ww40 William_D_WARREN at UMAIL.UMD.EDU
Tue Jul 13 16:16:00 EST 1993

>Some months ago there was a question about S35 PCR and the possibility that
>the label may be going through the tubes and contaminating the block.

[stuff deleted]

>My point to the net is, has anyone else seen this problem?  Does this also
>happen with standard thick-walled PCR tubes.  And CAUTION please check your

G'day Klaus,

You are not alone !!! IT's a common problem.

We've been going nuts (well actaully I have) ever since one member of our lab
started doing alot of hot PCR using 35S. After every use the block is
becomes contaminated. Sometimes more sometimes less. We've talked to
Perkin Elmer about it and it seems that some batches of their thin walled tubes
are more prone to this than others (we use their 9600 thermocyclier with the
thin walled tubes and strips of 8 lids which operate oil free as the lids are

We haven't tried any tubes from any other supplier. My gut feeling is that
as the tube lid combination produces a better vapour seal in some batches
than others. Cranking the lids down harder may help but then the risk of
cracking a tubes becomes high and the resulting contamination would be very
high indeed.

If there's a solution then I'd love to hear it. Right now we just manage the
problem and live with it. After each hot PCR the block is washed thoroughly
and then a wipe test is done to check the contamination level. Washing is
then repeated if the test shows >500 cpm (prior to cleaning our block can be
wipe test as high as 10 000 cpm).


William D. WARREN, PhD
Center for Agricultural Biotechnology     Email: ww40 at umail.umd.edu
University of Maryland at College Park    Phone: (301) 405-7681 


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