Electro-migration injection

Electro-migration injection. This technique, used in gel electrophoresis, is achieved by putting the sample at a potential of appropriate polarity compared to the other extremity and briefly dipping the capillary into it. In contrast to the previous procedure this mode of injection induces a discriminatory action upon the compounds present, which leads to a non-representative composition of the sample. 

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... 

Choosing an internal standard to correct errors due to sample preparation and injection reduced the impact of variability on the final trueness and precision of the developed method. Peak area can be corrected (peak area/migration time) to avoid the migration time drift influence, because of the temperature affecting both electro-osmosis and electrophoretic mobilities as well as buffer electrolysis, adsorption into the capillary wall and so on. 

Two electrically dependent phenomena contribute to the net mobility of an analyte, i.e., the intrinsic electrophoretic mobility and the electro-osmotic flow (EOF) [154], The mobility can be evaluated from the electropherogram using the migration time, t, of the analyte migrating a distance from the injection point to... 

The electrophoretic process begins when the source buffer vial is removed and replaced with a sample vial. The sample is injected onto the top of the capillary. Separation of components occurs as the analytes and buffer migrate through the capillary under then-own electrophoretic mobility and under the influence of electro-osmotic flow (EOF), which moves from anode to cathode. Eventually, each component migrates from the capillary as a narrow band (or peak). 

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