Electroosmotic flow rates

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. 

Wang, B., Chen, L., AbdulaM-Kanji, Z., Horton, J.H., Oleschuk, R.D., Aging effects on oxidized and amine-modified poly(dimethylsiloxane) surfaces studied with chemical force titrations Effects on electroosmotic flow rate in microfluidic channels. Langmuir, 2003, 19, 9792-9798. 

To calculate the electrophoretic mobility of an analyte, the contribution from the electroosmotic flow to the apparent mobility must be known. The most common way to estimate the electroosmotic flow rate is to record the migration time of an injected uncharged marker solute,8,9 which will be carried to the detector under the influence of only the EOF. The electroosmotic flow rate is obtained from the migration time of the neutral marker using Eq. (4.6)10 ... 

Equation 12.5 indicates that the electroosmotic flow rate is large when is large and when the interfacial region is small. 

The cationic analyte of Problem 33-14 was separated by capillary zone electrophoresis in a 50.0-cm capillary at 10.0 kV. Under the separation conditions, the electroosmotic flow rate was 0.85 mm s toward the cathode. If the detector were placed 40.0 cm from the injection end of the capillary, how long would it take in minutes for the analyte cation to reach the detector after the field is applied ... 

We observe here that in a capillary the volume flow rate due to a fixed pressure gradient is proportional to a Tra l8p. dpldx) for a circular capillary). The electroosmotic flow rate is proportional to U multiplied by the cross-sectional area TTa Therefore, the ratio of electroosmotic to hydraulic flow rate will be proportional to a. Thus, for example, if we employ a capillary model for a porous medium, it is evident that as the average pore size decreases electroosmosis will become increasingly effective in driving a flow through the medium, compared with pressure, provided... 

The economics and efficiency of the process usually depend on the degree of solubility of the contaminant species and the electroosmotic flow rate, although some charged species may be separated by mainly migration in silty deposits. The electroosmotic flow rate, qe, is usually defined empiric ly from cell tests. 

The experimental results of Popov et al. (2001) reveal the influence of the chelating agent HEDPA on the electroosmotic flow rate in a natural sod-podzolic soil contaminated with 0.003 g phenol per gram of dry soil. The introduction of a small amount of HEDPA into the system increases the coefficient of electroosmotic conductivity of the soil from 4 x 10 to 11.2 x 10 mW-s. Up to 80%-95% of the phenol was removed after 30-50 h of treatment, and the average electroosmotic flow rate remained constant throughout the tests. 

Huang, X.H., Gordon, M.J., and Zare, R.N., Current-monitoring method for measuring the electroosmotic flow-rate in capillary zone electrophoresis. Ana/. Chem., 1988, 60 1837-1838. 

The electroosmotic flow rate can then be calculated hy Q = Mave c- Although it is possible to directly measure the electroosmotic mobility using the ultramicroscope technique [1],... 

Of practical interest for micropumps, we also study the effect of the chaimel wall and packing particles on the overall electroosmotic flow rate in a microcapillary. Flow rate versus applied external electric field, for different packing particle sizes and the zeta potential ratio w/Cp> is plotted in Fig. 5. It is noted that the flow rate increases linearly with increasing applied voltage. For larger packing particles, the flow rate is... 

Fig. 5 Electroosmotic flow rate versus applied electric fleld for different values of particle diameter, dp, and zeta potential ratio, Cw/Cp...

Using the MD method, the electroosmotic flow in nanochannels with regular or random roughness on the walls has been studied. The results show that both types of roughness reduce the electroosmotic flow rate dramatically even though the roughness is very small compared to the channel width [8]. Figure 4a, b shows the schematic of the... 

In the past, the most common method for analysis of small anions has been ion chromatography. For cations, the preferred techniques have been atomic absorption spectroscopy and ICPMS. Figure 30-1(1 illustrates the speed and resolution of electrophoretic separations of small anions. Here, thirty anions were separated cleanly in just more than 3 minutes. Typically, an ion-exchange separation of only three or four anions can be accomplished in this brief period. Figure 30-11 further illustrates the speed at which separations can be carried out. In this example, nineteen cations were separated in less than 2 minutes. CE methods were once predicted to replace the more established methods because of lowerequipment costs, smaller-sample-size requirements, and shorter analysis times. However, because variations in electroosmotic flow rates make reproducing CE separations difficult, LC methods and... 

Up to here, it was shown that inclusion of one catalytic specie, like anatase, in the anode allowed increasing the oxidant specie production and the electroosmotic flow rate, but obtained phenanthrene removal was lowered. So next step is to analyze what happen if the catalytic activity is maintained at the anode, but cathode is chosen between different materials. Experimental set-up objective was data collection for two different cathode materials, and also to clarify how much the system becomes affected by inclusion of additional physical barriers like a thick filter paper. 

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