Exchangeable bonds

ANALYTICAL APPLICATION OF SILICAS WITH COVALENT AND ION-EXCHANGE BONDING OF IMMOBILIZED ORGANIC COMPOUNDS FOR SELECTIVE PRE-CONCENTRATION AND DETERMINATION OF PHENOLIC POLLUTANTS... 

Column. 15.0 cm x 4.6 mm, packed with a 5/on silica SCX (strong cation exchanger) bonded phase. 

Table 6. Selectivity of ion exchange bonding of antibiotics on crosslinked polyelectrolytes...

The polymeric resin beads fill a need that arises from the instability of silica gel and its products to mobile phases of extreme pH (outside a pH range of about 4.0-7.0) and, consequently, are employed in most ion exchange separations. Organic moieties containing ionic groups can be bonded to silica and produce an effective ion exchange media, but the restrictions of pH on phase stability still apply. It follows that ion exchange bonded phases are less popular than the polymer bead alternatives. 

Dizdaroglu, M., Krutzsch, H. C., and Simic, M. G., Separation of angiotensins by high-performance liquid chromatography on a weak anion-exchange bonded phase, Anal. Biochem., 123, 190, 1982. 

Amitrole (i. e., a weakly basic pesticide) and the insecticide Dimefox (tetra-methyl phosphorodiamidic fluoride) have been shown to be adsorbed by HA through ionic bonding [17, 151-153]. The interaction between the cationic pesticide Chlorodimeform and SPHA was studied and, based on IR data, Maqueda et al. [154] indicated that an ion exchange bonding mechanism occurred. 

Besides the formation of positive and negative ions, covalent bonding can arise. Electron exchange bonding effected by resonance energy results in either a metallic bond or a covalent bond. In the first case the bonding electrons are more or less mobile in the second, they are localized between the bound atoms to give a directed bond. As we saw in section IV, 2 these and intermediate bond types can arise. 

The ionic states are highly reactive because of polarization forces and in the solid state the parent ion radical or parent carbonium ion is the main reactant. The reactions of these ions with neutral molecules can be understood on the basis of energetics, the isoelectronic principle, and charge-exchange bonding. 

For example, a resonant atom contained in a surface-adsorbed species and a resonant atom exchanged onto a supporting material are cases where a measure of/ is a probe of the respective chemisorptive and exchange bond strengths. 

Applied Science Labs. Vydac Pellicular silica Pellicular ion exchangers Bonded phases on pellicular beads... 

B g = 1,915-1,925 Distorted Octahedron Ti3 + ions in chlorine environment, exchanged-bonded with one another or with TiCl3 associates... 

Needless to say, the fixation of inorganic chemicals in wood by interaction with the wood substrate and extractives is beneficial and greatly improves the durability of these preservatives. Contrarily, other interactions provide less desirable reactions. For example, under certain circumstances copper and zinc can become so tightly bound to the wood that their efficacy as wood preservatives is reduced. This result occurs when copper acetate and zinc acetate are used to treat wood (53). In this form, these elements are salts of acetic acid and they form ion-exchange bonds with the wood components that are stable in the weak acid environment and cannot be ionized readily by water. Conversely, this reduction in efficacy does not occur when copper sulfate and zinc chloride are used because they are salts of strong acids and the pH of the environment prevents insolubilization of these elements by the wood. 

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