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Dialysis excluded ions

In this case, most ions can pass through the interface but a few are excluded. This situation, which is depicted in Fig. 6.4, is common in dialysis when small ions and low molecular weight substrates can move across the dialysis membrane, but large polyelectrolyte ions, such as proteins, cannot. [Pg.123]

When dialysis bags full of pure water were immersed in freshwater systems (e.g. rivers and lakes) for several weeks, light element ions (mono- or divalent) migrated into the bags, and this result confirmed that these elements existed in the waters primarily as low-molecular-weight species. Excluded were multivalent ions (e.g. Alm, Fem, Th ) which were present mainly in colloidal or particulate form (Benes and Steinnes, 1974). [Pg.15]

The introduction of chelating functional groups (e.g. amino diacetate) into polymer beads yields a product with a high affinity for metal ions, but also capable of excluding large molecules and colloidal particles from the inner pores (i.e. in some situations the column can act as a size differentiation medium) (Florence, 1977). Compared with other techniques (such as dialysis, ultra-filtration and solvent extraction), chelating column separations can be claimed to be faster and simpler, with the equipment being relatively less expensive. [Pg.16]

Donnan dialysis is a membrane separation process that uses ion-selective membranes to prevent the flow of certain ions from one solution to another. A schematic of the process is presented in Figure 29.8. When a salt solution is separated from its corresponding acid by a cation-exchange membrane, the anions are excluded from the membrane, whUe the cations are redistributed across the membrane to attain Donnan equilibrium. By changing the salt solution periodically, it would be possible to shift the equilibrium favorably to effect simultaneous neutralization of acid on one side of the membrane (feed compartment) and acid recovery on the other side (receiver compartment). The driving force for ion migration is the chemical potential gradient for the cation across the membranes. [Pg.838]

An alternative to dialysis methods is the gel filtration technique of Hummel and Dreyer (57), as modified by Price (58). A column of Sephadex G-25 is equilibrated with a buffer containing a desired concentration of calcium and 45CaCl2, and is used for gel filtration of the binding protein. As the process of gel filtration proceeds, the protein migrates in the excluded volume of the column, removing calcium ions from the column buffer until equilibrium is reached. The protein peak, in the void volume of the column, contains above-base line amounts of calcium. The amount of calcium bound to the protein can be found by dividing the molar concentration of calcium above the base line value by the molar protein concentration. A separate gel filtration run is used to determine each point on the binding plot. This is at once time-consum-... [Pg.226]

Donnan dialysis is an ion exchange process in which an ion exchange membrane is placed between two solutions, i.e., the feed (I) and receiver (II) solutions. The membrane is permeable to counter-ions and excludes co-ions. The ionic strength of the feed solution is relatively low compared with that of the receiver electrolyte solution. At equilibrium, if concentrations are used instead of activities, there is the following Donnan relationship,... [Pg.257]

Physical separation of inorganic ions and other low-molecular analytes from the particulate and dissolved macromolecular fractions of the sample is useful in different flow instruments. Dialysis and UF membrane cells are amongst practical systems for flow injection analysis (FIA), which serve to exclude any unwanted sample material so that only the analyte reaches the reaction or sensing zone. SoHd particles and large interfering molecules can be separated using membranes from the smaller species of analytical interest. Such cells can also be used in the continuous-flow, stopped-flow, and sequential injection modes of flow analysis. The membrane preseparation units are very attractive because they are simple, repeatable, require little or no pretreatment of sample, and show no interferences from sample color and turbidity in most cases no reaction in the membrane interface is involved. [Pg.2985]

Permselective membranes exclude specific molecules from transport due to their size or other properties. With dialysis membranes, the molecular size is aitical. An important application is the exclusion of protein molecules which may contaminate the electrode surface. Lipophilic membranes block the transport of polar molecules, and in ion-exchanger membranes, only ions with a defined charge sign are mobile. Best known are Nafion membranes (Du Pont), which act as cation exchangers in wet state. Anions cannot penetrate the membrane. [Pg.168]


See other pages where Dialysis excluded ions is mentioned: [Pg.61]    [Pg.81]    [Pg.20]    [Pg.494]    [Pg.495]    [Pg.496]    [Pg.124]    [Pg.198]    [Pg.666]    [Pg.222]    [Pg.30]    [Pg.586]    [Pg.761]    [Pg.290]    [Pg.317]    [Pg.137]    [Pg.184]   
See also in sourсe #XX -- [ Pg.15 ]




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