EDTA at 0.5 M, pH 8.0, is one of the most-used stock solutions in molecular biology. The catch every newcomer hits: disodium EDTA will not dissolve until the pH is raised to about 8.0 with NaOH. This recipe builds that step in.
Ingredient amounts below update automatically.
Ingredients
| Component | Amount | Note |
|---|---|---|
| Disodium EDTA · 2H2O | 186.1 g | MW 372.24 g/mol |
| Deionised water | 800 mL | initial; top up to final volume |
| NaOH pellets | 20 g | approx., to reach pH 8.0 |
Method
- Add the disodium EDTA to about 80% of the final volume of deionised water with vigorous stirring.
- The EDTA will not fully dissolve yet. Slowly add NaOH pellets (or 10 M NaOH) while stirring to raise the pH toward 8.0.
- As the pH approaches 8.0 the EDTA dissolves and the solution clears. Adjust precisely to pH 8.0 with a calibrated meter.
- Make up to the final volume with deionised water.
- Sterilise by autoclaving if required, and store at room temperature.
Notes & safety
Use the disodium dihydrate salt for these quantities; the free acid form is far harder to dissolve. If you use 10 M NaOH solution instead of pellets, account for the added volume before the final make-up.
Consult the Safety Data Sheet for each reagent and follow your institution's protocols. Wear appropriate PPE.
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Equipment for this prep
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