50- 100mer needs page purification. For the purification of long oligonucleotides (50- 100mer), page purification method is recommended, which uses cross-linked polyacrylamide gel (electrophoresis) as the purification matrix. Although page shows a high purification efficiency (> 98%), there are some defects in the additional steps, such as extraction and desalination after page, which will lead to a decrease in purification yield. Commonly used primer purification methods include desalination, BioRP/OPC purification, PAGE purification and HPLC purification.