Organic complexing agents

The type of anion and cation, pH, ionic strength, concentration, addition of modifiers such as complexing agents, organic solvents, surfactants, etc., all are parameters of the bulk electrolyte in the capillary that can affect the selectivity of separation. Selectivity may be expressed in terms of mobility differences (A/i) or in mobility ratios (a) ... 

The great majority of small elemental forms are polar or ionic compoimds, and thus the first separation technique of choice to address speciation analysis is LC. Of special importance for small molecules are reversed phase, ion-pairing, micellar, and ion exchange techniques that have been reviewed elsewhere. The optimum separation conditions may not always be used in speciation studies. Compromises are sometimes necessary to avoid possible changes in natural species distribution due to their interaction with stationary and mobile phases (pH conditions, complexing agents, organic modifiers). ... 

Buffer additives Urea, surfactants, complexing agents, organic solvents Buffer additives Urea, surfactants, inorganic salts, organic solvents, sulfonic acids, chiral cyclodextrins, amines... 

Capillary Electrophoresis. Capillary electrophoresis (ce) is an analytical technique that can achieve rapid high resolution separation of water-soluble components present in small sample volumes. The separations are generally based on the principle of electrically driven ions in solution. Selectivity can be varied by the alteration of pH, ionic strength, electrolyte composition, or by incorporation of additives. Typical examples of additives include organic solvents, surfactants (qv), and complexation agents (see Chelating agents). 

Cosolvents ana Surfactants Many nonvolatile polar substances cannot be dissolved at moderate temperatures in nonpolar fluids such as CO9. Cosolvents (also called entrainers, modifiers, moderators) such as alcohols and acetone have been added to fluids to raise the solvent strength. The addition of only 2 mol % of the complexing agent tri-/i-butyl phosphate (TBP) to CO9 increases the solubility ofnydro-quinone by a factor of 250 due to Lewis acid-base interactions. Veiy recently, surfac tants have been used to form reverse micelles, microemulsions, and polymeric latexes in SCFs including CO9. These organized molecular assemblies can dissolve hydrophilic solutes and ionic species such as amino acids and even proteins. Examples of surfactant tails which interact favorably with CO9 include fluoroethers, fluoroacrylates, fluoroalkanes, propylene oxides, and siloxanes. 

Specificity for alkali and alkaline earth cations of synthetic and natural organic complexing agents in membranes. W. Simon, W. E. Morf and P. C. Meier, Struct. Bonding (Berlin), 1973, 16, 113-160 (123). 

Lehn J-M (1973) Design of Organic Complexing Agents. Strategies Towards Properties. 16 1-69... 

Neutral carriers are organic complexing agents which are capable of sequestering and transporting ionic species in a hydrophobic organic phase. The antibiotics, valino-mycin and nonactin were the first neutral carriers to be incorporated in an ISE These macrocyclic neutral carriers contain a polar internal cavity and an outer hydro-phobic shell. The excellent selectivity exhibited by valinomycin for potassium ions is... 

Simon, W., Morf, W. E., Meier, P. Ch. Specificity of Alkali and Alkaline Earth Cations of Synthetic and Natural Organic Complexing Agents in Membranes. Vol. 16, pp. 113-160. 

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