Single Photon Ionization Time-of-Flight Mass Spectrometry with a Pulsed Electron Beam Pumped Excimer VUV Lamp for On-Line Gas Analysis:  Setup and First Results on Cigarette Smoke and Human Breath

Abstract

Single-photon ionization (SPI) using vacuum ultraviolet (VUV) light produced by an electron beam pumped rare gas excimer source has been coupled to a compact and mobile time-of-flight mass spectrometer (TOFMS). The novel device enables real-time on-line monitoring of organic trace substances in complex gaseous matrixes down to the ppb range. The pulsed VUV radiation of the light source is employed for SPI in the ion source of the TOFMS. Ion extraction is also carried out in a pulsed mode with a short time delay with respect to ionization. The experimental setup of the interface VUV light source/time-of-flight mass spectrometer is described, and the novel SPI-TOFMS system is characterized by means of standard calibration gases. Limits of detection down to 50 ppb for aliphatic and aromatic hydrocarbons were achieved. First on-line applications comprised real-time measurements of aromatic and aliphatic trace compounds in mainstream cigarette smoke, which represents a highly dynamic fluctuating gaseous matrix. Time resolution was sufficient to monitor the smoking process on a puff-by-puff resolved basis. Furthermore, human breath analysis has been carried out to detect differences in the breath of a smoker and a nonsmoker, respectively. Several well-known biomarkers for smoke could be identified in the smoker's breath. The possibility for even shorter measurement times while maintaining the achieved sensitivity makes this new device a promising tool for on-line analysis of organic trace compounds in process gases or biological systems.

Electron beam induced light emission

“…Brilliant VUV excimer light sources have been developed. They are for example very successfully used in the ion sources of mass spectrometers for so called single photon ionization (SPI) which leads to mass spectra which are essentially free of fragmentation of the analyte molecules [22][23][24]. In test experiments the electron beam has also been used to induce chemical reactions (so called gas reformation), for example for hydrogen enrichment of fuel gases [25].…”

Pulsed electron beams in ion mobility spectrometry

“…This requires an exit window that is stable enough to uphold the vacuum inside the tube without leading to a high loss of electrons when they penetrate the window. A suitable device has been developed by (Wieser et al 1997 ), which has been applied, for example, in plasma experiments and other analytical chemistry-related applications ( M ü hlberger et al 2005( M ü hlberger et al , Morozov et al 2006( M ü hlberger et al , 2008a. The following part describes this source and its application in IMS spectrometers, together with the innovative analysis of IMS signal decay curves.…”

Real-time monitoring of trace-level VOCs by an ultrasensitive lamp-based VUV photoionization mass spectrometer

“…However, they suffer from limitations such as the use of expensive, bulky, and sophisticated laser systems to achieve nonlinear optical processes (Muhlberger et al, 2002). Meanwhile, the lamp-based vacuum ultraviolet photoionization MS (VUV-PIMS) is another type of instrument that has been attracting significant attention (Muhlberger et al, 2005a). Mühlberger et al (2007Mühlberger et al ( , 2005a2002) have developed a series of VUV-PIMSs with an electron-beam-pumped rare gas excimer VUV lamp.…”