Spectrophotometric measurement of DNA concentration

The concentration of DNA and RNA should be determined by measuring the absorbance at 260 nm (A₂₆₀) in a spectrophotometer. For accuracy, absorbance readings at 260 nm should fall between 0.15 and 1.0.

Pure DNA has an A₂₆₀/A₂₈₀ ratio of 1.8–2.0 in 10 mM Tris·Cl, pH 8.5.

Strong absorbance at A₂₈₀ resulting in a low A₂₆₀/A₂₈₀ ratio indicates the presence of contaminants, such as proteins.

Strong absorbance at 270 nm and 275 nm may indicate the presence of contaminating phenol.

Absorbance at 325 nm suggests contamination by particulates in the solution or dirty cuvettes.

Spectrophotometric conversions from absorbance at 260 nm