DNA PURITY

RPSCOTT RSCOTT at IRRI.CGNET.COM
Fri Jan 29 00:54:03 EST 1993


Seyed at "b7jp at musict.mcgill.ca" writes:
>...what does a ratio of A260nm/A280nm between 2 to 4 mean?

Will you please check the A325nm of your samples? Very clean DNA preps
should not absorb appreciably at 325nm (only ca. 0.01 nm). Significant
A325 readings would mean contamination with suspended particulates
or also unclean cuvettes (but I assume you're working with clean ones
and are wiping them before each reading) (see S. R. Gallagher article
on nucleic acids quantitation/purity assay in Curr. Protocols in Molec.
Biol.). A325 readings would reflect up to five-folds reading at 260 nm
according to Gallagher's article. I suspect that if you do have
particulate problems these could be dispersed polysaccharides (are your
samples turbid?). This might help just in case: spin your samples (around
2-5 min to pellet down dispersed particles) then carefully transfer your
supernatants into new tubes.

Good luck :-)
Scott

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RPScott
Genetics Lab
Intl Rice Res Inst
PO Box 933, 1099 Manila
Philippines
e-mail: rscott at irri.cgnet.com
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