Anion exhange

Method development in SPE begins with an analysis of the sample matrix as well as the sample analytes. One of the most efficient mechanisms of SPE is to use mixed-mode ion exchange sorbents. If the analytes are bases, cation exchange is the most selective SPE mode. If the analytes are acids, anion exhange is the most efficient. However, it is sometimes easier to capture the matrix components and allow the analytes to pass through the sorbent unretained. 

Oxidation of alcohols to aldehydes or ketones is accomplished with chromate bound to an anion-exhange resin (XXXIX with A = HC1O4 ) [Frechet et al., 1981 Taylor, 1986]. Other oxidants include polymers functionalized with CIO-, CICr04, and RuOj [Kirschning et al.,... 

Treatments with hydrogen (at 480°C) resulted in complete and partial losses in activity (139) for impregnated and ion-exchanged catalysts, respectively. This could be correlated with the degree of reduction which was incomplete under these conditions for the ion-exhanged catalysts. It was therefore concluded that the active site involved Ni2+ ions bonded to the oxygen anions of the zeolite framework and that nickel metal was inactive in the temperature range 150-250°C. 

The chemical behavior of clays is also mimicked by the title complexes in two respects the presence of cation-exhange capabilities and the reduced water content in the ammonium salt [20]. Currently, other similarities between clays and the water-soluble calixarenes are being probed. In particular, the size- and polarity-selective cavity of the calix[4]arene sulfonates is finding utility in the separation of organic substances, cations, anions, and neutral molecules, from aqueous feed streams. 

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