Pneumatically assisted desorption/ionization: 1. Some thoughts on the possible ionization mechanism(s).

Area of Science:

• Analytical Chemistry
• Mass Spectrometry

Background:

• Direct analysis in real time (DART) mass spectrometry typically requires electrical fields or acidic additives for ionization.
• Zopiclone tablets offer enhanced signal stability compared to direct deposition on stainless steel surfaces.

Purpose of the Study:

• To investigate the formation of MH(+) ions from zopiclone tablets under pneumatical conditions without external electrical fields or acidic modifiers.
• To elucidate the underlying mechanisms responsible for ion generation in the absence of conventional ionization methods.

Main Methods:

• Solvent droplet spraying onto zopiclone tablets.
• Analysis using mass spectrometry.
• Variation of sheath gas (nitrogen) flow rate.
• Use of deuterated acetonitrile (CD(3)CN) to probe solvent and gas roles.

Main Results:

• MH(+) ions were generated solely through pneumatical effects, independent of electrical fields or added acids.
• Acetonitrile (ACN) proved to be a surprisingly effective solvent for ion production.
• Increased nitrogen gas flow enhanced MH(+) ion intensity, suggesting an active role for nitrogen.
• Experiments with CD(3)CN confirmed ACN is not the protonating agent, and indicated potential ionization of N(2) via collisional phenomena.

Conclusions:

• A novel mechanism for MH(+) ion formation is proposed, involving pneumatical effects and potentially nitrogen ionization through collisional processes.
• This mechanism offers an explanation for ion generation without electrical fields or acidic additives, expanding the scope of DART-like analyses.
• The findings highlight the importance of gas-phase ion-molecule reactions and pneumatics in mass spectrometry ionization.