From a DNA sample with A260 0.430 at 1:100, the undiluted concentration is

From a DNA sample with A260 0.430 at 1:100, the undiluted concentration is

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

Answer: (B)

Quantifying DNA by absorbance at 260 nm uses the standard that double-stranded DNA has a concentration of 50 μg/mL per unit of A260 for a 1 cm path length. If the diluted sample shows A260 = 0.430 at a 1:100 dilution, the concentration in the diluted solution is 0.430 × 50 = 21.5 μg/mL. Since this reading comes from a 1:100 dilution, the original undiluted sample is 100 times more concentrated: 21.5 × 100 = 2150 μg/mL (2.15 mg/mL). The key idea is applying the A260-to-concentration factor for dsDNA and then correcting for the dilution factor.

Quantifying DNA by absorbance at 260 nm uses the standard that double-stranded DNA has a concentration of 50 μg/mL per unit of A260 for a 1 cm path length. If the diluted sample shows A260 = 0.430 at a 1:100 dilution, the concentration in the diluted solution is 0.430 × 50 = 21.5 μg/mL. Since this reading comes from a 1:100 dilution, the original undiluted sample is 100 times more concentrated: 21.5 × 100 = 2150 μg/mL (2.15 mg/mL). The key idea is applying the A260-to-concentration factor for dsDNA and then correcting for the dilution factor.