Generally, ionic molecules are not retained by the hydrophobic stationary phase in reversed-phase chromatography. By adding an ion-pair reagent to the mobile phase with a hydrophobic tail and an ionic end, the hydrophobic tail of the reagent is retained by the stationary phase. Therefore an ion-exchange group is created on the stationary phase surface. An ion pair reagent adds in the mobile phase to increase the retention time and peak shape. The ion-pairing agent has to be inversely charged than the sample component and has good hydrophobicity.
It can be used to positively and negatively charged molecules. To retain positively charged ionic bases negatively charged reagents are used and to retain negatively charged ionic acids positively charged reagents can be used.
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