Direction of Electroosmotic Flow

TABLE 3.1. Details of the Experiment on Controlling of Electroosmotic Elow Direction 

Stage Treatment Time (t) Treatment Duration (h) Reservoir Solution DC Electric Field Applied (V/m) Electroosmotic Flow Volume (ml) Average Coefficient of Electroosmotic Conductivity (k, m7Vs) 

6 SORPTION AND DESORPTION OF CONTAMINANTS ONTO/FROM SOIL PARTICLE SURFACES 

Moreover, the sorption and desorption characteristics of contaminants on soil particle surfaces can be altered by the addition of other chemicals, such as surfactants or cleanup enhancement agents, to the system (Yeung, Hsu, and Menon, 1996 Ottosen et a/., 2005 Yeung and Hsu, 2005 Mukhopadhyay, Sundquist, and Schmitz, 2007 Pazos et al, 2007). Addition of these chemicals adds another variable to the complex situation. 

TABLE 3.2. Testing Parameters of Sorption/Desorption Experiments on Cadmium 

---

The direction of electroosmotic flow and, therefore, the order of elution in CZE can be reversed. This is accomplished by adding an alkylammonium salt to the buffer solution. As shown in Figure 12.45, the positively charged end of the alkylammonium ion binds to the negatively charged silanate ions on the capillary s walls. The alkylammonium ion s tail is hydrophobic and associates with the tail of another alkylammonium ion. The result is a layer of positive charges to which anions in the buffer solution are attracted. The migration of these solvated anions toward... 

State three different methods to reduce electroosmotic flow. Why does the direction of electroosmotic flow change when a silica capillary is washed with a cationic surfactant ... 

Fig. 6.4. Diagram illustrating the principle for counterflow (a) and normal-flow (b) gradients (Reprinted with permission from [31]. Copyright 1999 American Chemical Society). The direction of electroosmotic flow is opposite to that of the electrophoretic movement in both methods and is opposite to the net migration velocity, vmigr (= ve0 - ve ph), in (a) and coincides with the net migration direction in (b). veo is not constant along the capillary, and velph is higher in the direction of the electrophoretic migration.

Cationic surfactants Use to reverse the direction of electroosmotic flow... 

The migration of pore fluid, ions, charged particles, colloids, and bacteria can be utilized to remove contaminants from polluted soil and/or to inject enhancement agents, nutrients, and so on to facilitate various remediation processes. The geochemical processes can be used to provide the necessary environmental conditions to control the direction of electroosmotic flow and to solubilize contaminants in the soil, so as to enhance the efficiency of the electrochemical remediation processes. 

Many separations of anions require that the direction of electroosmotic flow be reversed. This is accomplished by adding a flow modifier, such as a quaternary ammonium salt with a long hydrocarbon chain, to the BGE. A thin layer of the flow modifier is adsorbed on the capillary surface. This gives the surface a positive charge and causes electrolyte anions to give an electroosmotic flow toward the anode. 

The magnitude and direction of electroosmotic flow can be changed by various treatments of the silica inner wall. For example, addition of a cationic surfactant to the background electrolyte results in a positive surface that gives a reversed EOF, i.e., toward the anode. 

When analyzing primarily for anions, the analysis time can be decreased by reversing the direction of electroosmotic flow. The flow is then toward the anode rather than the cathode, and the anions will elute first. To reverse the... 

The addition of surfactants to the processing fluid usually increases its viscosity and modifies the interaction with the soil particle surface. It results in a reduction of the electroosmotic flow, which is the main transportation mechanism. The use of neutral surfactants has been preferred for low toxicity, which is a very important property to consider in the selection of the surfactant. Anionic surfactants have a great solubilizing potential and do not interact with soil, so the retention of the surfactant in the soil is very low. However, anionic surfactants migrate in the opposite direction of electroosmotic flow. Besides, they are much more toxic, especially for aquatic organisms. Cationic surfactants have not been used in soil electrokinetics. 

---