Atmospheric Pressure Photoionization FT-ICR Research Articles

Characterization of polycyclic aromatic hydrocarbons (PAHs) in atmospheric particles (PM2.5) in the North China Plain using positive-ion atmospheric pressure photoionization (APPI) coupled with fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS)

Many aromatic compounds, including 16 types of U.S. EPA priority PAHs, exist in substituted or unsubstituted forms and have high toxicities. Aromatic compounds in aerosols collected in the North China Plain (NCP) were characterized by GC-MS and atmospheric pressure photoionization (APPI) Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). The concentrations of the 16 types of PAHs in the collected samples ranged from 277.0 to 876.8 ng/m3, which were higher than those collected in other regions and countries. Previous studies reported that only 27 wt% of aromatic compounds could be eluted using the GC system and demonstrated that APPI FT-ICR MS is a useful method for identifying large-molecular aromatics. In this study, two samples collected from the NCP were successfully characterized by APPI FT-ICR MS. In the APPI + mode, 231 and 228 CH formulas (containing only C and H and having a double bond equivalent (DBE) of 4 or greater) were identified, accounting for 10% of the numerical fraction and more than 40% of the intensity fraction. The FT-ICR data revealed that condensed PAHs with 6–8 aromatic rings had relatively high abundances and that a series of PAH homologs (alkylated PAHs) with identical DBE values ranging from 4 to 30 were present. Furthermore, heteroatom groups were also identified as significant components of the aromatic fractions. The O1, O2, N1, NO2, and S1 class species with DBE values of 3–34 and carbon numbers of 11–42 were identified by APPI FT-ICR MS. The heteroatom PAHs had DBE values and carbon number distributions similar to regular PAHs. The aromatic fractions determined in this work provide useful data for future quantitative analyses of aromatic compounds with high toxicities and our findings will help improve the current understanding of PAH compositions in the northern China. However, further research is needed to determine the abundances and toxicities of various apparent or substituted PAHs outside of the 16 types identified by the U.S. EPA as priority PAH compounds, which have been extensively researched.

Molecular transformation of dissolved organic matter in refinery wastewaters: Characterized by FT-ICR MS coupled with electrospray ionization and atmospheric pressure photoionization

Dissolved organic matter (DOM) in refinery wastewater is an extremely complex mixture of various organic compounds. Using mass spectrometry, it is impossible to characterize all of the DOM molecules with only one ionization source. In this study, negative-ion, electrospray ionization (ESI), positive-ion ESI, and positive-ion atmospheric pressure photoionization (APPI) were coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to analyze the molecular composition of DOM in a refinery wastewater stream during the treatment process. There were obvious differences in the heteroatom composition, number of DOM constituents, and chemical properties in refinery wastewater under the three ionization modes. Acidic CHO and CHOS compounds detected by (−)ESI, basic CHN and CHON compounds detected by (+)ESI, and hydrocarbons detected by (+)APPI were analyzed to determine the molecular transformations that occurred during treatment. In an anaerobic biological treatment process, acidic CHO and CHOS compounds with a high oxygen content were preferentially removed, and acidic CHO and CHOS compounds with a low oxygen content were produced. In an aerobic biological process, acidic CHO and CHOS compounds with a low oxygen content were preferentially removed, and acidic CHO and CHOS compounds with a high oxygen content were produced. The whole biological treatment process has a poor removal efficiency for CHN and CHON compounds, and hydrocarbons. An activated carbon (AC) adsorption process removed different heteroatom compounds mainly with a low oxygen content for acidic and basic compounds. The transformation mechanism of CHO and CHOS compounds in the biological treatment process was analyzed by the Kendrick mass defect (KMD) theory and a mass difference network analysis. In the anaerobic process, large amounts of oxygenated CHO and CHOS compounds were degraded by decarboxylation, deoxydation, demethoxylation, and dehydration reactions, and converted to lower oxygen content compounds. In the aerobic processes, these low oxygen CHO and CHOS compounds mainly underwent carboxylation and oxidation reactions. This study determined the transformation characteristics and mechanisms of different types of organic compounds in refinery wastewater during the treatment process. The results provide guidance for the design and optimization of technologies for refinery wastewater treatment. • Molecular composition of DOM in refinery wastewater was characterized by ESI and APPI FT-ICR MS. • Transformation characteristics and mechanism of different types of compound were investigated. • Biological process could remove acidic CHO and CHOS compounds. • AC adsorption process removed various different heteroatom compounds.

Characterization of Mineral and Synthetic Base Oils by Gas Chromatography–Mass Spectrometry and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Base oil is a main component of engine oil that enables smooth operation of an internal combustion engine. There are two types of base oils, such as mineral oil and synthetic oil. In this study, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and gas chromatography-mass spectrometry (GC-MS) were used to characterize the base oils. One difficulty in analyzing base oils using MS is that the ionization of alkanes can be problematic due to low ionization efficiencies and the predominance of fragmentation. Despite these limitations, the combination of GC-MS and FT-ICR MS data can provide qualitative insights into the composition differences for these various sample types. The distinctive total ion chromatogram obtained by GC-MS of the different base oils allowed the classification of mineral oil from synthetic oil. The additional structural characteristics of paraffinic compounds were also inferred by GC-MS. FT-ICR MS coupled to two different ionization methods, atmospheric pressure photoionization (APPI) and atmospheric pressure chemical ionization (APCI), was tested for the analysis of base oils. It was determined that APPI was suitable for the analysis of aliphatic hydrocarbon compounds, where APPI minimizes the decomposition of hydrocarbon compounds compared to atmospheric pressure chemical ionization. Using APPI FT-ICR MS, the components of the oils were characterized, including not only paraffinic compounds but also cyclic compounds. In addition, the alpha olefin monomer of the synthetic oil was determined, and the homogeneity of the branched compound of the synthetic base oil was confirmed using GC-MS and FT-ICR MS results.

Innate Sulfur Compounds as an Internal Standard for Determining Vacuum Gas Oil Compositions by APPI FT-ICR MS

Innate sulfur components in high boiling petroleum samples were used as an internal standard for the estimation of the sample’s composition through atmospheric pressure photo ionization (APPI) Four...

Profiling Murchison Soluble Organic Matter for New Organic Compounds with APPI- and ESI-FT-ICR MS.

The investigation of the abundant organic matter in primitive meteorite such as carbonaceous chondrites is of major interest in the field of origin of life. In this study, the soluble organic fraction of the Murchison meteorite was analyzed by atmospheric pressure photoionization (APPI) and electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), in both detection modes. Such an approach ensured that we obtained an extensive description of the organic matter of the CM2 meteorite. Indeed, while in total close to 16,000 unique features were assigned, only 4% are common to all analyses, illustrating the complementarity of both the detection modes and the ionization sources. ESI FT-ICR MS analysis, in negative-ion mode, ensured to observe specifically CHOS and CHNOS species, whereas the positive-ion mode is more dedicated to the detection of CHNO and CHN species. Moreover, new organomagnesium components were observed in (+) ESI. Eventually, (+) APPI FT-ICR MS analysis was a preferred method for the detection of less polar or nonpolar species such as polycyclic aromatic hydrocarbons but also heteroatom aromatic species composing the organic matter of Murchison.

Combating selective ionization in the high resolution mass spectral characterization of complex mixtures.

Direct "dilute and shoot" mass spectral analysis of complex naturally-occurring mixtures has become the "standard" analysis in environmental and petrochemical science, as well as in many other areas of research. Despite recent advances in ionization methods, that approach still suffers several limitations for the comprehensive characterization of compositionally complex matrices. Foremost, the selective ionization of highly acidic (negative electrospray ionization ((-) ESI)) and/or basic (positive electrospray ionization ((+) ESI)) species limits the detection of weakly acidic/basic species, and similar issues (matrix effects) complicate atmospheric pressure photo-ionization (APPI)/atmospheric pressure chemical ionization (APCI) analyses. Furthermore, given the wide range of chemical functionalities and structural motifs in these compositionally complex mixtures, aggregation can similarly limit the observed species to a small (10-20%) mass fraction of the whole sample. Finally, irrespective of the ionization method, the mass analyzer must be capable of resolving tens-of-thousands of mass spectral peaks and provide the mass accuracy (typically 50-300 ppb mass measurement error) required for elemental composition assignment, and thus is generally limited to high-field Fourier transform ion cyclotron mass spectrometry (FT-ICR MS). Here, we describe three approaches to combat the above issues for (+) ESI, (-) ESI, and (+) APPI FT-ICR MS analysis of petroleum samples. Each approach relies on chromatographic fractionation to help reduce selective ionization discrimination and target either specific chemical functionalities (pyridinic and pyrrolic species (nitrogen) or carboxylic acids (oxygen)) or specific structural motifs (single aromatic core (island) or multi-core aromatics (archipelago)) known to be related to ionization efficiency. Each fractionation method yields a 2-10-fold increase in the compositional coverage, exposes species that are undetectable using direct "dilute and shoot" analysis, and provides coarse selectivity in chemical functionalities that can both increase the assignment confidence and optimize ionization conditions to maximize compositional coverage.

Analysis of Petroleum Products by Gel Permeation Chromatography Coupled Online with Inductively Coupled Plasma Mass Spectrometry and Offline with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

We have examined the aggregation behavior of a typical atmospheric residue feedstock by gel permeation chromatography (GPC). The size profiles for compounds containing sulfur, vanadium, and nickel were determined online from elemental detection by inductively coupled plasma (ICP) mass spectrometry. Four fractions that vary in aggregation state were analyzed by positive atmospheric pressure photoionization (APPI) 9.4 T Fourier transform ion cyclotron resonance mass spectrometry (APPI FT-ICR MS). Results showed an inverse relationship between fraction aggregate size and monomer ion yield and revealed that aggregation tendency did not correlate with higher polar or aromatic species abundance. Aggregation in the atmospheric residue more closely correlated with increased relative abundance of larger and more aliphatic compounds. The molecular composition of the GPC aggregate fractions suggests that nonpolar intermolecular forces between saturated, long-chain alkyl substituents contribute more to aggregation th...

Characterization of Asphaltenes Precipitated at Different Solvent Power Conditions Using Atmospheric Pressure Photoionization (APPI) and Laser Desorption Ionization (LDI) Coupled to Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS)

In the present work, asphaltenes obtained using different n-heptane/crude oil ratios (HCORs) were analyzed using atmospheric pressure photoionization (APPI) and laser desorption ionization (LDI) coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The main objective was to improve the understanding of the components of the crude oil that precipitate under different solvent power conditions. Analysis of the compositional distribution of the asphaltenes reveals that the decrease in solvent power produces an increase in double bond equivalent (DBE) and the number of heteroatoms per molecule, while the carbon number remains almost unaltered. This finding seems to indicate that one of the main drivers for precipitation is aromaticity as HCOR increases and, consequently, the solvent power decreases. Both APPI and LDI FT-ICR MS produce average values that describe the general tendencies obtained using other techniques. Additionally, APPI FT-ICR MS closely matches bulk data of the m...

Polycyclic Aromatic Hydrocarbons (PAHs) in Ambient Aerosols from Beijing: Characterization of Low Volatile PAHs by Positive-Ion Atmospheric Pressure Photoionization (APPI) Coupled with Fourier Transform Ion Cyclotron Resonance

Aromatic fractions derived from aerosol samples were characterized by gas chromatography and mass spectrometry (GC-MS), high temperature simulated distillation (SIMDIS), and positive-ion atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), respectively. It was found that about 27 wt % compounds in aromatic fractions could not be eluted from a GC column and some large molecule PAHs were neglected in GC-MS analysis. APPI FT-ICR MS was proven to be a powerful approach for characterizing the molecular composition of aromatics, especially for the large molecular species. An aromatic sample from Beijing urban aerosol was successfully characterized by APPI FT-ICR MS. Results showed that most abundant aromatic compounds in PM2.5 (particles with aerodynamic diameter ≤ 2.5 μm) were highly condensed hydrocarbons with 4-8 aromatic rings and their homologues with very short alkyl chains. Furthermore, heteroatom-containing hydrocarbons were found as the significant components of the aromatic fractions: O1, O2, N1, and S1 class species with 10-28 DBEs (double bond equivalents) and 14-38 carbon numbers were identified by APPI FT-ICR MS. The heteroatom PAHs had similar DBEs and carbon number distribution as regular PAHs.

An evaluation of the aromaticity of asphaltenes using atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry – APPI(±)FT-ICR MS

Asphaltenes can be considered like the ‘bad guys‘ when heavy petroleum are transported or upgraded. These compounds are not classified by the their chemical structures but by the solubility class, that is defined as solubles in aromatic solvents, such as toluene, and insolubles in n-alkanes, such as n-heptane. Here, we analyze three crude oil samples (classified as extra-heavy, heavy and asphaltic having API degree of 17.3, 22.0 and 13.5, respectively) and their asphaltenes by atmospheric pressure photoionization (APPI) coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in positive and negative ionization modes, APPI(±)-FT-ICR MS. We apply the DBE (double bond equivalent) versus carbon number (CN) plots as the aim of to predict the aromaticity of crude oil and their asphaltenes. Additionally, average molecular weight, Mw, heteroatomic-containing compounds profile and van Krevelen diagrams were constructed to visualize and interpret the MS data. MS data were compared and discussed with aromaticity parameters obtained from elemental analyses and 1H NMR measurements. For three crude oils analyzed with different magnitude of the viscosities (III>II>I), the amount of the asphaltene extracted follower the behavior analogous (7.63±0.65wt%; 2.23±0.25wt%; and 0.41±0.01wt%, respectively). The aromatic hydrogen content (Har, in molar%) was determined from 1H NMR, where the heavier crude oil and its asphaltene (Har=4.90 and 27.3M%, respectively) were slightly more aromatic than other. An inverse correlation was observed between Har values and the N and O concentrations determined from elemental analyses. For APPI(±)FT-ICR MS data, the values of Mw observed for asphaltenes (m/z 200–650) were significantly distinct, being correlated with the physico-chemical characteristics of their parent crude oil. Using the concept of planar limited, the line generated by connecting maximum DBE values at given CN in the DBE versus carbon number plots, it was possible to extract the aromaticity degree from APPI FT-ICR MS data. The slopes of these lines determined by DBE/carbon number ratio were calculated by linear regression for protonated hydrocarbons (HC[H]) and basic nitrogen (N[H]) compounds classes. We observed an increase in slopes in function of an increasing of the Har values.

Classification of crude oil samples through statistical analysis of APPI FTICR mass spectra

Characterization and classification of crude oil is done following different approaches. Geochemistry investigations on one hand are focused on finding and quantifying markers characteristic of the oil, to provide detailed information about the geological history, the conditions of sedimentation of the oil and of the source rock. On the other hand Fourier transform ion cyclotron mass spectrometry (FTICR MS) has been proved to be a powerful tool in the analysis of crude oil at the molecular level. In this study, a group of fourteen samples of crude oil coming from different fields around the world has been analyzed through Atmospheric Pressure Photoionization (APPI) coupled to FTICR MS. Since the comparison of the many complex APPI FTICR mass spectra is complicated, we have applied statistical methods such as Principal Component Analysis (PCA) and hierarchical clustering (HCA) considering the peaks of the mass spectra. The statistical analysis has found to be able to group the oils according to the well where they have been extracted and from their geographical origin.

Application of Comprehensive 2D GC-MS and APPI FT-ICR MS for More Complete Understanding of Chemicals in Diesel Fuel

In this study, comprehensive two dimension gas chromatography (2D GC-MS) and 15 T Fourier transform ion cyclo- tron resonance mass spectrometry (15T FT-ICR MS) connected to atmospheric pressure photo ionization (APPI) have been combined to obtain detailed chemical composition of a diesel oil sample. With 2D GC-MS, compounds with aliphatic alkyl, sat- urated cyclic ring(s), and one aromatic ring structures were mainly identified. Sensitivity toward aromatic compounds with more than two aromatic rings was low with 2D GC-MS. In contrast, aromatic compounds containing up to four benzene rings were identified by APPI FT-ICR MS. Relatively smaller abundance of cyclic ring compounds were found but no aliphatic alkyl com- pounds were observed by APPI FT-ICR MS. The data presented in this study clearly shows that 2D GC-MS and 15T FT-ICR MS provides different aspect of an oil sample and hence they have to be considered as complementary techniques to each other for more complete understanding of oil samples.

Compositional Characterization of Petroleum Heavy Oils Generated from Vacuum Distillation and Catalytic Cracking by Positive-mode APPI FT-ICR Mass Spectrometry

Molecular compositions of two types of heavy oil were studied using positive atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Vacuum gas oil (VGO) was generated from vacuum distillation of atmospheric residual oil (AR), and slurry oil (SLO) was generated from catalytic cracking of AR. These heavy oils have similar boiling point ranges in the range of 210-, but they showed different mass ranges and double-bond equivalent (DBE) distributions. Using DBE and carbon number distributions, aromatic ring distributions, and the extent of alkyl side chains were estimated. In addition to the main aromatic hydrocarbon compounds, those containing sulfur, nitrogen, and oxygen heteroatoms were identified using simple sample preparation and ultra-high mass resolution FT-ICR MS analysis. VGO is primarily composed of mono- and di-aromatic hydrocarbons as well as sulfur-containing hydrocarbons, whereas SLO contained mainly polyaromatic hydrocarbons and sulfur-containing hydrocarbons. Both heavy oils contain polyaromatic nitrogen components. SLO inludes shorter aromatic alkyl side chains than VGO. This study demonstrates that APPI FT-ICR MS is useful for molecular composition characterization of petroleum heavy oils obtained from different refining processes.