If this dilution is for use in PCR then the primers are in large excess so getting the exact concentration is not necessary.. Check the volume that you dissolved in and trust that the amount sent from the oligo company (because they are expert in calculating the primer amount) is correct and go with your dilution

· Most people will just take the number of nMol from the tube label or oligo information sheet and multiply by 10 to get the volume of TE needed to dissolve the oligo to a concentration of 100 µM and this should be accurate because companies look after their equipment well and know exactly the sequence needed to calculate the extinction coefficient so can be trusted. The general formula 1 OD260 Unit = 33 μg/ml ssDNA is based on an average distribution odf bases in the sequence so is not completely accurate but has worked well for many years.

· For more accurate data many companies list the extinction coefficient either on the tube supplied or on the information sheet but will use a formula like

· ε (in l/mmol) = amount of As x 15.4 + amount of Cs x 7.3 + amount of Gs x 11.4 + amount of Ts x 8.8

· and then you can use c (in mmol/l) = OD(260nm) / ε to get your concentration.

· This will work ok when the OD is less than 1.0 ( dilute the sample if not) and the extinction coefficient is quoted /calculated in the correct units