Post-source decay of alkylated and functionalized polycyclic aromatic compounds

Area of Science:

• Analytical Chemistry
• Environmental Science
• Spectrometry

Background:

• Post-source decay (PSD) is established for large molecule structural analysis in time-of-flight mass spectrometry (TOFMS).
• Laser desorption/ionization (LDI) is used for analyzing complex samples like diesel exhaust particles.
• Conventional TOFMS may lack resolution for distinguishing closely related pollutants.

Purpose of the Study:

• To adapt PSD for structural elucidation of small molecules, specifically polycyclic aromatic hydrocarbons (PAHs), in diesel exhaust.
• To enhance LDI efficiency for PAHs using a dual-laser system.
• To demonstrate the utility of LDI-PSD-TOFMS for identifying small molecules in complex environmental samples.

Main Methods:

• Utilized a time-of-flight mass spectrometer equipped with a nitrogen laser (337 nm) and a coupled Nd:YAG laser (266 nm) for two-photon ionization.
• Applied post-source decay (PSD) fragmentation analysis to ionized analytes.
• Investigated the LDI-PSD-TOFMS analysis of functionalized, alkylated, and sulfur-containing PAHs.
• Analyzed diesel engine exhaust particles as a complex environmental sample.

Main Results:

• Achieved two-photon single-step desorption/ionization of PAHs using the 266 nm laser.
• Obtained structural information from PSD fragmentation of various PAHs.
• Successfully applied LDI-PSD-TOFMS to identify small molecules within diesel exhaust particles.
• Demonstrated the capability to differentiate pollutants with very similar molecular weights, surpassing TOFMS resolution limitations.

Conclusions:

• LDI-PSD-TOFMS is effective for identifying small molecules in environmental samples like diesel exhaust.
• The dual-laser approach enhances PAH ionization and subsequent structural analysis.
• This technique provides valuable information for distinguishing closely related pollutants, improving environmental monitoring capabilities.