Strong Anion Retention

FIGURE 9.2. Nonspecific anion reactions at a solid/solution interface (a) adsorption, (b) anion exchange. (After F. J. Hlngston, R. J. Atkinson, A. M. Posner, and J. P. Quirk, 1967. Nature 215 1459-1461.) 

The Cl-, NOT, and SG anions are considered to be nonspecifically adsorbed. Table 9.1 shows typical data for Cl- and SO - adsorption by soils. The capacity of soils to adsorb anions increases with increasing acidity and is much greater for the kaolinitic soil, which has significant pH-dependent charge. At all pH values, the divalent SO - ion is adsorbed to a greater extent than the monovalent Cl- Ion, as would be expected on the basis of electrostatic attraction forces alone. 

Chloride, nitrate, and sulfate are common and important anions in most soils and have been studied extensively. Chloride, in particular, is often used as an indicator of NQ mobility in soils, since Cl is not subject to the complicating biological reactions characteristic of NOT. In most other respects, Cl- behaves similarly to 

Anions strongly retained by soils include PO -, AsO -, MoO -, CrO -, and F-. These anions are essential microelements for plants and animals and are present in trace concentrations in the solutions of native soils. Because the amounts and tenacity of soil retention of these ions is so much greater than Cl, NO3, and others, this retention has been misnamed as specific adsorption. These anions are simply 

The agricultural contribution to lake and stream contamination probably comes mostly from surface runoff of fertilized fields and from feed lots rather than from actual drainage water. Mixing, dilution, and time can mitigate soil contamination problems. 

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A high-performance liquid chromatographic method for nalidixic acid on a strong anion-exchange resin column has been reported, using a mobile phase of 0.01 M sodium tetraborate at pH 9.2 and 0.003 M sodium sulfate. The relative retention time for nalidixic acid in the system reported by Sondach and Koch was 0.86 with sulfanilic acid as the standard at... 

The separation of the same charged compounds were also accomplished on an ethyl-pyridine bonded silica surface and 30 0% methanol/C02 mobile phases without the need of added sulfonate modifier. Anionic compounds did not elute from the ethyl-pyridinium surface that lead the authors to hypothesize that the surface was positively charged. To further test this hypothesis, the separation of the same compounds on a strong anion exchange column, silica-based propyltri-methylammonium cationic surface, which exhibits are permanent positive charge was attempted. The same retention order was observed on the strong cation exchange surface. 

Fig. 1. Purification of 2 dNAD+ by strong anion exchange-HPLC. Retention time of boronate-purified compounds before (A) and after (B) treatment with bacterid alkaline phosphatase. (C) Retention time of pure 2 dNAD+ on a PartisiHO SAX column of 250 mm x 4.6 mm I.D. utilizing a low salt buffer system at a flow rate of 1 ml/min. 

Ion-retardation resins, which consist of acrylic acid polymerized inside a strong anion-exchange resin on a polystyrene divinylbenzene matrix [30], are also effective for removal of SDS from proteins. Passage of a protein-SDS complex through the resin results in complete retention of SDS and elution of protein with 80-90% recovery [31]. The capacity of the resin for SDS is more than 2.2mg/g, which effectively reduces the SDS level to less than one molecule of SDS per protein molecule. Because SDS binds tenaciously to the resin, it cannot be removed and the resin must be discarded after use. In the presence of buffers, adsorption of SDS by an ion-retardation column is reduced, resulting in incomplete removal of detergent from the protein. This can be circumvented by prior removal of buffer by SEC or, more conveniently, by the addition of a few grams of size exclusion gel to the head of the ion-retardation resin bed to retard the buffer [4]. 

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