Bonded counterions

There is a wide diversity of available trade names, synthetic nuances, or geometric ones such as column size and shape. However, over three-fourths of HPLC is done with chromatographic columns prepared as porous silica derivatives with bonded alkyl functional groups. Other bonded groups that are noteworthy include diol functionality for aqueous size exclusion and bonded counterions for ion-exchange. The result is an increasingly well focussed interest in relatively few, but widely used, column types. It is known that nominally identical column types do not exhibit identical separation behavior in practice. This nonuniformity has provoked user interest in the question of the extent to which sorptive reproducibility occurs from column to column and, similarly, among different manufacturers. 

Bonded counterions. Ion exchange, 83 Bonded phase, stable, micro HPLC, 115 Bonded-phase columns, stable, resolution enhancement, 30 Butane... 

Why are ionic micelles that have more tightly bonded counterions more likely to have nonspherical micelles ... 

It was shown in [77] that, irrespective of the electrolyte concentration, for a surface coverage exceeding 20%, the portion of adsorbed surface active l l-charged ions bonded to counterions in the S-H layer is approximately 90%, that is, the surface layer is almost electroneutral. The calculations performed in [80] for sodium tetradecyl sulphate solutions, with or without added NaCl, revealed that the extent of bonded counterions, while being somewhat lower than that reported in [77], is quite high, and amounts up to 80% for concentrated solutions. These results... 

Fig. 10.4. Diagram of the double layer of a charged particle and the electrostatic phenomena. R, distance from the particle Rp, radius of the charged particle RSp, hydrodynamic radius (including the layer of strongly bonded counterions, i.e. the fixed layer) Sp, edge of the cut plane between the fixed and diffuse layers of counterions (Lagune, 1994)...

Sugar analysis by hplc has advanced greatly as a result of the development of columns specifically designed for carbohydrate separation. These columns fall into several categories. (/) Aminopropyl-bonded siHca used in reverse-phase mode with acetonitrile—water as the eluent. (2) Ion-moderated cation-exchange resins using water as the eluent. Efficiency of these columns is enhanced at elevated temperature, ca 80—90°C. Calcium is the usual counterion for carbohydrate analysis, but lead, silver, hydrogen, sodium, and potassium are used to confer specific selectivities for mono-, di-, and... 

Initiation is an electrophilic addition of a cation across the double bond, but because of the poor nucleophilicity of the initiator s counterion. 

The anion-selective (AX) membranes (Eig. 2b) also consist of cross-linked polystyrene but have positively charged quaternary ammonium groups chemically bonded to most of the phenyl groups in the polystyrene instead of the negatively charged sulfonates. In this case the counterions are negatively... 

In the El mechanism, the leaving group has completely ionized before C—H bond breaking occurs. The direction of the elimination therefore depends on the structure of the carbocation and the identity of the base involved in the proton transfer that follows C—X heterolysis. Because of the relatively high energy of the carbocation intermediate, quite weak bases can effect proton removal. The solvent m often serve this function. The counterion formed in the ionization step may also act as the proton acceptor ... 

In the bonding of complex organic ions by densely crosslinked polyelectrolyte, not all active centers of ion exchanger are accessible to counterions [54]. For these systems Eq. (3.4) becomes... 

The thermodynamic analysis of the selectivity of ion exchange with the participation of ions of quaternary ammonium bases [56--58] has shown that an increase in bonding selectivity, when metal ions are replaced by organic ions, which is usually accompanied by an increase in entropy of the system (Table 5). It follows from Table 5 that a drastic increase in bonding selectivity upon passing to a triethylbenzylammonium counterion (the most complex ion) is due to a considerable increase in the entropy of the system. 

First, apart from ionic interactions non-ionic interactions between complex counterions and CP play a certain role. In a number of systems hydrophobic interactions play an important role in the selectivity of bonding of organic counterions [62],... 

In some cases, an alternative explanation is possible. It may be assumed that any very complex organic counterion can also interact with the CP matrix with the formation of weak non-ionic bonds, e.g., dipole-dipole bonds or other types of weak interactions. If the energy of these weak additional interactions is on the level of the energy of the thermal motion, a set of microstates appears for counterions and the surrounding CP matrix, which leads to an increase in the entropy of the system. The changes in Gibbs free energy of this interaction may be evaluated in a semiquantitative way [15]. 

High sorption capacities with respect to protein macromolecules are observed when highly permeable macro- and heteroreticular polyelectrolytes (biosorbents) are used. In buffer solutions a typical picture of interaction between ions with opposite charges fixed on CP and counterions in solution is observed. As shown in Fig. 13, in the acid range proteins are not bonded by carboxylic CP because the ionization of their ionogenic groups is suppressed. The amount of bound protein decreases at high pH values of the solution because dipolar ions proteins are transformed into polyanions and electrostatic repulsion is operative. The sorption maximum is either near the isoelectric point of the protein or depends on the ratio of the pi of the protein to the pKa=0 5 of the carboxylic polyelectrolyte [63]. It should be noted that this picture may be profoundly affected by the mechanism of interaction between CP and dipolar ions similar to that describedby Eq. (3.7). 

The anions belonging to groups one and three as well as N and CN- possess a nucleophilicity which is too strong and therefore form an ester bond which is too stable. For this reason, their activity as counterion during reactive cationic polymerization systems is insignificant. 

In both of these compounds, the central atom (B or Al) has four bonds and a negative charge. In the first compound (NaBH4), Na is used as the counter-ion. In the second compound (LAH), Li+ is used as the counter-ion. The choice of counterion is usually not relevant for our discussion, and we will choose to ignore it from... 

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