Convert OD260 spectrophotometer readings to nucleic acid concentration for DNA, RNA, and oligonucleotides using standard extinction coefficients
Nucleic Acid Concentration
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Concentration
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Extinction Coefficient Used
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The standard extinction coefficients are: dsDNA = 50 µg/mL per OD260, ssDNA = 40 µg/mL per OD260, RNA = 40 µg/mL per OD260, and oligonucleotides = 33 µg/mL per OD260. These are approximations as the exact values depend on sequence composition.
Nucleic acids have maximum absorbance at 260nm due to the aromatic bases in their structure. This makes OD260 the standard wavelength for quantifying DNA and RNA concentrations using spectrophotometry.
These units are equivalent: 1 µg/mL = 1 ng/µL. Both are commonly used in molecular biology, with ng/µL often preferred for smaller sample volumes typical in PCR and sequencing applications.
The dilution factor accounts for any dilution made to the original sample before measurement. If you diluted your sample 1:10, the dilution factor is 10, and the calculator multiplies the result by this factor to give the original concentration.
Standard spectrophotometer cuvettes have a 1 cm path length. Some microvolume spectrophotometers use shorter path lengths (0.2-1.0 mm), so always check your instrument specifications and adjust accordingly.
These calculations provide approximations based on average extinction coefficients. The actual values can vary by ±20% depending on the specific sequence composition, salt concentration, and pH of your sample.
Most spectrophotometers are most accurate in the OD260 range of 0.1-1.0. Readings below 0.1 may have poor signal-to-noise ratio, while readings above 1.0 may exceed the linear range and require dilution.