Ion-exchange technique

Europium oxide is now widely used as a phospor activator and europium-activated yttrium vanadate is in commercial use as the red phosphor in color TV tubes. Europium-doped plastic has been used as a laser material. With the development of ion-exchange techniques and special processes, the cost of the metal has been greatly reduced in recent years. 

Terbium has been isolated only in recent years with the development of ion-exchange techniques for separating the rare-earth elements. As with other rare earths, it can be produced by reducing the anhydrous chloride or fluoride with calcium metal in a tantalum crucible. Calcium and tantalum impurities can be removed by vacuum remelting. Other methods of isolation are possible. 

Finally, the techniques of nmr, infrared spectroscopy, and thin-layer chromatography also can be used to assay maleic anhydride (172). The individual anhydrides may be analyzed by gas chromatography (173,174). The isomeric acids can be determined by polarography (175), thermal analysis (176), paper and thin-layer chromatographies (177), and nonaqueous titrations with an alkaU (178). Maleic and fumaric acids may be separated by both gel filtration (179) and ion-exchange techniques (180). 

Yttrium and lanthanum are both obtained from lanthanide minerals and the method of extraction depends on the particular mineral involved. Digestions with hydrochloric acid, sulfuric acid, or caustic soda are all used to extract the mixture of metal salts. Prior to the Second World War the separation of these mixtures was effected by fractional crystallizations, sometimes numbered in their thousands. However, during the period 1940-45 the main interest in separating these elements was in order to purify and characterize them more fully. The realization that they are also major constituents of the products of nuclear fission effected a dramatic sharpening of interest in the USA. As a result, ion-exchange techniques were developed and, together with selective complexation and solvent extraction, these have now completely supplanted the older methods of separation (p. 1228). In cases where the free metals are required, reduction of the trifluorides with metallic calcium can be used. 

FP) in the aqueous phase. Subsequent separation of U and Pu depends on their differing redox properties (Fig. 31.3). The separations are far from perfect (see p. 1097), and recycling or secondary purification by ion-exchange techniques is required to achieve the necessary overall separations. 

Attempts to separate the isomeric deoxy ribose phosphates by ion exchange techniques met with no success this may be because of the fact that eluents having a pH lower than 5 were not used, as migration of phosphomonoesters is known to be acid catalysed, and, because of the free sugar involved, alkaline eluents could not be considered. 

In the ion-exchange technique, separated amino acids exiting (eluting) from the end of the chromatography column mix with a solution of ninhydrin and undergo a rapid reaction that produces an intense purple color. The color is detected by a spectrometer, and a plot of elution time versus spectrometer absorbance is obtained. 

The charged group introduced into products by the aldol donors (phosphate, carboxylate) facilitates product isolation and purification by salt precipitation and ion exchange techniques. Although many aldehydic substrates of interest for organic synthesis have low water solubility, at present only limited data is available on the stability of aldolases in organic cosolvents, thus in individual cases the optimal conditions must be chosen carefully. 

The physical nature of the sulfate complexes formed by plutonium(III) and plutonium(IV) in 1 M acid 2 M ionic strength perchlorate media has been inferred from thermodynamic parameters for complexation reactions and acid dependence of stability constants. The stability constants of 1 1 and 1 2 complexes were determined by solvent extraction and ion-exchange techniques, and the thermodynamic parameters calculated from the temperature dependence of the stability constants. The data are consistent with the formation of complexes of the form PuSOi,(n-2)+ for the 1 1 complexes of both plutonium(III) and plutonium(IV). The second HSO4 ligand appears to be added without deprotonation in both systems to form complexes of the form PuSOifHSOit(n"3) +. ... 

Ion exchange technique at Rocky Flats 378 Ion intensity measurements, vapor... 

Sea Water. The analysis of seawater (Parravano, C., State University of New York at Purchase Steams, C., unpublished) is a three-part experiment employing ion exchange techniques titrations to study the salt content of this familiar... 

The reaction of Na with Hg to form an amalgam that can then be separated from the NajO for oxygen analysis has been compared with the vacuum distillation technique . Ion-exchange techniques in which the sample is dissolved in a suitable solvent and the resulting separation of elements is achieved by an ion-exchange resin is less common. This technique is particularly suited to separating the volatile impurities such as K, Rb and Co. ... 

The sample drawn from the reactor consisted of an acid, several amines, and a neutral species. Two of the components were not resolved to baseline by reversed phase LC, so a dual column reversed phase ion-suppression/ ion-exchange technique was used. A chromatogram of the separation is shown in Figure 5. 

Reported concentrations of chromium in open ocean waters range from 0.07 to 0.96 xg/l with a preponderance of values near the lower limit. Methods used for the determination of chromium at this concentration have generally used some form of matrix separation and analyte concentration prior to determination [170-173], electroreduction [174,175] and ion exchange techniques [176,177]. 

Wood et al. [303] have described an ion exchange technique for the measurement of the copper complexing capacity of seawater samples taken in the... 

Cu and Ni were loaded by ion-exchange technique. Catalyst containing 6 wt% Ni 50 and 3 wt% Cu exhibits a high activity and H2 selectivity. 

Renberg [35] used an ion-exchange technique for the determination of chlorophenols and phenoxy acetic acid herbicides in soil. In this method the soil extracts are mixed with Sephadex QAE A-25 anion exchanger and the adsorbed materials are then eluted with a suitable solvent. The chlorinated phenols are converted into their methyl ethers and the chlorinated phenoxy acids into their methyl or 2-chloroethyl esters for gas chromatography. 

Separation and quantitation of carbohydrate mixtures may be achieved using HPLC, a method that does not necessitate the formation of a volatile derivative as in GLC. Both partition and ion-exchange techniques have been used with either ultraviolet or refractive index detectors. Partition chromatography is usually performed in the reverse phase mode using a chemically bonded stationary phase and acetonitrile (80 20) in 0.1 mol U1 acetic acid as the mobile phase. Anion- and cation-exchange resins have both been used. Carbohydrates... 

The major characteristic of technetium is that it is the only element within the 29 transition metal-to-nonmetal elements that is artificially produced as a uranium-fission product in nuclear power plants. It is also the tightest (in atomic weight) of all elements with no stable isotopes. Since all of technetiums isotopes emit harmful radiation, they are stored for some time before being processed by solvent extraction and ion-exchange techniques. The two long-lived radioactive isotopes, Tc-98 and Tc-99, are relatively safe to handle in a well-equipped laboratory. 

Using ion-exchange techniques, the selenato-species [ScCSeO )]" and [Sc(Se04)2] have been detected thermal decomposition of 802(8004)3,-5H2O gave SC2O3. 

The generation of monometallic catalysts with suitable characteristics is the first key step for obtaining supported bi- and organobimetallic catalysts via SOMC/M techniques. Ion-exchange techniques are generally used in the preparation of these catalysts, which lead to solids with good metallic phase dispersion and homo-... 

Ion exchange techniques have been widely applied in the separation process. In the large-scale ammonium thiocyanate process, the metal is retained on strong base anion exchanger thus, separating it from the lighter lanthanide elements which are not strongly absorbed on the resin. 

Minerals such as euxenite, fergusonite, samarskite, polycrase and loparite are highly refractory and complex in nature. These minerals may be opened up by treatment with hydrofluoric acid. While metals such as niobium, tantalum and titanium form soluble fluorides, rare earth elements form an insoluble residue of their fluorides. Such insoluble fluorides are filtered out of solution and digested with hot concentrated sulfuric acid. The rare earth sulfates formed are dissolved in cold water and thus separated from the insoluble mineral impurities. Rare earth elements in the aqueous solution are then separated by displacement ion exchange techniques outlined above. 

The method, however, is not as efficient as the ion-exchange technique discussed above. 

The insoluble calcium sulfate slurry is filtered out. Acid from this wet process is impure but can be purified by various methods. Purification steps involve precipitation, solvent extraction, crystallization, and ion exchange techniques. 

ANL claims the technology is promising because radionuclides are separated from waste streams by a simple, compact, cost-effective process that does not produce large secondary waste streams. The MACS process is intended to reduce the complexity of equipment when compared to solvent extraction and ion exchange techniques, and to facilitate scale-up due to the systems inherent simplicity. 

The ion exchange technique uses either natural zeolites or synthetic resins. It is a familiar process used in water softening where a calcium ion is exchanged for a sodium ion. 

In the method for the preparation of chiral 2-amino acids 610, the amino functionality is protected by a bis(methylthio)methylene group (see Table 8). This group is conveniently removed by acid hydrolysis in the same step that the methoxymethyl and the amides groups are cleaved. The 2-amino acids are then isolated in pure form using ion-exchange techniques. 

When treated with 5% sulfuric acid for 1.5 hours at 150°, pectin and D-galacturonic acid give reductic acid in yields of approximately 10% it is also formed on treatment of alginic acid with acid.96,119 The original preparation from pectin has been improved by using ion-exchange techniques,110 and synthetic preparations have been developed.188... 

The chief advantage of an ion exchange technique lies in simplicity and rapidity with which various separations or concentrations may be achieved. The application of ion exchange technique in analytical chemistry... 

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