PREPARATION OF 2% FORMALDEHYDE STOCK SOLUTION (2 METHODS)
METHOD 1:
Formaldehyde preservative – 2% formaldehyde solution in protein-free phosphate-buffered saline (PBS).
Prepare as follows:
Add 2 g paraformaldehyde powder (e.g., Sigma, St. Louis, MO) to 100 ml of 1 X PBS. Heat to 70°C (do not exceed this temperature) in a fume hood until the paraformaldehyde goes into solution (note that this happens quickly as soon as the suspension reaches 70°C). Allow the solution to cool to room temperature. Adjust to pH 7.4 using 0.1 M NaOH or 0.1 M HCl, if needed. Filter and store at 4°C protected from light.
METHOD 2: Formaldehyde preservative – 2% formaldehyde solution in protein-free PBS.
Prepare as follows:
10% formaldehyde* | 20 ml |
10 x PBS | 10 ml |
Distilled water | 70 ml |
* 10% formaldehyde solution (e.g., Polysciences, Warrington, PA, ultrapure, Cat.#04018), depolymerized paraformaldehyde, EM grade, methanol-free solution.
