The extinction coefficients of the single strands are added together to provide the final data on our Certificates of Analysis. When oligonucleotides are annealed; however, these constants are not entirely additive which can cause confusion when calculating the amount of product present in a sample.  Duplex extinction coefficients can be 15-25% lower than expected due to the hyperchromicity of the duplex.  Therefore, we provide a calculation on our duplex Certificates of Analysis to help better determine the actual amount of duplex present in a sample:

(Measured ODs/Total ODs of single strands) x Total Extinction Coefficient =  Duplex Extinction Coefficent