A simple and inexpensive device for freeze substitution at 183 K/-90 C

The freeze substitution device described here consists of commonly available materials, is easy to construct and to handle and provides maximal working safety. An adequate mass of copper and/or brass, serving as holder for 16 cryovials, is chilled to liquid nitrogen temperature. The vial holder is placed in a precooled thermos flask filled with ethanol and stored in an ultrafreezer at 193 K/-90 C. This ensures that the vial holder maintains temperatures of about 183 K/-90 C for more than 12 hr to minimize the risk of ice recrystallization.