How is the coupling efficiency determined?
Following the first coupling step, the amount of Trityl released during deblocking is directly proportional to the amount of full-length oligo made in the previous cycle. When the Trityl is cleaved during the deblocking step, the resulting Trityl cation is orange in color. The intensity of this color can be measure by UV spectrophometry. By comparing the intensities of the Trityl produced after the first and last coupling, one can calculate the average successful base coupling per cycle and hence the coupling efficiencies.
