Chelex 100

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Chelex® 100 is a chelating material from Bio-Rad[1] used to purify other compounds via ion exchange. It is noteworthy for its ability to bind transition metal ions.

It is a styrene-divinylbenzene co-polymer containing iminodiacetic acid groups.

A concentrated solution of metals is obtained by eluting the resin with a small volume of 2 M nitric acid, which protonates the iminodiacetate groups.

Chelex resin is often used for DNA extraction in preparation for PCR. The ChelexTM protects the sample from DNAases that might remain active after the boiling and could subsequently destroy the DNA. DNAases are enzymes, which naturally occur in all body tissues, they cut DNA into small fragments, rendering it unsuitable for PCR. Magnesium ions are essential cofactors for DNAases. ChelexTM resin binds with cations including Mg+. By binding with magnesium ions, the ChelexTM resin renders DNAases inoperable, thus protecting DNA from their action. After boiling the ChelexTM DNA preparation is stable and can be stored at 4oC for 3-4 months.[2] Polar resin beads bind polar cellular components after breaking open cells, while DNA and RNA remain in water solution above chelex.

It is also known that, after DNA is isolated from a cell, it is susceptible to DNases. However, the enzymes that degrade DNA require the cofactor Mg2+; based on this fact, Chelex tightly binds to all the Mg2+ in the extract to prevent DNA degradation. However, the heating steps do denature the double helix, and the resulting single-stranded DNA is less stable in storage.

Chelex® is a registered trademark of Bio-Rad Laboratories, Inc.


  1. ^ "Chelex® 100 and Chelex 20 Chelating Ion Exchange Resin Instruction Manual" (PDF). 
  2. ^ Walsh, P.S., Metzger D.A., and Higuchi, R. (1991). "Chelex 100 as a Medium for Simple Extraction of DNA for PCR-Based Typing from Forensic Material". BioTechniques 10 (4): 506–513. PMID 1867860. 
  • Daniel Harris. Quantitative Chemical Analysis, seventh edition, 2007. ISBN 0-7167-7041-5. Page 594.
  • R. N. Ceo, M. R. Kazerouni, and K. Rengan (1993). "Sorption of silver ions by Chelex 100 chelating resin". Journal of Radioanalytical and Nuclear Chemistry, Articles 172 (1): 43–48. doi:10.1007/BF02040660. 

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