18-12-2012, 06:32 PM
Capillary Electrophoresis
Capillary Electrophoresis.ppt (Size: 2.4 MB / Downloads: 41)
Capillary electrochromatography (CEC)
is an electrokinetic separation technique which involves applying voltages across capillaries filled with silica gel stationary phases. The voltages produce an EOF which removes the necessity for a pump.
Separation selectivity in CEC is a combination of both electrophoretic and chromatographic processes.
Capillary Electrophoresis
A high voltage (typically 10-30 kV) is applied across a narrow bore (25-100 mm) capillary.
The capillary is filled with electrolyte solution which conducts current through the inside of the capillary. The ends of the capillary are dipped into reservoirs filled with the electrolyte.
Electrodes (platinum) are inserted into the electrolyte reservoirs to complete the electrical circuit.
Detectors
UV-visible absorption
The majority of instruments have UV diode detectors available.
Alternative detector modes include commercially available fluorescence, laser induced fluorescence, conductivity and indirect detection.
The hyphenation of CE and mass spectrometers is frequently used to give structural information on the resolved peaks.
Stacking
Stacking occurs when the sample is dissolved in a lower ionic strength solution than that of the separation electrolyte.
Under these circumstances the field strength is higher in the sample zone than in the rest of the capillary which is filled with electrolyte.
The sample ions move forwards rapidly in the sample zone until they encounter the electrolyte boundary where they experience a lower applied field and their migration rate slows down.
In this way the sample zone is focused and this can lead to up a 10 fold reduction in the starting peak width. This process is optimized if the sample is dissolved in pure water or a 1 to 10 dilution of the run electrolyte.