Question.

Paraldehyde is a controlled substance, not that easy to obtain for laboratory use, and it also has a short shelf life. Is there a way to make the aldehyde-fuchsine stain without using paraldehyde?

Answer.

When aldehyde fuchsine is made in the traditional way, the paraldehyde decomposes in the presence of acid, yielding acetaldehyde. This reacts with pararosaniline to form a new dye, which is the active component of the stain. It is therefore possible to use acetaldehyde (obtainable from regular chemical suppliers) instead of paraldehyde.

Peggy Wenk, bless her heart, commented on this in the Journal of Histotechnology, vol 10, #4 (December 1996): Acetaldehyde as a substitute for paraldehyde.

2.5 ml acetaldehyde is used in place of 1.5 ml paraldehyde. The working solution must be refrigerated. It will stain hepatitis B for 3 - 4 weeks, but is good for elastin for several months.

Acetaldehyde cost about  $30 for 100 ml and is stable in a refrigerator for about 2 years. (Paraldehyde is stable for only a few months after opening, and is pricey due to handling/admin fees.) You need to be aware that acetaldehyde is a flammable liquid that boils at 21 C. The bottle must be cold when you open it!

Having struggled trying to get paraldehyde, this substitution has made aldehyde-fuchsin staining feasible in a research laboratory.

Gayle Callis
(uvsgc[AT]msu.oscs.montana.edu)
[With some editing and additional comments by J. A. Kiernan]