Oligonucleotide impurity profiling by liquid chromatography–mass spectrometry

Oligonucleotides (oligos) manufactured by solid-phase synthesis are an emerging class of drugs. Therapeutic oligonucleotides require stringent characterization of product-related impurities. Regulatory guidance demands identifying and quantifying both major and minor impurities. Oligonucleotide impurity profiling by liquid chromatography–mass spectrometry (LC–MS) is one of the specialized analytical techniques for oligonucleotide impurity characterization. A detailed overview is given covering the different types of impurities, the regulatory expectations regarding detection, identification and quantification of impurities, the analytical challenges associated with impurity profiling by LC–MS, and the practical considerations for developing LC–MS methods. A few examples of how to implement LC–MS workflows in alignment with regulatory expectations are presented. Overall, this mini-review intends to provide a background, and a jump-start for those who are new to oligo-nucleotide impurity profiling by LC–MS.