Preparation of oligonucleotides without aldehyde abasic sites

High-quality oligonucleotides are obtained by selective modification of sequences containing aldehyde apurinic sites with a new chromatographic tag followed by RP-HPLC separation. Hydroxylamine derivative 1 of a water soluble nonionic surfactant modifies oligonucleotides selectively at abasic sites leading to significantly increased retention.