To enhance the performance of charge detection mass spectrometry, we investigated the behavior of macromolecular single ions on their paths towards and within the Orbitrap analyzer. We discovered that ions in mass beyond one megadalton reach a plateau of stability and can be successfully trapped for seconds, travelling a path length of multiple kilometers, thereby enabling precise mass analysis with an effective resolution of greater than 100,000 at m/z 35,000. Through monitoring the frequency of individual ions, we show that these high mass ions, rather than being lost from the trap, can gradually lose residual solvent molecules and, in rare cases, a single elementary charge. Our observations highlight the importance of efficient desolvation for optimal charge detection mass spectrometry and inspired us to implement multiple improved data acquisition strategies. We demonstrate that the frequency drift of single ions due to desolvation and charge stripping can be corrected, which improves the effective ion sampling 23-fold and gives a two-fold improvement in mass precision and resolution, as demonstrated in the analysis of various viral particles.

Adeno-associated viruses (AAV) represent important gene therapy vectors with several approved clinical applications and numerous more in clinical trials. Genome packaging is an essential step in the bioprocessing of AAVs and needs to be tightly monitored to ensure the proper delivery of transgenes and the production of effective drugs. Current methods to monitor genome packaging have limited sensitivity, a high demand on labour, and struggle to distinguish between packaging of the intended genome or unwanted side-products. Here we show that Orbitrap based charge detection mass spectrometry allows the ultra-sensitive quantification of all these different AAV bioprocessing products. A protocol is presented that allows the quantification of genome packed AAV preparations in under half an hour, requiring only micro-liter quantities of typical AAV preparations with ~1013 viral genome copies per millilitre. The method quickly assesses the integrity and amount of genome packed AAV particles to support AAV bioprocessing and characterization of this rapidly emerging class of advanced drug therapies.