Capillary electrophoresis neutral analytes

Capillary electrophoresis (CE) has several unique advantages compared to HPLC, snch as higher efficiency dne to non-parabolic fronting, shorter analytical time, prodnction of no or much smaller amounts of organic solvents, and lower cost for capillary zone electrophoresis (CZE) and fused-silica capillary techniques. However, in CZE, the most popular separation mode for CE, the analytes are separated on the basis of differences in charge and molecular sizes, and therefore neutral compounds snch as carotenoids do not migrate and all co-elute with the electro-osmotic flow. 

AR Kranack, MT Bowser, DDY Chen. The effects of a mixture of charged and neutral additives on analyte migration behavior in capillary electrophoresis. Electrophoresis 19 388-396, 1998. 

Micellar electrokinetic capillary chromatography (MECC), in contrast to capillary electrophoresis (CE) and capillary zone electrophoresis (CZE), is useful for the separation of neutral and partially charged species [266,267]. In MECC, a surfactant, usually sodium dodecyl sulfate (SDS), is added to the buffer solution above its critical micellar concentration to form micelles. Although SDS is certainly the most popular anionic surfactant in MECC, other surfactants such as bile salts have proved to be very effective in separating nonpolar analytes that could not be resolved using SDS [268]. 

J. Palmer, N. J. Munro, and J. P. Landers, A Universal Concept for Stacking Neutral Analytes in Micellar Capillary Electrophoresis, Anal. Chem. 1999, 71, 1679 J. Palmer, D. S. Burji, N. J. Munro, and J. P. Landers, Electrokinetic Injection for Stacking Neutral Analytes in Capillary and Microchip Electrophoresis, Anal. Chem. 2001, 73, 725 J. P. Quirino, S. Terabe, and... 

In capillary zone electrophoresis microchips, where the background electrolyte consists only of aqueous buffer, analytes are separated based on a size-to-charge ratio, and neutral analytes are not resolved from each other. 

Palmer, J., Burgi, D.S., Munro, N.J., Landers, J.P., Electrokinetic injection for stacking neutral analytes in capillary and microchip electrophoresis. Anal. Chem. 

Ion chromatography can be used to measure ionic concentrations in solution. It requires a fairly large amount of solvent and usually a suppressor column to neutralize the acidity prior to detection by conductivity. For analytical purposes, most analyses previously performed by ion chromatography are now performed using capillary electrophoresis. However, Katagi et al. used ion chromatography with indirect photometric detection to analyze for nerve agents and hydrolysis products in human serum (8). 

Palmer J, Munro NJ, Landers JP. A universal concept for stacking neutral analytes in micellar capillary electrophoresis. Anal Chem 1999 71 1679. 

Mass spectrometric detectors for capillary electrophoresis are necessarily post-column detectors and must be interfaced to the cathodic end of the capillary. These detectors consist of four main components the interface, that joins the capillary to the ion source, the ion source, that generates ionic fragments from neutral analyte species, the mass analyzer, that distinguishes ions by their mass/charge (m/z) values, and the ion detector, that measures and amplifies the signal. The principles and instrumentation of bioanalytical MS are explained in Chapter 15. 

Capillary electrochromatography (CEC) is a method of chromatographically separating neutral analytes in an electroosmotically-generated flow. As with CE, the liquid matrix is propelled by an imposed electric field. Unlike capillary electrophoresis, however, solute molecules are not separated by differences in charge/mass ratio because they are neutral - thus a stationary phase is needed... 

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