Cation-exchange capability

Several other properties of selected dietary fibers may influence the bioavailability of calcium directly or indirectly. Those fibers which have cation exchange capabilities such as acid polysaccharides due to free carboxyl groups on the sugar residues may bind minerals such as calcium (3,17,33,36). Loss of calcium binding protein as a result of mucosa injury caused by the feeding of some kinds of dietary fiber was credited as being the partial cause of decreased calcium absorption in everted, rat gut sac studies by Oku et al. (16). 

Carboxylic acid (CBA) Si-O-Si-C -CH2CH2COOH Polar bonded phase Medium-polarity phase that has a weak cation exchange capability useful for strong cations above pH of 4.8, most of the functional groups are negatively charged, and therefore the phase can be used for cationic compounds lowering pH to 2.8 elutes retained analytes... 

The interlayer regions of clay minerals also have cation-exchange capability and can be modified by organotransition metal compounds. Montmorillonite is typical of these materials and is readily intercalated with transition metal complex ions. The layered stractme of montmorillonite is shown in Figure 3. 

Table 2 (second to fourth columns) summarizes some chemical features of the main sedimentary zeolites. It is evident that the mentioned zeolites are medium- to high-silica types. Phillipsite and chabazite belong to the first category, especially if we consider that the values of 7 Sl in the most common joint occurrences [see, e.g., 40] are in the ranges of 0.71-0.73 and 0.69-0.72, respectively. Instead, clinoptilolite, ferrieritc and mordenite are to be considered siliceous zeolites. This chemical character results naturally in different cation exchange capabilities, as it can be seen in the fourth column of Table 2 (CEC values). It is worth to observe that these values are merely indicative, as they refer to pure zeolite species, not to zeolite-rich rocks. On the basis of the theoretical CEC values (Table 2) and zeolite contents in tuff occurrences (see Sub-sec. 5.1), more realistic CEC values for the most common types of zeolitic luffs may be worked out, as follows ...

The most common of the natural sedimentary zeolites found in the United States in mineable quantities are chabazite, clinoptilolite, erionite, and mordenite (2). Many crystalline zeolites decompose in acids, although mordenite and, to a lesser extent, erionite have been reported to be stable in acid solutions (2). The goal of this research was to evaluate the stability and cation-exchange capabilities of these common, natural, sedimentary zeolites in acidic solutions. The basic concepts of zeolite ion-exchange, usually emphasizing synthetic zeolites, may be found elsewhere... 

Carboxymethyl (CM) cellulose is synthesised from monochloroacetic acid and cellulose and has weak cation exchange capability ... 

Clays are layered aluminosilicates that exhibit cation exchange capabilities and adsorption properties, while layered double hydroxides are aiuon exchangers with a hydrotalcite-like structure. Both have been incorporated in CPEs and exploited in electroanalysis, mostly to preconcentrate target analytes (usually by ion exchange or organic compounds by adsorption) prior to their voltammetric detectiOTi. 

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