PFA 4%

For 1 L of 4% Formaldehyde, add 800 mL of 1X PBS to a glass beaker on a stir plate in a ventilated hood. Heat while stirring to approximately 50 °C. Take care that the solution does not boil.

Add 40 g of paraformaldehyde powder to the heated PBS solution.

The powder will not immediately dissolve into solution. Slowly raise the pH by adding 1 N NaOH dropwise from a pipette until the solution clears.

Once the paraformaldehyde is dissolved.

Adjust the volume of the solution to 1 L with 1X PBS.

Recheck the pH, and adjust it with small amounts of dilute HCl to 7,4.

The solution can be aliquoted and frozen.