Simple Cationic Exchange

In another study Sellergren and Shea [78] modelled the chromatographic behaviour of a solute, PA, on imprinted and non-imprinted polymers using a simple cation-exchange model, and were able to describe the behaviour as a function of mobile phase pH. Moreover, the model they proposed was sufficient to explain the differences in selectivity between the two polymers. 

The most accurate measurements of creatinine involve some form of separation, so an on-line method is very useful. Figure 10.2 shows a simple cation exchange isocratic HPLC assay that can be easily set up in a metabolic laboratory. The urine is simply diluted prior to injection. Creatinine is detected by its UV absorption but the figure clearly shows that trace amounts of other compounds must be resolved if a precise assay is to be achieved. 

A recent paper on the co-impregnation of copper and chromium from their nitrate solutions again follows the pattern of simple cation exchange with the higher valent Cr ion being much more strongly adsorbed and indeed capable of displacing the Cu. The competitive situation was such as to exclude the close proximity of these two metals. These results could have important ramifications in the preparation of uniform bimetallic catalysts. 

Silica Catalysts. - Little problem is to be expected from depositing metals by simple cation exchange onto the surface of silica gel with appropriate control of pH to control the depth of metal penetration. Many high-surface-... 

Cation Exchange Extractants. This class of extractants includes phenols, branched alkyl carboxylic acids, alkyl phosphoric acids, diketones, and alkyl-aryl sulfonic acids. The last group listed, sulfonic acids, are analogous to sulfonic-acid cation exchange resins and have very little selectivity. Diketones, alkyl phosphoric acids and carboxylic acids can provide both cation exchange functions and coordination functions. This feature has made bis(2-ethylhexyl)phosphoric acid one of the most versatile and powerful extractants of this type. (5) The nation below illustrates simple cation exchange extraction. 

In principle, the small separation fiictors observed in simple cation-exchange systems could be used for separation of macroscopic concentrations of lanthanides on large ion... 

We now illustrate the nature of the ion exchange isotherm using the simple cation exchange of Na+ in solution with the resin in H" " form in molar concentration units ... 

The disadvantages of membranes in MFCs are their high cost and that they decrease system performance. Nafion can cost 1400/m, while a simple cation exchange membrane (CEM) costs far less—for example 80/m (CMI-7000, Membranes International, Inc.). These high costs would make the use of Nafion prohibitive in large-scale application of MFCs (for example, for wastewater treatment). The adverse effect of the membrane on performance is usually a result of increased internal resistance. If the solution conductance or effective diffusivity of a proton, or chemical species carrying a proton, is reduced by the presence of the membrane then the internal resistance of the system will increase and the power production will be reduced. 

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