Cation exchanger silica

Figure 12.22 SFC-GC analysis of aromatic fraction of a gasoline fuel, (a) SFC trace (b) GC ttace of the aromatic cut. SFC conditions four columns (4.6 mm i.d.) in series (silica, silver-loaded silica, cation-exchange silica, amino-silica) 50 °C 2850 psi CO2 mobile phase at 2.5 niL/min FID detection. GC conditions methyl silicone column (50 m X 0.2 mm i.d.) injector split ratio, 80 1 injector temperature, 250 °C earner gas helium temperature programmed, — 50 °C (8 min) to 320 °C at a rate of 5 °C/min FID detection. Reprinted from Journal of Liquid Chromatography, 5, P. A. Peaden and M. L. Lee, Supercritical fluid chromatography methods and principles , pp. 179-221, 1987, by courtesy of Marcel Dekker Inc.

Figure 10.2 Urinary creatinine assay. The chromatographic conditions were as follows column, 150 mm X 4.6 mm (5 pm) cation-exchange silica (SCX HPLC Technology, UKI eluent, 50mM sodium formate adjusted to ca. pH 6-methanol (80 20) flow rate, 1 mimin, injection, 20 pi temperature, ambient detector, variable wavelength UV detector (Cecil) set at 230 nm. Qiroraatogram courtesy Dr Ian James and the author. Department of Medicine St Barts. London.

To obtain a strong cation exchanger, silica can either be derivatized with an appropriate silane or it can first be reacted with a silane containing a phenyl group, which is then subjected to chlorosulfonation. Even under mild reaction conditions, some fraction of the phenyl silane is split off the silica during the sulfonation reaction. 

Like anion exchangers, cation exchangers are divided into polymer-based cation exchangers (PS-DVB, EVB-DVB, polymethacrylate, and polyvinyl copolymers), latex-agglomerated cation exchangers, silica-based, and other (e.g., crown ether, aluminia materials).Modern cation exchangers contain sulfonic, carboxylic, car-boxylic-phosphonic, and carboxylic-phosphonic-crown ether functional groups. 

The acid and base properties of catalytic activities of ion-exchanged silica-gel were also studied. Table 3.22 shows the acidity of the cation-exchanged silica gel which was evacuated at 373 or 573 The acidities were determined by an indicator method. 

Column. 15.0 cm x 4.6 mm, packed with a 5/on silica SCX (strong cation exchanger) bonded phase. 

The chemical adsorption of a relatively high molecular weight neutral polymer (poly(succinimide), M = 13000) on aminopropyl-Vydac 101 TP silica gel was applied by Alpert [47, 48] to prepare a reactive composite support for use in cation-exchange [47] and hydrophobic-interaction [48] chromatography of pro-... 

Alpert has shown [47] that poly(succinimide)-silica can be further hydrolyzed to poly (aspartic acid)-silica or condensed with [3-alanine in aqueous solution to form a covalently bonded copolymer of 2-carboxyethyl aspartamide and aspartic acid. The content of carboxyl groups generated by this way has not been quantified directly, but the cation-exchange hemoglobin capacity has been measured for a series of the packings. Thus, the optimal concentration of poly(succinimide) used in the synthesis was found to be 2 5%. 

Following the twin-bed with a third cation exchange bed or a mixed-bed (MB) polisher. Processes such as RO followed by twin-bed DI, plus twin MB polishers may yield treated water with silica leakage down to 0.5 ppb Si02. An alternative arrangement for the minimization of silica is the use of a double-pass RO followed by MB polishers. 

Analyses for the Saxitoxins. Early methods for analysis of the saxitoxins evolved from those used for toxin isolation and purification. The principal landmarks in the development of preparative separation techniques for the saxitoxins were 1) the employment of carboxylate cation exchange resins by Schantz et al. (82) 2) the use of the polyacrylamide gel Bio-Gel P2 by Buckley and by Shimizu (5,78) and 3) the development by Buckley of an effective TLC system, including a new solvent mixture and a new visualization technique (83). The solvent mixture, designated by Buckley as "E", remains the best for general resolution of the saxitoxins. The visualization method, oxidation of the saxitoxins on silica gel TLC plates to fluorescent degradation products with hydrogen peroxide and heat, is an adaptation of the Bates and Rapoport fluorescence assay for saxitoxin in solution. Curiously, while peroxide oxidation in solution provides little or no response for the N-l-hydroxy saxitoxins, peroxide spray on TLC plates is a sensitive test for all saxitoxin derivatives with the C-12 gemdiol intact. 

Strong cationic-exchange extraction and reversed-phase extraction (eliminates ion pairing when used in place of octadecyl silica. 

Alpert, A. J., Cation-exchange high-performance liquid chromatography of proteins on poly(aspartic acid)-silica, /. Chromatogr, 266, 23, 1983. 

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