Electrokinetic mobilization

Two-Step Isoelectric Focusing with Electrokinetic Mobilization... 

Hjerten et al. [19] derived expressions which describe the theoretical basis of electrokinetic mobilization. The electroneutrality condition at steady state in the separation tube during focusing is... 

Plastic microdevices for high-throughput screening with MS detection were also prepared for detection of aflatoxins and barbiturates. These devices incorporated concentration techniques interfaced with electrospray ionization MS (ESI-MS) through capillaries [2], The microfluidic device for aflatoxin detection employed an affinity dialysis technique, in which a poly (vinylidene fluoride) (PVDF) membrane was incorporated in the microchip between two channels. Small molecules were dialyzed from the aflatoxin/antibody complexes, which were then analyzed by MS. A similar device was used for concentrating barbiturate/antibody complexes using an affinity ultrafiltration technique. A barbiturate solution was mixed with antibodies and then flowed into the device, where uncomplexed barbiturates were removed by filtration. The antibody complex was then dissociated and electrokinetically mobilized for MS analysis. In each case, the affinity preconcentration improved the sensitivity by at least one to two orders of magnitude over previously reported detection limits. 

Einstein relation relates molecular diffusivity and electrokinetic mobility... 

Figure 14.11. Comparison of hematite (a) surface charge (C g ), (b) electrophoretic mobility, and (c) stability ratio, as a function of pH. Note that at pHp the net surface charge and mobility are both zero, and the stability is a minimum. The experimental stability ratio (IFexp). the potentiometrically determined surface charge, and the electrokinetic mobility of 70-nm particles over the pH range from 3 to 11 are shown. The solid line in (c) summarizes experiments obtained with / = 0.05-0.1. (Adapted from Liang and Morgan, 1990.) (d, e) Results of simple equilibrium calculations that have been made with equilibrium constants and surface characteristics of a-Fe203 given by Liang and Morgan (see Example 14.1).

The charge on emulsion stabilized by sulpha-pyridine was found to be negative. The electrokinetic mobility of the emulsion was measured and the zeta potential was calculated by the Helmholtz equation,... 

The effects of inert electrolyte on surface charging of salts other than Agl are not very well documented. The electrokinetic mobility of two samples of calcite was... 

Smoluchowski proposed an equation allowing to calculate the C potential from experimentally determined electrokinetic mobility jj, ... 

Electrokinetic mobilities can be measured by direct observation of the particle movement by use of a microscope or of the boundary between suspension and clear electrolyte separated from the suspension by centrifugation (moving boundary method). When electrolyte is forced through a fixed bed, e.g., of carbon fibers, a potential builds up between the ends of the bed. This streaming potential can also be used for the measurement of -potentials. Details of these methods are described in textbooks of colloid chemistry. 

Numerous electrokinetic studies have been carried out with monodispersed colloids, that is, assemblies of particles that have the same shape and size (with some scatter). Preparations and properties of monodispersed colloids are reviewed in [309,310]. The electrokinetics of monodispersed colloids are reviewed in [311]. In assemblies of identical spherical particles, the potential can be calculated exactly from the electrokinetic mobility. The advantage of spherical shape and monodis-persity, which make exact calculation of the potential possible, is attained at the expense of purity that is, monodispersed particles are usually not very pure. 

Zeta Potential Strictly called the electrokinetic potential, the zeta potential refers to the potential drop across the mobile part of the electric double layer. Any species undergoing electrokinetic motion, such as electrophoresis, moves with a certain immobile part of the electric double layer that is assumed to be distinguished from the mobile part by a distinct plane, the shear plane. The zeta potential is the potential at that plane and is calculated from measured electrokinetic mobilities (e.g., electrophoretic mobility) or potentials (e.g., sedimentation potential) by using one of a number of available theories. 

The results of Suer and Lifvergren (2003) indicate that mercury was removed from a field-contaminated soil by a combination of redox and complexation processes with iodide/iodine and electrokinetic mobilization. Iodide added to the cathode compartment was transported into the soil and oxidized to iodine near the... 

The determination of tTi is carried out in the absence of specific adsorption, but otherwise under the same soil conditions as exist for the determination of CEC and AEC in the presence of specific adsorption. 4. If it is assumed that the electrokinetic plane of shear near a soil particle coincides with the outer periphery of its surface complexes, then electrokinetic mobility experiments can be interpreted to provide an estimate of ap and, by Eq. 3.3a, of (Tjy. The theoretical basis for this method is discussed in Sec. 3.4. It may be noted in passing that no assumptions about the detailed structure of the interfacial region are required in order to measure a zero value for [Pg.80]

The utility of a series of different inorganic bases, including LHMDS, NaHMDS, KHMDS, f-BuONa, f-BuOK, f-BuOLi, LTMP, LDA, PhOLi, MeONa, and EtONa for the alkylation of cyclohexanone with benzyl bromide in a microreactor was studied. The microreactor employed a field-induced electro-kinetic flow acting as apump. To achieve a sufficient electrokinetic mobilization, the inorganic bases had to be solubilized by the addition of stoichiometric quantities of the appropriate crown ethers. With a single exception (LHMDS with 12-crown-4 ether), the desired electrokinetic mobility was reached with aU other bases under these conditions. 

Figure 6 demonstrates a continuous electroki-netic sorting of polyst3rene particles by size and surface charge simultaneously in an asymmetric double-spiral microchaimel [3]. The mixture of nonfluorescent 5 pm, nonfluorescent 10 pm, and fluorescent 10 pm particles is resuspended in 0.1 mM phosphate buffer. As the buffer solution is more conductive, all three t3q>es of particles undergo negative C-iDEP in the spiral. Under the application of a 33 kV/m DC electric field, the initially scattered particles in Fig. 6b are focused by C-iDEP to a tight stream flowing near the outer sidewall of the 100 pm wide first spiral as seen from Fig. 6c. Subsequently in the second spiral whose width increases from 100 pm to 200 pm, the focused particles are all displaced from the inner to the outer wall by C-iDEP at a particle size- and charge-dependent rate or, more accurately, the particle dielectrophoretic to electrokinetic mobility ratio in Eq. 6.

The gated injector is time dependent and has an electrophoretical sample bias [9]. The performance of this valve is measured by recording temporal profiles at 1 mm downstream of the valve for injection times of 0.2, 0.4, and 0.8 s. The peak maximum does not increase at longer injection times. The peak area reproducibility is better than 0.5 % relative standard deviation for 20 injections for each injection time. As with conventional electrokinetic injection schemes, this injection is also biased by the relative electrokinetic mobility of the sample ions. This valve dispenses sample volumes that are linearly proportional to the electrophoretic mobility for which this bias is easily compensated. 

Chromatography performs separation according to the size, charge, and affinity of the analyte, based on the different velocities that each compound is carried by a solvent in an appropriate porous medium. In electrophoresis, the separation is based on the electrokinetic mobility of... 

The injection process introduces the prepared sample or reagent into the flowing carrier stream within the manifold. Ideally, the injector system should be designed so as to provide a high sample flow rate. Injection systems typically employ electrokinetic mobility or hydrodynamic pressure techniques. In the former systems, the sample flow into the microchannel is controlled by the application of an external electric field to the reservoir, while in the latter systems, a pressure difference is created in the reservoir using either a positive pressure (pistmi-type) technique or a suction pressure (vacuum) technique. 

The reduced electrokinetic mobility p defined by Eq, (119) is again expected to depend on the set of dimensionless parameters ( ), Rc/a, kg, and Df. Its dependence on (f) can be analyzed with the help of the calculations of Levine and Neale [11,62]. By use of a cell model, these authors generalized Henry s [7] prediction of the mobility of a single spherical particle with radius a to concentrated systems. Their result is cast in the form... 

It is well known, that the vast majority of metal ions hydrolyze in aqueous solutions, yielding a variety of solutes, the complexity of which increases with the charge of the cation. It has been established with numerous adsorbents in aqueous solutions of metal salts, that the adsorptivity of cations increases dramatically, as a result of their hydrolysis [11]. Indeed, the ions which do not specifically interact with solid surfaces, do so once they form hydrolyzed complexes. The enhanced uptake has been documented by direct adsorption measurements and indirectly by determining electrokinetic mobilities (electrokinetic potentials) as a function of the pH. The latter experiments invariably show the formation of charged sites on neutral surfaces or charge reversal on negatively charged surfaces, due to the chemisorption of hydrolyzed cationic solutes. 

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