HPLC purification helps remove truncated synthesis products and enrich purity. Purification is recommended for oligos greater than 40 bases in length and for many modified oligos. In addition, many modifications require HPLC purification due to the nature of their synthesis chemistries. HPLC purification typically results in approximately 85% purity. Purity guarantees are issued on sequences up to 60 bases as long as they are not heavily modified or do not contain significant secondary structures. In general, HPLC tends to produce oligonucleotides that are slightly less pure than PAGE, but typically, with a higher guaranteed yield. We offer two different types of HPLC purification: Reverse Phase HPLC (RP-HPLC) and Ion Exchange HPLC (IE-HPLC). IE-HPLC is useful for oligos that will be transfected into living cells, while RP-HPLC is needed to purify oligos with fluorescent dyes and some other hydrophobic modifications. For those oligos that require the use of RP-HPLC purification and are to be used in living cells, we recommend following RP-HPLC with a Na+ salt exchange to remove any potentially toxic buffers such as triethylammonium acetate (TEAA). Please note that for very long sequences, over 80 bases, we recommend PAGE purification.