Studying Interfacial Dark Reactions of Glyoxal and Hydrogen Peroxide Using Vacuum Ultraviolet Single Photon Ionization Mass Spectrometry

Aqueous secondary organic aerosol (aqSOA) formation from volatile and semivolatile organic compounds at the air–liquid interface is considered as an important source of fine particles in the atmosphere. However, due to the lack of in situ detecting techniques, the detailed interfacial reaction mechanism and dynamics still remain uncertain. In this study, synchrotron-based vacuum ultraviolet single-photon ionization mass spectrometry (VUV SPI-MS) was coupled with the System for Analysis at the Liquid Vacuum Interface (SALVI) to investigate glyoxal dark oxidation products at the aqueous surface. Mass spectral analysis and determination of appearance energies (AEs) suggest that the main products of glyoxal dark interfacial aging are carboxylic acid related oligomers. Furthermore, the VUV SPI-MS results were compared and validated against those of in situ liquid time-of-flight secondary ion mass spectrometry (ToF-SIMS). The reaction mechanisms of the dark glyoxal interfacial oxidation, obtained using two different approaches, indicate that differences in ionization and instrument operation principles could contribute to their abilities to detect different oligomers. Therefore, the mechanistic differences revealed between the VUV SPI-MS and ToF-SIMS indicate that more in situ and real-time techniques are needed to investigate the contribution of the air–liquid interfacial reactions leading to aqSOA formation.

Threshold photoelectron spectroscopy of 9-methyl adenine: theory and experiment

We present a combined experimental and theoretical study of single-photon ionization of 9-methyl adenine (9MA) in the gas phase. In addition to tautomerism, several rotamers due to the free rotation...

Atmospheric Pressure Single Photon Laser Ionization (APSPLI) Mass Spectrometry Using a 157 Nm Fluorine Excimer Laser for Sensitive and Selective Detection of Non- to Semi-Polar Hydrocarbons

In this study, atmospheric pressure single photon ionization (APSPLI) mass spectrometry utilizing a fluorine excimer laser operated at 157 nm (7.9 eV) is presented for the first time. For evaluation and optimization, PAH standard mixtures introduced by gas chromatography were used. Atmospheric pressure laser ionization (APLI) approaches with laser wavelengths above 200 nm induce a multiphoton process, and ionization yields are strongly dependent on the heteroatom-content and isomeric structure. The presented technique using VUV photons allowed for the selective ionization of semi- to non-polar compounds in a single photon ionization process. Consequently, molecular radical cations were found as base peak, whereas protonated species were almost absent. Even though the ionization chamber is flushed by a high flow of pure nitrogen, remaining oxygen and water traces caused several side-reactions, leading to unwanted oxidized ionization artifacts. Installation of a water and oxygen filter cartridge significantly reduced the abundance of those artifacts, whereas the laser beam position was found to have a substantially lower effect. For evaluating complex mixture analysis, APSPLI was applied to characterize a light crude oil subjected to the ionization source by thermogravimetry and gas chromatography hyphenation. In addition to aromatic hydrocarbons, APSPLI also allowed for the sensitive ionization of sulfur-containing aromatic constituents, and even species with two sulfur-atoms could be detected. A comparison of APSPLI to APLI conducted at 266 nm revealed the additional compositional space accessible by the single photon process. This novel ionization concept is envisioned to have a high analytical potential further explored in the future.<br>

Atmospheric Pressure Single Photon Laser Ionization (APSPLI) Mass Spectrometry Using a 157 Nm Fluorine Excimer Laser for Sensitive and Selective Detection of Non- to Semi-Polar Hydrocarbons

In this study, atmospheric pressure single photon ionization (APSPLI) mass spectrometry utilizing a fluorine excimer laser operated at 157 nm (7.9 eV) is presented for the first time. For evaluation and optimization, PAH standard mixtures introduced by gas chromatography were used. Atmospheric pressure laser ionization (APLI) approaches with laser wavelengths above 200 nm induce a multiphoton process, and ionization yields are strongly dependent on the heteroatom-content and isomeric structure. The presented technique using VUV photons allowed for the selective ionization of semi- to non-polar compounds in a single photon ionization process. Consequently, molecular radical cations were found as base peak, whereas protonated species were almost absent. Even though the ionization chamber is flushed by a high flow of pure nitrogen, remaining oxygen and water traces caused several side-reactions, leading to unwanted oxidized ionization artifacts. Installation of a water and oxygen filter cartridge significantly reduced the abundance of those artifacts, whereas the laser beam position was found to have a substantially lower effect. For evaluating complex mixture analysis, APSPLI was applied to characterize a light crude oil subjected to the ionization source by thermogravimetry and gas chromatography hyphenation. In addition to aromatic hydrocarbons, APSPLI also allowed for the sensitive ionization of sulfur-containing aromatic constituents, and even species with two sulfur-atoms could be detected. A comparison of APSPLI to APLI conducted at 266 nm revealed the additional compositional space accessible by the single photon process. This novel ionization concept is envisioned to have a high analytical potential further explored in the future.<br>