Ion-depleted waters

This situation cannot persist for long the concentration of copper (II) ions in water will initially be extremely small, unless some other source is also involved, and will quickly be depleted. The important point is that, as soon as electrical contact is made, the zinc becomes an anodic electrode, and the copper a cathode. If another cathodic reaction besides reaction 16.2 is possible, however, then dissolution (i.e., corrosion) of the zinc will continue, while the copper will serve merely as an electrically conducting surface to deliver electrons for the alternative cathodic reaction. In pure water, the obvious alternative reaction is hydrogen evolution (reaction 16.3) for which Eh is —0.414 V at pH 7 ... 

When the sample size is small (10-20 pL), it becomes possible to effectively inject most of the ions in the sample in less than 30 s at 5 kV. A small water plug injected hydrodynamically has been shown to further improve sensitivity [51], though this was not the case for the above-mentioned application. Since the sample conductivity severely affects the amount of solute injected, internal standards are important for this mode of stacking. For quantitative analysis, make only a single injection out of each vial, as the sample becomes ion-depleted. 

An injection-related artifact can occur in gel buffers with consecutive electroki-netic injections from the same, low volume (10-200 mL) sample progressively smaller amounts of sample are introduced into the capillary, resulting in peak heights or areas that decrease with each injection (Schwartz et al., 1995). This effect is due to the migration of cations (e.g., Tris) from the gel buffer into the sample, changing its relative ionic strength. One solution to this problem is to perform an electrokinetic injection from a water vial prior to sample injection. This water injection generates a zone of ion depletion (i.e., rela-... 

When very small pores that are permissive for monovalent but not for divalent ions are required, alpha-toxin should be used in a concentration range of 0.5-5 ng/ml. Most cells will become perme-abilized.Note, however, that certain cells exhibit a natural resistance towards alpha-toxin and pore formation will not occur. A simple means to discern whether permeabilization has taken place is to observe whether the cells swell increases in cell volume are the consequence of an uncontrolled flux of monovalent ions and water, and can be observed microscopically or by flow cytometry. Another simple method is measurement of cellular ATP. One hour after toxin application, cells are lysed with Triton X-100, and ATP is quantified using the luciferase assay (method described in (Bhakdi ef al., 1989)). ATP depletion will always be found in cells that have been permeabilized. 

The ohmic resistance is located mainly in the boundary layer where ion depletion has occurred. Because of such depletion the resistance in the boundary layer will increase so that part of the eiecuical energy may be dissipated as heat (electrolysis of water) if the concentration becomes too low. The current density v in that layer can be obtained from eq. vn-56. 

Figure 1.4, Hydrolysis of sodium acetate (salt of strong base and weak acid). Na and OIF do not have a tendency to combine because they are derived from strong alkali CHfCOO", however, has a tendency to combine with H of water because it is a base corrugate to a weak acid. This depletes H ions of water while OH remain unchanged. The solution becomes alkaline. (Hff shown as H for the sake of simplicity)...

Figure 1.5. Hydrolysis of ammonium chloride (salt of strong acid and weak base). Cl and H have no tendency to combine. NH on the other hand can combine with OH ions. This depletes OH ions of water while H ions remain constant. The solution becomes acidic...

The depletion of the concentration of nitric acidium ion by appreciable quantities of water is expressed by the equilibrium... 

---