Applications of Ion Exchange Chromatography

Applications of Ion Exchange Chromatography:

Ion exchange chromatography has proved to be an excellent tool for solving many complicated problems in the field of biology, organic and inorganic chemistry.

(1) An application that can hit close to home is in the treatment of water for drinking use (commercial, industrial, and residential), and wastewater treatment. Ion exchangers can soften the water, deionize it and even be used in desalination. In industrial uses, pure water is often crucial for the successful development of a product.

(2) It can be utilized in the separation of Na and K in a mixture by using a cation exchange resin as a stationary phase.

(3) Transition metals Ni (II), Co (II), Mn (II), Fe (II), Cu (II) have been separated on a strongly basic anion exchange resin in the chloride form.

(4) Total content of cation in a solution- The stoichiometric nature of ion exchange resins allows us to find the total content of cation in a solution by titrating a number of protons equivalent to them and obtained by reaction of the cation exchanger and the solution being analyzed.

(5) Production of Analytical Concentrates- The concentration of substances can be increased 200-500 fold by percolating large volumes of dilute solutions through an ion exchanger layer and subsequent extraction of the adsorbed substance with a small amount of solvent. This method is generally used in the separation of non-ferrous metals in the production of rare earth elements, uranium, radioactive isotopes etc.

(6) Separation of complex mixtures of biochemical compounds- Ion exchange chromatography is an extremely valuable tool in the separation of complex mixtures of compounds of biochemical interest. Scott and coworkers have resolved peaks corresponding to over 100 constituents of urine using parallel columns of anion and cation exchangers, with gradient elution.

(7) Separation of Metals, Alloys and High Alloy Steels- Pure metals, alloys, and high alloy steels can be analyzed using a complexation process. The method is based on the different stability of the complexes formed at a definite pH value. For example, the addition of HCI to a mixture of Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺ and Bi³⁺ ions produces the chloride complexes [CuCl₄]^2-, [ZnCl₄]^2-, [CdCl₄]^2-, [PbCl₃]^– and [BiCl₄]^–. Their stability increases from copper to bismuth. The solution obtained is percolated through a column packed with an anion exchanger, which adsorbs all the complexes. The metals are then eluted successively with dilute HCl, water and nitric acid. 2N HCl elutes copper, 6N HCl elutes zinc, 0.3N HCl elutes cadmium, lead is eluted with water and bismuth is eluted with water and bismuth is eluted with HNO₃.

(8) Concentration of Traces of an Electrolyte- Concentration of traces of an ion from a very dilute solution can also be carried out by making use of ion exchange resins. For example, traces of metallic elements can be collected from larger volumes of natural waters by making use of cation exchange resins. The resin is first treated with HCl to liberate the ions. As a result, the solution becomes more concentrated for further analysis.

(9) Separation of substances possessing related properties- Ion exchange chromatography has also been used for the separation of substances possessing related properties such as cations of alkali and alkaline earth metals, rare earth and transuranium elements, twin elements such as zirconium and hafnium, cis-trans isomeric complexes of cobalt and platinum. It is only this method that is applied to the quantitative separation of copper from Cu-Fe alloys with iron content below 50%.

(10) Identification of Ions- In the separation of simple ions (monovalent cations) on a strongly acidic exchanger, the relative affinities for water are Li⁺ < H⁺ < Na⁺ < NH₄⁺ < K⁺ < Rb⁺ < Cs⁺ < Ag⁺ and Ti⁺. This shows that lithium ion is least strongly held on the resin comparable scale for divalent ions is-

UO₂²⁺ < Mg²⁺ < Zn²⁺ < Co²⁺ < Cu²⁺ < Cd²⁺ < Ni²⁺ < Ca²⁺ < Sr²⁺ < Pb²⁺ < Ba²⁺

Methods for separating and identifying all the important ions are developed. Methods for a partial and complete analysis of mixtures of cations as well as anions have also been developed. The chromatograms so obtained are then examined visually, in U.V light, with radioactive indicators, by measuring optical properties, dielectric constant etc.

(11) Radiochemistry- The technique of ion exchange chromatography has been used extensively in radiochemistry. For radioactive isotopes to be separated and concentrated, use is made of natural minerals or synthetic substances capable of exchanging their atoms or group of atoms for ions from the solution.