocols for the separation of samples like rare metal ions, protein isoforms, multiprotein complexes, peptides, organelles, cells, DNA origami, blood serum and nanoparticles exist. The advantage of FFE is the fast and gentle separation of samples dissolved in a liquid solvent without any need of a matrix, like polyacrylamide in gel electrophoresis. This ensures a very high recovery rate since analytes do not adhere to any carrier or matrix structure. Because of its continuous nature and high volume throughput, this technique allows a fast separation of preparative amounts of samples with a very high resolution. Furthermore, the separations can be conducted under native or denaturing conditions.

FFE was developed in the 1960s by Kurt Hannig at the Max-Planck-Institute in Germany. Until the 1980s, it was a standardized technology for the separation of cells and organelles, and FFE was even tested in space to minimize the sedimentation under zero gravity. As flow cytometry became the standard method for cell sorting, FFE developments focused on the separation of proteins and charged particles. Some groups are also working on miniaturized versions of FFE systems or micro FFEs.

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