If the A260/A280 ratio is lower than 1.8, what does this indicate?

If the A260/A280 ratio is lower than 1.8, what does this indicate?

• A. Protein contamination
• B. Pure DNA
• C. RNA contamination
• D. High salt

Answer: (A)

Nucleic acid purity is assessed by comparing absorbance at 260 and 280 nm. DNA and RNA absorb strongly at 260 nm, while proteins absorb at 280 nm due to aromatic amino acids. A pure DNA sample is expected to have a ratio near 1.8; if proteins are present, the 280 nm absorbance goes up, lowering the ratio. So a value lower than 1.8 indicates protein contamination rather than a pristine DNA sample. RNA contamination would not typically cause this drop and might even raise the ratio since RNA contributes to the 260 nm signal. High salt can affect measurements in some cases but doesn’t specifically reflect protein contamination, so it’s not the primary interpretation of a low ratio.

Nucleic acid purity is assessed by comparing absorbance at 260 and 280 nm. DNA and RNA absorb strongly at 260 nm, while proteins absorb at 280 nm due to aromatic amino acids. A pure DNA sample is expected to have a ratio near 1.8; if proteins are present, the 280 nm absorbance goes up, lowering the ratio. So a value lower than 1.8 indicates protein contamination rather than a pristine DNA sample. RNA contamination would not typically cause this drop and might even raise the ratio since RNA contributes to the 260 nm signal. High salt can affect measurements in some cases but doesn’t specifically reflect protein contamination, so it’s not the primary interpretation of a low ratio.