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Short answer: Chelex (Chelex 100) is a chelating resin from Bio-Rad that binds divalent metal ions such as magnesium and calcium. Labs use it to strip metal contaminants from buffers and to protect DNA in crude sample preparations, because removing Mg2+ and Ca2+ inhibits metallo-nucleases. It is a quick sample-prep reagent, not a purification column.
Definition and scope
Bio-Rad describes Chelex 100 as a chelating resin: a styrene divinylbenzene copolymer matrix carrying iminodiacetate groups, R-CH2N(CH2COO-)2, which act as the metal-binding sites. It behaves as a weak cation exchanger with chelating action. Bio-Rad lists a crosslinkage of 1%, an approximate exclusion molecular weight of 3,500, a nominal density of 0.65 and a minimum wet capacity of 0.4 meq/ml, and gives its selectivity for divalent over monovalent ions as approximately 5,000 to 1. It keeps its affinity for transition metals even in concentrated salt solutions, and its stated operating stability is pH 4 to 14 (Bio-Rad product page, read 2026-11-08).
In practice the name covers two quite different uses of the same resin: metal removal from reagents, and crude DNA or RNA sample preparation.
How Chelex is used in practice
Removing metal contaminants from buffers and ionic reagents
Bio-Rad lists ultrapurification of buffers and other ionic reagents, by removing metal contaminants, as a primary application. For background on the solutions involved, see our guides to buffer solutions and biological buffers.
Chelex DNA extraction from tissue, blood and other samples
Bio-Rad states that Chelex captures Mg2+ and Ca2+ from biological samples, which inhibits metallo-nucleases, and that it is used for DNA and RNA sample preparation as a lower-cost alternative to kits. Two published studies show what that looks like at the bench:
- Walsh, Metzger and Higuchi (BioTechniques 1991;10(4):506-513, PubMed 1867860) reported Chelex 100 extraction from semen and very small bloodstains as efficient as, or more efficient than, proteinase K with phenol-chloroform extraction, and the bloodstain DNA appeared less prone to carrying PCR inhibitors.
- Sepp, Szabo, Uda and Sakamoto (J Clin Pathol 1994;47(4):318-323, PMC501934) boiled archival tissue for 20 minutes in 5% Chelex-100 and compared it with water boiling, proteinase K digestion, and proteinase K followed by Chelex. The Chelex boil produced DNA suitable for amplification in all 45 samples and required minimal manipulation and time. However, it amplified p53 fragments of up to 647 bp, against up to 984 bp for the proteinase K digests.
The practical downstream test is PCR: a Chelex prep is judged by whether the target amplifies. The amplicon length reported by Sepp et al. is the clearest sourced limit on this approach.
Grades, ionic forms and mesh sizes
This table is drawn entirely from Bio-Rad’s product page (read 2026-11-08).
| Attribute | Options listed by Bio-Rad | What it means |
|---|---|---|
| Ionic form | Sodium; iron | The iron form is listed for glyphosate concentration, not for DNA sample prep. |
| Grade | Analytical; biotechnology; molecular biology | Biotechnology grade is specified at fewer than 100 microorganisms per gram. Molecular biology grade is certified endo- and exonuclease free with no ligase inhibitors. |
| Mesh (dry) | 50-100; 100-200; 200-400 | Wet bead sizes of 300-1,180 um, 150-300 um and 75-150 um respectively. |
Where it matters for labs
- Match the grade to the downstream use. Bio-Rad’s grade definitions are the sourced basis for choosing: molecular biology grade is the one certified free of endo- and exonucleases and of ligase inhibitors.
- Match the ionic form to the job. Sodium form versus iron form is a product distinction, so check it against the intended application.
- Know the trade-off. A Chelex boil is fast and minimal-handling, but the Sepp et al. comparison found shorter amplifiable fragments than proteinase K digestion. For assays that need long amplicons, test the method against your target rather than assume it works.
Common misunderstandings
- Chelex is not only a DNA reagent. Metal removal from buffers and ionic reagents is a listed use.
- A crude prep is not a column purification. The sourced evidence for Chelex prep is that the DNA is suitable for amplification, which is a different claim from high-purity DNA.
- Not every Chelex product is for DNA. The iron form is listed for glyphosate concentration.
FAQ
What is Chelex 100 used for?
Bio-Rad lists two main uses: ultrapurifying buffers and ionic reagents by removing metal contaminants, and preparing DNA or RNA samples by capturing Mg2+ and Ca2+ and inhibiting metallo-nucleases.
What is Chelex?
Chelex is the trade name for Bio-Rad’s chelating resin line, a styrene divinylbenzene matrix with iminodiacetate functional groups that bind divalent metal ions.
Does Chelex extraction work for PCR?
Sepp et al. (1994) reported Chelex-boiled tissue DNA suitable for amplification in all 45 samples, with amplified fragments up to 647 bp; Walsh et al. (1991) reported efficient extraction from semen and small bloodstains.
How does Chelex compare with proteinase K digestion?
In the Sepp et al. study, Chelex needed minimal manipulation and time, while proteinase K digests amplified fragments up to 984 bp against 647 bp for Chelex.
Sources
- Bio-Rad, Chelex 100 Resin product page, read 2026-11-08.
- Sepp R, Szabo I, Uda H, Sakamoto H. Rapid techniques for DNA extraction from routinely processed archival tissue for use in PCR. J Clin Pathol 1994;47(4):318-323. PMC501934, read 2026-11-08.
- Walsh PS, Metzger DA, Higuchi R. BioTechniques 1991;10(4):506-513. PubMed 1867860.
Related reading: Tris-HCl buffer and restriction endonucleases.
