On-line real-time analysis of organic compounds in mainstream tobacco smoke: An optimised coupling between a commercial smoke machine and fast photo-ionisation time-of-flight mass spectrometry
Since the chemical properties of tobacco smoke are changing very rapidly during the smoking process, time-resolved analysis is required to better understand the chemistry of smoking. Puff-resolved analysis of tobacco smoke can be done by conventional off-line analysis methods ( e.g. by gas chromatography/mass spectrometry) but are rather difficult and time-consuming. Recently it was demonstrated that single-photon ionisation (SPI) with vacuum-ultraviolet (VUV) light in combination with mass spectrometry (MS) is a promising tool for puff-by-puff resolved characterization of tobacco mainstream smoke in real time. SPI allows an efficient and soft ionisation of organic compounds, yielding mass spectra without fragment peaks. Furthermore, some selectivity is provided via the ionisation energy threshold (IP), as only compounds with an ionisation potential (IP) lower than the photon energy are ionized. For fast on-line, real-time measurements of the tobacco smoking process however, time-of-flight mass spectrometry (TOFMS) is predestined, as only TOFMS can record simultaneously all masses with very high repetition rates. Scanning MS systems, such as ion trap or quadrupole systems, on the other hand only can record a single mass at one time. In this work the coupling of an innovative ultra compact TOFMS system (TOFWERK AG, Thun, Switzerland) equipped with a novel VUV-lamp system (TUI-Laser AG, München, Germany) for SPI to a modern programmable smoke machine (Borgwaldt, Hamburg, Germany) is described. The TOFMS is equipped with a fast orthogonal acceleration ion source and records transients with up to 50 kHz. The high repetition frequency leads to a very good signal/noise ratio and dynamic range without loss of time resolution. Detection limits in the low parts-per-billion (ppb) range are easily achieved. Our previous experiments have showTTn how decisive the correct interfacing between smoking machine and MS analyzer is for reliable and quantitative puff resolved on-line analysis of organic compounds. A suitable venting- and cleaning puff-system as well as a specially designed transfer technology is important to ensure puff- and even sub-puff-resolution by minimization of condensation and memory effects of smoke constituents. The experimental setup of the coupled system is described and application data are shown. The coupled system is extremely well suited for continuous measurements of aromatic and aliphatic trace compounds in cigarette mainstream smoke on a puff-by-puff resolved basis. As electron impact ionisation can also be applied, small inorganic molecules, such as carbon dioxide or water can also be analysed. Application data will be shown and discussed.