Discrepancy between OD-value on spec and DNA on agarose gel

Jim Hutchins hutchins at netdoor.com
Sun Aug 11 17:48:14 EST 1996

Botma Visser (pbv at rs.uovs.ac.za) wrote:
: When I determined the 
: concentration of the plasmid DNA at 260 nm, I got a very 
: high reading...I then ran 500 ng plasmid DNA 
: (calculated using the determined concentration) on an 
: agarose gel, and saw nothing.

This could occur because you have nuclease contamination.  The A260/A280
ratio and A260 concentration only tell you that nucleic acids exist in the
sample, not whether they form intact DNA or RNA.

Also, it does not hurt to check the A230 and A325 of your sample.  Both
can cause spurious high values of A260 (see explanation in the Big Red
Book, i.e., _Current Protocols in Molecular Biology_).

Jim Hutchins    hutchins at netdoor.com   hutchins at umsmed.edu

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