Specific Cation Exchangers:

In the beginning of this Unit, it was mentioned that there have been so much developments in the field of ion exchange that you can more or less have ion exchangers tailor made for a specific job. Attempts within this direction led to what are called as 'specific cation exchangers'. This means these ion exchangers display unusual selectivity towards a cation or a group of cations. If we look at the common general purpose cation exchangers, they rather certain counter ions. There is some sort of specificity. But here we mean the ion exchanger to be exclusively specific. The basic idea to synthesize such resins comes from the fact that a reagent which either precipitates a cation or forms a strong complex may be introduced in the matrix of the resin. The first attempt in this direction was made by Skogseid who synthesized a resin containing group with a configuration similar to that of dipicrylamine.

Dipicrylamine

Dipicylamine is a known specific precipitating agent for K⁺ ions. The resin is synthesized from polystyrene through reduction, nitration, condensation along with picrylchloride and again nitration.