Organic cation adsorption

Organic matter can also adsorb basic molecules, and s-triazines in particular, by cation exchange. Adsorption is sensitive to pH, which not only determines the BH /B ratio in solution, but also the fraction of carboxylic acid groups that dissociate and thereby become potential adsorption sites for the organic cation. Adsorption isotherms are L-type or H-type, depending on the acidity of the soil organic matter. The steps involved in adsorption are ... 

Laird DA, Barriuso E, Dowdy RH, Koskinen WC (1992) Adsorption of atrazine on smectites. Soil Sci Soc Am J 56 62-67 LeBaron PC, Wang Z, Pinnavaia TJ (1999) Polymer-layered silicate nanocomposites an overview. Appl Clay Sci 15 11-29 Lee J-F, Crum JR, Boyd SA (1989) Enhanced retention of organic contaminants by soil exchanged with organic cations. Environ Sci Technol 23 1365-1372 Lee J-F, Mortland MM, Boyd SA, Chiou CT (1989a) Shape-selective adsorption of aromatic molecules from water by tetramethylammonium-smectite. J Chem Soc Faraday Trans I 8 2953-2962... 

Suppose (X 2, (X2)2+, and (X)1 are the organic cations of interest which are involved in the adsorption/desorption reactions experiment. 

Since (X )2+ and (X2)1+ are divalent organic cations with a higher adsorption affinity than the monovalent organic cation (X)+, replacement of (X)1 originally in the clay soil-solid system should occur, i.e., desorption of (X) occurs. 

MEKC is also performed using cationic, nonionic, and zwitterionic surfactants. Widely employed are cationic surfactant consisting of a long chain tetralkylammonium salt, such as cetyltrimeth-ylammonium bromide, which causes the reversal of the direction of the EOE, due to the adsorption of the organic cation on the capillary wall. Other interesting options include the use of mixed micelles resulting from the simultaneous incorporation into the BGE of ionic and nonionic or ionic and zwitterionic surfactants. Chiral surfactants, either natural as bile salts [207] or synthetic [208] are employed for enantiomer separations. 

At the surface of the solution the cationic soap constitutes a positive layer of organic cations neutralized by Cl" and PoCl62" ions 210Po emits a-rays. The surface density as well as the kinetics of the adsorption of PoCl62" are determined by measuring the radioactivity above the surface of the solution. An analogous technique is used to determine the density of the soap adsorbed at the air-solution interface, when the soap is labelled with 14C. Therefore, these measurements allow a direct analysis of the composition of the adsorbed soap films at equilibrium and during their formation. 

Equilibrium of Adsorption, (a) The Soap Films. The isotherms of adsorption of the organic cations of the soaps are reproduced on the Figure 2. Classical methods (20) are used to obtain the surface densities of the soaps I and IV. 

Brownawell, B.J., H. Chen, J.M. Collier, and J.C. Westall. 1990. Adsorption of organic cations to natural materials. Environ. Sci. Technol. 24, 1234-1241. 

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