How is DNA concentration measured?
Nucleic acids (DNA and RNA) absorb UV light maximally at a wavelength of 260 nm. By measuring the absorbance of a sample at 260 nm (using a spectrophotometer or NanoDrop), you can accurately determine the concentration of the nucleic acid in your solution.
Formula for DNA concentration
The concentration calculation is based on the Beer-Lambert Law. The standard formula used is:
Concentration = A₂₆₀ × Dilution Factor × Conversion Factor
The resulting concentration is typically expressed in µg/mL, which is mathematically identical to ng/µL.
Absorbance conversion factors
Depending on the type of nucleic acid, an optical density (OD) of 1.0 at 260 nm corresponds to different concentrations:
- Double-stranded DNA (dsDNA): 50 µg/mL per 1 OD₂₆₀
- Single-stranded DNA (ssDNA): 33 µg/mL per 1 OD₂₆₀
- Single-stranded RNA (ssRNA): 40 µg/mL per 1 OD₂₆₀
Calculating total yield
If you know the total volume of your sample, you can also determine the total mass (yield) of nucleic acid present.
Total Yield (µg) = Concentration (µg/mL) × Volume (mL)