Separator Universal Cation

The third product of this kind is offered by Grace Alltech (Deerfield, IL, USA) under the trade names Universal Cation [21] and Universal Cation HR. While the column dimensions of Universal Cation and LiChrosil IC CA are identical, the 7 pm particle diameter of the Universal Cation substrate is slightly larger. Remarkably, with a pure methanesulfonic acid eluent and subsequent use of a suppressor system, it is possible to elute alkali and alkaline-earth metals. As shown in Figure 4.43, some transition metals can be separated with this stationary phase, if an eluent mixture of two chelating agents is used [22]. Universal... 

Metal nanotube membranes with electrochemically suitable ion-transport selectivity, which can be reversibly switched between cation-permeable and anion-permselective states, have been reported. These membranes can be viewed as universal ion-exchange membranes. Gold nanotube molecular filtration membranes have been made for the separation of small molecules (< 400 Da) on the basis of molecular size, eg. separation of pyridine from quinine (Jirage and Martin, 1999). 

For the cationic surfactants, the available HPLC detection methods involve direct UV (for cationics with chromophores, such as benzylalkyl-dimethyl ammonium salts) or for compounds that lack UV absorbance, indirect photometry in conjunction with a post-column addition of bromophenol blue or other anionic dye [49], refractive index [50,51], conductivity detection [47,52] and fluorescence combined with postcolumn addition of the ion-pair [53] were used. These modes of detection, limited to isocratic elution, are not totally satisfactory for the separation of quaternary compounds with a wide range of molecular weights. Thus, to overcome the limitation of other detection systems, the ELS detector has been introduced as a universal detector compatible with gradient elution [45]. 

When the kinetics of a sorption process do appear to separate according to very small and very large time scales, the almost universal inference made is that pure adsorption is reflected by the rapid kinetics (16,21,22,26). The slow kinetics are interpreted either in terms of surface precipitation (20) or diffusion of the adsorbate into the adsorbent (16,24). With respect to metal cation sorption, "rapid kinetics" refers to time scales of minutes (16,26), whereas for anion sorption it refers to time scales up to hours TT, 21). The interpretation of these time scales as characteristic of adsorption rests almost entirely on the premise that surface phenomena involve little in the way of molecular rearrangement and steric hindrance effects (16,21). 

The lonsiv ion exchange resins are extraction technologies used to separate radionuclides from alkaline wastewater in the presence of competing cations. These resins include lonsiv IE-910 and lonsiv IE-911, which are manufactured using a new class of crystalline silicotitanates (CSTs) invented by researchers from Sandia National Laboratory (SNL) and Texas A M University. CSTs demonstrate high distribution coefficients in acidic, neutral, and alkaline solutions with high concentrations of competitive ions such as sodium and potassium. The affinity of CSTs for strontium in neutral or alkaline wastes is also high. 

Elegant work by Saul Winstein (of the University of California, Los Angeles) has revealed the detailed behavior of ion pairs that are intermediates in certain cases of solvolysis tight (or intimate) ion pairs, the cation of which is free enough to pivot about and lose configuration, and yet is held tightly enough that recombination to the covalently bonded compound is the favored process loose (or solvent-separated) ion pairs, the cation of which is susceptible to attack by outside nucleophiles. 

Ion-pair chromatography provides a useful alternative to ion-exchange chromatography. The selectivity of the separation in ion-pair chromatography is mainly determined by the make-up of the mobile phase, thus both anionic and cationic compounds can be separated. This universal applicability has helped ion-pair chromatography reach its present significance. 

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