Nonionic resin adsorption

The results of model compound recovery experiments, in part, support these selection criteria. For example, the anionic resin (MP-1) yielded the best recoveries of the anionic organics (little or no adsorption was observed on subsequent resins) glycine was equally distributed (but poorly recovered) on MP-1 and MP-50 (no adsorption was observed on the nonionic resins). Although some selective adsorption occurred on the lower surface area ionic resins, the nonpolar macro-porous XAD-2 showed its retentive power for low-polarity compounds as none were seen to break through to the more polar methacrylate polymer, XAD-7. XAD-7 was included in the system for use with reclaimed and surface waters (21) because literature reports indicated that the methacrylate XAD resins had significantly better retention of humics, fulvics, and smaller phenolics (9, 29, 30). However, in the... 

A wide variety of solvents have been utilized for the extractions. Other procedures have been used, particularly with urine in drug screening programs. Included are drug adsorption on cation-exchange resin paper, XAD-2 nonionic resin, and charcoal. 

There are also sample concentration/separation techniques used as pretreatment methods for trace analysis. Commonly used methods include chelating ion-exchange and, for trace organic analysis, solvent extraction, carbon adsorption, and resin adsorption using nonionic macroeticular resins. 

Only 10% of the dissolved organic carbon in seawater has been characterized on a molecular level. About 5 to 23% of this DOC can be isolated from seawater by adsorption onto a nonionic macroporous resin fiallowed by elution with an alkaline solution. 

Adsorption chromatography is an efficient way to isolate organic acids from large volumes of water. The nonionic, macroporous, Amberlite XAD-8 and the weak-base anion-exchange resin Duolite A-7 are two resins well suited for this purpose. These resins have been successfully used to extract organic acids from natural waters at sites where it was necessary to process thousands of gallons of sample. 

Analytes can be separated from complex matrices by sample preparation techniques that include liquid extraction, supercritical fluid extraction, and solid-phase extraction. Dilute ionic analytes can be preconcentrated by adsorption onto an ion-exchange resin. Nonionic analytes can be concentrated by solid-phase extraction. Derivatization transforms the analyte into a more easily detected or separated form. 

Solid-Phase Extractions Using XAD Resins. The Amberlite XAD series (Rohm and Haas Co., Philadelphia, PA, USA) have been most often used for isolation of marine DOM by SPE. XAD resins are nonionic macroporous copolymers that differ in pore size, surface area, and polarity. Their generally large specific surface areas and more-or-less reversible adsorption of organic solutes from aqueous solution have made them well-suited for isolation of selected fractions of DOM from natural waters. Even though XAD resins have been used far more often to... 

To remove the feedback regulation mechanism and to avoid product degradation various adsorbents have been used for the in situ separation of plant cell cultures as shown in Table 1. In situ removal with polymeric adsorbents stimulated anthraquinone production more than the adsorbent-free control in Cinchona ledgeriana cells [35]. It was found that nonionic polymeric resins such as Amberlite XAD-2 and XAD-4 without specific functional groups are suitable for the adsorption of plant metabolite [36]. The use of the natural polymeric resin XAD-4 for the recovery of indole alkaloids showed that this resin could concentrate the alkaloids ajmalicine by two orders of magnitude over solvent extraction [37] but the adsorption by this resin proved to be relatively nonspecific. A more specific selectivity would be beneficial because plant cells produce a large number of biosynthetically related products and the purification of a several chemically similar solutes mixture is difficult [16]. 

Immobilization. We have worked with different carriers for immobilization. Active immobilized preparations have been obtained by adsorption on macroporous, weakly basic anion exchange resins, and on nonionic adsorbent resins. Resins of both acrylic and phenol-formaldehyde have been used (8). In the following examples we have used lipase immobilized on nonionic adsorbent acrylic resin. 

Attempts to develop the sieving process as a tool for the isolation of a pure peptide containing the chromophore were not successful because it was found that the resins did not act as pure ionic sieves (Partridge, 1952) the colored peptides displayed strong adsorptive effects which appeared to be nonionic in character. However it was found that the strong adsorptive affinity of the colored peptides could itself be utilized for further enrichment of the fractions. 

The ion-exchange resins are mainly useful for compounds which may react with them, such as acids and amines. The distribution coefficient is not completely determined by the acidity or basicity of the compound being chromatographed, because adsorption also occurs. Ion-exchange columns may, therefore, also be used for nonionic compounds, but these are usually more effectively separated with the more common adsorbents. 

A nonionic cross-linked polymethacrylate resin (Am-berlite XAD7) was used in the reduction of the ketone (5.34) by an aqueous suspension of Zygosaccharomyces rouxii cells.145 Adsorption by the resin kept the concentrations of the substrate and product below levels that would be lethal to the cells, yet allowed enough to be in solution for the reduction to take place in 96% yield with more than 99.9% enantiomeric excess (often abbreviated %ee). 

Should solvent extraction be inapplicable as a primary purification stage, adsorption methods should be evaluated. Sequential use of ion exchangers and nonionic polymeric resins will often effect considerable purification. If the resins are to be used regularly such that >50 L will be used during a project, it will be more economical to obtain them directly from the manufacturers rather than from laboratory suppliers. Guidance in the use of ion exchangers is relatively sparse a useful introduction is provided by Harland (14) (see Chapter 5). 

Specific problems in speciation analysis When organic metal species are injected into an lEC system, hydrophobic interactions between the sample and the nonionic carbon skeleton of the stationary phase may cause adsorption of organic ions. The pore size of the resin particles may exclude the species from separation, and such species elute in the void volume. For the separation of such molecules, resin pore sizes need be increased, and this results in a decreased number of interaction sites. Often, loosely bound metal ions are lost or replaced by other metals originating from the buffer (Morrison 1989 Michalke 1994) Thus, lEC is predestined for the separation of covalently bound element species of different valence states, such as Cr(III)/Cr(VI) or Sb(III)/Sb(V)/methyl-Sb. Another frequent application is given for covalently bound Se-amino acids or arsenicals (Gilon et al. 1996 Michalke etal. 2000 Larsen etal. 

However, hydrophobic interactions between organometallic species and the nonionic carbon skeleton of the stationary phase may cause adsorption. The pore size of the resin particles may exclude high molecular-mass species from separation, which are then eluted in the void volume. Most important, labile species can be hampered by the... 

A. Adsorption. The physical adsorption of the nonionic, nonpolar chlorinated pesticides, lindane and toxaphene, were measured in two types of polymers ionic exchange resins and nonionic styreneidivinylbenzene polymers.The following results were obtained ... 

Prescher et al. [22] investigated the removal of four fluorinated surfactants by chemical and physical means. The structures of the fluorinated surfactants were the same as in their previous study [17]. The study showed that the nonionic surfactant can be removed by flocculation with aluminum oxychloride, by chlorination, or by adsorption on activated carbon. For the anionic fluorinated surfactant, adsorption on activated carbon or on a resin, such as Wofatit EA o. is the most effective removal method. 

The procedures used in column adsorption chromatography may also be used in batch mode, usually with less separation efficiency, but often with some saving of labor. For example, nonionic impurities may be separated from a variety of anionic sulfate and sulfonate surfactants by dissolving the material in a small amount of ethanol/water, mixing with diatomaceous earth, and washing the adsorbant with petroleum ether or 7 93 methylene chloride/petroleum ether. The anionic material remains adsorbed (70). APE may be isolated from water by batch wise separation on XAD-2 resin, 1 g to 0.5-1.0 L of sample. The surfactant is recovered by washing the resin with 100 mL methanol (71). 

Gorenc, B., D. Gorenc, A. Rosker, Preconcentration of nonionic surfactants by adsorption on ion-exchange resin in the cobaltithiocyanate form, Vestn. Slav. Kem. Drus., 1986,33,467 74. Barber, A., C. C. T. Chinnick, P. A. Lincoln, Mixtures of surface-active quaternary ammonium compounds and polyethylene oxide type of nonionic surface-active agents. Analyst, 956,81,18-25. 

Kudoh, M., S. Yamaguchi, Selective adsorption of nonionic surfactants using an anion-exchange resin in the cobaltithiocyanate form, J. Chromatogr., 1983,260,483-486. 

Nonionic surfactants are usually isolated from natural waters on XAD resin at neutral pH. This is to prevent the co-adsorption of fulvic acids which occurs under acidic conditions (98). Very hydrophilic metabolites, such as low molecular weight PEG and PEG carboxylates, may not be adequately retained on XAD resin unless the procedures are specifically optimized for these compounds (99). 

Gorenc, B., D. Gorenc, A. Rosker, Preconcentration of nonionic surfactants by adsorption on ion-exchange resin in the cobaltithiocyanate form, Vestn. Slav. Kern. Drus., 1986,33,467—474. 

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