Bouin’s fixative

2 g picric acid powder or saturated aqueous picric acid (see below)

20 g paraformaldehyde

Formalin (40% w/v formaldehyde), as an alternative to paraformaldehyde (see below)

NaOH (1 N)

2X phosphate-buffered saline (PBS)

Glacial acetic acid (to be used with saturated picric acid and formalin; see below)

To prepare 1 L of Bouin’s fixative, dissolve 2 g of picric acid in 500 mL of H₂O. Filter through a Whatman No. 1, or equivalent. Add 20 g of paraformaldehyde, and heat to 60°C in a fume hood. Add a few drops of 1 N NaOH to dissolve. Cool and add 500 mL of 2X PBS.

Picric acid is explosive in crystal form!

Alternatively, combine 75 mL of saturated picric acid, 25 mL of formalin, and 5 mL of glacial acetic acid. Store at 4°C.