High-resolution time and spatial imaging of tobacco and its pyrolysis products during a cigarette puff by microprobe sampling photoionisation mass spectrometry

The time- and space-resolved chemical signatures of gases and vapours formed in solid-state combustion processes are difficult to examine using recent analytical techniques. A machine-smoked cigarette represents a very reproducible model system for dynamic solid-state combustion. By using a special sampling system (microprobe unit) that extracts the formed gases from inside of the burning cigarette, which is coupled to a photoionisation mass spectrometer, it was possible to study the evolution of organic gases during a 2-s cigarette puff. The concentrations of various pyrolysis and combustion products such as 1,3-butadiene, toluene, acetaldehyde and phenol were monitored on-line at different sampling points within cigarettes. A near-microscopic-scale spatial resolution and a 200-ms time resolution were achieved. Finally, the recorded information was combined to generate time-resolved concentration maps, showing the formation and destruction zones of the investigated compounds in the burning cigarette. The combustion zone at the tip of cigarette, where e.g. 1,3-butadiene is predominately formed, was clearly separable from the pyrolysis zones. Depending on the stability of the precursor (e.g. lignin or cellulose), the position of pyrolytic formation varies. In conclusion, it was demonstrated that soft photoionisation mass spectrometry in conjunction with a microprobe sampling device can be used for time- and space-resolved analysis of combustion and pyrolysis reactions. In addition to studies on the model cigarette, further model systems may be studied with this approach. This may include further studies on the combustion of biomass or coal chunks, on heterogeneously catalysed reactions or on spray, dust and gas combustion processes.

Particle emissions from a marine engine: chemical composition and aromatic emission profiles under various operating conditions

The chemical composition of particulate matter (PM) emissions from a medium-speed four-stroke marine engine, operated on both heavy fuel oil (HFO) and distillate fuel (DF), was studied under various operating conditions. PM emission factors for organic matter, elemental carbon (soot), inorganic species and a variety of organic compounds were determined. In addition, the molecular composition of aromatic organic matter was analyzed using a novel coupling of a thermal-optical carbon analyzer with a resonance-enhanced multiphoton ionization (REMPI) mass spectrometer. The polycyclic aromatic hydrocarbons (PAHs) were predominantly present in an alkylated form, and the composition of the aromatic organic matter in emissions clearly resembled that of fuel. The emissions of species known to be hazardous to health (PAH, Oxy-PAH, N-PAH, transition metals) were significantly higher from HFO than from DF operation, at all engine loads. In contrast, DF usage generated higher elemental carbon emissions than HFO at typical load points (50% and 75%) for marine operation. Thus, according to this study, the sulfur emission regulations that force the usage of low-sulfur distillate fuels will also substantially decrease the emissions of currently unregulated hazardous species. However, the emissions of soot may even increase if the fuel injection system is optimized for HFO operation.

On-line process monitoring of coffee roasting by resonant laser ionisation time-of-flight mass spectrometry: bridging the gap from industrial batch roasting to flavour formation inside an individual coffee bean

Resonance-enhanced multiphoton ionisation time-of-flight mass spectrometry (REMPI-TOFMS) enables the fast and sensitive on-line monitoring of volatile organic compounds (VOC) formed during coffee roasting. On the one hand, REMPI-TOFMS was applied to monitor roasting gases of an industrial roaster (1500 kg/h capacity), with the aim of determining the roast degree in real-time from the transient chemical signature of VOCs. On the other hand, a previously developed μ-probe sampling device was used to analyse roasting gases from individual coffee beans. The aim was to explore fundamental processes at the individual bean level and link these to phenomena at the batch level. The pioneering single-bean experiments were conducted in two configurations: (1) VOCs formed inside a bean were sampled in situ, i.e. via a drilled μ-hole, from the interior, using a μ-probe (inside). (2) VOCs were sampled on-line in close vicinity of a single coffee bean's surface (outside). The focus was on VOCs originating from hydrolysis and pyrolytic degradation of chlorogenic acids, like feruloyl quinic acid and caffeoyl quinic acid. The single bean experiments revealed interesting phenomena. First, differences in time-intensity profiles between inside versus outside (time shift of maximum) were observed and tentatively linked to the permeability of the bean's cell walls material. Second, sharp bursts of some VOCs were observed, while others did exhibit smooth release curves. It is believed that these reflect a direct observation of bean popping during roasting. Finally, discrimination between Coffea arabica and Coffea canephora was demonstrated based on high-mass volatile markers, exclusively present in spectra of Coffea arabica.

Time-resolved analysis of the emission of sidestream smoke (SSS) from cigarettes during smoking by photo ionisation/time-of-flight mass spectrometry (PI-TOFMS): towards a better description of environmental tobacco smoke

In this study, the chemical composition of sidestream smoke (SSS) emissions of cigarettes are characterised using a laser-based single-photon ionisation time-of-flight mass spectrometer. SSS is generated from various cigarette types (2R4F research cigarette; Burley, Oriental and Virginia single-tobacco-type cigarettes) smoked on a single-port smoking machine and collected using a so-called fishtail chimney device. Using this setup, a puff-resolved quantification of several SSS components was performed. Investigations of the dynamics of SSS emissions show that concentration profiles of various substances can be categorised into several groups, either depending on the occurrence of a puff or uninfluenced by the changes in the burning zone during puffing. The SSS emissions occurring directly after a puff strongly resemble the composition of mainstream smoke (MSS). In the smouldering phase, clear differences between MSS and SSS are observed. The changed chemical profiles of SSS and MSS might be also of importance on environmental tobacco smoke which is largely determined by SSS. Additionally, the chemical composition of the SSS is strongly affected by the tobacco type. Hence, the higher nitrogen content of Burley tobacco leads to the detection of increased amounts of nitrogen-containing substances in SSS.

Experimental and statistical determination of indicator parameters for the evaluation of fly ash and boiler ash PCDD/PCDF concentration from municipal solid waste incinerators

On-line detectable indicator parameters in the flue gas of municipal solid waste incinerators (MSWI) such as chlorinated benzenes (PCBz) are well known surrogate compounds for gas-phase PCDD/PCDF concentration. In the here presented work derivation of indicators is broadened to the detection of fly and boiler ash fractions with increased PCDD/PCDF content. Subsequently these fractions could be subject to further treatment such as recirculation in the combustion chamber to destroy their PCDD/PCDF and other organic pollutants' content. Aim of this work was to detect suitable on-line detectable indicator parameters in the gas phase, which are well correlated to PCDD/PCDF concentration in the solid residues. For this, solid residues and gas-phase samples were taken at three MSWI plants in Bavaria. Analysis of the ash content from different plants yielded a broad variation range of PCDD/PCDF concentrations especially after disturbed combustion conditions. Even during normal operation conditions significantly increased PCDD/PCDF concentrations may occur after unanticipated disturbances. Statistical evaluation of gas phase and ash measurements was carried out by means of principal component analysis, uni- and multivariate correlation analysis. Surprisingly, well known indicators for gas-phase PCDD/PCDF concentration such as polychlorinated benzenes and phenols proved to be insufficiently correlated to PCDD/PCDF content of the solid residues. Moreover, no single parameter alone was found appropriate to describe the PCDD/PCDF content of fly and boiler ashes. On the other hand, multivariate fitting of three or four parameters yielded convenient correlation coefficients of at least r=0.8 for every investigated case. Thereby, comprehension of plant operation parameters such as temperatures and air flow alongside concentrations of inorganic compounds in the gas phase (HCl, CO, SO2, NOx) gave the best results. However, the suitable set of parameters suited best for estimation of PCDD/PCDF concentration in solid residues has to be derived anew for each individual plant and type of ash.

Changes in PCDD/PCDF formation processes during instationary phases of combustor operation--exemplified by the use of Cl4DD isomer patterns

In this paper results of various measurement campaigns at different municipal waste incineration (MWI) plants concerning the change of the PCDD/PCDF isomer distribution in the crude gas during transiently impaired combustion conditions are presented. The focus is on the Cl4DD isomer distributions exemplarily for all other homologue groups to demonstrate the change in PCDD/PCDF formation mechanism at transient combustion conditions. Additionally to crude gas samples, at one plant filter and boiler ash were investigated simultaneously to determine if there is any difference in the isomer distribution between the matrices. For the ash from an electrostatic precipitator (ESP ash), the boiler ash and the corresponding crude gas sample, nearly identical changes in the Cl4DD isomer distribution under transient combustion conditions in relation to the normal operation process could be detected. By comparing the Cl4DD isomer distributions from different incineration plants (two municipal waste incinerators and one little incinerator burning wood chips for heating domestic household) under transient combustion conditions, in all cases the 1,3,6,8- and 1,3,7,9-Cl4DD were dominating the isomer distribution, whereas under normal operation other isomers were predominant. Obviously PCDD/PCDF formation mechanisms under transient combustion conditions are independent from the type of incinerator and of the burned fuel, respectively. Data sets were analyzed with respect to the possible reaction mechanism via chlorophenols and a good correlation of 2,4,6-trichlorophenol during the second phase of a start-up process and during a CO experiment was found. To get more detailed information about possible formation mechanisms, at one plant the dependence of the PCDD/PCDF isomer distribution on the different matrices was studied. Separate analysis of fly ash collected at the boiler exit, subsequent gas phase, ESP ash and boiler ash under normal operation conditions showed that, apart from the fly ash, the Cl4DD isomer distributions are nearly the same in the different matrices. Surprisingly, the Cl4DD isomer distribution of the fly ash was more similar to the distributions found under transient combustion conditions.

Resonance-enhanced multiphoton ionization time-of-flight mass spectrometry for detection of nitrogen containing aliphatic and aromatic compounds: resonance-enhanced multiphoton ionization spectroscopic investigation and on-line analytical application

Resonance-enhanced multiphoton ionization (REMPI) combined with time-of-flight mass spectrometry (TOFMS) is an analytical method capable of on-line monitoring of trace compounds in complex matrices. A necessary prerequisite for substance selective detection is spectroscopic investigation of the target molecules. Several organic nitrogen compounds comprising aliphatic and aromatic amines, nitrogen heterocyclic compounds, and aromatic nitriles are spectroscopically investigated with a tunable narrow bandwidth optical parametric oscillator (OPO) laser system providing a scannable wavelength range between 220 and 340 nm. These species are known as possible precursors in fuel-NO formation from combustion of solid fuels such as biomass and waste. A newly conceived double inlet system was used in this study, which allows rapid change between effusive and supersonic molecular beams. The resulting REMPI spectra of the compounds are discussed with respect to electronic transitions that could be utilized for a selective ionization of these compounds in complex mixtures such as combustion and process gases. The practicability of this approach is demonstrated by wavelength selected on-line REMPI-TOFMS detection of aniline and cyanonaphthalene in the burning chamber of a waste incineration plant. REMPI mass spectra recorded at different excitation wavelengths as well as variations in time show the utilization of species-selective REMPI-TOFMS detection for on-line monitoring of crucial substances in pollutant formation.

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

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.

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

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.

Investigation of NO x precursor compounds and other combustion by-products in the primary combustion zone of a waste-incineration plant using on-line, real-time mass spectrometry and Fourier-transform infrared spectrometry (FTIR)

On-line analysis of trace and bulk gas compounds in the burning chamber of a waste-incineration plant has been performed, with high temporal resolution, by use of a variety of distinctly different measurement techniques. Time-of-flight mass spectrometry was performed with simultaneous use of three ionization techniques-resonance-enhanced multiphoton ionization (REMPI), single-photon ionization (SPI), and electron-impact ionization (EI). Chemical-ionization mass spectrometry (CIMS), Fourier-transform infrared spectrometry (FTIR), and electrochemical methods were also used. Sampling was conducted by means of a newly developed air-cooled stainless steel lance, to cope with the high temperatures and elevated particle concentrations at the sampling location. Nitrogen species were mainly nitrogen monoxide, ammonia, and hydrogen cyanide (HCN), with a small amount (approximately 0.3%) of aromatic nitrogen compounds. NO, NH(3), and HCN are the main contributors to the NO(x)-formation process in the postulated fuel-NO reaction scheme dominant at this location. The NO recycling process thereby plays a major role. Changes in plant operating conditions have a noticeable impact only when the air supply is varied. For example, reduction of oxygen leads to an increase in the HCN fraction of the total nitrogen content and a decrease in the NO fraction, and vice versa.

Discrimination of three tobacco types (Burley, Virginia and Oriental) by pyrolysis single-photon ionisation-time-of-flight mass spectrometry and advanced statistical methods

Pyrolysis single-photon ionisation (SPI)-time-of-flight mass spectrometry (TOFMS) and statistical analysis techniques have been applied to differentiate three major tobacco types, Burley, Virginia and Oriental, by means of the gas phase. SPI is known as a soft ionisation technique that allows fast and comprehensive on-line monitoring of a large variety of aliphatic and aromatic substances without fragmentation of the molecule ions. The tobacco samples were pyrolysed at 800 degrees C in a nitrogen atmosphere. The resulting pyrolysis gas contained signals from more than 70 masses between m/z 5 and 170. Mass spectra obtained were analysed by principal component analysis (PCA) and linear discriminant analysis (LDA) to distinguish between different tobacco types. Prior variable reduction of the data set was carried out by calculation of the Fisher ratios. Results achieved give information about chemical composition and characteristics of the smoke derived from each tobacco type and enable conclusions on plant cultivation to be drawn. Based on LDA, a model for tobacco type recognition of unknown samples was established, which was cross-checked by additional measurements of each tobacco type. Furthermore, first results on the recognition of tobacco mixtures based on principal component regression (PCR) are presented.

Resonance-Enhanced Multiphoton Ionization and VUV-Single Photon Ionization as Soft and Selective Laser Ionization Methods for On-Line Time-of-Flight Mass Spectrometry: Investigation of the Pyrolysis of Typical Organic Contaminants in the Steel Recycling Process

A newly conceived compact and mobile time-of flight mass spectrometer (TOFMS) for real-time monitoring of highly complex gas mixtures is presented. The device utilizes two selective and sensitive soft ionization techniques, viz., resonance-enhanced multiphoton ionization (REMPI) and single-photon ionization (SPI) in a (quasi)-simultaneous mode. Both methods allow a fragmentationless ionization. The REMPI method selectively addresses aromatic species, while with SPI applying vacuum ultaviolet light (118 nm) in principle all compounds with an ionization potential below 10.5 eV are accessible. This provides comprehensive information of the chemical composition of complex matrixes. The combustion and pyrolysis behavior of five organic materials typically used in steel processing in China was studied. The trace amounts of organic compounds in the gas phase during combustion and pyrolysis were monitored selectively and sensitively by real-time SPI/REMPI-TOFMS. The measurements were carried out at several constant temperatures in the range from 300 to 1190 degrees C in both synthetic air and nitrogen. Timely resolved mass spectra reveal the formation and subsequent growth of aromatic molecules. At lower temperatures, highly alkylated PAHs predominate, while at temperatures above 800 degrees C, the more stable benzene and PAHs without side chains prevail. Potential hyphenation of SPI/REMPI-TOFMS to methods of thermal analysis is discussed.

Cosmic ray radiation effects caused by proton-induced fragmentation

In space, radiation effects in which a large amount of energy is transferred by a single particle are observed. These effects can be caused by either the direct ionization of a cosmic ray heavy ion or alternatively by the ionization of short range target fragments which are produced inside the material by interactions of cosmic ray particles. Protons of the lower radiation belt contribute significantly to target fragmentation; especially in the South Atlantic Anomaly (SAA). To allow predictions of possible radiation hazards the characteristics of these interactions at energies below 100 MeV must be understood in detail. We have performed an experiment to measure the proton induced fragmentation cross sections for carbon target nuclei at about 70 MeV/nucleon and to determine some characteristics of the kinematics of the target fragments. For this purpose experimental setups with CR-39 track detectors were used. In this paper we describe the experimental technique and present some preliminary results.

Energy spectrum of iron nuclei measured inside the MIR space craft using CR-39 track detectors

We have exposed stacks of CR-39 plastic nuclear track detectors inside the MIR space craft during the EUROMIR95 space mission for almost 6 months. Over this long period a large number of tracks of high LET events was accumulated in the detector foils. The etching and measuring conditions for this experiment were optimized to detect tracks of stopping iron nuclei. We found 185 stopping iron nuclei inside the stack and identified their trajectories through the material of the experiment. Based on the energy-range relation the energy at the surface of the stack was determined. These particles allow the determination of the low energy part of the spectrum of iron nuclei behind shielding material inside the MIR station.

The high-LET radiation component measured during the EUROMIR-94 mission

Stacks of CR-39 plastic nuclear track detectors were mounted inside the MIR-station during the EUROMIR-94-mission. We present LET-spectra determined separately for long range cosmic ray heavy ions and for short range target fragments produced in nuclear interactions of cosmic rays and measured charge distributions for relativistic and stopping particles.