Electromigration dispersion

The peak distortion in CZE electrophoregrams by electromigration dispersion has been modelled and the peak centre was related by... 

G.L. Emy, E.T. Bergstrom and D.M. Goodall, Electromigration dispersion in capillary zone electrophoresis. Experimental validation of use of the Haarhoff-Van der Linde function. J. ChromatogrA 959 (2002) 229-239. 

The standards should match the samples in order to accurately determine the latter. Viscosity differences result in injected volume differences. If a compound is determined in the presence of high concentrations of other compounds in the sample, these can influence the migration time and peak shape by electromigration dispersion (EMD), and should therefore be present in the standards as well (Figure 1). ... 

Zone broadening or electromigrational dispersion also depends on the concentration of the BGE and the ionic strength of the sample. This means that one should ideally look not only for a probe with mobility close to the analyte, but also for a BGE with a high concentration and a sample volume that is as low as possible. 

Foret, R, Kfivankova, L., and Bocek, P. (1993). Unsteady-state migration electromigration dispersion. In Capillary Zone Electrophoresis (B. J. Radola, Ed.), pp. 27-H, VCH, Weinheim. 

C. Electromigration Dispersion Electromigration dispersion manifests itself in the form of either fronting or tailing peaks, as shown in Figure 4.8. The peak shapes occur as a result of conductivity differences between the analyte zones and the carrier electrolyte (buffer). Conductivity differences... 

Figure 4.8 Electromigration dispersion caused by mismatched analyte and electrolyte mobilites.

Electromigration dispersion determines the shapes of the peaks. Unless the mobilites of the analytes match that of the electrolyte, or unless the concentration of the analytes is at least two orders or magnitude lower than that of the buffer, the peaks will front or tail slower analytes tail while faster analytes front. 

In CE, only small quantities of sample can be introduced onto the capillary if the high efficiencies characteristic of the technique are to be maintained, as discussed in connection with electromigration dispersion in Section 4.3.4. In general, the sample length should be less than 2% of the total capillary length. Although this can be an advantage for applications with limited volumes of sample, it can be a problem from the point of view of detection. 

Figure 8 Effect of solute concentration on electromigration dispersion. Conditions capillary, 38 cm to detector x 50 p.m buffer, 20 mM borate, pH 9.2 voltage, 25 kV temperature, 50°C injection, 1 s at 0.5 psi vacuum detection, UV, 230 nm solute naproxen. (Reprinted with permission from Ref. 52, copyright Marcel Dekker, Inc.)...

Sustacek, V., Eoret, R, and Bocek, R, Selection of the background electrolyte-composition with respect to electromigration dispersion and detection of weakly absorbing substances in capfllary zone electrophoresis, J. Chromatogr, 545, 239, 1991. 

Gebauer, R and Bobek, R, A new type of migrating zone boundary in electrophoresis 1. General description of boundary behavior based on electromigration dispersion velocity profiles. Electrophoresis, 26, 453, 2005. 

According to the initial conditions two different cases can be distinguished. In the first case, electromigration results in a continuous broadening of the zone boundaries with time [15, 16], which is called electromigration dispersion. The mathematical and physico-chemical description of the electromigration phenomena is mentioned in section 3.1. 

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