A Mechanism for Ionization of Nonvolatile Compounds in Mass Spectrometry: Considerations from MALDI and Inlet Ionization

作者：Trimpin Sarah^*; Wang Beixi; Inutan Ellen D; Li Jing; Lietz Christopher B; Harron Andrew; Pagnotti Vincent S; Sardelis Diana; McEwen Charles N

来源：Journal of the American Society for Mass Spectrometry, 2012, 23(10): 1644-1660.

DOI：10.1007/s13361-012-0414-y

• Ionization mechanism
• Laserspray ionization
• LSI
• MALDI
• ESI
• MAII
• SAII
• Multiply charged ions
• Singly charged ions
• Clusters
• Charged droplets
• Superheating
• Matrix
• Decomposition
• Mechanism
• Ionization
• Charged clusters
• Chemical ionization model
• Gas phase model
• Matrix assisted inlet ionization
• Solvent assisted inlet ionization
• Photochemical ionization

Mechanistic arguments relative to matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) address observations that predominately singly charged ions are detected. However, recently a matrix assisted laser ablation method, laserspray ionization (LSI), was introduced that can use the same sample preparation and laser as MALDI, but produce highly charged ions from proteins. In MALDI, ions are generated from neutral molecules by the photon energy provided to a matrix, while in LSI ions are produced inside a heated inlet tube linking atmospheric pressure and the first vacuum region of the mass spectrometer. Some LSI matrices also produce highly charged ions with MALDI ion sources operated at intermediate pressure or high vacuum. The operational similarity of LSI to MALDI, and the large difference in charge states observed by these methods, provides information of fundamental importance to proposed ionization mechanisms for LSI and MALDI. Here, we present data suggesting that the prompt and delayed ionization reported for vacuum MALDI are both fast processes relative to producing highly charged ions by LSI. The energy supplied to produce these charged clusters/droplets as well as their size and time available for desolvation are determining factors in the charge states of the ions observed. Further, charged droplets/clusters may be a common link for ionization of nonvolatile compounds by a variety of MS ionization methods, including MALDI and LSI.

• 出版日期2012-10