Electrophoresis migration rates

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. 

Budtz-Olsen (B13) has shown that Hp grouping is possible on vertical paper electrophoresis if Consden and Powell s (C3) borate-barbiturate buffer is used, since differences between the migration rate of the different Hp s is then great enough. It is, however, doubtful whether this is possible when the concentration of the Hp is low. 

Under certain conditions chromatographic retention measurements can be used to determine the magnitude of equilibrium constants for reversible associations between a sample component and a complexing agent present in the eluent. The use of migration rate data to obtain equilibrium constants for interactions between eluents of the solvent and the solute is not novel. It has been developed for paper electrophoresis (297, 292). 

The third step is to determine the polypeptide chain end groups. If the polypeptide chains are pure, then only one N-terminal and one C-terminal group should be detected. The amino-terminal amino acid can be identified by reaction with fluorodinitrobenzene (FDNB) (fig. 3.18). Subsequent acid hydrolysis releases a colored dinitrophenol (DNP)-labeled amino-terminal amino acid, which can be identified by its characteristic migration rate on thin-layer chromatography or paper electrophoresis. A more sensitive method of end-group determination involves the use of dan-syl chloride (see Methods of Biochemical Analysis 3B). 

When a mixture of solutes is placed in an electrical field, the positively charged species are attracted to the anode and the negatively charged ones to the cathode. The separation of charged species based on their specific migration rates in an electrical field is termed electrophoresis. 

Electrophoresis causes the migration of charged molecules in solution along the %-axis in response to an electric field. The migration rate or velocity v can be obtained from a balance of electrical force and Stokes drag and expressed by Eq. (9.15). 

Electrophoresis Difference in migration rate of charged species in an electric field... 

Capillary electrophoresis (CE) MS is another technique used to separate and measure the m/z ratios of a mixture of peptides and proteins. In this method, the peptide mixture is separated by different migration rates through the electrophoresis media and the effluent is again directly sprayed into the mass spectrometer using a micro ESI device. This method is capable of femtomole or lower detection limits and is further discussed in a review. In 1996, a group at the University of Washington described a solid phase extraction (SPE) capillary electrophoresis MS-MS approach for the analysis of peptides and showed limits of detection at the 100 s of attomole level. " ... 

CZE is a high resolution method provided that the sample is concentrated (>1 mg/ml) so that it can be loaded in a narrow zone. The buffer and pH for separation can be freely chosen, but buffer concentration should not exceed O.OIM to minimize Joule heating. In a homogeneous gel, separation occurs on the basis of both charge and size. In contrast, in a gradient polyacrylamide gel migration rates decrease until each protein species reaches its pore limit (15-17). This technique is termed "pore limit electrophoresis" and separates proteins on the basis of size. 

Capillary zone electrophoresis (CZE) is a relatively recent separation technique based on the differential migration rates of ionic species in an electrical... 

Capillary Zone Electrophoresis (CZE). CZE is a widely used CE technique and separates peptides and proteins based on differences in their charge-to-mass ratios. Separations occur in a capillary filled with a buffer of constant composition. For CZE, the run buffer choice is extremely important because it determines the charge on the analyte molecule and its migration rate. Thus, the type of buffer, its ionic strength, and its pH are optimized for particular separation problems. Buffers based on sodium phosphate, citrate, acetate, or combinations thereof with concentrations ranging from 10 to 200 mM are frequently used [14]. 

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