how to measure DNA quantity, exclusive of RNA - (Sep/14/2006 )

Is there any easy way to measure DNA quantity exactly???
or measure RNA quantity in "DNA solution"??

when extracting plasmid from Ecoli, I often got about 3~4ug/ul value of DNA quantity measured by "nanodrop".(DNA solution had been dealt with RNase)

I am wondering about that both of DNA and RNA hava absorbance at 260nm, then how we differentiate RNA from DNA, or how to know the exact value of DNA quantity(exclusive fo RNA).


my teacher told me that because of RNA contamination, the correct DNA quantity may be only 1/10 of it.

is that true??

or is there any way to help me count DNA quantity correctly?

thanks for your help~

treat your DNA for 30' with RNase in Tris 10mM pH 8 without EDTA.working RNAse concentration should be 100µg/ml

Check by agarose gel.

hi april0210,

I agree with fred 33, but afterwards you have to purify to get rid of the small RNA fragments/nucleotides ( give also an absorption at OD260),
by ethanol precipitation or a silica column,

good luck

use picogreen