I ordered a 50 nM synthesis of oligonucleotide and did not get 50 nM of material. Why?
It has become industry standard to assign synthesis scales based on the amount of starting material for a synthesis. (For example, a 50 nanomole scale means that there is 50 nanomole of the initial base coupled to the solid support used for synthesis.) Of the starting material, a substantial proportion may be unavailable for use due to chemical modification or steric problems. The actual yield should be calculated as described above.