Electroosmotic hydrodynamic pumping

Stojkovic et al. [77] used superimposed hydrodynamic pumping to determine artificial sweeteners by CE with contactless conductivity detection employing a sequential injection manifold based on a syringe pump (Figure 24.7). As a result, aspartame, cyclamate, saccharin, and acesulfame-K could be determined concurrently, without requiring any special sample pretreatment. The analyses were carried out in an aqueous running buffer consisting of 150 mM 2-(cyclohexylamino)ethanesulfonic acid and 400 mM tris(hydroxymethyl)aminomethane at pH 9.1 in order to render all analytes in the fully deprotonated anionic form. The use of surface modification to eliminate or reverse the electroosmotic flow was not necessary due to the superimposed bulk flow. 

In an electric field, cations are attracted to the cathode and anions are attracted to the anode (Figure 26-20b). Excess cations in the diffuse part of the double layer impart net momentum toward the cathode. This pumping action, called electroosmosis (or electroen-dosmosis), is driven by cations within — lOnm of the walls and creates uniform pluglike electroosmotic flow of the entire solution toward the cathode (Figure 26-21a). This process is in sharp contrast with hydrodynamic flow, which is driven by a pressure difference. In hydro-... 

Dynamic pumps infuse energy to the fluid in a manner that increases either its momentum (centrifugal pumps) or its pressure (electroosmotic and electrohydro-dynamic pumps) as shown in Table 4. They involve centrifugal or hydrodynamic actuations and, more specifically, are driven by electro-/magneto-hydrodynamic [257], electroosmotic [254-256], electrokinetic [251-253], electrowetting [258], and acoustic forces [259]. Centrifugal pumps are typically less effective for fluids with low Reynolds numbers and have limitation in miniaturization. 

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