For an RNA sample, the 1:200 dilution yields an A260 of 0.210. What is the RNA concentration in μg/mL for the diluted sample?

For an RNA sample, the 1:200 dilution yields an A260 of 0.210. What is the RNA concentration in μg/mL for the diluted sample?

• A. 1680 μg/mL
• B. 8.4 μg/mL
• C. 0.210 μg/mL
• D. 84 μg/mL

Answer: (B)

When estimating RNA concentration from a spectrophotometer reading, a standard conversion is used: RNA concentration in μg/mL ≈ A260 × 40. This factor reflects how much RNA mass corresponds to an absorbance of 1 at 260 nm. Here, the diluted sample gives A260 = 0.210. Multiply by 40 to get the RNA concentration in the diluted solution: 0.210 × 40 = 8.4 μg/mL. Since the reading comes from the 1:200 dilution, this 8.4 μg/mL is the concentration of RNA in the diluted sample. If you wanted the original, undiluted sample’s concentration, you would multiply by 200, giving 1680 μg/mL.

When estimating RNA concentration from a spectrophotometer reading, a standard conversion is used: RNA concentration in μg/mL ≈ A260 × 40. This factor reflects how much RNA mass corresponds to an absorbance of 1 at 260 nm.

Here, the diluted sample gives A260 = 0.210. Multiply by 40 to get the RNA concentration in the diluted solution: 0.210 × 40 = 8.4 μg/mL. Since the reading comes from the 1:200 dilution, this 8.4 μg/mL is the concentration of RNA in the diluted sample. If you wanted the original, undiluted sample’s concentration, you would multiply by 200, giving 1680 μg/mL.