Chaotropic salts

At variance with traditional IPRs that tend to stick very strongly to the stationary phase and to impair the initial column properties also when their presence in 

However, Kazakevich and co-workers demonstrated the importance of the adsorption of chaotropic ions onto the reversed stationary phase [106]. The rank of an ion in the Hofmeister series is another measure of its tendency to accumulate at the stationary phase in RP-HPLC and be quantified via its adsorption isotherm [88]. Clearly a specific surface excess of the chaotropic reagent results in the development of a potential difference between the stationary phase and the bulk eluent, modulating retention of analytes [107]. We discussed in Chapter 3 the way a comprehensive theory can take this experimental evidence into account. 

The effect of the nature of a chaotropic mobile phase additive on retention behavior of basic drugs analytes was studied. They influence the selectivity, efficiency, and repeatability [87,95,108]. Interestingly, weakly chaotropic ions such as those coming from acetic [94,109-111] or phosphoric add were advantageously used as IPRs [16,89-91] and the results may be rationalized by the theory of chaotropicity [95]. 

Even if anionic chaotropes are the most popular neoteric IPRs, polarizable cations such as sulfonium and phosphonium reagents showed single selectivity toward polarizable anions their behavior was rationalized on the basis of their chaotropicity. Probe anion retention generally increases in the order of tributylsulfonium tetrabutylammonium tetrabutylphosphonium. Interestingly, retention was found to be influenced by the kosmotropic/chaotropic character of both the IPR and the probe anion [93] and this confirms the peculiarities of hydrophobic ion-pairing. Quaternary phosphonium salts provided increased selectivity compared to ammonium in the IPC of heavy metal complexes of unithiol [112]. 

Dependence of Retention of Positively Charged Analytes on Eluent Concentration of NaCI04 

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Breslow supported this suggestion by demonstrating that the cycloaddition can be further accelerated by adding anti cliaotropic salts such as lithium chloride, whereas chaotropic salts such as guanidium chloride led to a retardation " "" ". On the basis of these experiments Breslow excluded all other possible explanations for the special effect of water on the Diels-Alder reaction " . 

WA Klis, JM Stewart. Chaotropic salts improve SPPS coupling reactions, in JR Rivier, GR Marshall, eds. Peptides Chemistry, Structure, and Biology. Proceedings of the 11th American Peptide Symposium. Escom, Leiden, 1990, pp 904-906. 

In the reversed-phase mode, mixtures of aqueous buffer and acetonitrile are commonly used as mobile phase. Other modifiers are possible, but as shown in Figure 6, acetonitrile often produces the best separations and peak shapes. Several studies have shown the fundamental importance of keeping the chiral analytes neutral when working with polysaccharide stationary phases in the reversed-phase mode. ° ° Therefore, acidic compounds are preferably analyzed at low pFI while basic compounds will be analyzed either in basic media or at low pH in the presence of a chaotropic salt such as sodium perchlorate (NaC104) or potassium hexa-fluorophosphate Some illustrations of the effect of the addi-... 

The first step in the extraction of nucleic acids may require the lysis of cells and the inactivation of cellular nucleases. These two steps may be combined into one. For instance, a single solution may contain detergents to solubilize the cell membrane and strong chaotropic salts to inactivate the intracellular... 

High concentrations of stabilizing salts such as NaCl and Na2S04 were reported to increase, and chaotropic salts to decrease, the affinity of bacterial and fungal cellulases to crystalline cellulose. Denaturing agents are capable of eluting cellulases from the cellulosic substrate (Otter et al., 1989). 

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