Polyamide is a kind of high molecular polymer with repeating unit amide bond (CONH) in the structure. The general structural formula is [NHRNHCOR2CO] n. The O and N atoms on the amide group combine with protons in an acidic medium with positive Charges form anions in the adsorption solution with electrostatic attraction, so they can form hydrogen bonds with phenolic, acid, quinone, flavonoid, and other compounds rich in phenolic hydroxyl groups to adsorb. The strength of adsorption depends mainly on these two compounds. The number and position of hydroxyl groups, as well as the association capacity between the solvent and the compound or the solvent and the polyamide to form a hydrogen bond. The stronger the ability of the solvent molecule to form a hydrogen bond with the polyamide or flavonoid compound, the weaker the adsorption of polyamide to the two compounds. The polyamide chromatography column utilizes this property to adsorb, elute and separate flavonoids, tea polyphenols, etc. in various plants, which is the so-called "hydrogen bond adsorption" theory.
In addition to the "hydrogen bond adsorption" theory, the separation mechanism of polyamide chromatography also has the "dual chromatography" theory. The former cannot explain why when chloroform: methanol is used as the eluent, the flavonoid aglycone elutes earlier than the flavonoid glycoside. The latter believes that when eluting with a polar mobile phase (aqueous solvent system), the polyamide acts as a non-polar stationary phase, and its chromatographic behavior is similar to reversed-phase partition chromatography. Sexual stationary phase, its chromatographic behavior is similar to normal phase distribution chromatography. However, the polarity of the stationary phase (adsorbent) is determined by its own structure and properties, and should not change with the eluent. Moreover, polyamide chromatography is adsorption chromatography, not partition chromatography. Therefore, the "dual chromatography theory" has not revealed the root cause of these two opposite phenomena.