Snap Freezing: N2 or Isopentane?

[Kimberly Martin]

Hi,

Re:  snap freezing tissue for RNA extraction--According to a 
colleague, placing tissue in isopentane and then into liquid 
nitrogen is more efficient than just putting it in a cryotube and 
into liquid N2 because Iso-P is a liquid and 'immediately' 
reaches -196, whereas the nitrogen forms an insulating layer of 
gas around the tissue.  Questions:  (1) Is isopentane necessary 
or desirable; and (2) does isopentane affect the quality of the 
RNA subsequently extracted? 

Kimberly Martin
Dept. of Neuropathology
Institute of Psychiatry, London