Theoretical ion exchange capacity

Zeolite type Channel system Pore openings (A hydrated form) Typical Sl02 Al203 mole ratio Theoretical ion exchange capacity (meq/g Na form, anhydrous)... 

According to the XRD pattern all samples are well crystallized and show the typical feature of the MFI structure. Its largely pure formation is confirmed by the results of n-hexane adsorption. The values of the micropore volume (at p/ps = 0.5) are fairly close to the theoretical ones calculated for an ideal MFI-structure (0.19 cm /g, see Table 1). Table 1 gives the Si/Me ratios of the fnunework as further characteristic data. An equal concentration of Me in the lattice have been strived for. However, the results of the chemically determined Me concentration and the ammonium ion exchange capacity disagree especially for the In-Sil. It is less pronounced for Fe-Sil. Therefore the creation of extra-framework species in In-Sil and Fe-Sil has to be considered which do not contribute to the Bronsted acidity but to other kinds of acidic sites. This is in agreement with the results of the TPD measurements. 

Fig. 14 The ion exchange capacity (lEC) of styrene-grafted and sulfonated membranes as a function of DG. The solid line represents the theoretical lEC for 100% degree of sul-fonation, corresponding to one sulfonic acid group per aromatic ring (data for PFA120 crosslinked redrawn from [130] data for ETFE50 redrawn from [213] data for PSl FEP50 redrawn from [151])...

The ion exchange capacity (lEC) of the polymer composite containing SSA has been determined. Figure 13 gives the theoretical lEC and the obtained lEC as function of the SSA content in the polymer composite with silica. 

Both methods use a low-capacity cation exchanger as a stationary phase and a dilute mineral acid such as hydrochloric or nitric acid as a mobile phase. Although stationary phases and eluents have changed over the years, the principal difference between the methods is the same up to the present day. For his hypothetical experiments. Small kept constant the volume of the stationary phase, the ion-exchange capacity of the separator colunm, the selectivity coefficients for sodium and potassium relative to the hydronium ion, and the injection volume. With these values and the known acid concentration in the mobile phase, it is possible to calculate the elution volumes of sodium and potassium. To further simplify the calculation of the elution profiles, the chromatographic peaks are assumed to be symmetrical, so that they can be described by a Gaussian curve. One can further assume that the membrane-based suppressor system exhibits a very small dead volume and, therefore, subtracts negligibly from the efficiency of the separator column, which is estimated to be 3000 theoretical plates. 

The number of theoretical plates and, thus, the separation efficiency is determined by the length of the separator column. If two separator columns are used in series, the resulting enhancement of separation efficiency leads to a better resolution between ions with similar retention characteristics, with a corresponding increase in retention times. The separator column length also determines the ion-exchange capacity. An increase of the ion-ejodiange capacity via elongation of the separator column is recommended in all cases where the ion to be analyzed is present in an excess of another component. 

In summary, design, integration and performance optimization of advanced PEM needs systematic experimental-theoretical efforts to focus on studying the effects of chemical modifications of the base ionomer, thereby, increasing the ion exchange capacity (to improve transport properties without sacrificing stability) and reducing thickness. 

The peak capacity is not pertinent as the separation was developed by a solvent program. The expected efficiency of the column when operated at the optimum velocity would be about 5,500 theoretical plates. This is not a particularly high efficiency and so the separation depended heavily on the phases selected and the gradient employed. The separation was achieved by a complex mixture of ionic and dispersive interactions between the solutes and the stationary phase and ionic, polar and dispersive forces between the solutes and the mobile phase. The initial solvent was a 1% acetic acid and 1 mM tetrabutyl ammonium phosphate buffered to a pH of 2.8. Initially the tetrabutyl ammonium salt would be adsorbed strongly on the reverse phase and thus acted as an adsorbed ion exchanger. During the program, acetonitrile was added to the solvent and initially this increased the dispersive interactions between the solute and the mobile phase. 

Several theoretical models, such as the ion-pair model [342,360,361,363,380], the dyneuaic ion-exchange model [342,362,363,375] and the electrostatic model [342,369,381-386] have been proposed to describe retention in reversed-phase IPC. The electrostatic model is the most versatile and enjoys the most support but is mathematically complex euid not very intuitive. The ion-pair model emd dynamic ion-exchange model are easier to manipulate and more instructive but are restricted to a narrow range of experimental conditions for trtilch they might reasonably be applied. The ion-pair model assumes that an ion pair is formed in the mobile phase prior to the sorption of the ion-pair complex into the stationary phase. The solute capacity factor is governed by the equilibrium constants for ion-pair formation in the mobile phase, extraction of the ion-pair complex into the stationary phase, and the dissociation of th p ion-pair complex in the... 

The data in Figure 1 for y-globulin indicate that little further increase in adsorption is caused by MAAc levels past 1.5% which at first was puzzling However, the eflFective protein-binding capacities of ion exchangers is far below their theoretical capacities because of steric hindrance of the bulky protein molecules. For example, the number of titratable groups in CM-Sephadex C-50 indicates a capacity of 310 g... 

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