Mixed mobile ion effect

Mixed alkah effect (mixed mobile ion effect)... 

Besides amino acids, traces of borate in the mobile phase can also affect monosaccharide analysis due to complexation. Borate ions are among the first to be detected in the slip of water purification systems when their mixed-bed ion exchangers approach the capacity limit (Borate can be determined with ion-exclusion chromatography and subsequent conductivity detection down to the lowest ng/L level utilizing pre-concentration see Section 5.5.) If de-ionized water used for preparing the mobile phase contains traces of borate, a significant loss of peak symmetry is observed this effect is most pronounced with mannose and other reduced saccharides. Even borate concentrations in the lowest mg/L levels are sufficient to cause this effect. With a specially-designed BorateTrap column, which is placed between the analytical pump and the injection valve, borate can be completely removed from the mobile phase. 

Membranes exhibiting selectivity for ion permeation are termed electrochemical membranes. These membranes must be distinguished from simple liquid junctions that are often formed in porous diaphragms (see Section 2.5.3) where they only prevent mixing of the two solutions by convection and have no effect on the mobility of the transported ions. It will be seen in Sections 6.2 and 6.3 that the interior of some thick membranes has properties analogous to those of liquid junctions, but that the mobilities of the transported ions are changed. 

They further observed the stereoselective effect in several other systems containing other amino acids as the polymer ligands74, and identified certain prerequisites for effective resolution (i) mixed complexes are more stable and it is better to use Cu(II) or Ni(II), (ii) the sum of the dentation of the polymer ligands and the mobile ligands (amino acids) should be equal to the coordination number of the central metal ion. The difference in free energy of formation of the two dia-stereomeric complexes with L- and D-proline was estimated to be 0.4 to 0.5 kcal/mol for the L-proline-Cu resin. It was emphasized that the stereoselectivity of this process was sufficient for the complete resolution of racemic a-amino acids74. ... 

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