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Chelating resins are a class of ion-exchange resins. They are almost always used to bind cations, and utilize chelating agents covalently attached to a polymer matrix. Chelating resins have the same bead form and polymer matrix as usual ion exchangers. Their main use is for pre-concentration of metal ions in a dilute solution. Chelating ion-exchange resins are used for brine decalcification in the chlor-alkali industry, the removal of boron from potable water, and the recovery of precious metals in solutions.Apte, S. C.; Batley, G. E., "Trace metal speciation of labile chemical species in natural waters and sediments: non-electrochemical approaches", IUPAC Ser. Anal. Phys. Chem. Environ. Syst. 1995, 3, 259-306.Garg, B. S.; Sharma, R. K.; Bhojak, N.; Mittal, S., "Chelating Resins and Their Applications in the Analysis of Trace Metal Ions", Microchem. J. 1999, 61, 94-114.Sharma, R. K.; Mittal, S.; Koel, M., "Analysis of trace amounts of metal ions using silica-based chelating resins: A green analytical method", Crit. Rev. Anal. Chem. 2003, 33, 183-197.
Most chelating resins are polymers (copolymers to be precise) with reactive functional groups that chelate to metal ions.Sahni, S. K.; Reedijk, J., "Coordination chemistry of chelating resins and ion exchangers", Coord. Chem. Rev. 1984, 59, 1-139. The variation in chelating resins arises from the nature of the chelating agents pendant from the polymer backbone. Dowex chelating resin A-1, also known as Chelex 100, is based on iminodiacetic acid in a styrene-divinylbenzene matrix. Dowex A-1 is available commercially and is widely used to determine general properties of chelating resins such as rate determining step and pH dependence, etc. Dowex A-1 is produced from chloromethylated styrene-divinylbenzene copolymer via amination with aminodiacetic acid.
Poly metal chelating resin has almost negligible affinity to both alkali and alkaline earth metals; small quantities of resin can be utilized to concentrate trace metals in natural water systems or biological fluids, in which there are three or four orders of magnitude greater alkali and alkaline earth metal concentration than the trace metal concentrations.
Other functional groups bound to chelating resins are aminophosphonic acids, thiourea, and 2-picolylamine.
Chelating polymers (ion-exchange resins) were proposed for maintenance therapy of pathologies accompanied by iron accumulation, such as hereditary hemochromatosis (iron overload) or Wilson's disease (Copper toxicity), by chelating the metal ions in GIT and thus limiting its biological availability.
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