Etoh wash - confessions of a paranoid researcher....
daj at uk.ac.ic.nhm
Wed Sep 1 03:40:57 EST 1993
>When you do an ethanol wash of a DNA precipitate do you try to resuspend the
>pellet and spin, rinse the pellet and spin, rinse the pellet and just dry...
You'll never truely resuspend the pellet 'cos its a precipitate, but you
may dislodge it from the tube wall and break it into bits if it is big and
you vortex it like hell. Also, often, even with gentle handling, 70%
ethanol appears to dislodge pellets from the tube wall. So.....
(1) If you can see your pellet clearly and it is still attached to the wall
after addition of the 70% and a gentle mix/vortexing (remember, the aim of
the rinse is to help flush out salts so mixing must help) then there is
probably no need to spin, but if your pellet is small/invisible/loose then
what is the "cost" of an extra minute or two in the microfuge against peace
of mind (as the DNA is already precipitated into "lumps" (whether you can
see them or not) you only need to do a brief respin).
(2) For the record, I always vortex and respin after addition of 70%, I
always position the tubes with their cap hinges in the same orientation in
the micofuge so I know where to expect the pellet to be and I always
transfer the alcohol washes into a petridish so that I can retrieve the
pellet if it does still come away. OK so I am paranoid but I rarely loose a
pellet. For the hyper-paranoid out there I believe that NYCOMED do a
microfuge tube which has been specifically treated to hold onto
precipitated DNA more firmly than standard polypropylene tubes. I haven't
tried them ........yet.
David A. Johnston
Dept of Zoology, The Natural History Museum, Cromwell Road,
South Kensington, London SW7 5DB.
(tel 071 9389297, fax 071 9388754, email daj at nhm.ic.ac.uk)
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