A technique that separates charged compounds according to their mobilities in an electric field. In free zone electrophoresis the compounds are in a solution unsupported by any stabilising matrix. In gel electrophoresis the solution is stabilised by a gel (e.g. agarose, polyacrylamide, starch). In paper electrophoresis the stabilising matrix is buffer-soaked paper. In isotachophoresis, by contrast, charged solute molecules all travel at the same rate: a highly mobile leading ion (e.g. Cl^-) travels first and a relatively immobile ion (e.g. tricine) is the trailing ion; to avoid an electrostatic gap, other solute molecules travel between them, all at the same rate but ordered according to their relative mobilities. Capillary eletrophoresis uses a long, very-narrow-bore tube coated with the stationary phase; as the mixture passes along the length of the lumen, components are differentially retarded to effect a separation.