What does an OD260/OD280 ratio of 1.8 to 2.0 indicate about nucleic acid quality?

An OD260/OD280 ratio between 1.8 and 2.0 indicates that the nucleic acid sample is of high quality and is considered pure. This ratio measures the absorbance of nucleic acids (typically DNA or RNA) at two different wavelengths: 260 nm, where nucleic acids absorb light, and 280 nm, where proteins absorb light. A ratio in this range suggests that the nucleic acid is not significantly contaminated with proteins or other substances.

When the ratio is around 1.8, it specifically points to DNA purity, while ratios closer to 2.0 are often associated with RNA purity. Values lower than this range suggest potential contamination by proteins or other organic compounds, which would absorb at 280 nm, thereby affecting the ratio. This principle is widely used in molecular biology to assess the quality of nucleic acid preparations prior to downstream applications, such as sequencing, cloning, or PCR.