Electrokinetic pumping

Application of a potential between reservoirs 1 (sample) and 4 (injection waste) electrokinetically pumps sample solution as indicated in Fig. 3. In this way, a geometrically defined 150 pm (90 pi) section of the separation channel can be filled [19]. If the injection potential is applied long enough to ensure that even the slowest sample component has completely filled the injection volume, a representative aliquot of sample can be analyzed (so-called volume defined injection). This is in contrast to electrokinetic sample injection in conventional capillaries, which is known to bias the sample according to the respective ionic mobilities [61]. These characteristic differences are shown schematically in Fig. 4. It should be noted that this picoliter sample injector is exclusively controlled by the application of electric fields and does not require any active elements with moving parts such as valves and external pumps. The reproducibility of the peak height of the injected sample plugs has been reported to be within 2 % RSD (relative standard deviation) and less [19,23]. 

The "plug-like velocity flow profile for electrokinetically pumped capillary columns (see Figure 1) is important in minimizing resistance to mass transfer within the mobile phase (4). Hydrostatically-pumped capillaries, have parabolic flow profiles which tend to severely disperse solute bands unless extreme narrow-bore (i.d.s less than 10 pm) capillaries are employed (12). Fortunately, larger capillaries, with less stringent detector volume requirements, can be efficiently used in MECC. 

Electroosmotic flow is the most popular of the electrokinetic pumping techniques. One of the main reasons for its popularity with microfluidic... 

The two equations above indicate that the pressure drop increases and the average velocity decreases dramatically with decreasing channel radius. Thus, it is obvious, why electrokinetic pumping procedures find widespread application in fluid systems with micrometer dimensions. 

Chen L, Choo J, Yan B. The microfabricated electrokinetic pump a potential promising drug delivery technique. Expert Opin Drug Deliv 2007 4 119-129. 

Other miniaturised devices have used machined modules made of polymeric materials such as poly(methyl methacrylate) with diameters of 0.8 mm coupled with peristaltic or syringe pumps [106] or exploiting electrokinetic pumping [107], as well as silicon devices with piezo electric pumping [108]. 

Studer V, Pepin A, Chen Y, Ajdari A (2004) An integrated AC electrokinetic pump in a microfluidic loop for fast tunable flow control. Analyst 129 944-949... 

Min JY, Hasselbrink EF, Kim SJ (2004) On the efficiency of electrokinetic pumping of liquids through nanoscale channels. Stats Actuators B 98 368-377... 

Griffiths SK, Nilson RH (2005) The efficiency of electrokinetic pumping at a condition of maximiun work. Electrophoresis 26 351-361... 

Fluorescent Thermometry, Fig. 4 (a) Schematic of a microfluidic circuit through which flow is driven by electrokinetic pumping, (b-f) Temperatore fields through... 

In addition to pre-concentration applications, ion exchange membranes have started to be demonstrated for other appUcations in microfluidic devices. One application is using imi exchange membranes in conjunction with electrokinetic pumps [7], which are devices that pump liquid in a microdevice when an electric field is applied. In this device, the ion exchange membrane served to electrically isolate the pump from the rest of the solution while still enabling the liquid flow that is generated by the device to flow through the system. This extends the utility of on-chip... 

Wang M, Wang JK, Chen SY, Pan N (2006) Electrokinetic pumping effects of charged porous media in microchannels using the lattice Poisson-Boltzmann method. J Coll Interface Sci 304(l) 246-253... 

We relied on electrokinetic pumping to introduce analyte molecules into the cuvette at very low rates. The injection tip of the capillary was immersed in a small reservoir that contained B-phycoerythrin at a concentration of 1.7 x 10 mol 1 . A platinum electrode was also immersed in the sample, and a several kilovolt potential was applied to the electrode. It is important to encase the electrode in an interlock equipped enclosure to prevent accidental contact with the high voltage. 

Wang P, Chen Z, Chang H-C (2006) A porous electrospray emitter assisted by an integrated electrokinetic pump based on silica monoliths. Electrophoresis, 27 3964-3970... 

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