How can we calculate the oligo quantity from the light absorbance?
The quantity of oligos is often described in O.D. units which actually express light absorbance. One O.D. corresponds to the amount of oligo in a 1mL volume that results in an optical density of 1 in a 1cm path-length cuvette. This corresponds to approximately 33 g of oligo, although it varies for each particular oligo depending on its sequence. The concentration of an oligo of known sequence can be calculated since it is known that the extinction coefficient (in a 1cm path-length cuvette) for each of the bases at 260 nm is dG : 11.7 mL/mole dC : 7.3 mL/mole dA : 15.4 mL/mole dT : 8.8 mL/mole For any given oligo, multiply the number of times each base appears by its extinction coefficient. Then add the resulting four numbers to obtain the extinction coefficient (e) for the entire oligo. The concentration (C) can then be calculated from the equation (for a 1cm path-length cuvette): O.D.
