For a DNA sample, the 1:100 dilution yields an A260 of 0.430. What is the DNA concentration in μg/mL for the original sample?

For a DNA sample, the 1:100 dilution yields an A260 of 0.430. What is the DNA concentration in μg/mL for the original sample?

• A. 2150 μg/mL
• B. 430 μg/mL
• C. 21.5 μg/mL
• D. 860 μg/mL

Answer: (A)

Converting an absorbance reading to DNA concentration relies on the A260-to-concentration rule for double-stranded DNA: an A260 of 1.0 equals 50 μg/mL. The diluted sample has A260 = 0.430, so its concentration is 0.430 × 50 = 21.5 μg/mL. The dilution is 1:100, meaning the original sample is 100 times more concentrated. Multiply 21.5 μg/mL by 100 to get 2150 μg/mL for the original sample. Therefore, the DNA concentration in the original sample is 2150 μg/mL.

Converting an absorbance reading to DNA concentration relies on the A260-to-concentration rule for double-stranded DNA: an A260 of 1.0 equals 50 μg/mL. The diluted sample has A260 = 0.430, so its concentration is 0.430 × 50 = 21.5 μg/mL. The dilution is 1:100, meaning the original sample is 100 times more concentrated. Multiply 21.5 μg/mL by 100 to get 2150 μg/mL for the original sample. Therefore, the DNA concentration in the original sample is 2150 μg/mL.