ION Pairing Reagents
Used in the role of mobile phase additives, Ion Pairing Reagents are used in Chromatographic processes, particularly in High Performance Liquid Chromatography (HPLC) to achieve the objective of separating ionic and highly polar substances. Their addition in mobile phase acts as counter because in their ionic form, they have the opposite charge and interact with the sample species in the solution to form a neutral ion pair. This pair of formed ions interacts readily with the reverse phase packing material and allows for clean separation in the chromatography column, and all this happens due to interaction of non-polar/hydrophobic sample molecules and the non-polar stationary phase.
1) On addition of ion pairing reagents, retention occurs only when the sample molecule has sufficient hydrophobic nature and the process can be adjusted by making some changes to the aqueous to organic content ratio of the mobile phase.
2) In case the sample has ionic components, polarity can be too high for retention to take place in the reverse phase mode, and in this case, ion pairing proves to be particularly effective.
3) For chromatographic retention to take place, ions of opposite charge in the mobile phase gravitate towards the immobilized ion pair reagent.
4) Temperature of the column and organic content of the mobile phase have a major role in dictating the concentration of the stationary phase ion pair reagent.