Ionic modifiers eluent concentration

The electrified stationary phase carries the same charge status of the IL ion that shows the strongest adsorbophilic attitude. Furthermore, ionic interactions between the analyte ion and the IL anion and cation, respectively, are contradictory and concur to modulate analyte ion retention in a complicated way. It follows that by increasing IL in the eluent, overall retention of the analyte may potentially (1) decrease [4] or (2) increase [5,6], or (3) remain almost constant if the conflicting effects of the IL cation and anion balance each other [7], depending on the specific IL concentration in the mobile phase [8]. Furthermore a reversal of elution sequence with increasing IL concentration is possible [9]. The multiplicity of interactions in the presence of a mixture of these ionic modifiers offers wide versatility related to selectivity adjustment. 

This problem was resolved by Nakae et al. [7] using non-polar octadecylsilica as the stationary phase and a solution of 0.1 M of sodium perchlorate in methanol/water (80 20) as the mobile phase. The ternary system (water-alcohol-salt), previously used by Fudano and Konishi [8] as an eluent for the separation of ionic surfactants at higher concentrations, induced the so-called salting out effect . The addition of the organic solvent to the water modified the polarity of the eluent and produced a good separation within a short period of time [9]. It also has the function of dissociating the surfactant micelles in individual molecules that are dissolved in the eluent [8], The presence of the salt (NaC104) in the mobile phase has a considerable influence on... 

Variation of solute retention and separation selectivity as a function of the eluent temperature at constant organic modifier concentration, pH and ionic strength. Solutes tryptophane enantiomers column alpha-... 

Hydrophilic Interaction LC-MS-Based Approaches Hydrophilic interaction LC (HILIC) is a variant of normal-phase LC. HILIC uses hydrophilic stationary phases, but employs reversed-phase type eluents. Any polar chromatographic surface can be used for HILIC separations, even nonpolar bonded silicas. A typical mobile phase for HILIC includes acetonitrile with a small amount of water. However, any aprotic solvent miscible with water (e.g., tetrahydrofunan or dioxane) can be used. Alcohols can also be used with a higher concentration. Ionic additives, such as ammonium acetate and ammonium formate, are usually used to serve as the modifiers for controlling the pH and ion strength of the mobile phase. 

Cyclodextrin phases can be operated in RP and normal-phase modes, as well as in the polar ionic mode (see Table 3). Aqueous eluent systems are better suited for the formation of inclusion complexes of apolar or aromatic moieties in the inner cavity of the macrocycle. The selectivity of the cyclodextrins depends on ring size, pH, ionic strength, the nature and concentration of modifier, and temperature. 

---