Microelectrophoresis zeta potential

Size exclusion/molecular sieve chromatography Ultra Itration/dia lysis Ultracentrifugation Fluorescent probes Spin label EPR NMR probes Calorimetry Microelectrophoresis Zeta potential... 

However, the equilibrium of the indicator adsorbed at an interface may also be affected by a lower dielectric constant as compared to bulk water. Therefore, it is better to use instead pH, the interfacial and bulk pK values in Eq. (50). The concept of the use at pH indicators for the evaluation of Ajy is also basis of other methods, like spin-labeled EPR, optical and electrochemical probes [19,70]. The results of the determination of the Aj by means of these methods may be loaded with an error of up to 50mV [19]. For some the potentials determined by these methods, Ajy values are in a good agreement with the electrokinetic (zeta) potentials found using microelectrophoresis [73]. It is proof that, for small systems, there is lack of methods for finding the complete value of A>. 

Figure 6.2 The effect of pH on the zeta potential of cellulosic fines and fibres as measured by streaming potential and microelectrophoresis (figures in brackets are negative).

The content of vaccine within the small liposomes is estimated as in the section Estimation of Vaccine Entrapment in Dehydration-Rehydration Vesicles Liposomes for both microfluidized and sucrose liposomes and expressed as percentage of DNA and/or protein in the mixture subjected to freeze drying as in the section Preparation of Vaccine-Containing Small Liposomes by the Sucrose Method in the case of sucrose small liposomes or in the original DRV preparation (obtained in the section Estimation of Vaccine Entrapment in DRV Liposomes ) for microfluidized liposomes. Vesicle size measurements are carried out by PCS as described elsewhere (6,8,17). Liposomes can also be subjected to microelectrophoresis in a Zetasizer to determine their zeta potential. This is often required to determine the net surface charge of DNA-containing cationic liposomes. 

The generation of colloidal charges in water.The theory of the diffuse electrical double-layer. The zeta potential. The flocculation of charged colloids. The interaction between two charged surfaces in water. Laboratory project on the use of microelectrophoresis to measure the zeta potential of a colloid. 

A good example of the use of microelectrophoresis experiments is supplied by the study of ferric floes, which are widely used in municipal water treatment plants. The zeta potentials shown below were derived from the measured floe electromobilities using the Smoluchowski equa-... 

From microelectrophoresis measurements on a spherical colloid particle, the observed elctromobility L7e is directly related to the zeta potential by the equation ... 

Zeta potential was the first, experimentally available value characterizing edl. The potential of the solid particles in the electrolyte solutions may be determined on the basis of one of the four following phenomena microelectrophoresis, streaming potential, sedimentation potential and electroosmosis. The most popular of them and the best described theoretically and methodically is the electrophoresis. Other papers, concerning the electrophoretic mobility, stationary level determination and the theory of the charged particles transportation in the electric field are still published. 

Microelectrophoresis is used to measure the electrophoretic mobility or, in other words, the movement of liposomes under the influence of an electric field. From the electrophoretic mobility the electrical potential at the plane of shear or (zeta) potential can be determined (by the Helmoholtz-Smoluchowski equation). From the zeta potential values the surface charge density (o) can be calculated. 

In spite of a major improvement gained from the rotating prism method, there are still serious limitations in the use of microelectrophoresis in determining zeta potential. First, this technique cannot be applied to dense dispersions, i.e., the number density of the particles must be very low. This can sometimes, but not always, be remedied by filtering the sample and diluting a small amount of the original dispersion with a large volume of filtrate. Second, it cannot be applied... 

Figure 7.29 Schematic drawing of a microelectrophoresis apparatus showing the positioning of the anode and cathode and the capillary in which the velocity of particulates is monitored to allow calculation of zeta potential.

Adsorption isotherms are habitually obtained using the solution depletion method, which consists of comparing the solute concentrations before and after the attainment of adsorption equilibrium. Electrokinetic or zeta potentials are determined by two techniques microelectrophoresis [12,14,17] and streaming potential [13,58,59]. The former is employed to measure the mobility of small particles of chemically pure adsorbents, whereas the latter is adopted to investigate the electrophoretic behaviour of less pure coarser mineral particles. A correlation between the adsorption and electrophoretic results is usually examined with the aim of sheding light on the mechanism by means of which the surfactants are adsorbed at the solution-solid interface. This implies the necessity of maintaining the same experimental conditions in both experiments. For this purpose, the same initial operational procedure is applied. 

Yang, Ch. et al.. Measurement of the zeta potential of gas bubbles in aqueous solutions by microelectrophoresis method, J. Colloid Interf. Sci., 243, 128, 2001. 

Doren, A., Lemaitre, J., and Rouxhet, P.G., Determination of zeta potential of macroscopic specimens using microelectrophoresis, 7. Colloid Interf. Sci., 130, 146, 1989. 

To evaluate the double-layer potential as a function of pH, zeta potential estimates of solid and virus are required. The zeta potentials of Si02 were obtained by direct microelectrophoresis as a function of pH (8). For the virus, this information is not available directly from experimental measurements. Here we applied the Nernst equation (27) to Mandel s (62) isoelectric points (A state = pH 7.0, B state = pH 4.5) to estimate surface potentials (if o)-... 

Sanders et al. applied the microelectrophoresis 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 interface. The act of grinding may alter the zeta potential of the original material and is stiU a topic of debate. 

The electrophoretic motion is either measured microscopically or by light scattering. The former way is called microelectrophoresis and usually employs ultramicroscopes when dealing with colloidal particle systems. The optical instrumentation can be identical to that of DUM, while the software has to be modified because only the displacement in the direction of the electric field is relevant. The method yields a number weighted distribution of zeta-potentials. Similar to DUM, a sufficiently large number of trajectories has to be evaluated in order to keep the statistical uncertainty within an acceptable level. Moreover, the method may be insensitive to weak scatterers within a polydisperse colloidal suspension. 

An instmmental alternative to microelectrophoresis is electrophoretic light scattering (ELS). The light scattering at migrating particles leads to phase shift (Doppler effect), which can be detected by a heterodyne DLS set-up (i.e. reference-beating with frequency shift). The method yields an intensity weighted distribution of the zeta-potential. 

The electrophoretic motion of colloidal particles is superposed by their Brownian motion. Ideally, both can be separated because of their different space-time correlations, in practice however, diffusion broadens the measured zeta-potential distribution. In microelectrophoresis, the Brownian contribution can be minimised by long observation times t D,/v ). For ELS, diffusion is least pronounced at small scattering angles (Xu 2008). 

Surface or zeta potential of particles Yes (microelectrophoresis) Stability of colloidal dispersions... 

---