A260/A280 ratios of oligonucleotide

Pete pkursula at cc.oulu.fi
Wed Dec 11 06:14:54 EST 1996

On 9 Dec 1996 nhwu at PUBLIC3.BTA.NET.CN wrote:

> I know DNA has an A260/A280 ratio of 1.6~1.8, while as RNA has ratio of 
> 1.8~2.0. But what about oligonucleotide? I want to check the puriety of 
> some primers systhesised, but I don't know what range of A260/A280 ratio is 
> all right.
> any help will be appriciated!
> Xiao-yu Liu

OK, this is how it goes:

Each nucleotide has a characteristic A260/A280 ratio. If you have a DNA 
or an RNA sample, you assume that you have a certain frequency of each 
nucleotide in the nucleic acid. Thus, you generally expect an A260/A280 
ratio of 1.8 for DNA (taken from the ratios of A,C,G and T) and 2.0 for 
RNA (taken from A,C,G and U). 

When you have an oligonucleotide, however, the situation is a bit 
different: the ratio you expect depends on the nucleotide composition of 
the oligo. If you really want to check this, you should dig out the 
absorption spectra for the nucleotides and calculate what ratio you 
expect, I think. Certainly, if you have an oligo with approximately equal 
amounts of each nucleotide, you will be somewhere between, say, 1.5-2.0. 
But if it's just poly-(T) or something like that, you should check the 
characteristic absorption ratios for the nucleotides if you want to do it 
properly. There must also be computer programs that will do this for you.


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