Orthogonal chromatographic method

Where RPLC often fails in separating polar compounds from the injection peak, ordinary CE mostly succeeds efficiently. As a consequence, it can be very useful to add at least one CE method to an orthogonal chromatographic set. ... 

Chromatographic and electrophoretic separations are truly orthogonal, which makes them excellent techniques to couple in a multidimensional system. Capillary electrophoresis separates analytes based on differences in the electrophoretic mobilities of analytes, while chromatographic separations discriminate based on differences in partition function, adsorption, or other properties unrelated to charge (with some clear exceptions). Typically in multidimensional techniques, the more orthogonal two methods are, then the more difficult it is to interface them. Microscale liquid chromatography (p.LC) has been comparatively easy to couple to capillary electrophoresis due to the fact that both techniques involve narrow-bore columns and liquid-phase eluents. 

Two-dimensional (2D) separation systems are of interest because of their increased peak capacity over one-dimensional separations. Microfabricated devices (microchips) are potentially useful for multidimensional separations because high-efficiency separations can be achieved and small sample volumes can be manipulated with minimal dead volumes between interconnecting channels. Various techniques may be adopted for the fabrication of chromatographic columns in microchips for p-CEC following integration with other orthogonal separation methods as well as sample pretreatment proaches for rapid, automated analysis of more complicated biosamples with possible coupling to mass spectrometric detection. 

Some workers nsed SEC for the first fractionation, and TLC [2,3] and high-performance precipitation liqnid chromatography [4, 5] were applied as the second chromatographic method. Balke and Patel [6,7] performed cross-fractionation by orthogonal chromatography (SEC-SEC) in which different mobile phases were used. Tanaka and co-workers [8] used the... 

---