The amount of oligonucleotide in nanomoles that, when dissolved in 1 mL volume, results in 1 unit of absorbance at 260 nm with a standard 1 cm path-length cuvette. nmmole/OD260 is calculated from an oligonucleotide's molar extinction coefficient. OD260 is calculated from the following equation,

OD260 = (A260 * V) / p 

where A260 is absorbance at 260 nm, V is the solution volume in mL, and p is the length of the light path through the sample (cm). Thus, OD260 has the units mL/cm. Starting from the oligo molar extinction coefficient, ε260,

ε260 = L/(mol · cm) = 103 mL/(mol · cm) 

Since OD260 has the units of mL/cm, the equation can be written as,

103 OD260/mol = 103 OD260/ 109 nmol = OD260/ 10-6 nmol

Combination of both equations yields,

ε260 = OD260 / 10-6 nmol

and this can be rearranged as,

nmole/OD260 = 106 / ε260