Pressure Photoionization Research Articles

Characterization of deasphalted heavy fuel oil using APPI (+) FT-ICR mass spectrometry and NMR spectroscopy

Asphaltenes are n-alkane insoluble compounds found in crude oils and heavy fuels (high and non-boiling petroleum fractions). Asphaltene molecular structure has not been fully elucidated, and their presence in fuels is a source of concern. They reduce combustion efficiency and are responsible for particulate matter emissions. Removing the asphaltenes, or deasphalting, is a way of upgrading the fuel to improve its quality. This study reports the removal of asphaltenes from heavy fuel oil (HFO) using a solvent extraction method, and the detailed molecular characterization of the deasphalted oil (DAO) using positive ion atmospheric pressure photo ionization Fourier transform-ion cyclotron resonance mass spectrometry (APPI (+) FT-ICR/MS) and 1H and 13C Nuclear magnetic resonance (NMR) spectroscopy. Approximately 8.2 mass % of asphaltenes were removed from HFO using n-heptane as solvent. This resulted in significant improvements in the HFO’s physical properties. The resulting DAO was five times less viscous and contained significantly less heavy metals (e.g., Ni and V). There was also a slight reduction in the sulfur content from 3.3 to 3.1 mass %. 52,753 and 46,315 ions with a mass to charge ratio (m/z) ranging from 154 to 1200 were detected in HFO and DAO samples, respectively, using APPI FT-ICR/MS. Amongst them, 6729 (HFO) and 6030 (DAO) ions were resolved into their underlying elemental compositions (C, H, O, N and S) and a unique chemical formula was assigned to each mass. The resolved masses were then further classified based on their molecular class and were analyzed as a function of double bond equivalent (DBE) vs carbon number. 1H and 13C NMR analyses of HFO and DAO were performed and the results indicate the total aromatic groups in HFO (1H 7.7 mol %, 13C 37.6 mol %) are more compared to DAO (1H 4.7 mol %, 13C 32.6 mol %). The average molecular parameters (AMPs) of HFO and DAO were also calculated from the 1H and 13C NMR spectra and compared. A surrogate molecule that visualizes the average molecular structure of the entire fuel was developed for both HFO and DAO using the data from the above analytical techniques. Understanding the molecular chemistry of these fuels provides valuable data to develop better desulfurization techniques for these sulfur laden fuels and help predict fuel properties using structure-property relationships.

Characterization of ion transmission in UV-FAIMS by incorporating ion recombination

High-field asymmetric waveform ion mobility spectrometry (FAIMS) is a powerful technique for the separation and characterization of gas-phase ions. However, the quantitative model for this technique is incomplete because previous studies on ion loss have mostly focused on ion neutralization and diffusion in the separation process and neglected ion annihilation owing to ion recombination in the transmission process. In this work, an ion recombination model of UV-FAIMS was described and validated using a broad range of experimental gas flow rates (0–800 L/h) and concentrations (10 ppb–100 ppm). The theoretical analysis provided a new solution method for important parameters and indicated the existence of a linear growth interval and a point of saturated signal intensity, both of which were explained by the introduced recombination loss factor and validated experimentally. In particular, the existence of saturation was verified for the first time. Based on this theory, ionization efficiencies of 4.56 × 10−5, 5.41 × 10−5, and 4.47 × 10−6 were calculated for 1,3-butadiene, acetone, and ammonia, respectively, at atmospheric pressure, with corresponding the recombination coefficients of 2.56 × 10−7, 3.74 × 10−7, and 1.89 × 10−8 cm3s−1. Further, an optimized quantitative model of UV-FAIMS was proposed by incorporating ion recombination theory, providing the optimum quantitative interval and a parameter optimization method for UV-FAIMS, which were also validated using a wide range of experimental conditions. This work provides a basis for parameter optimization for UV-FAIMS and a new method of determining the ionization efficiency and recombination coefficient of a gas-phase analyte. Furthermore, the incorporation of ion recombination theory is instructive for the construction of quantitative models of atmospheric-pressure photoionization mass spectrometry and UV-ion mobility spectrometry.

ESI outcompetes other ion sources in LC/MS trace analysis.

Choosing an appropriate ion source is a crucial step in liquid chromatography mass spectrometry (LC/MS) method development. In this paper, we compare four ion sources for LC/MS analysis of 40 pesticides in tomato and garlic matrices. We compare electrospray ionisation (ESI) source, thermally focused/heated electrospray (HESI), atmospheric pressure photoionisation (APPI) source with and without dopant, and multimode source in ESI mode, atmospheric pressure chemical ionisation (APCI) mode, and combined mode using both ESI and APCI, i.e. altogether seven different ionisation modes. The lowest limits of detection (LoDs) were obtained by ESI and HESI. Widest linear ranges were observed with the conventional ESI source without heated nebuliser gas. In comparison to HESI, ESI source was significantly less affected by matrix effect. APPI ranked second (after ESI) by not being influenced by matrix effect; therefore, it would be a good alternative to ESI if low LoDs are not required. Graphical abstract.

Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Characterization of Oil Sand Process-Affected Water in Constructed Wetland Treatment

The remediation of oil sand process-affected water (OSPW) generated during the bitumen extraction in the oil sand region of Canada is an area of ongoing research interest. One of the primary remediation challenges is the removal of residual complex organic compounds present in the OSPW. In the present study, the molecular constitution of OSPW from aerated and nonaerated wetland treatments were characterized in constructed wetland treatment systems. Negative-ion and positive-ion atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was used to provide extensive molecular-level analysis of the samples. Multiple aerated and nonaerated treatment wetland systems were characterized in terms of naphthenic acids (NAs), oxy-NAs, heteroatom NAs class, and double bond equivalent (DBE) versus carbon number to evaluate their molecular composition and variability. A broad range of heteroatom compound classes with variable relative abundances were identified....

Molecular-level investigation of soils contaminated by oil spilled during the Gulf War.

In this study, molecular-level chemical compositions of soils contaminated by oil spilled during the Gulf War were studied. Two soil samples, respectively collected at 0.1 m and between 0.5 and 1 m below the surface from an oil spill site, were extracted with organic solvents and water. The extracts were analyzed via ultrahigh resolution FT-ICR and two-dimensional gas chromatography/high resolution mass spectrometry. The data showed that the spilled oil was significantly affected by vaporization due to high surface temperatures in the desert. The data obtained with (+) atmospheric pressure photo ionization (APPI) and (-) electrospray ionization (ESI) coupled with ultrahigh resolution-mass spectrometry (UHR-MS) indicated that the degradation of aromatic compounds and increase in oxygen-containing classes occurred in the following order: surface soil > below surface soil > crude oil. The oxygenated compounds were confirmed by principal component analysis. The score and loading plots of Ox and SOx showed that they were the major contributors to differentiate the samples. However, a comparison with previously reported oceanic oil spills showed that less significant degradation occurred even after almost 30 years. Our data can provide an information basis for designing a strategy for clean-up and restoration efforts of Gulf War oil spills.

Comprehensive Petroporphyrin Identification in Crude Oils Using Highly Selective Electron Transfer Reactions in MALDI-FTICR-MS

Petroprophyrins are biomarkers used to extract information about petroleum genesis among other characteristics. Identification of particular types, such as Ni, Cu, Mn, vanadyl (VO), and oxygenated or sulfur-containing porphyrins, typically involves exhaustive isolation and purification processes followed by high-resolution mass spectrometry analysis using atmospheric pressure photoionization [APPI-(+)] or electrospray [ESI-(+)] sources. Simultaneous identification of all porphyrins present in a particular crude oil or organic-matter-rich sediment still remains an analytical challenge. Here, we report a straightforward petroporphyrin isolation and identification methodology based on a single-step liquid–liquid (L–L) extraction (crude oil: acetonitrile) and high-performance thin-layer chromatography fractionation (HPTLC, aminopropyl-bonded silica) followed by selective ionization via electron transfer in matrix-assisted laser desorption ionization (MALDI-FTICR). Mass spectrometric analysis of the extracts r...

Direct target and non-target analysis of urban aerosol sample extracts using atmospheric pressure photoionisation high-resolution mass spectrometry

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous atmospheric pollutants of high concern for public health. In the atmosphere they undergo oxidation, mainly through reactions with ·OH and NOx to produce nitro- and oxygenated (oxy-) derivatives. In this study, we developed a new method for the detection of particle-bound PAHs, nitro-PAHs and oxy-PAHs using direct infusion into an atmospheric pressure photoionisation high-resolution mass spectrometer (APPI-HRMS). Method optimisation was done by testing different source temperatures, gas flow rates, mobile phases and dopants. Samples were extracted with methanol, concentrated by evaporation and directly infused in the APPI source after adding toluene as dopant. Acquisition was performed in both polarity modes. The method was applied to target analysis of seasonal PM2.5 samples from an urban background site in Padua (Italy), in the Po Valley, in which a series of PAHs, nitro- and oxy-PAHs were detected. APPI-HRMS was then used for non-target analysis of seasonal PM2.5 samples and results compared with nano-electrospray ionisation (nanoESI) HRMS. The results showed that, when samples were characterised by highly oxidised organic compounds, including S-containing compounds, like in summer samples, APPI did not bring any additional information with respect to nanoESI in negative polarity (nanoESI(-)). Conversely, for winter samples, APPI(-) could detect a series of aromatic and poly-aromatic compounds, mainly oxidised and nitrogenated aromatics, that were not otherwise detected with nanoESI.

Laser Desorption Combined with Laser Postionization for Mass Spectrometry.

Lasers with pulse lengths from nanoseconds to femtoseconds and wavelengths from the mid-infrared to extreme ultraviolet (UV) have been used for desorption or ablation in mass spectrometry. Such laser sampling can often benefit from the addition of a second laser for postionization of neutrals. The advantages offered by laser postionization include the ability to forego matrix application, high lateral resolution, decoupling of ionization from desorption, improved analysis of electrically insulating samples, and potential for high sensitivity and depth profiling while minimizing differential detection. A description of postionization by vacuum UV radiation is followed by a consideration of multiphoton, short pulse, and other postionization strategies. The impacts of laser pulse length and wavelength are considered for laser desorption or laser ablation at low pressures. Atomic and molecular analysis via direct laser desorption/ionization using near-infrared ultrashort pulses is described. Finally, the postionization of clusters, the role of gaseous collisions, sampling at ambient pressure, atmospheric pressure photoionization, and the addition of UV postionization to MALDI are considered.

Thermogravimetry coupled to an atmospheric pressure photo ionization quadrupole mass spectrometry for the product control of pharmaceutical formulations and the analysis of plasticizers in polymers

The development of a thermogravimetry coupled to an atmospheric pressure photoionization mass spectrometry (TG-APPI-MS) with a high temperature and flexible transfer line is presented. A method was developed to analyze plasticizers in solution which consist of a solvent evaporation step and subsequent evaporation of the analyte. These solutions of dibutyl phthalate (DBP) in hexane were used to investigate the repeatability (RSD: 3.6%) and linearity (R2: 0.9995) of the new developed system. With the new device the detection of different phthalates in a standardized PVC (polyvinyl chloride) polymer is shown. On the example of ASA, the degradation of a pharmaceutical drug is investigated. The dimerization and the possible trimerization of ASA during the thermal degradation is shown. Ten tablets of different ASA manufacturers were analyzed with the new developed analysis platform. The active substance was found in every tablet. Differences in mass spectral data as well as the studying of the pack insert were used to assign the tablets to companies and their subsidiaries. A unique formulation of ASA was found to have a different mass pattern when analyzed with TG-APPI-qMS. The developed device is a promising tool for the product control and the identification of falsified drugs.

Atmospheric Pressure Photoionization Mass Spectrometry: New Capabilities for the Determination of the Numbers of Components in Complex Mixtures and Their Identification

The atmospheric pressure photoionization and photochemical ionization mass spectrometry (APPI/APPCI−MS) makes it possible to compare the number of peaks in a mass spectrum with the number of components in the test mixture because of the measurements of the mass spectra of individual compounds, which mainly consist of the peaks of a molecular ion (M+) or a protonated molecule (MH+). The capabilities of gas chromatography–electron ionization (EI) and atmospheric pressure ionization mass spectrometry for the identification of trace components of complex mixtures are considered. The advantages of APPI/APPCI−MS, which makes it possible to increase the reliability of the detection of components in the complex mixtures of organic compounds, over EI mass spectrometry are shown. The work was performed at the Department of Analytical Chemistry, Faculty of Chemistry, Moscow State University.

Molecular-Level Characterization of Asphaltenes Isolated from Distillation Cuts

Asphaltenes challenge nearly all analytical techniques because of their immense polydispersity in molecular composition and structure. This operationally defined fraction of crude oil, insoluble in n-alkanes but soluble in aromatic solvents, is known to concentrate in vacuum residues and islinked to fouling and deposition issues. However, presence and subsequent characterization of asphaltenes are seldom discussed in conventional/unconventional distillate fractions. Here, we isolate asphaltenes from conventional ( 593 °C) distillation cuts and provide molecular-level characterization by electrospray ionization and atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry as a function of boiling point. Our results indicate that asphaltene molecular composition starts in the vacuum gas oil range and extends into vacuum residues. Moreover, we report that distillable asphaltene composition exists as both highly polar (heteroatom rich)...

Petroleomic depth profiling of Staten Island salt marsh soil: 2ω detection FTICR MS offers a new solution for the analysis of environmental contaminants

Staten Island is located in one of the most densely populated regions of the US: the New York/New Jersey Estuary. Marine and industrial oil spills are commonplace in the area, causing the waterways and adjacent marshes to become polluted with a range of petroleum-related contaminants. Using Rock-Eval pyrolysis, the hydrocarbon impact on a salt marsh was assessed at regular intervals down to 90 cm, with several key sampling depths of interest identified for further analysis. Ultrahigh resolution data are obtained by direct infusion (DI) atmospheric pressure photoionization (APPI) on a 12 T solariX Fourier transform ion cyclotron resonance mass spectrometer (FTICR MS) allowing trends in the compositional profile with depth to be observed, such as changes in the relative hydrocarbon intensity and the relative contributions from oxygen- and sulfur-containing groups. These trends may correlate with the timing of major oil spills and leaks of petroleum and other industrial chemicals into the waterways. The use of gas chromatography (GC) coupled to a 7 T solariX 2XR FTICR MS equipped with an atmospheric pressure chemical ionization (APCI) ion source offers retention time resolved and extensive compositional information for the complex environmental samples complementary to that obtained by DI-APPI. The compositional profile observed using GC-APCI FTICR MS includes contributions from phosphorous-containing groups, which may be indicative of contamination from other anthropogenic sources.

Is methanol a dopant under atmospheric pressure photoionization conditions?

Using a modified atmospheric pressure photoionization (APPI) source coupled to a tunable vacuum ultraviolet source at the SOLEIL synchrotron radiation facility, we determined the appearance energy of protonated methanol monomer and dimers at different source temperatures. The experimental data indicated that protonated monomers can be formed through the direct photoionization of neutral methanol by the second emission band of a krypton discharge UV lamp at 116.49 nm (10.64 eV) explaining why methanol can be considered as a weak dopant under APPI conditions. This point is in contradiction with the previously proposed mechanism where photoionization of methanol dimer was followed by the dissociation of the protonated methanol dimer into protonated methanol monomer.

Sweep Jet Collection Laser-Induced Acoustic Desorption Atmospheric Pressure Photoionization for Lipid Analysis Applications.

Laser-induced acoustic desorption coupled to microplasma-based atmospheric pressure photoionization (LIAD-APPI) using a nebulized sweep jet to aid in dopant introduction and ion transmission has been applied to the analysis of model, apolar lipid compounds. Specifically, several sterols, sterol esters, and triacylglycerols were detected using dopants such as anisole and toluene. Additionally, several triacylglycerols, sterols, carboxylic acids, and hopanoids were detected from complex mixtures of olive oil and Australian shale rock extract as a first demonstration of the applicability of LIAD-APPI on real-world samples. Detection limits using a sweep jet configuration for α-tocopherol and cholesterol were found to be 609 ± 61 and 292 ± 29fmol, respectively. For sterol esters and triacylglycerols with a large number of double bonds in the fatty acid chain, LIAD-APPI was shown to yield greater molecular ion or [M+NH4]+ abundances than those with saturated fatty acid chains. Dopants such as anisole and toluene, with ionization potentials (IPs) of 8.2 and 8.8eV, respectively, were tested. A greater degree of fragmentation with several of the more labile test compounds was observed using toluene. Overall, LIAD-APPI with a nebulized sweep jet requires minimal sample preparation and is a generally useful and sensitive analysis technique for low-polarity mixtures of relevance to biochemical assays and geochemical profiling. Graphical Abstract.

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.

Atmospheric pressure chemical ionisation (APCI) and photoionisation (APPI) mass spectrometry for detection of unsaturated fatty acids: potential for rapid detection of adulteration of vegetable oils

Unsaturated fatty acids of vegetable oils can be rapidly determined with APCI and APPI mass spectrometry by comparison to standards. The difference in the ionization efficiencies of FA can be addressed by calculation of correction factors.

Direct and rapid analysis of trace levels steroids in water by thermal desorption atmospheric pressure photoionization mass spectrometry

A novel TD-APPI technique for steroid analysis at trace levels from a 10 μL water sample without derivatization and chromatographic separation.

High‐resolution GC/MS studies of a light crude oil fraction

The continuous development in analytical instrumentation has brought the newly developed Orbitrap-based gas chromatography / mass spectrometry (GC/MS) instrument into the forefront for the analysis of complex mixtures such as crude oil. Traditional instrumentation usually requires a choice to be made between mass resolving power or an efficient chromatographic separation, which ideally enables the distinction of structural isomers that is not possible by mass spectrometry alone. Now, these features can be combined, thus enabling a deeper understanding of the constituents of volatile samples on a molecular level. Although electron ionization is the most popular ionization method employed in GC/MS analysis, the need for softer ionization methods has led to the utilization of atmospheric pressure ionization sources. The last arrival to this family is the atmospheric pressure photoionization (APPI), which was originally developed for liquid chromatography / mass spectrometry (LC/MS). With a newly developed commercial GC-APPI interface, it is possible to extend the characterization of unknown compounds. Here, first results about the capabilities of the GC/MS instrument under high or low energy EI or APPI are reported on a volatile gas condensate. The use of different ionization energies helps matching the low abundant molecular ions to the structurally important fragment ions. A broad range of compounds from polar to medium polar were successfully detected and complementary information regarding the analyte was obtained.

Interfacing Digital Microfluidics with Ambient Mass Spectrometry Using SU-8 as Dielectric Layer.

This work describes the interfacing of electrowetting-on-dielectric based digital microfluidic (DMF) sample preparation devices with ambient mass spectrometry (MS) via desorption atmospheric pressure photoionization (DAPPI). The DMF droplet manipulation technique was adopted to facilitate drug distribution and metabolism assays in droplet scale, while ambient mass spectrometry (MS) was exploited for the analysis of dried samples directly on the surface of the DMF device. Although ambient MS is well-established for bio- and forensic analyses directly on surfaces, its interfacing with DMF is scarce and requires careful optimization of the surface-sensitive processes, such as sample precipitation and the subsequent desorption/ionization. These technical challenges were addressed and resolved in this study by making use of the high mechanical, thermal, and chemical stability of SU-8. In our assay design, SU-8 served as the dielectric layer for DMF as well as the substrate material for DAPPI-MS. The feasibility of SU-8 based DMF devices for DAPPI-MS was demonstrated in the analysis of selected pharmaceuticals following on-chip liquid-liquid extraction or an enzymatic dealkylation reaction. The lower limits of detection were in the range of 1–10 pmol per droplet (0.25–1.0 µg/mL) for all pharmaceuticals tested.

Synthesis, APPI Mass-Spectrometric Characterization, and Polymerization Studies of Group 4 Dinuclear Bis(ansa-metallocene) Complexes

New ligand platforms of the type p- or m-Ph{-CR(3,6-tBu2Flu)(Cp)}2 (para-, R = Me (2a), H (2b); meta-, R = Me (2c)) were synthesized via nucleophilic addition of the 3,6-tBu2-fluorenyl-anion onto the parent phenylene-bridged difulvenes (1a–c). The corresponding discrete homodinuclear zirconium and hafnium bis(dichloro ansa-metallocene) complexes, Ph[{-CR(3,6-tBu2Flu)(Cp)}MCl2]2 (p-, R = Me (3a-Zr2, 3a-Hf2), R = H (3b-Zr2); m-, R = Me (3c-Zr2), were prepared by salt metathesis reactions. An attempt to generate in situ a heterodinuclear complex 3a-Zr-Hf was also undertaken. For the first time, Atmospheric Pressure PhotoIonization (APPI) mass-spectrometric data were obtained for all dinuclear compounds and found to be in excellent agreement with the simulated ones. Preliminary studies on the catalytic performances of these dinuclear complexes, upon activation with MAO, in ethylene homopolymerization and ethylene/1-hexene copolymerization revealed a few differences as compared to those of the monometallic analogues. In particular, slightly lower molecular weights and a greater formation of short methyl and ethyl branches were obtained with the dinuclear systems.