Comprehensive On-Line Characterization of Complex Gas Mixtures by Quasi-Simultaneous Resonance-Enhanced Multiphoton Ionization, Vacuum-UV Single-Photon Ionization, and Electron Impact Ionization in a Time-of-Flight Mass Spectrometer:  Setup and Instrument Characterization

Abstract

This paper reports on a newly developed mobile mass spectrometer for comprehensive on-line analysis of complex gas mixtures such as ambient air or industrial process gases. Three ionization methods, namely, the resonance-enhanced multiphoton ionization (REMPI), vacuum-ultraviolet single-photon ionization (SPI), and electron impact ionization (EI) are implemented in this instrument and can be operated (quasi-) simultaneously. By means of this setup, a wide range of compounds can be analyzed due to the unique ionization selectivitiy and sensitivity profiles provided by the different ionization techniques. The mass spectrometer is designed for field application even under severe conditions. The REMPI technique is suitable for the selective and soft ionization (without fragmentation) of aromatic compounds at trace level (ppbv/pptv). The also soft but less selective SPI technique with 118-nm vacuum-ultraviolet laser pulses is used as a second laser-based ionization method. Mass spectra obtained by this technique show profiles of most organic compounds (aliphatic and aromatic species) and of some low IP inorganic substances (e.g., ammonia, nitrogen oxide) down to ppbv concentrations. In addition to the laser-based ionization techniques, EI ionization can be used for analysis of the bulk components such as water, oxygen, nitrogen, and carbon dioxide as well as for detection of inorganic minor components such as HCN or HCl from combustion flue gases at ppmv concentration levels. Each method yields specific mass spectrometric information of the sample composition. Special techniques have been developed to combine the three ionization methods in a single mass spectrometer and to allow the quasi-parallel application of all three ionization techniques.

Ionization of EPA Contaminants in Direct and Dopant-Assisted Atmospheric Pressure Photoionization and Atmospheric Pressure Laser Ionization

“…All the PAHs of the present study have IEs well below the two-photon energy. PAHs have been reported to be efficiently ionized by REMPI in several publications, including APLI [13,14,[23][24][25]. However, significantly lower signals were a c h i e v e d f o r a c en a p h t h y l e n e, a n t h r ac e n e , a n d fluorantherene than the seemingly similar acenaphthene, phenanthrene, and pyrene, respectively.…”

Looking into individual coffee beans during the roasting process: direct micro-probe sampling on-line photo-ionisation mass spectrometric analysis of coffee roasting gases

“…Only a short description of the SPI-TOFMS device employed is given here, as the instrumental set-up has been presented in detail elsewhere [36,37]. The system can be operated with two photo-ionisation modes, REMPI and SPI.…”

Online monitoring of coffee roasting by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS): towards a real-time process control for a consistent roast profile

“…An alternative to chemical ionization is selective and soft laser photo ionization using either resonance-enhanced two photon ionization (RE2PI) or vacuum UV single-photon ionization (VUV-SPI) [21][22][23][24][25][26][27][28][29]. RE2PI exhibits a very selective ionization, depending on the functionality and structure of the VOC.…”