TOPIC VI "TA/PIMS-Application"

On-line analysis of combustion processes

On-line combustion analysis is carried out by mobile, field-capable time-of-flight mass spectrometers (TOFMS), equipped with an Nd:YAG laser for photo-ionisation. Two different ionisation methods are employed: Resonance-enhanced multi-photon ionisation (REMPI) at 266 nm is a selective and sensitive ionisation technique for aromatic and polyaromatic substances. Those aromatic compounds absorb 266 nm photons and get in an electronically excited state. Single photon ionisation (SPI) at 118 nm is a more universal ionisation technique, which is capable to ionise any compound with an ionisation energy below the photon energy. Both SPI and REMPI predominantly generate molecular ions, which simplifies the interpretation of mass spectra of complex mixtures.

The research focus is on the investigation of volatile emissions from wood stoves and (ship) diesel engines. The latter are investigated in cooperation with the chair of piston machines and internal combustion engines (LKV) at the University of Rostock. Relations between emissions and different fuels such as heavy fuel oil and diesel as well as variations in engine conditions are among the research topics.

The high time resolution of the SPI/REMPI-TOFMS gives access to dynamic real-world combustion scenarios and the detection of single species in real-time. Thereby, temporal resolved emission maxima and rapid shifts in the emission profile can be identified.

Czech, H. et al.: On-line analysis of organic emissions from residential wood combustion with Single-Photon Ionisation Time-Of-Flight Mass Spectrometry (SPI-TOFMS). Fuel 177, 334-342 (2016).

Scientists involved: Hendryk Czech

Analysis of particulate matter (PM) by TOCA-PIMS

Thermal-optical carbon analysis (TOCA) is a standard method for the characterization of PM. Collected on quartz fibre filters, PM is subjected to a specific temperature program and organic matter is desorbed and pyrolyzed in four thermal fractions in an inert helium atmosphere. The evolved compounds are oxidized to CO2 by a manganese dioxide catalyst. The formed carbon dioxide is reduced catalytically to methane, which is quantified by a flame ionization detector (FID). Carbon that can be detected in the first four fractions is referred to as organic carbon (OC), where the carbon that can only be detected in a He/O2 atmosphere is referred as elemental carbon (EC).

The project deals with modifications of the TOCA instrument, whereby a small part of the desorbed gas flow is transferred to a photoionization time-of-flight mass spectrometer (PIMS) prior to the oxidation unit. Evolved compounds are ionized softly and detected in real time by a time-of-flight mass spectrometer, which provides an insight into the molecular chemistry of the distinct carbonaceous fractions. Further modifications will involve a seven wavelength laser for determination of the absorption properties of PM samples and a quadrupole mass analyzer to extend the elemental analyses.

Diab, J. et al.: Hyphenation of a EC / OC thermal-optical carbon analyzer to photo-ionization time-of-flight mass spectrometry: An off-line aerosol mass spectrometric approach for characterization of primary and secondary particulate matter. Atmos. Meas. Tech. 8, 3337-3353 (2015).  

Scientists involved: Toni Miersch

Thermal Analysis Photo-Ionisation Mass Spectrometry (TA-PIMS)

Thermal Analysis yields information about mass loss and enthalpy changes as function of temperature, thereby applying a controlled temperature program to solid or liquid samples. Coupling to photo-ionisation mass spectrometry allows characterizing the evolved gases in real time.

In this respect, laser based resonance-enhanced multi photo-ionisation (REMPI) and single photon ionisation (SPI) are applied in our device. Concerning REMPI, an optional optical parametric oscillator (OPO) enables wavelength selectivity.

One research focus lies on the characterization of crude oils and petrochemical products. Especially interesting is the investigation of heavy crude oil fractions, such as asphaltenes. Another project is the analysis of the composition of polymeric residues from steam cracker facilities.

Fendt, A. et al.: Hyphenation of two simultaneously employed soft photo ionization mass spectrometers with thermal analysis of biomass and biochar. Thermochim. Acta 551, 155-163 (2013).  

 Scientists involved: Christoph Grimmer

Thermal Analysis/Gas Chromatograph/ Photo-Ionisation Mass Spectrometry (TA-GC-PIMS)

Evolved Gas Analysis (EGA) of very complex samples such as crude oil and fuels in combination with Thermal Analysis gives rise to the simultaneous evaporation of numerous compounds. As a consequence, isobaric compounds are very difficult to distinguish in the mass spectrum. Therefore, in order to improve compound separation in the evolved gases, an additional fast chromatography device with a Peltier cooled modulator is inserted between the thermal balance and the inlet of the mass spectrometer, allowing to record a chromatogram every 60 seconds.

This device is applied for the investigation of several heating oils, including pure fossil fules, blends of fossil and biofuels as well as pure biofuels. Heating oil combustors sometimes exhibit the formation of unwanted deposits, severely impairing the combustion process. The analyses provide information on the molecular composition of evaporated fractions of the oils, since even small changes in composition could decide whether a specific oil is prone to produce such deposits or not.

Wohlfahrt, S. M. et al.: Dual-Stage Consumable-Free Thermal Modulator for the Hyphenation of Thermal Analysis, Gas Chromatography, and Mass Spectrometry. Analytical chemistry 88 (1): 640-644. (2016).

 Scientists involved: Thorsten Streibel

Membrane inlet mass spectrometry

Fast and sensitive analysis of aromatic and polyaromatic compounds (PAH) is of high importance due to their environmental behavior, high biological activity and toxicity. Very low concentrations of such compounds in marine environments make their detection and monitoring difficult. Therefore, time-consuming enrichment techniques (such as purge-and-trap and laborious extraction techniques) are applied.

A promising alternative constitutes the application of membrane inlets coupled to resonance enhanced photo-ionisation (REMPI) time-of-flight mass spectrometers (TOF-MS) to extract and analyze these compounds directly without sample preparation.

A challenge for the utilization of REMPI in aquatic systems is the transfer of dissolved analytes to the gas phase. An auspicious approach constitutes the application of membrane inlets. For membrane inlet mass spectrometry (MIMS) analytes are transported selectively from the liquid phase through a semipermeable membrane (e.g. silicon-membrane) into the vacuum of the mass spectrometer by a process called pervarporation, losing the matrix in the process. Analytes are transported through the membrane based on the gradient of concentration and pressure.

Scientists involved: Christian Gehm, Image: Christian Gehm

Carbon Concrete Composite (C3)

Armored concrete with steel as reinforcement material has the disadvantage, that a very thick concrete coverage is needed to prevent corrosion. A promising alternative is carbon concrete composite, where carbonaceous material replaces steel as reinforcement. Such concrete does not corrode, leading to a prolonged life time of the structures.

However, in order to overcome potential concern about an area-wide introduction into the market, it has to be ensured that working with carbon concrete will not give rise to hazards for the human health. In particular, it should be made transparent that evolving particulate matter and dust during mechanical or thermal stress of carbon concrete exhibits no adverse health effects. Therefore, such particles are investigated with respect to their biological impact on human lung cells and macrophages via an air-liquid interface. Exposed cell cultures are afterwards analyzed for changes in transcriptome and proteome and for toxicological effects. The biological analyses are accompanied by a physical and chemical characterization of the evolved aerosols. In the end, the data will be put together to get a comprehensive overview of potential health effects of carbon concrete related particulate matter.

Scientists involved: Thorsten Streibel, Image: Vitrocell Systems GmbH