Freezing PCR products

Jim Owens jow at
Fri Mar 11 08:59:00 EST 1994

In article <9403102355.AA08771 at> Marion Freistadt,
mfreis at writes:
> A colleague of mine says that freezing a PCR product makes it
>Does anyone have any information on this subject?  The topic came up
when a
>PCR product was frozen prior to gel analysis.  My colleague attributed
>absence of product to freezing.  Naturally we are testing it.  The
>identical reaction did work a few days ago.

I have not frozen PCR products.  Instead I store them at 4oC in TE.  I
would assume that a single freezing should not hurt them.  I would expect
them to behave like restriction fragments.

Now for my standard ramblings on freezing:

When I was a grad student my advisor was an organic chemist who found
greater academic opportunities in biochemistry and had fled to a biology
department in a large university.  

At a journal club he presented a paper by a physical chemist who had
studied freezing drops of aqueous solutions by different methods: placing
in a deep freezer; placing on dry ice; placing in acetone/dry ice bath;
placing on liquid nitrogen.  There was a pH gradient in the samples
frozen by all means except liquid nitrogen.  The gradient went from
highest pH at the periphery to lowest pH in the center, the last part
frozen.  And the gradient was higher (greater) in the slower freezing
methods than in the faster ones.  

The discussion proposed that hydrogen (hydronium) ions have a higher
velocity than hydroxide ions and therefore are trapped less often by the
advancing ice front.  So the last part frozen had concentrated hydrogen
ions.  The reason liquid nitrogen did not set up a pH gradient was that
the ice front advanced faster than the H+ did.

My advisor was impressed with this paper since it gave him a rationale
for how he stored the enzyme whose mechanism he studied.  He had always
frozen the preps by freezing drops from a Pasteur pipet (about 20-25ul)
on liquid nitrogen.

End of lecture.

Good luck,

Jim Owens

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