Electrokinetic injection, injector design

Figure 12.3 shows three microinjector designs that have been used for electrokinetic injection of very small samples, from microenvironments such as single nerve cells. The capillary tip diameters in these injectors are 10 pm o.d. or less, and can penetrate and sample from single cells. The design shown in Figure 12.3(c) has been shown to be the most effective, because electrolysis occurs away from the capillary tip and therefore does not introduce bubbles that would insulate the capillary ends from each other. 

The injection process introduces the prepared sample or reagent into the flowing carrier stream within the manifold. Ideally, the injector system should be designed so as to provide a high sample flow rate. Injection systems typically employ electrokinetic mobility or hydrodynamic pressure techniques. In the former systems, the sample flow into the microchannel is controlled by the application of an external electric field to the reservoir, while in the latter systems, a pressure difference is created in the reservoir using either a positive pressure (pistmi-type) technique or a suction pressure (vacuum) technique. 

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