Agilent Technologies 7100 User Manual page 118

5 Using the Agilent 7100 Capillary Electrophoresis System
Capillary Electrophoresis, CE
Hydrodynamic Injection
When using injection by pressure, the sample level only needs to touch the
capillary. The minimum liquid level in the sample vials for this technique is
5 mm for standard and short electrodes. The short electrode filling height
should not exceed 6 mm. This electrode is designed to minimize take-over of
sample that absorbs to or simply coats the electrode.
Electrokinetic Injection
When using injection by voltage or current, the sample level needs to touch the
electrodes. Therefore, the minimum liquid level in the sample vial is 10 mm.
Short electrodes (G7100-60033) are not suitable for electrokinetic injection.
The effective length in capillary electrophoresis, defined by the distance from the injection
N O T E
end to the detector, generally ranges from 40 to 75 cm. Much shorter effective lengths,
such as 8.5 cm from outlet side to the detector are also sometimes very useful. Short
effective lengths have the advantage of reduced analysis times, as well as improved peak
efficiency and sensitivity.
Hydrodynamic or electrokinetic injection from the short end of the capillary can be achieved
by placing the sample vial at the outlet, the buffer vial at the inlet, and then applying a
vacuum or a respective electrical field. With the Agilent CE system, up to 100 mbar
pressure or vacuum can be applied to the inlet to inject sample at the inlet and outlet,
respectively.
Buffer Vials
When the run is started, the liquid level in the vial should touch the electrodes
to enable a current to flow. Therefore, the minimum liquid level in the buffer
vials is 1 cm for standard electrodes and 1.5 cm for short electrodes. A buffer
level of 1.4 cm is recommended for standard electrodes and 1.8 mm for short
electrodes. You can use the replenishment system to fill the buffer vials. You
can also use the replenishment system to precisely lower the liquid level for all
buffer vials to an equal height if you overfill them initially.
118 Agilent 7100 Capillary Electrophoresis System User Manual