Characterization of Sulfur-Rich Microbial Organic Matter in Jurassic Carbonates Using Laser-Assisted Mass Spectrometry.

Laser desorption-ionization mass spectrometry (MS) shows great potential for in situ molecular analysis of planetary surfaces and microanalysis of space-returned samples or (micro)fossils. Coupled with pyrolysis gas chromatography-mass spectrometry (Py-GC-MS) in ESA's ExoMars project, this technique could help assess further the origin of sulfur-bearing organic matter (OM) recently detected on Mars. To unravel this potential, we analyzed sulfurized microbial OM from ca. 150 million year-old carbonates with laser desorption-ionization mass spectrometry (single- and two-step: LDI-MS and L2MS), in comparison with time-of-flight secondary-ion mass spectrometry (ToF-SIMS), gas chromatography-mass spectrometry (GC-MS), and Py-GC-MS. We show that LDI-MS and L2MS readily detect sulfur-bearing moieties such as (alkyl)thiophenes and (alkyl)benzothiophenes. The mineral matrix, however, made the identification of sulfur-bearing molecules challenging in our L2MS experiment. The dominance of small aromatic hydrocarbons (≤14 carbons) in the LDI-MS and L2MS of the extracted soluble and insoluble OM and of the bulk rock is consistent with the low thermal maturity of the sediment and contrasts with the predominance of larger polycyclic aromatic structures commonly observed in meteorites with these techniques. We detected inorganic ions, in particular VO+, in demineralized OM that likely originate from geoporphyrins, which derive from chlorophylls during sediment diagenesis. Finally, insoluble OM yielded distinct compositions compared with extracted soluble OM, with a greater abundance of ions of mass-to-charge ratio (m/z) over 175 and additional N-moieties. This highlights the potential of laser-assisted MS to decipher the composition of macromolecular OM, in particular to investigate the preservation of biomacromolecules in microfossils. Studies comparing diverse biogenic and abiogenic OM are needed to further assess the use of this technique to search for biosignatures.

Electron Beam Processing as a Promising Tool to Decontaminate Polymers Containing Brominated Flame Retardants.

Electron Beam (EB) irradiation was utilized to decontaminate model systems of industrial polymers that contain a brominated flame retardant (BFR). Acrylonitrile-butadiene-styrene (ABS) and Polycarbonate (PC) are two types of polymers commonly found in Waste Electrical and Electronic Equipment (WEEE). In this study, these polymers were exposed to EB irradiation to degrade DecaBromoDiphenylEther (DBDE), one of the most toxic BFRs. Fourier-transform infrared spectroscopy analysis demonstrated an 87% degradation rate of DBDE for the ABS-DBDE system and 91% for the PC-DBDE system following an 1800 kGy irradiation dose. Thermal analysis using Differential Scanning Calorimetry revealed the presence of crosslinking in ABS and a minor reduction in the glass transition temperature of PC after EB processing. Polymers exhibited thermal stability after photolysis, as indicated by thermogravimetric analysis. In summary, EB irradiation had no impact on the overall thermal properties of both polymers. High-resolution mass spectrometry analysis has confirmed the debromination of both ABS-DBDE and PC-DBDE systems. Therefore, the results obtained are promising and could offer an alternative approach for removing bromine and other additives from plastic E-waste.

Degradation processes of brominated flame retardants dispersed in high impact polystyrene under UV-visible radiation.

In order to protect human health and the environment, several regulations have been introduced in recent years to reduce or even eliminate the use of some brominated flame retardants (BFRs) due to their toxicity, persistence and bioaccumulation. Dispersions of these BFRs in polymers are widely used for various applications. In this report, four different brominated molecules, decabromodiphenyl ether (DBDE), hexabromocyclododecane (HBCDD), decabromodiphenyl ethane (DBDPE) and tris(tribromophenoxy)triazine (TTBPT), were dispersed in the solid matrix of an industrial polymer, high impact polystyrene (HIPS). The possibility of degradation of these BFRs within HIPS under UV-visible irradiation in ambient air was investigated. The degradation kinetics of DBDE and HBCDD were followed by Fourier transform infrared spectroscopy (FTIR) and high-resolution two-step laser mass spectrometry (L2MS). The thermal properties of the pristine and irradiated polymer matrix were monitored by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), which showed that these properties were globally preserved. Volatile photoproducts from the degradation of DBDE, DBDPE and TTBPT were identified by headspace gas chromatography/mass spectrometry analysis. Under the chosen experimental conditions, BFRs underwent rapid degradation after a few seconds of irradiation, with conversions exceeding 50% for HIPS/DBDE and HIPS/HBCDD systems.

Evidence on the formation of dimers of polycyclic aromatic hydrocarbons in a laminar diffusion flame.

The role of polycyclic aromatic hydrocarbons (PAHs) in the formation of nascent soot particles in flames is well established and yet the detailed mechanisms are still not fully understood. Here we provide experimental evidence of the occurrence of dimerization of PAHs in the gas phase before soot formation in a laminar diffusion methane flame, supporting the hypothesis of stabilization of dimers through the formation of covalent bonds. The main findings of this work derive from the comparative chemical analysis of samples extracted from the gas to soot transition region of a laminar diffusion methane flame, and highlight two different groups of hydrocarbons that coexist in the same mass range, but show distinctly different behavior when processed with statistical analysis. In particular, the identified hydrocarbons are small-to-moderate size PAHs (first group) and their homo- and heterodimers stabilized by the formation of covalent bonds (second group).

A comprehensive protocol for chemical analysis of flame combustion emissions by secondary ion mass spectrometry.

RATIONALE: Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is used to provide detailed information on the surface chemical composition of soot. An analytical protocol is proposed and tested on a laboratory flame, and the results are compared with our previous measurements provided by two-step laser mass spectrometry (L2MS). METHODS: This work details: (1) the development of a dedicated apparatus to sample combustion products from atmospheric flames and deposit them on substrates suitable for TOF-SIMS analysis; (2) the choice of the deposition substrate and the material of the sampling line, and their effect on the mass spectra; (3) a method to separate the contributions of soot and condensable gas based on impact deposition; and finally (4) post-acquisition data processing. RESULTS: Compounds produced during flame combustion are detected on the surface of different deposition substrates and attributed a molecular formula based on mass defect analysis. Silicon and titanium wafers perform similarly, while the surface roughness of glass microfiber filters results in a reduced mass resolution. The mass spectra obtained from the analysis of different locations of the deposits obtained by impaction show characteristic patterns that are attributed to soot/condensable gas. CONCLUSIONS: A working method for the analysis of soot samples and the extraction of useful data from mass spectra is proposed. This protocol should help to avoid common experimental issues like sample contamination, while optimizing the setup performance by maximizing the achievable mass resolution.

CO2 capture using semi-clathrates of quaternary ammonium salt: structure change induced by CO2 and N2 enclathration.

Semi-clathrates of tetrabutylammonium bromide (TBAB) are investigated for their potential application in the CO2 capture context based on hydrate technology. The three-phase lines of semi-clathrates of CO2-TBAB-H2O and N2-TBAB-H2O are established simultaneously with their structure using in situ Raman scattering performed at high pressure. The preferred crystal phase obtained at ambient pressure from solutions of 5 and 40 wt % TBAB initial concentrations is shown to change upon enclathration of CO2 or N2, or by applying a higher pressure on the system. Deep in the stability field, metastable hydrate phases are occurring at the onset of the formation and correspond to the ones expected under ambient pressure conditions. Depending on the pressure, they progressively transformed into the most stable ones when approaching equilibrium and dissociation points. Besides, it is shown that a 5 wt % TBAB original solution forms preferentially a mixed structure of both type B and type A at low gas pressure with CO2 as the guest gas. A new structure is spectroscopically characterized at pressures higher than ∼2 MPa CO2. Type A is demonstrated to be stable at 5 wt % initial TBAB concentration with N2 as the guest molecule and pressure between 8 and 12 MPa. These structural data address new insights on the relationship between the hydrophilic-anion and hydrophobic-cation intercalation with a guest gas producing hydrophobic interaction in a distorted water lattice.

R2PI spectroscopy of aromatic molecules produced in an ethylene-rich flame.

Laser spectroscopy, combined with mass spectrometry, was applied to study the spectra of aromatic molecules produced in a premixed ethylene-rich flat flame. These studies produce new gas-phase electronic spectra of polyaromatic compounds, which ultimately will guide the understanding of the chemical processes that lead to polycyclic aromatic hydrocarbon (PAH) growth or PAH formation locking. Resonant two-photon ionization (R2PI) spectra of all species detectable in a specific fuel-rich flame were recorded simultaneously during a single scan of the laser wavelength, within the 220-330 nm range. Comparison with spectra available in the literature allowed us to identify 16 aromatic species. In the PAH forming region of this flame, we found that the main PAHs are accompanied by a great diversity of other species, including in particular various side-chains on aromatic networks. We also show that this technique allows, at least in some cases, to distinguish between different isomers associated with the same mass peak, although the extracted PAHs are only cooled down to room temperature.