In article <53tt16$9gc at info.service.rug.nl>,
g.j.e.j.hooiveld at farm.rug.nl (Guido Hooiveld) wrote:
>>After performing a prep I estimate the amount and purity of my plasmid DNA
sample by measuring
>the A260 and A280. I use the ratio of A at 260 and 280 nm to get an indication
of the purity of
>>I was told an A280/A260 ratio of 1.8 to 1.9 indicates a highly purified DNA
preparation and its
>theoretically limit is 2.0. However, I often find a ratio larger than 2.0; like
2.1 to 2.2. So,
>is this (theoretically) value of 2.0 correct, if yes, does anybody have a
suggestion why I find
>values >2; if not, what is this value?
>>And what about the factor you have to use to determine the concentration of DNA
>multiply A260 with 50 to obtain the concentration (ug/ml), or use 35? Which
value is correct?
>>Any comments would be appreciated!
>>Thanks in advance,
>You should look at the scan from 220 to 300nm to see if there are other peaks
or shoulders. If there are your preps are not pure. A260/280 ratio is applicable
only to preps that are pure.