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.