OD ratios of 3 to 4!?

tflanigan at molbiol.ox.ac.uk tflanigan at molbiol.ox.ac.uk
Thu Apr 18 08:20:24 EST 1996

Recently we've been getting OD 260/280 ratios of greater than 2.0 and 
sometimes as high as 3-4 for RNA and plasmid preps.  I suspect that something 
may be wrong with the UV spec since our signals on ethidium gels suggest that 
the 260 readings are underestimating the amount of nucleic acid in our 
samples.  Has anyone else encountered this problem/phenomenon and if so can I 
have your comments please?   Also i'm often asked why a ratio of 2.0 indicates 
a good prep and give the standard Maniatis answer about protein and 
phenol/chloroform contamination.  However this does not answer the specific 
question....Why 2.0?  Can anyone provide a more scientific explanation?
Thanks in advance,
Tom.  tflanigan at molbiol.ox.ac.uk

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