Paraformaldehyde 4%

Materials
''Use caution when working with strong acid (HCl) and strong base (NaOH). ''
 * Paraformaldehyde
 * ddH2O
 * NaOH (4 N)
 * 10X PBS
 * pH papers

''Paraformaldehyde is a suspected carcinogen and is available as a fine powder. Wear lab coat and thick vinyl gloves as well as a face mask to prevent inhalation of powder or vapors when working with such chemicals.''

Materials (makes 100 mL of fixative)

 * 1) Add 80 mL of ddH2O in a 200 mL or larger glass bottle and heat the water slowly. Do not heat water above 70 C. PFA will break down at temperatures above 70 C.
 * 2) Add 4 g of paraformaldehyde while stirring the 60 C ddH2O.
 * 3) Add 4 N NaOH drop-wise until the solution turns clear and continue to stir.
 * 4) Allow solution to stir until paraformaldehyde dissolves.
 * 5) Add 10 mL of 10X PBS and mix.
 * 6) Add ddH2O to a final volume of 100 mL and adjust the pH to ~7.4 using pH paper.
 * 7) Filter the 4% PFA solution through a 0.45 μm filter into 15 mL conical tubes.
 * 8) Freeze the aliquots at -20 C for long-term storage.  Upon removal from -20 C, aliquots may become viscous. Thaw aliquots at room temperature and PFA will re-dissolve into solution.