10% neutral buffered formalin (NBF) recipe
The standard fixative for histopathology (paraffin sections): 37% formaldehyde diluted 1:10 (≈3.7% formaldehyde) in phosphate buffer.
🧮 Volume calculator
| Component | Amount | Final concentration (1X) |
|---|---|---|
| 37% formaldehyde (formalin) | 100 mL | 10% formalin (≈3.7% HCHO) |
| NaH₂PO₄·H₂O | 4 g | 29 mM |
| Na₂HPO₄ (anhydrous) | 6.5 g | 46 mM |
| Water (distilled) | to final volume |
Steps
- In a fume hood, dissolve the phosphates in about 80% of the final volume of water.
- Add the formalin and bring to volume.
- Store at room temperature.
Good to know
- Use 10–20 volumes of fixative per tissue volume; fix 3–5 mm pieces for 24–48 h.
- "10% formalin" ≈ 4% formaldehyde — similar to 4% PFA but containing methanol stabiliser.
⚠ Safety Formaldehyde is carcinogenic and irritating — use a fume hood.
FAQ
What about over-fixation?
More epitopes are masked and IHC signal weakens; extend antigen retrieval if needed.
This is a widely used standard composition. Amounts depend on the hydrate form and purity of your reagents — check the formula weight (FW) on the bottle and follow your institution's safety rules and the manufacturers' instructions.