Ion-exchange methods

Ion-exchange methods are based essentially on a reversible exchange of ions between an external liquid phase and an ionic solid phase. The solid phase consists of a polymeric matrix, insoluble, but permeable, which contains fixed charge groups and mobile counter ions of opposite charge. These counter ions can be exchanged for other ions in the external liquid phase. Enrichment of one or several of the components is obtained if selective exchange forces are operative. The method is limited to substances at least partially in ionized form. 

Spectroscopic methods for the deterrnination of impurities in niobium include the older arc and spark emission procedures (53) along with newer inductively coupled plasma source optical emission methods (54). Some work has been done using inductively coupled mass spectroscopy to determine impurities in niobium (55,56). X-ray fluorescence analysis, a widely used method for niobium analysis, is used for routine work by niobium concentrates producers (57,58). Paying careful attention to matrix effects, precision and accuracy of x-ray fluorescence analyses are at least equal to those of the gravimetric and ion-exchange methods. 

The batch and fed-batch procedures are used for most commercial antibiotic fermentations. A typical batch fermentor may hold over 150,000 Hters. When a maximum yield of antibiotic is obtained, the fermentation broth is processed by purification procedures tailored for the specific antibiotic being produced. Nonpolar antibiotics are usually purified by solvent extraction procedures water-soluble compounds are commonly purified by ion-exchange methods. Chromatography procedures can readily provide high quaHty material, but for economic reasons chromatography steps are avoided if possible. 

Another approach, the so-called seeding technique, provides preferential sites for the nucleation of scale, which permits the heat-transfer surfaces to remain clean of scale. Extensive studies of this technique have been conducted, and field use was reported ia the former USSR as early as the mid-1960s (42). The use of ion-exchange methods is another possible approach. Eor calcium, the exchange can be represented as... 

Fig. 6. Size-distribution of metal crystallites on the surface of Co-silica made by precipitalion-ion-exchange method.

Isolation of Inosine by Ion Exchange Method Half of the above clear centrifugate (1.15 liters) is treated with 250 cc of anion exchange (bicarbonate form) and stirred together therewith for 16 hours at room temperature. The pH value is increased thereby to about 4 to 5. The ion exchanger is filtered off under suction and washed 3 times, each time with 150 cc of water. The solution is brought to a pH value of 7 by means of normal sodium hydroxide (total volume of the solution about 1.55 liters), and concentrated to a volume of about 100 cc under vacuum. 

Nonionic surfactants, including EO-PO block copolymers, may be readily separated from anionic surfactants by a simple batch ion exchange method [21] analytical separation of EO-PO copolymers from other nonionic surfactants is possible by thin-layer chromatography (TLC) [22,23] and paper chromatography [24], and EO-PO copolymers may themselves be separated into narrow molecular weight fractions on a preparative scale by gel permeation chromatography (GPC) [25]. 

The radioisotope Cr was used to tag the species and the separation of Cr from CrX " was achieved using an ion-exchange method, after oxidation of the Cr to Cr with Fe(III) or oxygen. The reactions were carried out in the absence of oxygen in perchlorate media. For the systems involving chloride, fluoride, and azide . King et al. have found a rate law... 

Separation of the products was achieved using an ion-exchange method, the reaction taking place in sealed vessels with the Cr(Vl) labelled ( Cr). Under various conditions only 40% of the Cr appears in the product Cr2(OH)2. This led these workers to propose a modified mechanism in which the step involving Cr(V) proceeds in two ways... 

Na-ZSM-5(a molar SiOz/AlaOa ratio=23.8) provided by Tosoh Corp. was used. ln(4wt%)/H-ZSM-5 and lr(1wt%)/H-ZSM-5 catalysts were prepared by the ion exchange method using NH4-ZSM-5 derived from the Na-ZSM-5 with aqueous solutions of ln(NOs)3 at 368 K for 8 h and lrCI(NH3)sCl2 at room temperature for 24 h, respectively. Addition of precious metals, 1wt% platinum and iridium to ln/H-ZSM-5 was carried out by impregnating the ln/NH4-ZSM-5 in aqueous solutions of Pt(NH3)4Cl2 and lrCI(NH3)5Cl2, respectively. The catalysts were calcined at 813 K for 3 h. 

Dufresne, C., Isolation by ion-exchange methods, in Methods in Biotechnology, vol. 4, in Natural Products Isolation, R. J. P. Cannell, Ed., Humana Press, Totowa, NJ, 1998, 141. 

Catalysis of supported metal ions is an area of interest. There are a number of advantages in depositing catalytically active metal ions on a support. The ion exchange method of catalyst immobilization is simple and the attractiveness of this method is further increased by providing stable inorganic ion exchangers of known structures as supports. 

Catalyst F was made by the ion exchange method given by Hathaway and Lewis 45). 

Selective catalytic reduction of NOx by NH3 on V-Mo-zeolite prepared by solid-state ion exchange method... 

The NH4-Beta-300 (Zeolyst International, number denote Si02/Al203 molar ratio) was transformed to corresponding proton form using a step calcination procedure at 500 °C. H-Beta-300 was partially modified with Fe by repeated ion-exchange method (Fe(III)nitrate). The surface areas as well as acidities (Bronsted and Lewis acid sites) of Fe-Beta (iron content - 0.1 wt %) were determined by nitrogen adsorption and pyridine desorption at 250, 350 and 450 °C using FTIR spectroscopy [6]. 

Fe3+, La3+ and Ce3+ ion-exchanged MAPO-36 was prepared by wet ion-exchange method. The materials were characterized by XRD, TGA and TPD (ammonia). Lewis acid metal ions are suggested to remain as charge compensating MO+ species after calcination in ion-exchanged MAPO-36. Beckmann rearrangement of cyclohexanone oxime was studied over these catalysts in the vapour phase. 

Spedding, F. H. and Powell, J. E. (1956). Ion exchange methods of separating rare earths, page 37 in Rare Earths in Biochemical and Medical Research A Conference Sponsored by the Medical Division, Oak Ridge Institute of Nuclear Studies, October 1955, Report No. ORINS-12, Kyker, G. C. and Anderson, E. B., Eds. (Office of Technical Services, Washington). 

Klenk, D.C., Hermanson, G.T., Krohn, R.I., Fujimoto, E.K., Mallia, A.K., Smith, P.K., England, J.D., Wiedmeyer, H.M., Little, R.R., and Goldstein, D.E. (1982) Determination of glycosylated hemoglobin by affinity chromatography Comparison with colorimetric and ion-exchange methods, and effects of common interferences. Clin. Chem. 28(10), 2088-2094. 

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