Electrophoresis, zeta potential measurement

Zeta potential. Zeta potential measurements are used to investigate the electric potential of the interface. It is usually measured with electrophoresis or streaming potential.30 These techniques are less commonly applied than the two described above. It is difficult to use electrophoresis with heterogeneous samples such as soil. This technique has to be used with more homogeneous samples such as purified clay. 

Zeta potential measurements are also performed on the NanoZS. All samples are diluted 1 10 (v v) with water. A folded electrophoresis cell is used (Malvern instruments GmbH, Germany) for Laser Doppler Anemometry (LDS) measurements. 

Particle charge plays a major role on the stabilization of colloidal systems. Especially when nanoparticles are stabilized by an adsorption layer of polyelectrolytes, zeta potential measurements are very useful. The stabilization of the nanoparticles results from a combination of ionic and steric contributions. The zeta potential can be detected by means of electro-osmosis, electrophoresis, streaming potential, and sedimentation potential measmements. The potential drop across the mobile part of electric donble layer can be determined experimentally, whenever one phase is made... 

Zeta Potential Measurement, Fig. 3 Stationary level, fluid velocity, and particle velocity distribution in an electrophoresis cell [1]... 

Such a relative motion can be induced by external electric fields or by pressure gradients or bulk forces (e.g. gravity). It is possible that particles move in a quiescent solvent or that the solvent flows through a fixed bed of particles. A detailed description on electrokinetic phenomena is e.g. given by Hunter (1988). Zeta-potential measurements on colloidal suspensions are fiequently conducted via electrophoresis or by means of electroacoustics. Besides this, there are recent techniques based on non-linear optics that are sensitive to interfacial changes. 

The ability of these cationic polyrotaxanes to condense pDNA into particulate structures was evaluated by agarose gel electrophoresis, particle size analysis, and zeta-potential measurements. All the cationic polyrotaxanes could completely complex the pDNA at N/P ratios of 2 and above, which displayed a similar or slightly better DNA condensation ability than PEI (25K). The particle size of the polyrotaxane/DNA complex decreased with the increase of N/P ratio, and when the N/P ratio reached 6, the particle size remained in the 150-250-nm range. Similarly, the surface net charge of the complexes increased from negative to positive as the N/P ratio increased from 0 to 4 and reached a plateau at N/P ratio of 4 and above. The transfection efficiency of the cationic polyrotaxane was also... 

Sanders et al. applied the micro-electrophoresis technique to measure the zeta potential of finely ground glass slides as a function of pH [9]. The results show that for glass particles suspended in a 0.1 M NaCl the zeta potential varies from —20 mV for a pH of 3 to —75 mV for a pH of 10 demonstrating the importance of pH on zeta potential. One problem that arises with this method is whether the zeta potential measured using finely crushed particles corresponds to the zeta potential of the uncrushed solid-liquid... 

Response to Electric and Acoustic Fields. If the stabilization of a suspension is primarily due to electrostatic repulsion, measurement of the zeta potential, can detect whether there is adequate electrostatic repulsion to overcome polarizabiUty attraction. A common guideline is that the dispersion should be stable if > 30 mV. In electrophoresis the appHed electric field is held constant and particle velocity is monitored using a microscope and video camera. In the electrosonic ampHtude technique the electric field is pulsed, and the sudden motion of the charged particles relative to their counterion atmospheres generates an acoustic pulse which can be related to the charge on the particles and the concentration of ions in solution (18). 

Electroultrafiltration (EUF) combines forced-flow electrophoresis (see Electroseparations,electrophoresis) with ultrafiltration to control or eliminate the gel-polarization layer (45—47). Suspended colloidal particles have electrophoretic mobilities measured by a zeta potential (see Colloids Elotation). Most naturally occurring suspensoids (eg, clay, PVC latex, and biological systems), emulsions, and protein solutes are negatively charged. Placing an electric field across an ultrafiltration membrane faciUtates transport of retained species away from the membrane surface. Thus, the retention of partially rejected solutes can be dramatically improved (see Electrodialysis). 

Electrophoresis involves the movement of a charged particle through a liquid under the influence of an applied potential difference. A sample is placed in an electrophoresis cell, usually a horizontal tube of circular cross section, fitted with two electrodes. When a known potential is applied across the electrodes, the particles migrate to the oppositely charged electrode. The direct current voltage applied needs to be adjusted to obtain a particle velocity that is neither too fast nor too slow to allow for errors in measurement and Brownian motion, respectively. It is also important that the measurement is taken reasonably quickly in order to avoid sedimentation in the cell. Prior to each measurement, the apparatus should be calibrated with particles of known zeta potential, such as rabbit erythrocytes. 

The zeta potential can be measured by electrophoresis, which determines the velocity of particles in an electric field of known strength [144]. This particle velocity, v, can then be related to the electrical field strength, E, as the electrophoretic mobility, fi. This is shown by... 

Effect of adsorbed polymer on the double-layer. Because of the presence of adsorbed train segments, the double layer is modified. The zeta-potential, , is displaced because the adsorbed polymer displaces the plane of shear. The parameters for describing adsorbed polymers are the fraction of the first layer covered by segments, 0, and the effective thickness, A, of the polymer layer, The insert gives the distribution of segments over trains and loops for polyvinyl alcohol adsorbed on silver iodide. Results obtained from double layer and electrophoresis measurements. 

In the quantitative sections of this chapter the primary emphasis has been on establishing the relationship between the electrophoretic properties of the system and the zeta potential. We saw in Chapter 11 that potential is a particularly useful quantity for the characterization of lyophobic colloids. In this context, then, the f potential is a valuable property to measure for a lyophobic colloid. For lyophilic colloids such as proteins, on the other hand, the charge of the particle is a more useful way to describe the molecule. In this section we consider briefly what information may be obtained about the charge of a particle from electrophoresis measurements. 

Criticize or defend the following proposition Zeta potentials for three different polystyrene latex preparations were calculated by the Helmholtz-Smoluchowski equation from electrophoresis measurements made in different concentrations of KCl.f... 

Figure 4. The zeta potential of crushed, untreated 6% B.()- E-glass fibers (O) and silica glass (Oi in 10 M KNO, solution and in a 4% solution of y-aminopropylsilane f ) and ( ) measured using a Rank Brothers Electrophoresis analyzer.

The charge on the liposomal surface is a property that has major effects on the stability, biodistribution, and cellular uptake of liposomes, and is governed by lipid headgroup composition and by pH. It can be monitored by micro electrophoresis (i.e., capillary zone electrophoresis), or by measurement of the zeta potential (Egorova, 1994). 

The first four methods are described in Refs. [81,253,254] and the electroacoustical methods in [130,255-257]. Of these, electrophoresis finds the most use in industrial practice. The electroacoustic methods are perhaps the best suited to studying concentrated suspensions and emulsions without dilution [258], In all of the electro-kinetic measurements, either liquid is made to move across a solid surface or vice versa. Thus the results can only be interpreted in terms of charge density (a) or potential (zeta potential, ) at the plane of shear. The location of the shear plane is generally not exactly known and is usually taken to be approximately equal to the potential at the Stern plane, = W d), see Figure 4.9. Several methods can be used to calculate zeta potentials [16,81,253], Some of these will be discussed here, in the context of electrophoresis results. 

Dalgleish, D.G. 1984. Measurement of electrophoretic mobilities and zeta-potentials of particles from milk using laser Doppler electrophoresis. J. Dairy Res. 51, 425 138. 

Electrophoresis The most familiar electrokinetic experiment consists of setting up an electric field, E, in a solution containing charged particles and determining their velocity. The particle velocity, V, is measured by direct microscopic observation at the stagnation point (i.e., zero velocity point for electro-osmosis at the radius 0.707i c) in a capillaiy as shown in Figure 9.19. The zeta potential is then computed... 

Determination of Zeta-Potentials.—The measurement of the velocity of electrophoresis of a moving particle, by one of the procedures to be described shortly, provides a convenient method for evaluating the zeta-potential, utilizing equation (22). The value of Ue as given by this equa-... 

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