Separations alkali metal cations

The proportion of hydrochloric acid in the mobile phase was not to exceed 20%, so that complex formation did not occur and zone structure was not adversely affected. An excess of accompanying alkaline earth metal ions did not interfere with the separation but alkali metal cations did. The hthium cation fluoresced blue and lay at the same height as the magnesium cation, ammonium ions interfered with the calcium zone. 

The anions MeF6 and X approach each other closely to form the heptacoordinated complex MeF6X(n+1)", or separate from one another, according to the polarization potential of the outer-sphere cation (alkali metal cation -M+). This process is unique in that the mode frequencies of the complexes remain practically unchanged despite varying conditions. This particular stability of the complexes is due to the high charge density of Ta5+ and Nbs+. 

All alkali metal hypersilanides display highly pyramidal central silicon centers with Si-Si-Si angles around 100°. Remarkably, these angles do not differ in the contact or separated ion pairs, further indicating the large degree of charge transfer from the alkali metal cation to the silanide anion. The pyramidalization is also an expression of the increased />-character of the Si-Si bond, and consequent increase in the alkali metal-silicon bond. 

Figure 4. Ion chromatographic separations of a series of anions on polymer-based column with covalently bonded (A) 2.2.2 and (B) 2.2.1. using gradient capacity step changes from one alkali metal cation to another. Anions 1) fluoride 2) chloride 3) nitrite 4) bromide 5) nitrate 6) sulfate 7) thiosulfate 8) phosphate 9) iodide 10) thiocyanate 11) perchlorate (from ref. 31)...

Although the majority of reports of macrocycles in analytical chromatography have involved ligand association with the stationary phase, their use as mobile phase constituents has also been investigated. Lamb and Drake [11] showed that addition of water-soluble crown ethers to the mobile phase altered the retention of alkali metal cations on an underivatized reversed phase column. Nakagawa et al. [63-66] also used crown ether-containing mobile phases in the separation of protonated amines, amino acids and peptides, and [1-lactam antibiotics. 

Addition of thiocyanate ions to chloride or perchlorate solntions of zirconium and hafnium yields complexes containing from one to eight isothiocyanate groups per metal atom. These systems are of interest because of the importance of thiocyanate complexes in the extraction and separation of the elements. IR spectroscopy indicates that M-N bonds are present in the violet (Zr) and pink (Hf) complexes [NEt4]2[M(NCS)6] analogous complexes have been obtained with alkali metal cations. In the presence of pyridine, the dodecahedral Zr(bipy)2(NCS)4 complex is produced see Ammonia N-donor Ligands). 

An increase of the dispersion part of interactions takes place with enrichment of the cation electron shell, while the smaller the cation radius is—i.e., the higher the concentration of the positive charge— the more pronounced the electrostatic interaction is. This may be illustrated taking the example of separation of the mixture hydrogen-methane-carbon monoxide on type X zeolites with alkali metal cations. 

Hasegawa Y, Watanabe K, Kusakabe K, and Morooka S. The separation of CO2 using Y-t)fpe zeohte membranes ion-exchanged with alkali metal cations. Sep PurifTechnol 2001 22-3(l-3) 319-325. 

It appears that whatever the behavior of uranium is in molten nitrates, the end product is most likely to be an alkali metal uranate. Separation of the alkali metal cation and uranium is perhaps the greatest unknown in the development of a... 

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