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Measuring DNA Concentration: UV absorption shift?

Yvonne Thorstenson yvonne at SEQUENCE.STANFORD.EDU
Tue Feb 4 18:52:31 EST 1997

In trying to improve measurement of DNA concentration, I obtained a
spectrum of UV absorbance by scanning from 200 to 325 nm.  In five
samples, there was only a very weak absorbance at 253 nm, and a stronger
absorbance at 217 nm.  The absorbance at 253 nm is too weak to account
for the amount of DNA I see on an agarose gel, but the absorbance at 217
nm is about right.

  I suspect that the DNA samples are contaminated with something.  They
were purified from agarose using two different gel extraction methods. 
What would cause the absorbance of a DNA sample to shift from the
expected maximum at 260 nm to 253 nm, or even 217 nm?

Yvonne Thorstenson

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