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Minimum proton affinity for efficient ionization with atmospheric pressure desorption/ionization on silicon mass
Pekka Ostman1, Jaana M H Pakarinen, Pirjo Vainiotalo
1Division of Pharmaceutical Chemistry, Department of Pharmacy, PO Box 56, FIN-00014 University of Helsinki, Helsinki, Finland.
Rapid Communications in Mass Spectrometry : RCM
|November 23, 2006
Summary
Atmospheric pressure desorption/ionization on silicon mass spectrometry (AP-DIOS-MS) efficiently ionizes compounds with high proton affinities (PAs) above 920-950 kJ/mol, yielding clean mass spectra.
Area of Science:
- Analytical Chemistry
- Physical Chemistry
- Spectrometry
Background:
- Atmospheric Pressure Desorption/Ionization on Silicon (AP-DIOS) is a versatile mass spectrometry technique.
- Understanding ionization efficiency is crucial for optimizing AP-DIOS performance.
- Proton affinity (PA) is a key molecular property influencing gas-phase basicity and ionization.
Purpose of the Study:
- To systematically investigate the relationship between proton affinity (PA) and ionization efficiency in AP-DIOS-MS.
- To determine the threshold PA required for efficient ionization of aromatic compounds using AP-DIOS-MS.
- To evaluate the impact of PA on the quality of mass spectra generated by AP-DIOS-MS.
Main Methods:
- A set of aromatic compounds with varying proton affinities were studied.
- Proton affinities were calculated using ab initio and hybrid density functional theory (B3LYP/6-31G(d)).
- Compounds were analyzed using atmospheric pressure desorption/ionization on silicon mass spectrometry (AP-DIOS-MS).
Main Results:
- Compounds with proton affinities exceeding a threshold of 920-950 kJ/mol were efficiently ionized.
- Ionization efficiency strongly correlated with the proton affinity of the analytes.
- AP-DIOS-MS produced very clean mass spectra for compounds meeting the PA threshold.
Conclusions:
- Proton affinity is a critical determinant of ionization efficiency in AP-DIOS-MS.
- A PA threshold of 920-950 kJ/mol is identified for effective ionization and clean spectra.
- This finding aids in method development and analyte selection for AP-DIOS-MS applications.
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