A DNA preparation has A260 = 0.260 and A280 = 0.230. Based on the ratio, the sample is

A DNA preparation has A260 = 0.260 and A280 = 0.230. Based on the ratio, the sample is

• A. Contaminated with RNA
• B. Contaminated with protein
• C. Pure DNA
• D. Contaminated with solvent

Answer: (B)

A260/A280 ratio is used to gauge nucleic acid purity, because nucleic acids absorb at 260 nm while proteins absorb more strongly at 280 nm. For pure DNA, the ratio is typically around 1.8; for pure RNA it's about 2.0. In this sample, the ratio is 0.260 divided by 0.230, which equals roughly 1.13—much lower than the expected 1.8. This drop indicates substantial protein contamination, since proteins raise absorbance at 280 nm relative to 260 nm. Therefore the sample is contaminated with protein.

A260/A280 ratio is used to gauge nucleic acid purity, because nucleic acids absorb at 260 nm while proteins absorb more strongly at 280 nm. For pure DNA, the ratio is typically around 1.8; for pure RNA it's about 2.0. In this sample, the ratio is 0.260 divided by 0.230, which equals roughly 1.13—much lower than the expected 1.8. This drop indicates substantial protein contamination, since proteins raise absorbance at 280 nm relative to 260 nm. Therefore the sample is contaminated with protein.