Separation and identification of phosphorothioate oligonucleotides by HILIC-ESIMS

A combined hydrophilic interaction chromatography (HILIC) electrospray ionization mass spectrometry (ESI-MS) approach for the separation and identification of phosphorothioate oligonucleotides is described. Phosphorothioate 21-mer and 23-mer were separated by HILIC and detected using selected ion monitoring (SIM) ESI-MS. Phosphorothioates could be detected from 50 nM solutions suggesting effectiveness comparable to ion pairing reversed phase chromatography approaches.