Abstract: Amphoteric ion exchange resins(AIER) may be divided into two kinds:First one can not form inner salt and there is no interaction between anionogen and cationogen in it, its property is similar to that of the mixture of anion and cation exchange resins. The second kind can form inner salt,from which a series of new properties ate produced. The selectivity, swelling and absorption capacity of the second kind of AIER all are increased with the concentration of the electrolyte solution in a definite concentration range. The second kind of AIER is useful for separation and purification of concentrated electrolyte solution. This review puts emphasis on the formation of inner salt, especially on the effect of crosslinking and ionogen on it.

Key words: amphoteric resin, snake-cage resin, inner salt, desalination, water treatment