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How do I calculate the extinction coefficient of an oligonucleotide?

For your convenience, please use our online calculation tool MOPS or apply the formula below:

The extinction coefficient at 260 nm (e260) is a unique physical property of each oligonucleotide. It is defined as the absorbance at 260 nm of a 1 M aqueous solution measured at 20 °C in an optical cell with 1 cm pathway (Lambert-Beer's law).
Purinic bases show a higher absorption (OD260) than pyrimidinic bases. Interactions between neighbouring bases, as well as modifications that absorb at 260nm, also influence optical absorbance. As a consequence, the extinction coefficient strongly depends on oligonucleotide sequence and composition.
The extinction coefficient of an oligonucleotide can be approximately (error up to 20 %) calculated using the following formula:

ε260 (mM-1 x cm-1) = (15.4 x nA) + (7.5 x nC) + (11.7 x nG) + (9.2 x nT)

where 15.4, 7.5, 11.7 and 9.2 are the monomer extinction coefficients in mM-1 cm-1 measured at
260 nm for dA, dC, dG and dT.

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