Silica gels anion exchangers

In situ amine-impregnated silica gel Amine- or amide-bonded phases Diol- and polyol-bonded silica gel Anion exchangers Cation exchangers... 

Silica gel anion exchanger R is a very fine silica gel (3-10 pm), whose surface is chemically changed by modification with quaternary ammonium groups. In this case, good chromatograms can be obtained on HPTLC plates NH2 and NH2 F254S. 

Medium basic polydextran or silica gel anion exchangers, com-parision... 

Silica-based anion-exchangers tend to have short life-times. This may be extended somewhat by proper sample clean-up and by the use of a silica-gel-saturation column, but this rapid degradation remains the biggest disadvantage of these phases. The resin-based phases are very stable, unless operated above 65°. Unfortunately, because of the slow diffusion processes in these resins, they must be operated at higher temperatures in order to achieve good efficiencies. 

Fig. 3-29. Separation of various inorganic anions on a TSK Gel IC-SW silica-based anion exchanger. - Eluent 0.001 mol/L tartaric acid (pH 3.2) flow rate 1.5 mol/L detection direct conductivity injection volume 100 pL solute concentrations 10 ppm each.

Silica-based anion exchangers are available from a number of manufacturers. Typical trade names include Vydac (Separations Group, Hesperia, CA, U.S.A.), Wescan (Alltech, Deerfield, IL, U.S.A.), TSK Gel (Toyo Soda, Tokyo, Japan) and Nucleosil... 

Unloaded silica does not recover HPA from aqueous solution. The surface of silica gel modified with quarternary ammonium salts (QAS) gets anion-exchange properties. The aim of the work is the elaboration of solid-phase reagents on the base of ion associate of HPA with QAS immobilized onto silica surface for the determination of phosphoms and organic reductants. Heterocyclic (safranine and lucigenine) and aliphatic (trinonyloctadecyl ammonium iodide and tetradecyl ammonium nitrate) compounds have been examined as QAS. 

Last time development of methods of iodine determination, which include preliminary sorption preconcentration of microcomponents and their subsequent determination in phase of concentrate get great practical significance. Silica gel (SG) with adsorptively modified quaternary ammonium salts (QAS) gets properties of anion-exchange resin. The sorbents modified in this way can be used successfully for determination of different anions. 

Silica gel supported sodium metaperiodate was used for the selective oxidation of dibenzyl sulphide80. Metaperiodate anion soaked on strongly basic-ion-exchange resins Amberlite IRA-904 or Amberlyst A-26 was found to be able to oxidize sulphides into the corresponding sulphoxides in 82-99% yield81. 

Purification methodologies for estrogens have been carried out by SPE with C18 [53, 54], polymeric [56, 60-62], silica [56-59] and anion exchange materials [59], preparative LC [53, 62], gel permeation chromatography (GPC) [54, 59, 97], liquid-liquid extraction [56], combination of them, or simple filtration [51]. However, the latter corresponds to the method with the highest reported method detection limits (MDL) [up to 175 ng/g dry weight (dw)]. 

The adsorbent should have a high affinity and capacity for the enzyme and it should not absorb the reaction product or enzyme inhibitors. Among the materials used the more popular are cation and anion exchange resins, activated charcoal, silica gel, alumina, control pore glasses and ceramics. 

The first reversed-phase SPE sorbents were based on silica gel particles, similar to the particles used in HPLC. A number of phases are available ranging from C8 to C18 to anion- and cation-exchange functionalities. Recent advances in particle technology have included polymeric materials that combine the benefits of a water-wettable particle to retain polar analytes with a reversed-phase, hydrophobic moiety to... 

To date, typical SPE materials are based on silica gel or highly cross-linked styrene-divinylbenzene (PS-DVB). The former is functionalised with distinct chemical groups to yield various sorbents with non-polar or polar characteristics. Non-polar materials are modified with alkyl groups of different chain length (C18, C8, C2), while polar sorbents have cyano-, amino-, or diol-bonded groups. Ion-exchange phases have either anionic or cationic functional groups. 

Anion-exchanger. Phenyl-bonded silica gel is suspended in chloromethyl methyl ether and boiled under reflux. Then, chloromethyl methyl ether containing anhydrous ZnCl2 is added and the mixture boiled under reflux. After filtration,... 

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