How to determine the extinction coefficient of the PNAs in water at room temperature?

Normally, the extinction coefficient (e) could be calculated at wave length 260 nm, based on the # of base A, C, G, T in a PNA and their extinction coefficient respectively. The formula is:

e = [ 13.7 × # of A + 6.6 × # of C +11.7 × # of G + 8.6 × # of T ] mL/(µmole × cm)

If known the concentration (c) of a PNA solution, the extinction coefficient (e) could also be calculated by measuring its absorbance (A) at 260 nm. The calculation formula is:

e = A/(c × l)

note: l is the path length of the light travels through the solution

In order to get a good result, the value of absorbance (A) should be within 0.1 ~1.0 when do the measurement.