The following protocol makes a 2% paraformaldehyde and 2.5% glutaraldehyde in 0.1M cacodylate buffer.
1. Wear gloves and make in a fume hood; cacodylate and aldehydes are carcinogenic.
2. Heat 100 ml dH2O to about 55 °C.
3. Add 10 g paraformaldehyde and stir.
4. Add a few drops 1M NaOH to clear.
5. Add 50 ml 25% glutaraldehyde and 250 ml 0.2 M cacodylate buffer stock solution.
6. Cool to room temperature. Adjust pH to 7.2-7.4.
7. Add dH2O to make 500 ml total volume.
8. Store in fridge and use cold.
9. Do not use more than 48 hrs after it is made.
10. Paraformaldehyde fix solution is sometimes buffered with PBS.
See also Formaldehyde/paraformaldehyde/formalin.