ABSTRACT
I. HISTORICAL REVIEW Over the last 10 years, capillary electrophoresis has matured into a powerful analysis technique focusing on water-soluble ionic analytes. It therefore complements the long-established method of reversed-phase HPLC, where separation is based on hydrophobic interactions of the mainly nonpolar analytes. Pioneering work using electrophoresis as a separation method was first performed by Tiselius dating back to 1937 (1). He found that proteins in buffer solution migrate in the electric field in one direction and at a rate determined by their charge and size. In the early years electrophoretic separation was performed in anticonvective media such as agarose and polyacrylamide gels to minimize solute-zone broadening caused by thermal diffusion and convection. The introduction of open tubular colums in the early 1970s with column diameters in the submillimeter range was an important milestone in free solution electrophoresis, and led to a significant increase in separation efficiency (2,3). Due to their small diameters (50-100 /Lm), the currents flowing through the capillary are very small, only in the microampere range, thus allowing a high separation voltage up to 30,000 volts at a concurrently low power consumption in the range of milliwatts. Because of the favorable ratio of surface area to volume of narrow-bore capillaries, the negative effects of Joule heating could be minimized, resulting in considerably enhanced separation efficiencies of typically 250,000 theoretical plates (4). A further advantage of the possibility of utilizing high voltages is the significant reduction in analysis time, which in tum decreases zone broadening, leading to high separation efficiency. During the 1980s many
practical aspects of sample introduction and analyte detection were solved, helping to establish capillary zone electrophoresis (CZE) as a high-performance analytical technique. The first capillary zone electrophoresis systems became commercially available in the late 1980s.
