Cryogenic vials...really necessary?

[David Micklem]

In article <pxpst2-0810971834020001 at pelli.pathology.pitt.edu>,
pxpst2 at vms.cis.pitt.delet.edu (Peter) wrote:


>Depends on how long you plan to store them and what you will store them in.  
>The drawback to snap caps is firstly contaimination.  Snap cap seals are
>not 100% airtight.   And with the way they(the snap cap tubes) will be
>opened and closed, one will greatly increase the chance of
>contaimination.  Obviously, if they are bacterial cells and can be grown
>under selection this is not that big of a deal but for eukaryotic cells
>this is a big problem.
>As I said earlier the snap caps are not air tight so exchange of air
>between the inside and outside does occur, and since the outside air is
>very dry(air at -20C does not have the capability of holding moisture in a
>liquid state) the moisture will be drawn out of the tubes.  Remember back
>to general chemistry the princible of sublimation(  WATER(solid)------>
>WATER(gas) skips the liquid pase altogether).  It is what drives the water
>out of the tube and onto the ice sheet in the freezer on the condensor. 
>Since you have glycerol this process will be greatly impeeded due to the
>lowering of the water Vapor pressure.
>Storage time for bacteria in this manner would probably be no more than 9
>months to a year and assuming that you put a secondary seal of parafilm
>around the top.


Hmm.  While this may be true in principle, I suspect that the rate of air
flow between the snap-top tube and the freezer is low enough not to be a
problem.  I certainly have glycerol stocks (at -80, FWIW) that are several
years old but which are still viable (got some out just last week!).  They
have no secondary seal of parafilm either.

Maybe I'm just lucky....

David

-- 
D.R.Micklem,                                Time flies like an arrow... 
Wellcome/CRC Institute,            Fruit flies like a banana.       
Cambridge CB2 1QR, UK               Email:drm21 at mole.bio.cam.ac.uk
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