1 M potassium phosphate buffer (pH 7.4) recipe
A phosphate buffer stock made by mixing K₂HPO₄ and KH₂PO₄ to the pH you need; used for enzyme assays, media and protein work.
🧮 Volume calculator
| Component | Amount | Final concentration (1X) |
|---|---|---|
| K₂HPO₄ (anhydrous) | 13.97 g | 0.802 M |
| KH₂PO₄ | 2.695 g | 0.198 M |
| Water (distilled) | to final volume |
Steps
- Dissolve in about 80% of the final volume of water.
- Check the pH and fine-tune with more K₂HPO₄ (raises) or KH₂PO₄ (lowers) solution.
- Bring to the final volume with water.
- Autoclave (121 °C, 20 min) and store at room temperature.
Good to know
- Other pHs (mix 1 M K₂HPO₄ : 1 M KH₂PO₄ by volume): pH 6.8 = 49.7 : 50.3, 7.0 = 61.5 : 38.5, 7.2 = 71.7 : 28.3, 7.6 = 86.6 : 13.4, 8.0 = 94.0 : 6.0.
- The pH rises slightly on dilution — check it at working strength.
FAQ
Sodium vs potassium phosphate?
Buffering is the same, but potassium precipitates SDS (as KDS), so use sodium phosphate with SDS.
This is a widely used standard composition. Amounts depend on the hydrate form and purity of your reagents — check the formula weight (FW) on the bottle and follow your institution's safety rules and the manufacturers' instructions.