The discussion on the problems using isopentane is the reason that
Instrumedics recommends liquid nitrogen for freezing tissue  Liquid nitrogen
must be used with caution, but it is neither fammable or explosive and since
it boils
at -196C it is the coldest freezing agent easily available.

We snap freeze tissue by chilling a weighty chrome-polished brass heat
extractor in liquid nitrogen. The tissue is placed on top of dispensed
CryoGel, a very viscous embedding medium. The heat extractor is placed on
the Gentle Jane device and falls at a controlled rate, contacting the tissue
first. This will produce the best freezing  because the metal surface is
at -196C and the mass of the cold heat extractor acts as a conductor.
Through thermal exchange heat is rapidly removed from the tissue,  producing
small ice crystals that mnimize ice crystal damage
The steps in the Gentle Jane process can be found on our web site
www.instrumedics.com

Bernice
schiller@instrumedics.com