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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.

Laser induced Resonance-Enhanced Multi-Photon Ionization Time-Of-Flight Mass Spectrometry (REMPI TOFMS) is a highly selective as well as sensitive analytical technique, well suited for species selective, on-line monitoring of trace-substances. In this contribution some analytical applications of a mobile REMPI-TOFMS are presented. This includes REMPI-TOMS on-line analysis of coffee roasting gas and waste incineration flue gas as well as headspace measurements of pulp processing lye or rapid analysis of polycyclic aromatic hydrocarbons from soil samples via thermal desorption.

A novel interface for hyphenation of gas chromatography (GC), resonance enhanced multi-photon ionization (Jet-REMPI) spectroscopy and mass spectrometry (MS) for organic trace analysis is presented. Technical details and results are given in this contribution.

A concept for the use of Resonance Ionization Laser Mass Spectrometry for on-line emission analysis of chlorinated aromatic compounds in waste incinerator flue gas is presented. New analytical results suggest that low chlorinated benzenes can be used as indicator parameter for dioxin emissions.

Resonance-enhanced multi-photon ionization time-of-flight mass spectrometry (REMPI/TOFMS) has been applied to the detection of volatiles in the headspace of brewed coffee and in the coffee roasting process-gas. A frequency quadrupled Nd:YAG laser (266 nm) was used for REMPI ionization (REMPI@266nm) of the volatiles in an effusive molecular beam inside the ion source of a linear TOF mass spectrometer. A special sampling system provided a time correlated sampling. Under these circumstances REMPI@266nm is highly selective for ionization of phenolic compounds. Several phenolic compounds, such as the flavour-active 4-vinylguaiacol, can be detected in the headspace of coffee brew as well as in the roast off-gas with the application of this approach. Moreover, the nitrogen heterocyclic compounds, indole and caffeine, were detected in both cases. During the roasting process the relative changes in concentration of some volatile components of coffee have been recorded by EMPI@266nm with a time resolution of 1 Hz. The different volatiles exhibit characteristic concentration profiles as a function of the roast time. These results demonstrate the applicability of REMPI-TOFMS for on-line monitoring of coffee processing technologies. Such an on-line monitoring technique is of particular interest for process-control purposes, e.g. quality-protection or feedback process control. For example, monitoring of off-gases from the coffee roast process or monitoring of certain unit operations during the instant-coffee manufacturing could be promising industrial applications.

Resonance-enhanced multiphoton ionization (REMPI) allows different degrees of optical ionization selectivity. The selectivity achievable with the REMPI-method is compared with that of other ionization methods for on-line mass spectrometry. “Semiselective” REMPI with effusive molecular beam inlet allows group selective ionization of mono- and polycyclic aromatic compounds and their methylated derivatives (REMPI at 266 nm). The patterns of the above mentioned aromatic compounds in flue gases can be used for characterization of industrial combustion processes. In this work, a novel approach of “semi-selective” REMPI for measure ment of the patterns of mono- and polycyclic aromatic compounds, with additional simultaneous target compound monitoring, is presented. By using REMPI at 269.8 nm monochloro benzene, which is an important indicator for the toxicity of the flue gas, can be monitored, together with the other aromatics. On-line recorded REMPI mass spectra from the flue gas of an industrial hazardous waste incineration plant are presented. The applications of REMPI on-line monitoring at incineration plants are discussed.