Why isn the yield for 1 µm scale syntheses five times higher than 0.2 µm scale syntheses?
For 0.2 µmol scale, the monomer coupling is done at a 40-50-fold excess. To do so for larger scale syntheses (such as 1.0 µmol scale) would be cost-prohibitive. Large-scale syntheses are done only at 10-fold mole excess of amidites and 1 µmol columns have not been fully optimised for flow, dead space and diffusion so far. However, to increase the yields for these larger scale syntheses, the coupling times are extended to increase coupling efficiencies.
