On the Certificate of Analysis you received with your product, you are supplied with two numbers needed for this calculation: the number of OD₂₆₀ units of product (the absorbance reading you would obtain from a 1 cm cell path if you dissolved your sample in 1 ml of water, and usually serially diluted for the reading) and its calculated extinction coefficient (ε). The ε is given in units that are readily used for our application, OD₂₆₀ units per μmole. Divide the number of OD₂₆₀ units by ε to calculate the number of μmoles directly. For example, if you obtain 60 OD₂₆₀ units of an oligonucleotide with an ε of 300 OD₂₆₀units/μmole, you have received 0.2 μmoles of product.