Characterization of aromatic organosulfur model compounds relevant to fossil fuels by using atmospheric pressure chemical ionization with CS2 and high-resolution tandem mass spectrometry

Nondesulfurizing benzothiophene biotransformation to hetero and homodimeric ortho-substituted diaryl disulfides by the model PAH-degrading Sphingobium barthaii

Understanding the biotransformation mechanisms of toxic sulfur-containing polycyclic aromatic hydrocarbon (PASH) pollutants such as benzothiophene (BT) is useful for predicting their environmental fates. In the natural environment, nondesulfurizing hydrocarbon-degrading bacteria are major active contributors to PASH biodegradation at petroleum-contaminated sites; however, BT biotransformation pathways by this group of bacteria are less explored when compared to desulfurizing organisms. When a model nondesulfurizing polycyclic aromatic hydrocarbon-degrading soil bacterium, Sphingobium barthaii KK22, was investigated for its ability to cometabolically biotransform BT by quantitative and qualitative methods, BT was depleted from culture media but was biotransformed into mostly high molar mass (HMM) hetero and homodimeric ortho-substituted diaryl disulfides (diaryl disulfanes). HMM diaryl disulfides have not been reported as biotransformation products of BT. Chemical structures were proposed for the diaryl disulfides by comprehensive mass spectrometry analyses of the chromatographically separated products and were supported by the identification of transient upstream BT biotransformation products, which included benzenethiols. Thiophenic acid products were also identified, and pathways that described BT biotransformation and novel HMM diaryl disulfide formation were constructed. This work shows that nondesulfurizing hydrocarbon-degrading organisms produce HMM diaryl disulfides from low molar mass polyaromatic sulfur heterocycles, and this may be taken into consideration when predicting the environmental fates of BT pollutants.

Differentiation of Seven Isomeric n-Pentylquinoline Radical Cations Based on Energy-Resolved Medium-Energy Collision-Activated Dissociation

Asphaltenes, a major and undesirable component of heavy crude oil, contain many different types of large aromatic compounds. These compounds include nitrogen-containing heteroaromatic compounds that are thought to be the main culprit in the deactivation of catalysts in crude oil refinery processes. Unfortunately, prevention of this is challenging as the structures and properties of the nitrogen-containing heteroaromatic compounds are poorly understood. To facilitate their structural characterization, an approach based on ion-trap collision-activated dissociation (ITCAD) tandem mass spectrometry followed by energy-resolved medium-energy collision-activated dissociation (ER-MCAD) was developed for the differentiation of seven isomeric molecular radical cations of n-pentylquinoline. The fragmentation of each isomer was found to be distinctly different and depended largely on the site of the alkyl side chain in the quinoline ring. In order to better understand the observed fragmentation pathways, mechanisms for the formation of several fragment ions were delineated based on quantum chemical calculations. The fast benzylic α-bond cleavage that dominates the fragmentation of analogous nonheteroaromatic alkylbenzenes was only observed for the 3-isomer as the major pathway due to the lack of favorable low-energy rearrangement reactions. All the other isomeric ions underwent substantially lower-energy rearrangement reactions as their alkyl chains were found to interact mostly via 6-membered transition states either with the quinoline nitrogen (2- and 8-isomers) or the adjacent carbon atom in the quinoline core (4-, 5-, 6-, and 7-isomers), which lowered the activation energies of the fragmentation reactions. The presented analytical approach will facilitate the structural characterization of nitrogen-containing heteroaromatic compounds in asphaltenes.

Oil biodesulfurization: A review of applied analytical techniques

The wide use of fossil fuels and their associated environmental concerns, highlighted the importance of affordable and clean energy (goal 7), as adopted by the Sustainable Development Goals of the United Nations for 2030. For years now, the detection of sulfur components in liquid fuels is performed mainly for environmental and health purposes in compliance with the respective legislations. Towards this, the aerobic and anaerobic biodesulfurization (BDS) process, which entails the use of microorganisms to limit the sulfur concentration is followed. To ensure effective BDS, several traditional analytical methods are utilized, although they require bench-top, bulky, costly, and time-consuming instruments along with skilled personnel. The currently employed analytical methods are mostly chromatographic techniques (e.g. liquid and gas) coupled with various detectors. To start with, high-performance liquid chromatography with ultraviolet detector (HPLC-UV), as well as electrospray ionization-LC-mass spectrometry (ESI-LC-MS) were mostly reported. Additionally, many detectors were coupled to gas chromatography (CG) including atomic emission detector (GC-AED), flame ionization detector (GC-FID), flame photometric detector (GC-FPD), sulfur fluorescence detector (GC-SFD), mass selective detector (GC-MS), etc. The solid-phase microextraction (SPME) technique provides extra capabilities when added to the separation techniques. Towards the continuous interest in oil supercomplex synthesis, other atmospheric and surface desorption ionization techniques, as well as the multidimensional 2D chromatographic systems (GC × GC and LC × LC) were also investigated, due to their unsurpassed resolution power. The current review ends with final remarks per applied methodology and the necessity to respect and protect the human environment and life.

Facile fabrication of functional groups-rich sorbent for the efficient enrichment of aromatic N- and S-containing compounds in environmental waters

Extraction strategy is designed for the pretreatment of low contents of aromatic N- and S-containing compounds (ANSCs) in environmental waters prior to chromatographic analysis. To enrich studied ANSCs effectively, poly (9-vinylanthracene/4-vinylphenylboronic acid-co-ethylene dimethacrylate/divinylbenzene) polymeric monolithic sorbent were facilely fabricated using the one-step free radical polymerization. Various technologies were employed to investigate the structure and morphology of the resultant monolith. Combining with solid-phase microextraction format, the sorbent exhibited satisfying concentrated performance for ANSCs through multiply interactions under the optimized conditions. After desorption with eluent, the retained analytes were analyzed by HPLC. Results showed that the extraction efficiencies ranged from 51.6 to 93.2%. The linear ranges and limits of detection were 0.01-150 μg/L and 0.63-2.64 ng/L, respectively. Furthermore, the precisions were all below 10%. The introduced approach was productively practiced on three real water samples for simultaneous quantification of studied ANSCs, and the fortified recoveries ranged from 81.5 to 118%. All the results well evidenced that prepared sorbent can enrich ANSCs effectively and the introduced method is reliable alternative for routine analysis of ANSCs in environmental waters.

Evaluation of coal-related model compounds using tandem mass spectrometry

RATIONALE

Gas chromatography/mass spectrometry (GC/MS) is a routine and basic instrumental method for the analysis of complex coal conversion products in the chemical industry. To further enhance the practical potential of GC/MS in chemical industry, a tandem MS method for the selection of ion pairs applied in monitoring coal conversions was established using GC/quadrupole time-of-flight MS (GC/Q-TOF MS). The corresponding fragmentation pathways were explored and suitable ion pairs were screened.

METHODS

Fourteen coal-related model compounds (CRMCs) were analyzed using GC/Q-TOF MS with different collision-induced dissociation (CID) energies (5-20 eV). The fragmentation pathways can offer a better understanding of chemical bond breaking, hydrogen transfer, rearrangement reactions and elimination of neutral fragments for CRMCs during the CID process.

RESULTS

The precursor ions of aromatic hydrocarbons without alkyl chains were difficult to fragment with a CID energy of 20 eV. But aromatic hydrocarbons with branched chains were prone to fragment via the loss of alkyl chains and further fragmented through ring-opening reactions. Compared with the C_alk C_ar bond, the C_ar C_ar bond was difficult to fragment due to its high bond dissociation energy. The existence of heteroatoms facilitated fragmentation that was conducive to the screening of ion pairs.

CONCLUSIONS

The CID technique of GC/Q-TOF MS will contribute to studies on the organic composition of coals and to building monitoring methods for coal conversions via fragmentation and ion pair selection.