Paraformaldehyde (A)

Recipe

Reagent	Quantity (for 50 mL)	Final concentration
Paraformaldehyde	2 g	4% (w/v)
NaOH (1 N)	5 mL
HCl (1 N)	5 mL
Phosphate-buffered saline (PBS) (10X)^a	5 mL	1 X
Tween 20 (10%)	0.5 mL	0.1% (v/v)

To dissolve paraformaldehyde, add 2 g to 5 mL of 1N NaOH. Heat to 60°C to dissolve.
Add 5 mL of 1 N HCl, 5 mL of 10X PBS, and 30 mL of diethyl pyrocarbonate (DEPC)-treated H₂O. Adjust the pH to 7.4 if necessary, and then add 0.5 mL of 10% Tween 20 and DEPC-treated H₂O to give a final volume of 50 mL. Dispense the solution into 10-mL aliquots and store at −20°C.
^aTreat the PBS with 1 mL of diethyl pyrocarbonate for 1 h at 37°C and autoclave for 20 min at 15 psi on liquid cycle. Store at room temperature.