PREPARATION OF 2% FORMALDEHYDE STOCK SOLUTION  (2 METHODS)

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.

Prepare as follows:

* 10% formaldehyde solution (e.g., Polysciences, Warrington, PA, ultrapure, Cat.#04018), depolymerized paraformaldehyde, EM grade, methanol-free solution.