Deionization is the process of removing all ions from a solution. Solutions of urea, acrylamide, formamide and glyoxal can dissociate over time into ionic species. These ionic species can often be detrimental to proteins, RNA etc.
- AG 501-X8(D) resin from Bio-Rad (catalog number 143-6425)
- A solution to be deionized
- Weigh 5g of resin for every 100mL of formamide or acrylamide solution. Use 1 g of resin per mL of glyoxal.
- This amount is sufficient for any concentration.
- Add resin to solution.
- Molecular Cloning suggests washing the resin with 1mL of the solution to be deionized per mL of resin and discard prior to addition of resin to solution.
- Stir for 1 hour.
- Check pH to insure deionization is complete. If the resin turns gold, more resin is needed.
- If deionization is not complete, remove the resin by filtration or decanting and add more resin.
- The resin comes in Biotechnology grade and Molecular Biology grade. Biotechnology grade is certified to contain less than 100 microorganisms per gram. Molecular Biology grade is certified to be endo- and exonuclease-free and contains no ligase inhibitors. Use Molecular Biology grade for deionizing glyoxal for use in denaturing RNA. Biotechnology grade may be sufficient for deionizing urea during protein purifications. Not entirely sure it matters.
- Formamide interferes with color change of the dye.
- Sugars, polyhydric alcohols and hydrophilic proteins may bind to the resin. Use minimum amounts of resin or place the resin in dialysis tubing to prevent sample adsorption.
- Urea should always be freshly prepared and deionized just prior to use.