How to prepare a potassium-phosphate buffer solution

Updated February 21, 2017

Chemistry research requires buffer solutions used to wash the cells and allow them to carry out chemical reactions. A standard buffer solution found in many labs is the potassium-phosphate buffer solution, which is made by combining potassium and phosphate with water. As with any buffer solution, the trick is knowing the correct amounts of each ingredient so that your working solution has the proper concentration. All buffer solutions must be sterilised in an autoclave before being stored at room temperature.

Pour 500ml distilled water into a sterile volumetric flask.

Stir in 434ml 0.2 M monobasic potassium phosphate with a glass stir rod.

Stir in 66ml 0.2 M dibasic potassium phosphate with a glass stir rod.

Place the flask containing your potassium-phosphate buffer solution in a metal pan to catch any drips, and put a piece of autoclave indicator tape on the exterior of the flask. Set the autoclave for 15 minutes. Check the autoclave tape to be sure that it has changed colours, indicating that your autoclave was successful.

Put a sterile top on your flask, and store it at room temperature.


Your buffer solution will be hot when you remove it from the autoclave. Wear hot mitts to prevent burns.

Things You'll Need

  • 500ml distilled water
  • Sterile volumetric flask with top
  • 434ml 0.2 M monobasic potassium phosphate
  • 66ml 0.2 M dibasic potassium phosphate
  • Glass stir rod
  • Autoclave machine
  • Autoclave indicator tape
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