Electroosmotic pumping

Lazar, I. M., Karger, B. M., Multiple open-channel electroosmotic pumping system for microfluidic sample handling. Anal. Chem. 74 (2002) 6259-6268. 

P 61] For the dehydration of ethanol to ethane, electroosmotic pumping was applied for liquid transport [19], A flow rate of 0.9-1.1 pi min was applied, giving longer residence times as in [P 60]. The other details of the protocol are idenhcal with those for [P 60],... 

Salimi-Moosavi, H., Tang, X, Harrison, D. )., Electroosmotic pumping of organic solvents and reagents in microfabricated reactor chips,... 

There are three types of mass transport processes within a microfluidic system convection, diffusion, and immigration. Much more common are mixtures of three types of mass transport. It is essential to design a well-controlled transport scheme for the microsystem. Convection can be generated by different forces, such as capillary effect, thermal difference, gravity, a pressurized air bladder, the centripetal forces in a spinning disk, mechanical and electroosmotic pumps, in the microsystem. The mechanical and electroosmotic pumps are often used for transport in a microfluidic system due to their convenience, and will be further discussed in section 11.5.2. The migration is a direct transport of molecules in response to an electric field. In most cases, the moving... 

The electroosmotic pumping is executed when an electric field is applied across the channel. The moving force comes from the ion moves in the double layer at the wall towards the electrode of opposite polarity, which creates motion of the fluid near the walls and transfer of the bulk fluid in convection motion via viscous forces. The potential at the shear plane between the fixed Stem layer and Gouy-Champmon layer is called zeta potential, which is strongly dependent on the chemistry of the two phase system, i.e. the chemical composition of both solution and wall surface. The electroosmotic mobility, xeo, can be defined as follow,... 

D.J. Harrison, A. Manz, and P.G. Glavina, Electroosmotic pumping within a chemical sensor system integratedon silicon. Proceedings Transducers (San Francisco, USA) 792-795 (1991). 

Ramsey, R. S., and Ramsey, J. M. (1997). Generating electrospray from microchip devices using electroosmotic pumping. Anal. Chem. 69, 1174—1178. 

Since the driving force of the flow is uniformly distributed across the diameter of the capillary, the flow profile is essentially flat. This flat profile contributes to the very high separation efficiency of CZE. Electroosmotic pumping therefore is beneficial, in contrast to laminar flow generated by a HPLC pump, where a parabolic flow profile is established. The electroosmotic flow rate and its flat profile are generally independent of the capillary diameter. However, if the internal diameter of the capillary exceeds 250 pun, the flat profile is increasingly disrupted. 

Electroosmotic pumps lack mechanical parts and specific localization in the manifold, producing an even electroosmotic flow. Besides, the flow in interconnected and branched channels can be controlled by switching voltages only. Just two decades ago electroosmotic pumps were attractive and feasible ways for mobile phase flow into microfluidic devices [13] but in the 1990s the conventional pumps available showed a major problem with the high pressures... 

Figure 3.6 A schematic representation of the fabrication process for an electroosmotic pump. (Left) (a) milled PMMA chip, (b) channels containing fixed capillaries, and (c) blank PMMA top plate attached. (Right) A schematic view of the monolithic column inside the channel sections [12].

Electrohydrodynamic pumps, electroosmotic pumps, ultrasonic pumps and... 

FIGURE 3.7 Diagram of the microfabricated electroosmotic pumping system. (1) Open-channel electroosmotic pump, (2) micropump inlet reservoir, (3) micropump outlet reservoir, (4) double-T sample injection element, (5) channel for sample infusion or separation, (6) sample inlet reservoir, (7) sample waste reservoir, (8) channels for sample inlet, (9) channels for sample outlet, (10) ESI emitter to a MS detector. The inset shows an expanded view of the micropump outlet reservoir (3) containing the porous glass disk [115]. Reprinted with permission from the American Chemical Society. 

Manz, A., Effenhauser, C.S., Burggraf, N., Harrison, D.J., Seiler, K., Fluri, K., Electroosmotic pumping and electrophoretic separations for miniaturized chemical analysis systems. J. Micromech. Microeng. 1994, 4(4), 257-265. 

Jin, L.J., Ferrance, J., Sanders, J.C., Landers, J.P., A microchip-based proteolytic digestion system driven by electroosmotic pumping. Labchip 2003, 3, 11-18. 

Guenat, O.T., Ghiglione, D., Morf, W.E., de Rooij, N.F., Partial electroosmotic pumping in complex capillary systems Part 2 Fabrication and application of a micro total analysis system (TAS) suited for continuous volumetric nanotitrations. Sensors Actuators B 2001, 72, 273-282. 

Harrison, D.J., Manz, A., Glavina, P.G., Electroosmotic pumping within a chemical sensor system integrated on silicon. Transducer, 1991, 91, 792-795. 

Razunguzwa, T.T., Umperman, A.T., Fabrication and characterization of a fritless microfabricated electroosmotic pump with reduced pH dependence. Anal. Chem. 2004, 76, 1336-1341. 

Manz, A., Harrison, D.J., Fettinger, J.C., Verpoorte, E., Liidi, H., Widmer, H.M., Integrated electroosmotic pumps and flow manifolds for total chemical analysis systems. Transducer 1991, 939-941. 

Chien, R.L., Bousse, L., Electroosmotic pumping in microchips with nonhomo-geneous distribution of electrolytes. Electrophoresis 2002, 23, 1862-1869. 

The most obvious advantage of an electroosmotic pumping system is the flow profile. Electrochromatography has the same pluglike profile that is characteristic of all other modes of CE. Although the pluglike flow is less perfect in packed columns than in open tubes, it is still more uniform than the laminar flow profile of a pressure-driven system. Consequently, the same capillary would be expected to provide higher efficiencies when used in CEC than when used in pressure-driven systems.31 35,36... 

Alternatively, electroosmotic pumping could be used in this application. For generation of electroosmosis it is necessary to apply an electric voltage at both ends of the column. However, when we used electroosmotic flow instead of a pressurized pumping method, we encountered several problems. The hardest problem was evolution of gas at the electrode due to electrolysis. Elimination of this gas from the chromatographic system was one of the key challenges we faced in designing our system. 

There are still signiflcant technical hurdles that must be overcome for microchips to develop into an accepted and widespread technique. The unreliability of electroosmotic pumping and other microfluidic processes contributes to the lack of robustness of these systems. The miniaturization and integration of other components, such as pumps, valves, and detection schemes, onto the chip is another essential step for future development. The reader is referred to the reviews cited in the references for research performed with microchips [46-48]. 

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