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Highlights • A method to evaluate the bias of three MS ionization methods was proposed for coal. • Elemental compositions obtained from ultimate analysis was set as a reference. • Elemental compositions derived from APCI-MS showed closer values to ultimate analysis. • Adjusted compound classes offer a closer measurement to the actual values. Abstract The relative abundances of compound classes (e.g. CHO 1 , CHO 2 and CHNO 1) in fossil fuels have been widely used in previous researches based on the data from mass spectrometry (MS). However, such observations are susceptible to the ionization bias of MS due to the variation of ionization efficiency, which may affect the downstream quantitative analysis. Many efforts have been devoted to investigating the ionization efficiencies of a variety of model compounds, but not complex and diverse mixtures. Therefore, it is necessary to investigate how quantitatively ionization bias affects the MS analysis of complex mixtures. In this study, ionization bias was preliminarily investigated by comparing the elemental compositions obtained from MS-analysis via different ionization methods with the data acquired by a standard elemental analyzer. A coal-derived liquid and mixtures of five model compounds were ionized by atmospheric-pressure chemical ionization (APCI), electrospray ionization or direct analysis in real-time, followed by analyzing using a high-resolution Orbitrap MS to obtain elemental compositions. MS-based results via APCI ion source showed the closest elemental compositions to those obtained from the elemental analyzer. For the MS-based analysis, the abundances of S- and O-containing compounds were significantly lower and that of N-containing compounds was clearly higher compared to ultimate analysis. The abundances of compound classes were adjusted to provide a closer approximation of the actual contents, which might better serve for the downstream quantitative analysis. Although absolute quantification still needs additional work, the adjusted MS-based analysis provides not only the molecular level data, but also a better quantification ability compared to previous analytical approaches. [ABSTRACT FROM AUTHOR]

Highlights • HCA and EMGM are introduced to reach in-depth statistic results for coal extracts. • The similarities and differences of clusters are visually exhibited in a plot via HCA. • Molecular structures in the same EMGM model have a certain similarity. Abstract A coal was extracted and thermally dissolved with cyclohexane, acetone and methanol sequentially. The ultrasonic extracts and thermal dissolution (TD) products were analyzed using an Orbitrap mass spectrometer (MS) with an atmospheric pressure chemical ionization source in positive ion mode. Large amounts of MS data were obtained but there were challenges in obtaining meaningful information from the data. The purpose of cluster analysis is to reduce complex multivariate data into meaningful groups. Two cluster analysis methods, hierarchical cluster analysis and expectation maximum algorithm based on Gaussian mixture model (EMGM), run by R language were introduced to obtain in-depth statistical results for compounds in both extracts and TD products. Seven types of heteroatomic compounds (O 1 , O 2 , N 1 , S 1 , O 1 N 1 , O 1 S 1 and N 1 S 1) in the extracts under the condition of ultrasonic extraction with cyclohexane were clustered with EMGM and possible structures of the related models can be inferred by analyzing the relationship between carbon number and double bond equivalent. The application of cluster analysis will provide methodological guidance in studying the structure of coal molecules. [ABSTRACT FROM AUTHOR]

Highlights • Fragmentation patterns of 22 model compounds with varied energies were discussed. • The optimal collision energy to investigate aromatic core structures should be 80 eV. • Energy-resolved ISCAD showed potential for in-depth structural analysis of coal/biomass. Abstract In-source collision activated dissociation (ISCAD) is an effective method to obtain molecular structure of coal and biomass and provide basic knowledge for coal/biomass conversion. Twenty two coal/biomass-based model compounds and one coal extract were studied via ISCAD to understand the relationship between collision energy and molecular structure and the application of ISCAD in the characterization of coal. Model compounds showed different fragmentation patterns with the increase of collision energy and the detailed fragmentation pathways in context of collision energies were proposed. According to the ISCAD results of coal extract, the weighted mean molecular weight (MW) and weighted mean double-bond equivalent (DBE) values of ionized coal molecules decreased over collision energy of 80 eV. The decrease of weighted mean MW and DBE were mainly caused by the cleavage of alkyl chains, bridged bonds, and minor cracking of small aromatic cores from precursor ions upon fragmentation. Therefore, the optimal ISCAD collision energy for the investigation of aromatic core structures of the coal extract should be around 80 eV. [ABSTRACT FROM AUTHOR]

Thermal dissolution (TD) plays an important role in obtaining soluble components from low-rank coals. Characterization of the TD product is essential for both optimization of TD conditions and in-depth understanding of molecular structures in coal that is crucial for the refining processes. In-source collision-activated dissociation (ISCAD) combined with high-resolution mass spectrometry (MS) was employed in this study to analyze four TD products of a low-rank coal obtained by using cyclohexane, acetone, methanol and ethanol as solvents. ISCAD-MS allows the evaluation of distributions of oxygen and nitrogen atoms located within aromatic cores or on alkyl chains based on the abundances of heteroatom-containing precursor ions and fragment ions. In addition, ISCAD-MS can evaluate the abundance of multi-core compounds based on the change of average double bond equivalent value upon fragmentation. These structural details advance the current understanding of the TD products at the molecular level. [ABSTRACT FROM AUTHOR]

Dayan lignite (DL) was subjected to thermal dissolution sequentially with cyclohexane, acetone and methanol to obtain three filtrates. The filtrates were characterized by Fourier transform infrared spectroscopy, gas chromatography/mass spectrometry (GC/MS), and time-of-flight mass spectrometry (TOF-MS) equipped with atmospheric pressure photoionization (APPI), electrospray ionization (ESI) or direct analysis in real time (DART) to understand the structural features of DL. Aliphatic hydrocarbons, furans and alcohols were enriched in the filtrate of cyclohexane, acetone and methanol, respectively, according to the data of GC/MS. One ring aromatics was also identified by GC/MS as major species in the three filtrates. Both GC/MS and APPI-MS can well analyze compounds with low polarity, but APPI-TOF-MS in this work successfully characterized polycyclic aromatics and extended the measurement range (molecular weight and ring size) of GC/MS. ESI-TOF-MS is suitable to analyze polar compounds in coal. Data from ESI-TOF-MS indicated that heteroatom compounds including non-aromatics and aromatics with 1-2 rings are the major polar components in DL. As an ambient MS ionization method, DART shortened the analysis time without sample pretreatment and more aromatics over 4 rings were identified by DART-TOF-MS. Characterization of the complex coal filtrates with multiple mass spectrometers provided a full view of the molecular information of DL. [ABSTRACT FROM AUTHOR]

Shengli lignite (SL) was oxidized and depolymerized in aqueous sodium hypochlorite under mild conditions followed by sequential extraction with ethoxyethane and ethyl acetate. The extracts were analyzed by Fourier transform infrared spectroscopy, gas chromatograph/mass spectrometry (GC/MS), time-of-flight mass spectrometry (TOF-MS) equipped with electrospray ionization (ESI), and direct analysis in real time (DART) to understand the structural features of SL. In total, 130, 272, and 818 compounds were identified by GC/MS, ESI-MS, and DART-MS, respectively, and the corresponding molecular mass distributions are between 70 and 322, 114 and 664, 113 and 753 u , respectively. GC/MS detected molecules with low molecular mass and polarity, and the major species include aliphatic acids, benzene polycarboxylic acids, chloro-substituted species and nitrogen-containing compounds. A large number of heteroatom-containing compounds (oxygen, nitrogen and sulfur) with relatively high molecular mass and unsaturation degree were determined using ESI-MS. As an ambient ionization technique, DART speeded up the analysis time with little or no sample pretreatment. Compared to the other two MS techniques, DART-MS broadened the measurement range, and O x N 5 , and O x N 6 classes were only detected by DART-MS. [ABSTRACT FROM AUTHOR]

A Xinjiang subbituminous coal was directly oxidized in aqueous sodium hypochlorite and sequentially extracted with diethyl ether and ethyl acetate. The extracts were esterified with diazomethane and the esterified products were analyzed using a high performance liquid chromatograph/mass spectrometer (HPLC/MS) equipped with atmospheric pressure photoionization (APPI) or electrospray ionization (ESI) ion source. Toluene and a toluene/anisole mixture (vol/vol = 95:5) were used as dopant for APPI-MS. The relative of organic species with molecular mass over 500 u detected by ESI-MS is much higher than that identified by APPI-MS with and without dopant. The addition of dopant greatly enhanced the ionization efficiency and toluene induced better ionization effects compared to the mixture in both ion signal intensity and number of detected species. However, according to the ionization mechanism of APPI, a small portion of analytes could be well ionized under direct APPI mode rather than dopant-assisted mode. [ABSTRACT FROM AUTHOR]

Highlights: [•] ASAP was applied to analyze CRMCs, exploring a new application field. [•] The ionization mechanism of produced M+ and [M+H]+ for CRMCs were investigated. [•] The ASAP/MS fragmentation pathways for selected CRMCs were proposed. [Copyright &y& Elsevier]