Capillary electrophoresis, separation samples

FIGURE 15.1 One-dimensional capillary electrophoresis separation of a protein homogenate prepared from the hTERT cell line. Both separations were preformed in 30 pm ID, 145 pm OD, 20 cm long capillaries at 20,000 V. (a) Micellar electrokinetic chromatography performed with a 100 mM CHES, 100 mM Tris, and 15 mM SDS buffer at pH 8.7. Sample is electro-kinetically injected with 0.25 kV for 1 s (b) Capillary sieving electrophoresis performed in 5% Dextran (513 kDa), 100 mM CHES, 100 mM Tris, 3.5 mM SDS, pH 8.7. 

Figure 3.33 Capillary electrophoresis. The sample is introduced through the inlet, washed in with a wash buffer and then separated under the influence of a potential difference between the two electrodes. The zones are monitored as they pass through the detector and the data captured and computed.

The hyphenation of CE and NMR combines a powerful separation technique with an information-rich detection method. Although compared with LC-NMR, CE-NMR is still in its infancy it has the potential to impact a variety of applications in pharmaceutical, food chemistry, forensics, environmental, and natural products analysis because of the high information content and low sample requirements of this method [82-84]. In addition to standard capillary electrophoresis separations, two CE variants have become increasingly important in CE-NMR, capillary electrochromatography and capillary isotachophoresis, both of which will be described later in this section. 

Zhou SY, Zuo H, Stobaugh JE, Lunte CE, Lunte SM. 1995. Continuous in vivo monitoring of amino acid neurotransmitters by microdialysis sampling with on-line derivatization and capillary electrophoresis separation. Anal Chem 67(3) 594-599. 

Seiler, K., D. J. Harrison, and A. Manz. Planar glass chips for capillary electrophoresis Repetitive sample injection, quantitation, and separation efficiency, Anal. Chem. 65, 1481-1488 (1993). 

A. Manz, D.J. Harrison, E.M.J. Verpoorte, J.C. Fettinger, A. Paulus, H. Ludi and H.M. Widmer, Planar chips technology for miniaturization and integration of separation techniques into monitoring systems Capillary electrophoresis on a chip, J. Chromatogr. A, 593 (1992) 253-258. D.J. Harrison, A. Manz, Z.H. Gan, H. Ludi and H.M. Widmer, Capillary electrophoresis and sample injection systems integrated on a planar glass chip, Anal. Chem., 64 (1992) 1926-1932. 

Capillary electrophoresis separation is performed in a flexible fused silica capillary tube that is filled with an appropriate buffer solution of defined pH and ionic strength (aqueous/nonaqueous). A small volume of sample (lower than 3-4% of the column volume) is needed to achieve efficient separation. This volume is introduced hydrodynamically (or less often electrokinetically) into the capillary to which an electrical potential is applied (Figure 13.7). Charged species of the sample exhibit... 

In capillary electrophoresis a sample, usually containing charged species, is introduced into the end of a capillary that has been filled with a solution of buffer (or electrolyte). Under the influence of an electric field, the analytes migrate away from the injection end of the capillary toward the detector end, where they are visualized. Three distinct separation mechanisms have been developed for the separation of analytes by CE. 

Figure 15. Electropherogram illustrating the capillary electrophoresis separation of poly d(A) 40-60 mer sample, P-labeled at the 5 end. Detection was accomplished using the coincidence detector. The separation was accomplished using a polyacrylamide gel-filled capillary and a constant potential of 15 kV. The sample activity in this example was approximately 4800 DPM/nL.

Capillary electrophoresis separations are dependent on the relative mobilities of analytes under the influence of an electric field and do not depend on mobile phase/stationary phase interactions. A fused silica capillary is filled with a buffer and both ends submerged into two reservoirs of the buffer. A platinum electrode is immersed in each reservoir and a potential difference (5-30 kV) is applied across the electrode. An aliquot of sample of a few nanoliters is injected onto the capillary by either hydrostatic or electrokinetic injection, and the components migrate to the negative electrode. Separations of analytes arise from differences in the electrophoretic mobilities, which are dependent on the mass-to-charge ratio of the components, physical size of the analyte, and buffer/analyte interactions. An electro-osmotic flow (EOF) of the buffer occurs in the capillary and arises as a result of interactions of the buffer with dissociated functional groups on the surface of the capillary. Positive ions from the buffer solution are attracted to negative ions... 

Chen, Z.L., Lin, J.-M., Naidu, R. Separation of arsenic species by capillary electrophoresis with sample-stacking techniques. Anal. Bioanal. Chem. 375, 679-684 (2003)... 

Seiler, K., Harrison, D. J., and Manz, A., planar glass chips for capillary electrophoresis—repetitive sample injection, quantitation, and separation efficiency. Analytical Chemistry 65, 1481-1488, 1993. Jacobson, S. C., Hergenroder, R., Koutny, L. B., and Ramsey, J. M., High-speed separations on a microdchp, Analytical Chemistry 66, 1114-1118, 1994. 

The direct sampling of solutions is often necessary in a variety of situations such as biological fluids and eluants from liquid chromatography and capillary electrophoresis separation devices. Liquid solutions are difficult to handle by the mass spectrometry vacuum system and require some novel introduction and ionization systems. The last two decades have witnessed the development of some unique ionization methods that are suitable for direct analysis of sample solutions the important ones are discussed below. 

In capillary electrophoresis, the sample is dispersed in a medium (such as methylcellulose) and held in a thin glass or plastic tube with diameters ranging from 20 to 100 pm. The small size of the apparatus makes it easy to dissipate heat when large electric fields are applied. Excellent separations may be achieved in minutes rather than hours. 

Arce, L., M. T. Tena, A. Rios, and M. Valcarcel. 1998b. Determination of trans-resve-ratrol and other polyphenols in wines by a continuous flow sample clean-up system followed by capillary electrophoresis separation. Anal. Chim. Acta 359 27-38. 

In capillary electrophoresis the conducting buffer is retained within a capillary tube whose inner diameter is typically 25-75 pm. Samples are injected into one end of the capillary tube. As the sample migrates through the capillary, its components separate and elute from the column at different times. The resulting electrophero-gram looks similar to the chromatograms obtained in GG or HPLG and provides... 

Capillary Electrophoresis. Capillary electrophoresis (ce) or capillary 2one electrophoresis (c2e), a relatively recent addition to the arsenal of analytical techniques (20,21), has also been demonstrated as a powerful chiral separation method. Its high resolution capabiUty and lower sample loading relative to hplc makes it ideal for the separation of minute amounts of components in complex biological mixtures (22,23). 

Capillary Electrophoresis. Capillary electrophoresis (ce) is an analytical technique that can achieve rapid high resolution separation of water-soluble components present in small sample volumes. The separations are generally based on the principle of electrically driven ions in solution. Selectivity can be varied by the alteration of pH, ionic strength, electrolyte composition, or by incorporation of additives. Typical examples of additives include organic solvents, surfactants (qv), and complexation agents (see Chelating agents). 

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