A260/A280 ratio around 0.23 for a DNA sample most closely indicates contamination with

A260/A280 ratio around 0.23 for a DNA sample most closely indicates contamination with

• A. RNA
• B. Protein
• C. DNA
• D. Salts

Answer: (B)

The A260/A280 ratio is used to gauge nucleic acid purity by comparing how strongly the sample absorbs at 260 nm (nucleic acids) to 280 nm (protein-related absorbance). A pure DNA sample typically yields a ratio around 1.8. When proteins are present, they contribute more absorbance at 280 nm, which lowers the overall ratio. A value as low as about 0.23 indicates substantial protein contamination, since the protein component is elevating the 280 nm absorbance relative to 260 nm. If the sample were contaminated with RNA, the ratio would trend higher—closer to 2.0—because RNA also absorbs at 260 nm, not because of a decrease at 280 nm. DNA contamination doesn’t inherently shift this ratio in a way that would explain a drastic drop. Salts or other non-nucleic acid contaminants mainly affect measurements at other wavelengths (like 230 nm) or alter the baseline, not drive the ratio down to such a low value.

The A260/A280 ratio is used to gauge nucleic acid purity by comparing how strongly the sample absorbs at 260 nm (nucleic acids) to 280 nm (protein-related absorbance). A pure DNA sample typically yields a ratio around 1.8. When proteins are present, they contribute more absorbance at 280 nm, which lowers the overall ratio. A value as low as about 0.23 indicates substantial protein contamination, since the protein component is elevating the 280 nm absorbance relative to 260 nm.

If the sample were contaminated with RNA, the ratio would trend higher—closer to 2.0—because RNA also absorbs at 260 nm, not because of a decrease at 280 nm. DNA contamination doesn’t inherently shift this ratio in a way that would explain a drastic drop. Salts or other non-nucleic acid contaminants mainly affect measurements at other wavelengths (like 230 nm) or alter the baseline, not drive the ratio down to such a low value.