Hans Jörg Heger

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.

A Mobile Resonance-enhanced Multiphoton Ionization Time-of-flight Mass Spectrometry Device for On-line Analysis of Aromatic Pollutants in Waste Incinerator Flue Gases: First Results

We have applied a newly designed, mobile, resonance-enhanced multiphoton ionization (REMPI) time-of-flight mass spectrometer for real-time on-line emission analysis of flue gases from a technical waste incineration pilot plant. With one-color REMPI (laser wavelength: 248 nm), benzene, toluene, phenol, several polycyclic aromatic hydrocarbons (PAH, here naphthalene, anthracene/phenanthrene, pyrene etc.) and methylated PAH were detected in the flue gas, mostly in the 10-100 ppb concentration range. Time resolutions up to 5 Hz were achieved. A change of combustion process operating conditions caused significant variations in the time-intensity profiles of different combustion products. This demonstrates the feasibility of the REMPI approach for real-time on-line trace analysis of process gases and combustion flue gases. Numerous practical industrial applications, ranging from emission monitoring and control, to process control in the chemical, mineral oil, or food industries, and to quality control are possible.

On-line measurement of chlorobenzene in waste incineration flue gas as a surrogate for the emission of polychlorinated dibenzo-p-dioxins/furans (I-TEQ) using mobile resonance laser ionization time-of-flight mass spectrometry

Mobile resonance-enhanced multiphoton ionization time-of-flight mass spectrometry (REMPI-TOFMS) was applied for on-line detection of surrogates for polychlorinated dibenzo-p-dioxins/furans (PCDD/F) in the flue gas of an industrial hazardous waste incineration plant (thermal power: 22 MW). Conventional gas chromatography/mass spectrometry (GC/MS) measurements have been performed to establish an indicator relation between the best suited surrogate (monochlorobenzene) and the PCDD/F concentration in the flue gas (measured in international toxicity equivalents, I-TEQ). The indicator relation allows the estimation of the actual PCDD/F emission from the on-line registered MCBz signal. Furthermore, several other aromatic components have been measured on-line. During transient instabilities of the combustion conditions, e.g. due to barrel uptake, highly dynamic changes in the emission profiles of substituted benzenes and polycyclic aromatic hydrocarbons (PAH) were observed. Copyright

Application of Laser Ionization Mass Spectrometry for On‐line Monitoring of Volatiles in the Headspace of Food Products: Roasting and Brewing of Coffee

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.

On-line real-time measurements at incineration plants: PAHs and a PCDD/F surrogate compound at stationary combustion conditions and during transient emission puffs

Laser mass spectrometry has been applied for on-line monitoring of traces of aromatic compounds from flue gas of incineration plants. The experiments have been carried out at two sampling sites in an industrial hazardous-waste incinerator. With laser mass spectrometry resonance-enhanced multiphoton ionization (REMPI) with time-of-flight mass spectrometry (TOFMS) (REMPI-TOFMS), using the group selective multi-component monitoring approach, aromatic compounds are selectively ionized from the complex flue-gas matrix. In this case, the result of an REMPI-TOFMS on-line measurement is a distinct pattern of aromatic compounds. These patterns are dependent on: (i) the point of measurement, (ii) the incineration plant, (iii) the temperature, and (iv) the fuel. This contribution focuses on the fuel dependence of the pattern. The most transient behavior can be observed when containers filled with hazardous waste are burnt, leading to puffs. Real-time monitoring results of puffs are given. Furthermore, as an approach towards on-line monitoring of the TEQ (PCDD/F toxicity equivalent), REMPI-TOFMS on-line analysis results of chlorobenzene are presented.

A Mobile Laser Mass Spectrometer (REMPI-TOFMS) for Continuous Monitoring of Toxic Combustion Byproducts: Real-time On-line Analysis of PAH in Waste Incineration Flue Gases

The combination of laser induced Resonance-Enhanced Multi-Photon Ionization and Time-Of-Flight Mass Spectrometry (REMPI-TOFMS) represents a highly selective and sensitive analytical technique ideal for real-time determination of organic trace components. For example, aromatic hydrocarbons can be continuously monitored in industrial off gases. We introduce a new mobile REMPI-TOFMS instrument, which is robust and easy to operate, even under industrial conditions. Instead of an on-line sampling system also a gas chromatograph can be coupled for ultratrace analytical work. The instrument can be equipped with different inlet techniques (effusive inlet, free and skimmed supersonic jet), different TOF mass spectrometric options (linear mode and reflectron mode for higher mass resolution) or different laser systems (robust fixed wavelength lasers or tunable lasers for more sophisticated applications). This flexibility allows the instrument to be readily adapted to a given analytical problem. New time-resolved dat...

On-line resonance-enhanced multiphoton ionization time-of-flight laser mass spectrometry for combined multi-component-pattern analysis and target-compound monitoring: non-chlorinated aromatics and chlorobenzene in flue gases of combustion processes

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. “Semi-selective” 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 measurement 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.

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.