How to Brew a Batch of Paraformaldehyde Solution (PFA)

For the study of various organisms, the cells of these creatures must often be preserved. This is called fixation, and it is done to inhibit fungal growth, prevent autodigestion, and to make the cells hardier for processing. To this end, paraformaldehyde solution (PFA) is a popular fixative.

Difficulty: Moderate

Instructions

Things You'll Need:

• Water
• One-liter beaker
• Phosphate buffer powder
• Bunsen burner
• Thermometer
• Chips of NaOH (sodium hydroxide)
• Ph meter
• Fume hood

1. Dissolve phosphate buffer powder into 200 milliliters of water. This will produce a 1 molar solution of phosphate buffer (PB).

2. Heat 500 milliliters of water in a 1-liter beaker or flask, adding 3 or 4 chips of NaOH when the water reaches around 50 to 60 degrees Celsius.

3. Add 50 milliliters of PB, and 40 grams of paraformaldehyde. The temperature should not exceed 60 C.

4. If the NaOH has dissolved, but the paraformaldehyde has not, check the pH. If the pH is below 7, add another chip of NaOH, stirring until the paraformaldehyde has dissolved. Repeat as necessary.

5. When complete, all the batch to cool to room temperature. Adjust the volume to one liter, and adjust the pH to approximately 7.3 with the addition of distilled H2O.

Tips & Warnings

• This process should take place under a fume hood, or at least in a very well ventilated space.
• Do not use PFA when hot.
• Store PFA in a glass container, as it will be absorbed into plastic.