Electrophoresis: the march of pennies, the march of dimes.

The present review encompasses ca. 65 years of history of developments in electrokinetic separations, taking as a starting point the year 1937, i.e. the official launching of Tiselius' moving boundary electrophoresis (MBE). The 1950s have been particularly rich in introducing novel methodologies in zone electrophoresis (ZE), thus bringing about the decline of MBE. Among them of extraordinary importance was the development of electrophoresis on agar gels coupled to immuno-diffusion at right angles, which brought a big revolution not only in biochemistry but also in clinical chemistry. Also the by now forgotten paper electrophoresis was a landmark in separation science, in that it implemented, in its "fingerprinting" version, the first genuine two-dimensional (2D) map, coupling orthogonally a charge to a hydrophobic scale separation, while permitting for the first time the detection of spot mutations, i.e. single amino acid replacements in a polypeptide chain, that paved the way to modern genetic analysis. Equally important was the introduction of starch-block electrophoresis, that brought about the notion of sieving and the first discontinuous buffers, refined, in the 1960s, by Ornstein and Davies with their classical papers combining multiphasic buffer systems to polyacrylamide gels, that went down to history as disc-electrophoresis. The 1960s also contributed with two fundamental techniques, isoelectric focusing (IEF) and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) that permitted to discriminate proteins solely on the basis of surface charge and molecular mass, respectively. The 1970s gave other fundamental contributions, such as isotachophoresis, the first example of a fully instrumental approach to electrophoresis, both in its analytical and preparative version (Tachophor and Tachofrac), 2D maps combining IEF to SDS-PAGE at right angles and silver staining techniques, that incremented sensitivity by 3 orders of magnitude. The 1980s generated immobilized pH gradients and capillary zone electrophoresis (CZE), two big players that dominated the electrokinetic horizon for all the 1990s and still in vigorous use in present days. The review terminates with a glimpse, in the third millennium, onto microchip technology and hyphenated techniques, notably direct interfacing of various electrophoretic separation methods with mass spectrometry (MS).