Migration time, in capillary electrophoresis

Generally, migration times in capillary electrophoresis (CE) are inversely proportional to the applied voltage in terms of analysis time, the voltage should, therefore, be as large as possible ... 

Identification of sample components based solely on migration time in capillary electrophoresis (CE) requires reproducibilities not normally obtained. These are caused, mainly, by two effects temperature effects and electro-osmotic affects. Migration times in CE are determined by the electro-osmotic velocity Ueof and effective electrophoretic migration velocity Ueef the net migration velocity Vt is the vector sum of both velocities ... 

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... 

In capillary electrophoresis instruments, the electro-osmotic flow is used to impose, on all charged species in the sample, a direction of migration that is oriented from the anode towards the cathode. An increase in the electro-osmotic flow vEOS decreases, at the detector, the gap in migration times of ions travelling in the same direction. The use of fused silica capillaries partially deactivated by coating the inner wall allows modulation of the electro-osmotic flow. A voltage gradient can also be used to this end. 

The parameter normally measured in capillary electrophoresis is migration (retention) time, /. In a given CE system this parameter is inversely proportional to the electrophoretic mobility, pi. The pt (cm /V) is a normalized parameter allowing for comparison of data obtained in different CE systems. If a series of analytes are analyzed under the same conditions then the 1/r and pt are equivalent. There are only a few reports on QSRR analysis of CE data. This may suggest the unsuitability of routinely determined mobility parameters as the LEER descriptors of analyte behaviour. Probably the reproducibility of analyte migration times in CE is poor due mainly to the non-reproducible electroosmotic flow velocity 26. ... 

The main challenge for CE detectors is the small diameter of the capillary and the small sample volumes encountered. Detection schemes employed for capillary electrophoresis include measurement of UV absorption, fluorescence and refractive index. Electrochemical signals and conductivity as well as radioactivity from radioisotopes have also been measured. The signals obtained are plotted against the migration time in the form of an electropherogram. In recent years, coupling of CE to a mass spectrometer (CE-MS) has been achieved. 

Ross GA., Voltage pre-conditioning technique for optimisation of migration time reproducibility in capillary electrophoresis. J. Chromatogr. A, 718, 444-447 (1995). 

Generally, migration times t in capillary electrophoresis (CE) are inversely proportional to the applied voltage. 

Solutes in capillary electrophoresis are separated in the capillary due to differences in electrophoretic mobility, or the rate of migration. In chromatography, separation is the result of interaction with the stationary phase, or the retention of the solutes. This leads to a difference in terminology for electrophoresis compared to chromatography. The identification of species is based on the migration time (t ) rather than retention time (// ), and... 

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. 

Capillary electrophoresis offers several useful methods for (i) fast, highly efficient separations of ionic species (ii) fast separations of macromolecules (biopolymers) and (iii) development of small volume separations-based sensors. The very low-solvent flow (l-10nL min-1) CE technique, which is capable of providing exceptional separation efficiencies, places great demands on injection, detection and the other processes involved. The total volume of the capillaries typically used in CE is a few microlitres. CE instrumentation must deliver nL volumes reproducibly every time. The peak width of an analyte obtained from an electropherogram depends not only on the bandwidth of the analyte in the capillary but also on the migration rate of the analyte. 

Fan et al. [106] developed a high performance capillary electrophoresis method for the analysis of primaquine and its trifluoroacetyl derivative. The method is based on the mode of capillary-zone electrophoresis in the Bio-Rad HPE-100 capillary electrophoresis system effects of some factors in the electrophoretic conditions on the separation of primaquine and trifluoroacetyl primaquine were studied. Methyl ephedrine was used as the internal standard and the detection was carried out at 210 nm. A linear relationship was obtained between the ratio of peak area of sample and internal standard and corresponding concentration of sample. The relative standard deviations of migration time and the ratio of peak area of within-day and between-day for replicate injections were <0.6% and 5.0%, respectively. 

Anions and uncharged analytes tend to spend more time in the buffered solution and as a result their movement relates to this. While these are useful generalizations, various factors contribute to the migration order of the analytes. These include the anionic or cationic nature of the surfactant, the influence of electroendosmosis, the properties of the buffer, the contributions of electrostatic versus hydrophobic interactions and the electrophoretic mobility of the native analyte. In addition, organic modifiers, e.g. methanol, acetonitrile and tetrahydrofuran are used to enhance separations and these increase the affinity of the more hydrophobic analytes for the liquid rather than the micellar phase. The effect of chirality of the analyte on its interaction with the micelles is utilized to separate enantiomers that either are already present in a sample or have been chemically produced. Such pre-capillary derivatization has been used to produce chiral amino acids for capillary electrophoresis. An alternative approach to chiral separations is the incorporation of additives such as cyclodextrins in the buffer solution. 

Affinity capillary electrophoresis (ACE), reviewed by Shimura and Kasai,42 is a method for studying receptor-ligand binding in free solution using CE. The technique depends upon a shift in the electrophoretic mobility of the receptor upon complexation with a charged ligand. Pure receptor preparations or accurate concentration values are not required because only migration times are measured. 

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