Why do Oligos require purification?
Following DNA synthesis, the completed DNA chain is released from the solid support by incubation in basic solutions such as ammonium hydroxide. This solution contains the required full length oligo but also contains all of the DNA chains that were aborted during synthesis (failure sequences). If a 20mer was synthesized, the solution would also contain 19mer failures, 18mer failures, 17mer failures etc. in small amounts. The amount of failure sequences present is influenced by the coupling efficiency and length of oligo (see Table 1). These failure sequences can compete with the full-length product in some applications such as Subcloning, Gene Synthesis, Antisense, … and may therefore need to be removed before the oligo can be used successfully and highly efficiently. Remember that in general, the higher the purity, the lower the final yield!
