Ion exchange separation methods

The exchange of °Co between the EDTA complexes of Co(II) (CoY ) and Co(IlI) (CoY ), in aqueous perchlorate and nitrate media at pH = 2, has been investigated by Adamson and Vorres . Using a ion-exchange separation method, a rate law... 

Apart from the amino acids (which will be discussed in the next section) the most extensively investigated ligands are the different substituted hydroxy acids. In the ion exchange separation method of the rare earths and the actinides, the hydroxy acids play a great part as eluants. 

When use of the ion-exchange separation method developed in this study was considered it was determined from the separation factor calculated from the stability constants 4] of their complexes with EDTA that a column ratio greater than 40 would be needed to separate them. Experiments showed that a column ratio nearly 10 times larger would be needed to affect their separation with CIEC. Theoretically based studies [7-9] led to success in separation Eu and Gd by the use of HPIEC and a binary displacer. This technique has made the separation of Gd and Eu simple and useful enough to warrant its use as an industrial process. 

Among ion exchange separation methods for transuranics, strong base anion exchange in hydrochloric and nitric acids is important (Keder, 1962 Keder et al., 1960 Horowitz et al., 1990 Chu, 1971 Wong, 1971 Diamond et al., 1954 Korkisch, 1989). Among solvent extraction reagents for transuranics, thenoyltrifluoroacetone (TTA) and trioctylamine (TOA) are important (Keder, 1962 Chieco et al., 1990). 

Wittwer described an ion-exchange separation method for some drugs of abuse. Quinine... 

Ion-exchange separation methods are based on the retention of the palladium chloride complex on strongly basic anion-exchangers, and of the cationic ammine complex on cation-exchangers [16]. A cellulose anion-exchanger has been used to separate Pd from Pt and Ir [17], and from Ir [16]. 

Newer approaches to the development of ion exchange separation methods in biochemistry are represented by two general trends (a) medium and high pressure liquid chromatography (MPLC, HPLC), (b) chromatofocusing both trends are briefly discussed here. 

Allan and Parthasarathy (11) and Kukula et al. (502) offer some specific radiochemical methods based on the use of solvent extraction separations. Ion exchange separation methods applied to activation analysis have been described by Aubouin and Laverlochere (40), Co mar and lePoec (193, 194), Cram and Brownlee (208), Eisner et al. (250), Hadzistelios and... 

An interesting consequence of selective sorption is that conditions for partition chromatography arise which may enhance the normal ion exchange separation factors. This aspect has been utilised by Korkisch34 for separation of inorganic ions by the so-called combined ion exchange-solvent extraction method (CISE). 

Electrolysis with a mercury cathode or with controlled cathode potential. (g) Application of physical methods utilising selective absorption, chromatographic separations, and ion exchange separations. 

Vermillion, W. D. and Crenshaw, M. D., In-line respeciation an ion-exchange chromatographic method applied to the separation of degradation products of chemical warfare nerve agents in soil, /. Chromatogr. A, 770, 253, 1997. 

A detailed description of IC is given in reference 1 however, the basic principles of the method can best be described by an example. Figure 1 schematically represents both an anion and a cation IC analysis. In both cases, the instrumentation involves a pumping system, an eluent, an injection valve, an ion-exchange separator column, an ion-exchange suppressor column and a conductivity cell. The sample is first injected into the flow system then the well known reaction equilibrium shown in Figure 1 results in the separation of sample anions or cations on the separator column (2). 

Erbium metal is produced from rare-earth minerals. Methods of preparation are similar to dysprosium, involving sulfuric acid treatment, ion exchange separation from other lanthanides, roasting, conversion to hahde, and finally high temperature reduction with calcium or sodium, (see Dysprosium). 

Various processes separate rare earths from other metal salts. These processes also separate rare earths into specific subgroups. The methods are based on fractional precipitation, selective extraction by nonaqueous solvents, or selective ion exchange. Separation of individual rare earths is the most important step in recovery. Separation may be achieved by ion exchange and solvent extraction techniques. Also, ytterbium may be separated from a mixture of heavy rare earths by reduction with sodium amalgam. In this method, a buffered acidic solution of trivalent heavy rare earths is treated with molten sodium mercury alloy. Ybs+ is reduced and dissolved in the molten alloy. The alloy is treated with hydrochloric acid, after which ytterbium is extracted into the solution. The metal is precipitated as oxalate from solution. 

Heras JM, Marina ML, Garcia MC. Development of a perfusion ion exchange chromatography method for the separation of soybean proteins and its application to cul-tivar characterization. Journal of Chromatography A 2007 1153 97-103. 

Kaiser [3U used on-line sample preparation to determine trace anions in solvents, including isopropanol, acetone and Af-methylpyrrolidone. A large solvent injection can interfere with both the ion exchange separation and the conductivity detection by causing large disturbances in the baseline. In this application the anions were concentrated on a AG9-HC guard column and then the solvent was sent to waste before it could enter the analytical column. After the solvent was cleared from the AG9-HC concentrator column, the AG9-HC concentrator was switched in line with the AS9-HC analytical column for the separation. The method detection limits for chloride, sulfate, phosphate and nitrate are reported in the sub pg/1 range. 

An ion exchange chromatographic method has been described [16] for the determination of the various forms of vanadium in fresh water. These include tetravalent cationic, pentavalent anionic and neutral complexed forms of vanadium. Separation is achieved on two columns in series involving the absorption of the sample on Chelex 100 and Dowex 1x8 columns followed by the selective elution of the different vanadium species and their assay by neutron activation analysis. Experiments were carried out using vanadium-48... 

Capillary electrochromatography (CEC) is a rapidly emerging technique that adds a new dimension to current separation science. The major "news" in this method is that the hydrodynamic flow of the eluting liquid, which is typical of HPLC, is replaced by a flow driven by electro-endoosmosis. This increases considerably the selection of available separation mechanisms. For example, combinations of traditional processes such as reversed-phase- or ion-exchange- separations with electromigration techniques are now possible. Also, CEC is opening new horizons in the separation of non-polar compounds, and thus represents an alternative to the widely used micellar electrokinetic chromatography. 

FIGURE 2-12. Comparison of ion-exchange and reverse-phase methods of amino-acid analysis, (a) The ion-exchange separation, (b) The method of reference 8 (commercialized by Waters under the name of Pico-Tag Amino Acid Analysis ). 

Ion exchange separations may also be done in preparation for electrothermal atomisation. An interesting variant on this method is where the resin itself, containing the bonded analyte element, is subjected to direct analysis in the solid phase. In one example one litre of seawater is passed through 500 mg of chitosan (a natural chelating polymer). The resin was then homogenized and 5 mg samples of this were analysed for vanadium. Response of vanadium from the resin and from aqueous standards was shown to be the same. 

While the selection of a stationary phase to be used in the analytical column may appear complex, the decision can be greatly simplified by considering the three basic methods of separation currently in use. These are gel filtration or size-exclusion separation, reversed-phase or hydrophobic separation, and ion-exchange separation. In general, each type of separation uses a different kind of packing material, and since each type of separation exploits a different property of the molecules, the choice of packing really comes down to which property of the molecules would be most useful in achieving the separation. 

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