Etoh wash - confessions of a paranoid researcher....

David Johnstondaj 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.

Cheers

DAJ
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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