Question

You analyze a dna sample which gives an a260 of 1.74 and a280 of 0.64. What is the concentration of this dna sample? Is it sufficiently pure?

Answer 1

The ratio of $\frac{A_{260}}{A_{280}}$  indicates the purity of nucleic acid.For pure DNA it should lie between 1.8-2.0.Whereas for RNA it should be greater than 2.

This is calculated for DNA using the given values of absorbance-

$\frac{A_{260}}{A_{280}}$= 2.71

As the value is greater than 2.0,it reflects the RNA contamination in the sample.