The potassium phosphate buffer calculator simplifies the process of determining the correct quantities of potassium phosphate salts needed to create a buffer solution with a specific pH and molarity.
For example, if you need to prepare a 0.1 M potassium phosphate buffer with a pH of 7.2, the calculator provide the exact amounts of K₂HPO₄ (dipotassium hydrogen phosphate) and KH₂PO₄ (potassium dihydrogen phosphate) required.
This precision is crucial for maintaining optimal conditions in various experimental procedures, such as enzyme assays or protein purification.
Potassium Phosphate Buffer Calculator
| Desired pH | Molarity | Volume | K₂HPO₄ (g) | KH₂PO₄ (g) |
|---|---|---|---|---|
| 6.0 | 0.1 M | 1 L | 6.655 | 15.885 |
| 6.5 | 0.1 M | 1 L | 8.709 | 13.609 |
| 7.0 | 0.1 M | 1 L | 10.800 | 11.500 |
| 7.2 | 0.1 M | 1 L | 11.700 | 10.600 |
| 7.5 | 0.1 M | 1 L | 13.500 | 8.800 |
| 8.0 | 0.1 M | 1 L | 15.200 | 7.100 |
| ———— | ———- | ———- | ———— | ———— |
| 6.0 | 0.05 M | 500 mL | 3.328 | 7.942 |
| 6.5 | 0.05 M | 500 mL | 4.354 | 6.804 |
| 7.0 | 0.05 M | 500 mL | 5.400 | 5.750 |
| 7.2 | 0.05 M | 500 mL | 5.850 | 5.300 |
| 7.5 | 0.05 M | 500 mL | 6.700 | 4.450 |
| ———— | ———- | ———- | ———— | ———— |
| 6.8 | 0.075 M | 750 mL | 6.534 | 5.953 |
| 7.2 | 0.075 M | 750 mL | 7.200 | 5.300 |
| ———— | ———- | ———- | ———— | ———— |
| 8.0 | 0.15 M | 2 L | 41.404 | 2.041 |
| 8.2 | 0.15 M | 2 L | 43.000 | 1.600 |
| 8.5 | 0.15 M | 2 L | 44.800 | 1.200 |
Potassium Phosphate Buffer Calculation Formula
The formula for calculating potassium phosphate buffer components is based on the Henderson-Hasselbalch equation:
pH = pKa + log([A⁻] / [HA])Where:
- pH is the desired pH of the buffer
- pKa is the negative logarithm of the acid dissociation constant
- [A⁻] is the concentration of the conjugate base
- [HA] is the concentration of the weak acid
For potassium phosphate buffers, we use the following equations:
Total phosphate concentration: [Total] = [K₂HPO₄] + [KH₂PO₄]
Ratio of base to acid: R = [K₂HPO₄] / [KH₂PO₄]
The ratio R can be calculated using:
R = 10^(pH - pKa)With these equations, we can determine the required amounts of K₂HPO₄ and KH₂PO₄ for a given pH and molarity.
How do you make potassium phosphate buffer?
To prepare a potassium phosphate buffer, follow these general steps:
- Determine the desired pH and molarity of your buffer.
- Calculate the required amounts of K₂HPO₄ and KH₂PO₄ using the formulas mentioned above or a buffer calculator.
- Weigh out the salts accurately using an analytical balance.
- Dissolve the salts in about 80% of the final volume of deionized water.
- Adjust the pH using a calibrated pH meter, adding small amounts of concentrated HCl or NaOH if necessary.
- Bring the solution to the final volume with deionized water.
- Filter the buffer through a 0.22 μm filter for sterility if required.
For a 1 L of 0.1 M potassium phosphate buffer at pH 7.0, you might need approximately 61.5 mL of 1 M K₂HPO₄ and 38.5 mL of 1 M KH₂PO₄. Mix these, then adjust the pH and volume as described above.
How to prepare 0.1 M potassium phosphate buffer?
- Decide on the pH of your buffer. Let’s use pH 7.2 for this example.
- Calculate the amounts of K₂HPO₄ and KH₂PO₄ needed. For pH 7.2, you’ll need approximately:
- 68.5 mL of 1 M K₂HPO₄
- 31.5 mL of 1 M KH₂PO₄
- Mix these solutions in a beaker or flask.
- Add deionized water to bring the volume to about 800 mL.
- Check the pH and adjust if necessary using HCl or NaOH.
- Bring the final volume to 1 L with deionized water.
- Recheck the pH and make any final adjustments.
This method will yield 1 L of 0.1 M potassium phosphate buffer at pH 7.2.
How do you prepare a 0.05 M potassium phosphate buffer?
Choose your target pH. Let’s use pH 6.8 for this example.
Calculate the required amounts. For pH 6.8, you’ll need approximately:
- 25.2 mL of 1 M K₂HPO₄
- 24.8 mL of 1 M KH₂PO₄
Combine these solutions in a suitable container.
Add deionized water to about 900 mL.
Check and adjust the pH as needed.
Bring to a final volume of 1 L with deionized water.
Verify the pH one last time and make any necessary adjustments.
This procedure will produce 1 L of 0.05 M potassium phosphate buffer at pH 6.8.
How to prepare 20 mM KH₂PO₄?
To prepare a 20 mM KH₂PO₄ solution, follow these steps:
Calculate the amount of KH₂PO₄ needed:
- Molecular weight of KH₂PO₄ = 136.09 g/mol
- For 1 L of 20 mM solution:
- 136.09 g/mol × 0.02 mol/L = 2.7218 g
Weigh out 2.7218 g of KH₂PO₄ using an analytical balance.
Transfer the salt to a 1 L volumetric flask.
Add about 800 mL of deionized water and swirl to dissolve completely.
Fill to the 1 L mark with deionized water.
Mix thoroughly by inverting the flask several times.
This method yields 1 L of 20 mM KH₂PO₄ solution. Note that this is not a buffer but a simple salt solution; to create a buffer, you would need to combine this with an appropriate amount of K₂HPO₄ and adjust the pH.
Related Tools:
References
- Mohan, C. (2003). Buffers: A guide for the preparation and use of buffers in biological systems. Calbiochem. https://www.sigmaaldrich.com/deepweb/assets/sigmaaldrich/marketing/global/documents/114/741/buffers-calbiochem.pdf
- Cold Spring Harbor Protocols. (2006). Phosphate-buffered saline (PBS). http://cshprotocols.cshlp.org/content/2006/1/pdb.rec8247
- Beynon, R. J., & Easterby, J. S. (1996). Buffer solutions. Oxford University Press. https://global.oup.com/academic/product/buffer-solutions-9780199633418
