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.