How to get aliquots from frozen serum samples?

[Tom Anderson]

On Tue, 21 Aug 2007, WS wrote:

> we want to analyze about 70 serum samples which currently are stored in
> cryotubes (about 2ml) and which are frozen at -80. I am looking for
> suggestions on how to obtain small aliquots (sufficient for a few
> ELISAs, less than 100ul in total) without actually thawing all the
> material.

Take the metal block out of an electric hot block and chill it in the -80
overnight. Put it on the bench; take the tubes out, and one by one, put
them in it and scrape away at the top of the slug of frozen serum with a
micropipette tip until enough is melted. Put the tip on a micropipette and
suck it up.

A caveat about the whole approach, though: when solutions freeze slowly,
soluble molecules become unevenly partitioned, getting progressively
concentrated in the fraction of the sample that remains liquid. Think
about the concentration of sugar during the making of ice wine, or of
alcohol in making applejack. Thus, if you froze the samples in the first
place by putting them in the -80, they won't be uniform throughout, so a
sample scraped from the top won't be representative. If you flash-froze
them in LN2, this should not be such a problem. Of course, it might not
matter to you anyway.

tom

-- 
Tom Anderson, MRC Laboratory for Molecular Cell Biology, UCL, London WC1E 6BT
(t) +44 (20) 76797264   (f) +44 (20) 76797805   (e) thomas.anderson from ucl.ac.uk