Importance of ion pair reagents on reverse phase HPLC

What are the ion pair reagents
And it s applications

The ion-pairing agent (IPA) is an ion species selected so that it has an opposite charge to the analyte and is able to form a molecular association with it (or with a targeted solute). Compounds used as IPA can be, for example, quaternary amines (with various chain lengths of the substituent) in the case of analyzing acids, or strong organic acids (e.g., sulfonic acid with various chain substituents) in the case of analyzing amines.
Ion pairs are used for the separation of analytes (organic or inorganic) that contain ionizable or strongly polar groups, which lead these compounds to have a poor retention on hydrophobic columns (e.g. C18 or C8). Among these analytes are organic acids, amino acids, and amines. IP makes these compounds amenable to RP-HPLC type separation, using hydrophobic stationary phases (e.g., C18, C8). This can be achieved with the help of an ion-pairing agent (IPA or hetaeron), which is added to the mobile phase usually at concentrations between 10 and 100 mM/L.