Electrokinetic technique

Lynntech, Inc. s (Lynntech s), electrokinetic remediation of contaminated soil technology is an in situ soil decontamination method that uses an electric current to transport soil contaminants. According to Lynntech, this technology uses both direct current (DC) and alternating current (AC) electrokinetic techniques (dielectrophoresis) to decontaminate soil containing heavy metals and organic contaminants. A non homogeneous electric field is applied between electrodes positioned in the soil. The field induces electrokinetic processes that cause the controlled, horizontal, and/or vertical removal of contaminants from soils of variable hydraulic permeabilities and moisture contents. 

In this section we describe electroosmosis and in the following section the streaming potential. These two electrokinetic techniques also permit the evaluation of f, but are subject to objection 1. In Section 12.8 we examine in greater detail the location of the surface of shear, which is the essence of objection 2 above. 

Different physical techniques can also be used for prefractionation of samples to be analyzed by 2-D gels. Corthals et al. have fractionated human serum by an electrokinetic technique [67], Fountoulakis et al. have used chromatofocus-ing as a prefractionation step in the analysis of low-abundance proteins in H. 

Good descriptions of practical experimental techniques in conventional electrophoresis can be found in Refs. [81,253,259]. For the most part, these techniques are applied to suspensions and emulsions, rather than foams. Even for foams, an indirect way to obtain information about the potential at foam lamella interfaces is by bubble electrophoresis. In bubble microelectrophoresis the dispersed bubbles are viewed under a microscope and their electrophoretic velocity is measured taking the horizontal component of motion, since bubbles rapidly float upwards in the electrophoresis cells [260,261]. A variation on this technique is the spinning cylinder method, in which a bubble is held in a cylindrical cell that is spinning about its long axis (see [262] and p.163 in Ref. [44]). Other electrokinetic techniques, such as the measurement of sedimentation potential [263] have also been used. 

The work of Larson et al. (62) represented the first detailed study to show agreement between AFM-derived diffuse layer potentials and ((-potentials obtained from traditional electrokinetic techniques. The AFM experimental data was satisfactorily fitted to the theory of McCormack et al. (46). The fitting parameters used, silica and alumina zeta-potentials, were independently determined for the same surfaces used in the AFM study using electrophoretic and streaming-potential measurements, respectively. This same system was later used by another research group (63). Hartley and coworkers 63 also compared dissimilar surface interactions with electrokinetic measurements, namely between a silica probe interacting with a polylysine coated mica flat (see Section III.B.). It is also possible to conduct measurements between a colloid probe and a metal or semiconductor surface whose electrochemical properties are controlled by the experimenter 164-66). In Ref. 64 Raiteri et al. studied the interactions between... 

Electrokinetic charges (o ) can, under a number of conditions, be obtained from one of the electrokinetic techniques, as detailed in chapter 4. For simple surfaces (flat, homogeneous, no hairs) is probably close to o. Electrokinetics are therefore not alternatives to colloid titrations but rather serve as additional means of establishing the (counter-) charge distribution. Only in media of very low dielectric permittivity, where Stem layers are absent, is CT = (j -CT° a good approximation. 

The various electrokinetic techniques are comprehensively reviewed and discussed in an excellent book by Chankvetadze )524. In addition, there are review articles dealing with various aspects of CE [525,526), MEKC [499). and CEC )524) enantioseparation methods. 

Barron, W. et al.. The streaming current detector A comparison with conventional electrokinetic techniques. Colloids Surf. A, 88, 129, 1994. 

Another very important issue in this respect is the way to account for the surface conductivity. The formula of Bikerman (Equation 5.359), the correction factor to the electrophoretic mobility of Henry 3 (Equation 5.368), and the formula of O Brien and Hunter (Equation 5.371), quoted above are derived under the assumption that only the ions in the movable part (x > x Figure 5.67) of the EDL contribute to the surface conductivity, Xs- Moreover, the ions in the EDL are taken to have the same mobility as that in the bulk electrolyte solution. A variety of experimental data ° suggest, however, that the ions behind the shear plane (x < x ) and even those adsorbed in the Stem layer may contribute to Xs- Th term anomalous surface conductance was coined for this phenomenon. Such an effect can be taken into account theoretically, but new parameters (such as the ion mobility in the Stem layer) must be included in the consideration. Hence, the interpretation of data by these more complex models usually requires the application of two or more electrokinetic techniques which provide complementary information. Dukhin and van de Ven specify three major (and relatively simple) types of models as being most suitable for data interpretation. These models differ in the way they consider the surface conductivity and the connection between i and "Q. 

AC electrokinetic techniques, particularly DEP, have been used for the manipulation, separation, focusing, trapping and handling of latex spheres [31-34], viruses [35-39], bacteria [40-45] and cells [46-50], Many different electrode geometries have been used to perform DEP. 

Individual cells can be identified on the basis of differences in size and dielectric properties using electrical techniques that are non-invasive and label-free. Characterization of the dielectric properties of biological cells is generally performed in two ways, with AC electrokinetics or impedance analysis. AC electrokinetic techniques are used to study of the behavior of particles (movement and/or rotation) and fluids subjected to an AC electric field. The electrical forces act on both the particles and the suspending fluid and have their origin in the charge and electric field distribution in the system. They are the basis of phenomena such as dielectrophoresis [10-14], travelling wave dielectrophoresis [15, 16], electrorotation [17, 18] and electroorientation [19]. 

As an electrokinetic technique, it requires a conductive mobile phase and, as such, would be more suited to monitor fermentations and other bioprocesses. Eor very comprehensive treatises on EOF microchips covering their current applications, interested readers are referred to excellent reviews by Bruin [20], Lacher et al. [21], Verpoorte [22], Khandurina and Guttman [23] and Pumera [24]. 

The potential may be obtained from measurements of particle mobility using electrokinetic techniques, such as electrophoresis or sedimentation potential [70]. Electrophoresis, the standard technique for submicrometer particles, is based on the movement of charged particles in response to an applied electrical field. Optical scattering methods are used to measure the distribution of particle velocities for a given field strength, and may then be calculated using the Henry equation. 

Therefore, the problem of effective remediation of soils of radioactive nuclides is very relevant. Most technologies of soil decontamination that are currently developed are based on flushing soils with various chemicals and include processes of chemical leaching and selective extraction of radioactive nuclides (Prozorov et flZ., 2000 Shevtsova, 2003). The electrokinetic technique is a new and perspective method of soil remediation, whose main advantage consists in its applicability to decontaminating soils with low filtration ability directly at the site of its local pollution (e.g. in a rock mass) (Pamukcu and Wittle, 1992 Acar et al, 1993, 2001 Janosy and Piot, 1998 Korolev, 2001, 2006 Korolev, Barkhatova, and Shevtsova, 2007). 

Hopkinson L, Cundy AB. (2003). FIRS (ferric iron remediation and stabilisation) A Novel Electrokinetic Technique for Soil Remediation and Engineering. CL AIRE Research Bulletin. RB2-.1-4. 

Additional research is encouraged to scale up to field experiments in order to evaluate the level of accomplishment of the combination of phytoremediation and electrokinetic techniques. 

Heating resulting from electrokinetic techniques in the subsurface involves the resistance to the passage of electrical current through soil moisture. It is this... 

All the above-mentioned processes followed the fundamental electrokinetic techniques, but with some modifications in the process either by adding additional chemicals or in the configuration or construction of electrodes. From the cited literatures, an electrokinetic remediation setup essentially consists of the following... 

Cabrera, C. R. and Yager, R, Continuous concentration of bacteria in a microiluidic flow cell using electrokinetic techniques. Electrophoresis, 22,355-362, 2001. 

Regnier FE, He B, Lin S, Busse J (1999) Chromatography and electrophoresis on chips critical elements of future integrated, microfluidic analytical systems for life science. Trends Biotechnol 17 101-106 Cabrera CR, Yager P (2001) Continuous concentration of bacteria in a microfluidic flow cell using electrokinetic techniques. Electrophoresis 22(2) 355-362 5. Xuan X, Li D (2005) Focused electrophoretic motion and selected electrokinetic dispensing of particles and cells in cross-microchannels. Electrophoresis 26(18) 3552-3560... 

The last equation demonstrates that the starting point for the solution of the problem is the calculation of ci(double layer (this makes low-frequency dielectric dispersion [LFDD] measurements a most valuable electrokinetic technique). Probably, the first theoretical treatment is the one due to Schwarz [61], who considered only surface diffusion of counterions (it is the so-called surface diffusion model). In fact, the model is inconsistent with any explanation of dielectric dispersion based on double-layer polarization. The generalization of the theory of diffuse atmosphere polarization to the case of alternating external fields and its application to the explanation of LFDD were first achieved by Dukhin and Shilov [20]. A full numerical approach to the LFDD in suspensions is due to DeLacey and White [60], and comparison with this numerical model allowed to show that the thin double-layer approximations [20,62,63] worked reasonably well in a wider than expected range of values of both and ku [64]. Figure 3.12 is an example of the calculation of As. From this it will be clear that (i) at low frequencies As can be very high and (ii) the relaxation of the dielectric constant takes place in the few-kHz frequency range, in accordance with Equations (3.56) and (3.57). 

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