1. Ion exchange chromatography is a separation method that mainly applies the principle of ion exchange, using low exchange capacity ion exchange resins to separate ions. It is also a widely used method in ion chromatography. The main filler type is organic ion exchange resin, which uses styrene diethylene benzene copolymer as the skeleton, introduces sulfonic acid groups on the benzene ring to form strong acid cation exchange resin, and introduces tertiary amine groups to form quaternary amine strong alkaline anion exchange resin. This exchange resin has a physical structure of large pores, thin shells or porous surface layers to quickly reach exchange equilibrium. The ion exchange resin is acid and alkali resistant and can be used in any pH range. It is easy to regenerate and has a long service life. The disadvantages are poor mechanical strength, easy swelling, and susceptibility to organic pollution.

2. Ion exclusion chromatography is mainly based on the Donnon membrane exclusion effect, where ionized components are excluded and not retained, while weak acids have a certain degree of retention. The ion exclusion chromatography is mainly used to separate organic acids and inorganic oxygen-containing acid ions, such as borate, carbonate, and sulfate organic acids. It mainly uses sulfonated H-type cation exchange resin with high exchange capacity as filler and * as eluent.

3. Ion pair chromatography uses hydrophobic neutral fillers as the stationary phase, which can be styrene divinylbenzene resin or octadecyl silica gel (ODS), as well as C8 silica gel or CN. The mobile phase of the stationary phase is composed of an aqueous solution containing a so-called counter ion reagent and an appropriate amount of organic solvent. The counter ion refers to its charge opposite to the ion to be tested and can generate hydrophobic ions with it. The surfactant ions of the compound are alkyl amines such as tetrabutylammonium hydroxide and hexadecyl * alkane used for anion separation, and the counter ions used for cation separation are alkyl sulfonic acids such as sodium hexane sulfonate and sodium heptanesulfonate. The non-polar end of the counter ion is lipophilic and the polar end is hydrophilic, while the CH2 end is hydrophilic The longer the bond, the stronger the retention of ions in the stationary phase of the compound. In polar mobile phases, organic solvents are often added to accelerate the elution rate. This method is mainly used for the separation of hydrophobic anions and metal complexes. As for its separation mechanism, there are three different hypotheses: reverse ion pair distribution ion exchange and ion interaction.