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.     

A mobile mass spectrometer for comprehensive on-line analysis of trace and bulk components of complex gas mixtures: parallel application of the laser-based ionization methods VUV single-photon ionization, resonant multiphoton ionization, and laser-induced electron impact ionization

A newly developed compact and mobile time-of-flight mass spectrometer (TOFMS) for on-line analysis and monitoring of complex gas mixtures is presented. The instrument is designed for a (quasi-)simultaneous application of three ionization techniques that exhibit different ionization selectivities. The highly selective resonance-enhanced multiphoton ionization (REMPI) technique, using 266-nm UV laser pulses, is applied for selective and fragmentationless ionization of aromatic compounds at trace levels (parts-per-billion volume range). Mass spectra obtained using this technique show the chemical signature solely of monocyclic (benzene, phenols, etc.) and polycyclic (naphthalene, phenathrene, indol, etc.) aromatic species. Furthermore, the less selective but still fragmentationless single photon ionization (SPI) technique with 118-nm VUV laser pulses allows the ionization of compounds with an ionization potential below 10.5 eV. Mass spectra obtained using this technique show the profile of most organic compounds (aliphatic and aromatic species, like nonane, acetaldehyde, or pyrrol) and some inorganic compounds (e.g., ammonia, nitrogen monoxide). Finally, the nonselective ionization technique laser-induced electron-impact ionization (LEI) is applied. However, the sensitivity of the LEI technique is adjusted to be fairly low. Thus, the LEI signal in the mass spectra gives information on the inorganic bulk constituents of the sample (i.e., compounds such as water, oxygen, nitrogen, and carbon dioxide). Because the three ionization methods (REMPI, SPI, LEI) exhibit largely different ionization selectivities, the isolated application of each method alone solely provides specific mass spectrometric information about the sample composition. Special techniques have been developed and applied which allow the quasi-parallel use of all three ionization techniques for on-line monitoring purposes. Thus, a comprehensive characterization of complex samples is feasible jointly using the characteristic advantages of the three ionization techniques. Laboratory applications show results on rapid overview characterization of mineral oil-based fuels and coffee headspace. The first reported field applications include timely resolved on-line monitoring results on automobile exhausts and of waste incineration flue gas.     

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.     

Laser mass spectrometric analysis of polycyclic aromatic hydrocarbons with wide wavelength range laser multiphoton ionization spectroscopy

In many analytical techniques, 1+1 resonance-enhanced multiphoton ionization (1+1 REMPI) is used because it is an efficient and optically selective soft ionization method. While 1+1 REMPI of jet-cooled molecules has been extensively studied, little has been reported so far about this mechanism as it is used in analytical techniques, that is, in the cases where the molecules are not jet-cooled and where widely varying ionization wavelengths are employed. We used two-step laser mass spectrometry (L2MS) to study the wavelength (238-310 nm) dependence and the laser pulse energy dependence of the ion yield for 17 polycyclic aromatic hydrocarbons (PAHs). We discuss how these data allow prediction of the efficiency of 1+1 REMPI for a given compound. These advances open new perspectives for better understanding the L2MS spectra obtained directly from complex mixtures such as environmental samples.     

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

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.     

In-line catalytic derivatization method for selective detection of chlorinated aromatics with a hyphenated gas chromatography/laser mass spectrometry technique: a concept for comprehensive detection of isomeric ensembles

The combination of gas chromatography (GC) and laser-based resonance-enhanced multiphoton ionization-time-of-flight mass spectrometry (REMPI-TOFMS) represents a three-dimensional analytical method, using the gas chromatographic retention time, the wavelength of the ionization laser for REMPI, and the molecular mass as analytical parameters. In this work, a novel analytical scheme for detection of chlorinated aromatic compounds, including isomeric ensembles, by GC/REMPI-TOFMS is presented. The concept uses an in-line hydrodechlorination catalyst for post- or precolumn derivatization of chlorinated aromatic compounds. The chlorinated aromatics are quantitatively reduced, forming their respective aromatic skeletons. These aromatic skeletons are detected selectively by REMPI-TOFMS. The first results for substance class selective detection of chlorinated benzene isomers are given, and potential applications in the field of the analysis of compounds such as polychlorinated dibenzo-p-dioxins and -furans are discussed.     

Development of a Jet-REMPI (Resonantly Enhanced Multiphoton Ionization) Continuous Monitor for Environmental Applications

The need for a continuous monitor for environmentally important pollutants at realistic [parts-per-trillion (parts in 10(12))] concentrations measured in real time (minutes) is widely recognized. We developed an instrument that is based on supersonic-jet expansion and cooling, followed by resonantly enhanced multiphoton ionization (REMPI) into a mass spectrometer. This approach furnishes the dual selectivity of narrow-band tuned laser absorption and mass analysis. We initiated a spectroscopic characterization of the jet's collisional cooling behavior to optimize the instrument's sensitivity and selectivity, made measurements of several aromatic compounds (including polychlorinated dioxins) by use of a one-color REMPI scheme, and demonstrated a two-color excitation scheme.     

Laser mass spectrometry as on-line sensor for industrial process analysis: process control of coffee roasting

The objective of the project is to develop on-line, real-time, and noninvasive process control tools of coffee roasting that help deliver a consistent and high-quality coffee aroma. The coffee roasting process was analyzed by direct injection of the roaster gas into a time-of-flight mass spectrometer and ionized either by resonance enhanced multiphoton ionization (REMPI) at 266 and 248 nm or vacuum ultraviolet single-photon ionization (VUV-SPI) at 118 nm. The VUV ionization scheme allows detecting mainly the most volatile and abundant compounds of molecular mass below 100 m/z, while REMPI ionizes mainly aromatic compounds of molecular mass larger than 100 m/z. Combining the compounds ionized by resonant and single-photon ionization, approximately 30 volatile organic compounds are monitored in real time. Time-intensity profiles of 10 important volatile coffee compounds were discussed in connection with their formation chemistry during roasting. Applying multivariate statistics (principle component analysis) on time-intensity traces of nine volatile coffee compounds, the roasting degree could be traced as a consistent path in the score plot of the two most significant principle components (including 68% of the total variance), for a range of roasting temperatures (200-250 degrees C).     

Online laser desorption-multiphoton postionization mass spectrometry of individual aerosol particles: molecular source indicators for particles emitted from different traffic-related and wood combustion sources

Direct inlet aerosol mass spectrometry plays an increasingly important role in applied and fundamental aerosol and nanoparticle research. Laser desorption/ionization (LDI) based techniques for single particle time-of-flight mass spectrometry (LDI-SP-TOFMS) are a promising approach in the chemical analysis of single aerosol particles, especially for the detection of inorganic species and distinction of particle classes. However, until now the detection of molecular organic compounds on a single particle basis has been difficult due to the high laser power densities which are required for the LDI process as well as due to the inherent matrix effects associated with this ionization technique. By the application of a two-step approach, where an IR desorption laser pulse is applied to perform a gentle desorption of organic material from the single particle surface and a second UV-laser performs the soft ionization of the desorbed species, this drawback of laser based single particles mass spectrometry can be overcome. The postionization of the desorbed molecules has been accomplished in this work by resonance enhanced multiphoton ionization (REMPI) using a KrF excimer laser (248 nm). REMPI allows an almost fragmentation free trace analysis of polycyclic aromatic hydrocarbons (PAHs) and their derivatives from individual single particles (laser desorption-REMPI postionization-single particle-time-of-flight mass spectrometry or LD-REMPI-SP-TOFMS). Crucial system parameters of the home-built aerosol mass spectrometer such as the power densities and the relative timing of both lasers were optimized with respect to the detectability of particle source specific organic signatures using well characterized standard particles. In a second step, the LD-REMPI-SP-TOFMS system was applied to analyze different real world aerosols (spruce wood combustion, gasoline car exhaust, beech wood combustion, and diesel car exhaust). It was possible to distinguish the particles from different sources by their molecular signature. Finally, exemplary ambient aerosol measurements have been carried out, which demonstrate the potential of the method for investigating urban aerosol and making contributions to source attribution studies.     

Single-photon ionization quadrupole mass spectrometry with an electron beam pumped excimer light source

The application of soft ionization methods for mass spectrometry (MS), such as single-photon ionization (SPI) using vacuum ultraviolet (VUV) light, provides powerful analytical instrumentation for real-time on-line monitoring of organic substances in gaseous matrixes. A compact and mobile quadrupole mass spectrometer (QMS) system using a novel electron beam pumped rare gas VUV lamp for SPI has been developed for on-line analysis of organic trace compounds (ppb concentrations). The VUV radiation of the light source is employed for SPI in the ion source of the QMS. The concept of the interfacing of the VUV light source with the QMS is described and the SPI-QMS is characterized. On-line detection limits down to 50 ppb for benzene, toluene, and m-xylene were achieved. The instrument is well suited for continuous measurements of aromatic and aliphatic trace compounds and can therefore be used for on-line monitoring of trace compounds in dynamically fluctuating process gases. First measurements of gas standards, petrochemical samples, and on-line monitoring of automotive exhaust are presented.     

Real-Time Quantitative Analysis of Combustion-Generated Polycyclic Aromatic Hydrocarbons by Resonance-Enhanced Multiphoton Ionization Time-of-Flight Mass Spectrometry

We have combined resonance-enhanced multiphoton ionization (REMPI) time-of-flight mass spectrometry with on-line flame sampling to determine the centerline concentrations of naphthalene, fluorene, and anthracene in a pure methane + oxygen/argon (1:5) diffusion flame. Naphthalene concentrations between 100 parts per billion by volume (ppbV) and 6 parts per million by volume (ppmV) and fluorene concentrations below 50 ppbV are determined using one-color REMPI on jet-cooled samples extracted from the flame; anthracene concentrations in the 5-40 ppbV range are determined using two-color REMPI. The REMPI ion signals are converted to absolute concentrations in real time by performing gas-phase standard additions to the flame sample. Isomer-selective detection of larger polycyclic aromatic hydrocarbons, such as perylene and benzo[a]pyrene, is possible using the two-color REMPI approach.     

On-line derivatization for resonance-enhanced multiphoton ionization time-of-flight mass spectrometry: detection of aliphatic aldehydes and amines via reactive coupling of aromatic photo ionization labels

Resonance-enhanced multiphoton ionization time-of-flight mass spectrometry (REMPI-TOFMS) is a powerful technique for the on-line analysis of aromatic compounds with unique features regarding selectivity and sensitivity. Aliphatic compounds, however, are difficult to address by REMPI due to their unfavorable photo ionization properties. This paper describes the proof of concept for an on-line derivatization approach for converting nonaromatic target analytes into specific, photoionizable aromatic derivatives that are readily detectable by REMPI-TOFMS. A multichannel silicone trap or poly(dimethylsiloxane) (PDMS) open tubular capillary was used as a reaction medium for the derivatization of volatile alkyl aldehydes and alkylamines with aromatic "photoionization labels"and to concentrate the resulting aromatic derivatives. The aldehydes formaldehyde, acetaldehyde, acrolein, and crotonal, which when underivatized are poorly detectable by REMPI, were converted into their easily photoionizable phenylhydrazone derivatives by the on-line reaction with phenylhydrazine as reagent. Similarly, the methyl-, ethyl-, propyl-, and butylamines were converted into their REMPI-ionizable benzaldehyde alkylimine derivatives by the on-line reaction with benzaldehyde as reagent. The derivatives were thermally desorbed from the PDMS matrix and transferred into the REMPI-TOFMS for detection. The REMPI-TOFMS detection limits obtained for acetaldehyde; acrolein; crotonal; and methyl-, ethyl-, propyl-, and butylamine using this photo ionization labeling method were in the sub-parts-per-million range and, thus, readily below the permissible exposure limits set by OSHA.     

Simultaneous measurement of nitric oxide (NO) and nitrogen dioxide (NO2) in simulated automobile exhaust using medium pressure ionization-mass spectrometry

In previous papers we have demonstrated two different, two-color resonance-enhanced multiphoton ionization (REMPI) schemes for the simultaneous measurement of trace amounts (ppbV to pptV) of nitrogen monoxide (NO) and nitrogen dioxide (NO(2)). The goal of this study is to provide a laser ionization-mass spectrometric scheme capable of measuring ppmV to ppthV concentrations of NO and NO(2) within vehicle exhaust containing up to ppthV of aromatic hydrocarbons and a time frame of seconds. Two ionization schemes are used here to measure NO and NO(2) in simulated automobile exhaust with three different sources. REMPI Scheme 1 uses broad-bandwidth light and an effusive source to measure NO (limit of detection (LOD) 300 ppmV), NO(2) (LOD 100 ppmV), and aromatic hydrocarbons (via photoionization) along with fragments (via electron impact). REMPI Scheme 2 uses narrow-bandwidth light and a medium pressure laser ionization (MPLI) source to measure NO (LOD 60 ppmV), NO(2) (LOD 3 ppmV), and fragments (via electron impact). The LOD is determined using 10-second sampling times. A newly developed delayed-ion extraction technique for MPLI is then applied to REMPI Scheme 2, dramatically reducing the electron impact signal, so that only NO and NO(2) are observed. We conclude that Scheme 2 with delayed-electron extraction is best suited for measuring in situ NO and NO(2) within engine exhaust.     

Online comprehensive two-dimensional characterization of puff-by-puff resolved cigarette smoke by hyphenation of fast gas chromatography to single-photon ionization time-of-flight mass spectrometry: quantification of hazardous volatile organic compounds

This work presents the direct coupling of a custom-made smoking machine (SM) to fast gas chromatography combined with single-photon ionization mass spectrometry (GC × SPI-MS) utilizing a six-port, two-position valve for online puff-resolved comprehensive two-dimensional investigation of cigarette smoke. The innovative electron-beam pumped rare gas excimer light source (EBEL) filled with argon provided vacuum ultraviolet (VUV) photons of 9.8 ± 0.4 eV (126 ± 9 nm) for SPI. Puff-by-puff quantification of 14 hazardous volatile organic smoke constituents from the 2R4F Kentucky research cigarette was enabled for two smoking regimes, i.e., ISO and Canadian Intense, after determination of photoionization cross sections. The investigated analytes comprised NO, acetaldehyde, butadiene, acrolein, propanal, acetone, isoprene, furan, crotonaldehyde, isobutanal, butanal, 2-butanone, benzene, and toluene. The determined amounts of these compounds in cigarette smoke agreed excellently with the literature values. Furthermore, the two well-known patterns of puff-by-puff behaviors for these different smoke constituents were obtained for both whole smoke and gas-phase measurements.     

Experiments concerning resonance-enhanced multiphoton ionization probe measurements of flame-species profiles

Resonance-enhanced multiphoton ionization (REMPI) detection of radical species in low-pressure laboratory flames is a promising tool for the development and refinement of combustion models. For accurate REMPI species concentration measurements in flame zones with inherently high background ionization levels, an understanding of the influence of plasma sheaths on REMPI probe response is required. Proper probe response is found to depend on careful control of probe-biasing and laserfocusing conditions. Only negatively biased probes are suitable, because of the influences of secondary ionization on the response of positively biased probes. In situ probe calibration procedures with the (2 + 2) REMPI of N(2) at 270.6 nm are described. Detection of O atoms in a stoichiometric 20-Torr methane-oxygen flame permits a precise comparison of both laser-induced fluorescence and REMPI measurements with flame-modeling results.     

Single photon ionization (SPI) via incoherent VUV-excimer light: robust and compact time-of-flight mass spectrometer for on-line,real-time process gas analysis

Fast on-line detection of organic compounds from complex mixtures, such as industrial process gas streams, require selective and sensitive analytical methods. One feasible approach for this purpose is the use of mass spectrometry (MS) with a selective and soft (fragment-free) ionization technique, such as chemical ionization (CI) or photo ionization (PI). Single photon ionization (SPI) with vacuum ultraviolet (VUV) light is a particularly sof tionization technique, well-suited for detection of both aromatic and aliphatic species. Problematic, however, is the generation of the VUV light. In general, the vacuum ultraviolet (VUV) light sources for SPI-MS are based either on lasers (e.g., 118-nm radiation generated by frequency-tripling of the third harmonic of a Nd:YAG laser) or on conventional VUV lamps, such as deuterium lamps. Althoughthe laser-based techniques are very sophisticated and expensive, the conventional lamps have serious drawbacks regarding their optical parameters, such as low-output power, low spectral power density, and broad emission bands. In this work, a novel excimer VUV light source, in which an electron beam is used to form rare gas excimer species, is used. The excimer VUV light sourceproduces brilliant and intense VUV light. The novel VUV light source was coupled to a compact and mobile time-of-flight mass spectrometer (TOFMS). A special interface design, including optical (VUV optics) as well as electronic measures (e.g., pulsed ion extraction) was realized. The use of the excimer VUV lamp for SPI will allow the realization of very compact, rugged, and sensitive SPI-TOFMS devices, which preferably will be adapted for process analytical application or monitoring issues (e.g., chemical warfare detection). The excimer VUV-lamp technology delivers VUV light with a good beam quality and high-output power at low costs. Furthermore, it allows changing the emitted wavelength as well as the bandwidth of the excimer VUV lamp in t he 100-200-nm region by changing the gas filling. Consequently, SPI-TOFMS with an excimer light source is a fast detection technique that can be used for online monitoring, for example, in environmental studies or industrial manufacturing processes. In this paper, technology and characteristics of the new excimer light source, as well as the combination with the TOFMS, are presented. Furthermore, a first characterization of the SPI-TOFMS instrument, regarding analytical parameters such as detection limits and selectivity, is given. This includes a discussion of potential improvements that probably will be achievable within a future prototype genertation. Finally, first applications of the system for on-line measurement of organic trace species in a complex gas mixture (here, motorcycle exhaust gas) are presented.     

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.     

On-Line Emission Analysis of Polycyclic Aromatic Hydrocarbons down to pptv Concentration Levels in the Flue Gas of an Incineration Pilot Plant with a Mobile Resonance-Enhanced Multiphoton Ionization Time-of-Flight Mass Spectrometer

A newly developed, mobile laser mass spectrometer (resonance-enhanced multiphoton ionization - time-of-flight mass spectrometer, REMPI-TOFMS) was applied to on-line measurements at a waste incineration pilot plant. REMPI-TOFMS combines the optical selectivity of resonance-enhanced multiphoton ionization with a time-of-flight mass analysis to give a two-dimensional analytical method. Special care was taken to build up a sampling and inlet system suitable for on-line measurements of large, semivolatile polycyclic aromatic hydrocarbons (PAHs). An effusive molecular beam inlet in combination with a fixed frequency UV laser (Nd:YAG at 266 nm or KrF excimer at 248 nm) was used. Under these conditions, many different PAHs can be ionized selectively from the complex flue gas matrix. For example, the achieved detection limit for naphthalene is in the 10 parts-per-trillion by volume (pptv) concentration range. Calibration was performed by using external concentration standards supplied in low ppbv concentrations. The instrumentation is sufficiently robust to be operated under industrial conditions at incineration plants, for instance. The REMPI mass spectra can be acquired at 5-50 Hz. Time profiles of the concentrations of different PAHs in the flue gas were monitored with a time resolution of 200 ms. Significant variations in the concentration profile of several PAHs up to mass 276 amu (e.g., benzo[ghi]perylene) and methylated PAHs have been observed while combustion parameters were changing. In summary, it was demonstrated that laser mass spectrometry (REMPI-TOFMS) enables a real-time on-line trace analysis of combustion flue gases or industrial process gases.     

Derivatization of surface-bound peptides for mass spectrometric detection via threshold single photon ionization

Chemical derivatization of peptides allows efficient F2 laser single photon ionization (SPI) of Fmoc-derivatized peptides covalently bound to surfaces. Laser desorption photoionization mass spectrometry using 337-nm pulses for desorption and 157.6-nm pulses for threshold SPI forms large ions identified as common peptide fragments bound to either Fmoc or the surface linker. Electronic structure calculations indicate the Fmoc label is behaving as an ionization tag for the entire peptide, lowering the ionization potential of the complex below the 7.87-eV photon energy. This method should allow detection of many molecular species covalently or electrostatically bound to surfaces.