How do you compare the purity of the DNA samples ran on agarose gel electrophoresis based on their absorbance at 230nm and 280nm? It is said that at 230nm, its ratio from the absorbance at 260nm should be greater than 1.5, while the ratio of 260nm to 280nm should be greater than 1.85nm. What if both samples are greater than the said values? Which sample would be considered as the purer one, the sample with higher ratios or the samples nearer to the said values?

 

Absorbance

The most common technique to determine DNA yield and purity is measurement of absorbance

A ratio of A₂₆₀/A_{230 should be greater than 1.5nm--} The lower the ratio, the greater the amount of thiocyanate salt is present, for example. As a guideline, the A₂₆₀/A₂₃₀ is best if greater than 1.5. 

The ratio of 260nm to 280nm should be greater than 1.85nm. Good-quality DNA will have an A₂₆₀/A₂₈₀ ratio of 1.7-2.0. A reading of 1.6 does not render the DNA unsuitable for any application, but lower ratios indicate more contaminants are present.

What if both samples are greater than the said values

greater values than the required ratios shows the DNA is of good quality unlike lower values compared to the recommended ratio shows the DNA is contaminated

Which sample would be considered as the purer one, the sample with higher ratios or the samples nearer to the said values?

the sample with higher ratios--higher ratios depicts that the sample is pure and free of contaminants