Paraformaldehyde in potassium phosphate

Paraformaldehyde, EM grade

Potassium phosphate (0.1 M, pH 6.5)

NaOH

For a 4% paraformaldehyde solution, dissolve 4 g of EM grade paraformaldehyde in 100 mL of 0.1 M potassium phosphate (pH 6.5). Add a few drops of NaOH and heat in a hood (keep bottle cap loose) at 60°C to dissolve. Cool to room temperature and adjust pH to 6.5. Make fresh prior to use.