The ratio of absorbance at 260 nm and 280 nm is used to assess the purity of DNA and RNA. A ratio of ~1.8 is generally accepted as pure” for DNA; a ratio of ~2.0 is generally accepted as “pure” for RNA. If the ratio is appreciably lower in either case, it may indicate the presence of protein, phenol or other contaminants that absorb strongly at or near 280 nm
Some researchers encounter a consistent 260/280 ratio change when switching from a standard cuvette spectrophotometer to the
NanoDrop® ND-1000 spectrophotometer. The three main explanations for this observation are listed below: