OD260 - (Jun/17/2006 )

Im a little confused i need to know what concentration of DNA is present in a sample with 0.5 OD260, obtained by using 1ul of stock in 1000ul water? because Im not sure about the optical density value. Thanks

ok
dilution : 1000
so calcul is : OD x dilution x 50ng/µl
C=1000*0.5*50
C=25µg/µl
Seems little high to work directly with . I would try to dilute a sample from the stock solution to get reduced concentration (how would you pipett 5µg, and be accurate and reproducible?...)

A 1ug/ul DNA solution reads 20 OD. Therefore, since your solution reads 0,5, you have 0.025 ug/ul.
If you multiply this by the dilution factor 1000, you get 25ug/ul.

The formula you should use every time is:

1ug/ul : 20 OD = x ug/ul : OD you read

The obtained value has to be then multiplied by the dilution factor.