Alkali concentration gradient

The importance of maintaining precise concentration gradients is highlighted by the severe effects of metabolic disorders involving alkali metal cations. For example, high sodium intake is linked intimately with the development of high blood pressure on the other hand, aged... 

The CMMS micromembrane suppressor also allows the application of concentration gradients in combination with conductivity detection that is indispensable for cation detection. A mixture of hydrochloric acid and 2,3-diaminopropionic acid suitable for chemical suppression is used as the eluent. The gradient technique, however, plays a secondary role in cation analysis, since it can only be applied for the analysis of alkali and alkaline-earth metals as well as a number of short-chain aliphatic amines. It is definitely not suitable for the analysis of heavy and transition metals, where different... 

For all these cases, the total amount of each chemical was the same. The core flood results are shown in Figure 13.21. We can see that the incremental oil recovery factors over waterflooding in Schemes 2 and 4 were obviously higher than that in Scheme 1. The alkali and surfactant concentration gradients from high to low can overcome the negative effects at the displacement front caused by dilution, alkali consumption, and surfactant adsorption. 

FIGURE 13.21 Effect of alkali and surfactant concentration gradients on oil recovery. Source Yang etal. (2002b). 

Detailed lipid bilayer studies with valinomycin and macrotetrolides established that both antibiotics have the following effects on (i) membrane potential and (ii) conductance92,126,159>279) (j) if the aqueous solutions on both sides of the membrane contain different K+ concentrations, a potential is observed which shows approximately Nemstian dependence on the K+-concentration gradient. By using K+ in one aqueous solution and a different alkali ion in the other aqueous solution, potentials are also measured. From these, cation permeability ratios can be calculated which give the same cation selectivity sequence as observed with complexation. (ii) The membrane conductance (measured with the same alkali ion solution in both aqueous compartments) increases linearly with the aqueous concentration of the antibiotic. At fixed concentration of the antibiotic, the membrane conductance increases linearly with the alkali ion concentration. The conductance values measured with different alkali cations correlate with the ion selectivity sequence of complexation. 

Initial measurements carried out on PEO-alkali metal salt complexes indicated that the observed conductivities were mostly ionic with little contribution from electrons. It should be noted that the ideal electrolyte for lithium rechargeable batteries is a purely ionic conductor and, furthermore, should only conduct lithium ions. Contributions to the conductivity from electrons reduces the battery performance and causes self-discharge on storage. Salts with large bulky anions are used in order to reduce ion mobility, since contributions to the conductivity from anions produces a concentration gradient that adds an additional component to the resistance of the electrolyte. 

It should be mentioned that diffusiophoresis, the movement of particles in suspension under the influence of an externally imposed solution concentration gradient, can affect the nonequilibrium measurements of alkali halide particles. When a particle of an alkali halide salt is dissolving in solution, it is possible that a concentration gradient will be established in the volume adjacent to the outer boundary of the double layer. The concentration gradient thus established can influence the measured electrophoretic mobilities by laser-Doppler electrophoresis. However, in the case of alkali halide particles, the slope of the concentration... 

Diffusion results from the concentration gradient dC/dx in the medium and hence, occurs when the NaCl concentration in the anode compartment differs from that in the cathode compartment. In a chlor-alkali cell, the anolyte is nearly a saturated NaCl solution, whereas the catholyte contains only traces of NaCl. Although Cl ion is subjected to the same diffusional driving force as Na+ ion, it is rejected by the fixed anions in the membrane, which also retard the transport of Na" " to some degree to maintain the charge balance. 

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