Molecular Characterization of Volatiles and Petrochemical Base Oils by Photo-Ionization GC×GC-TOF-MS

Micro gas chromatographic column with copper benzene-1,3,5-tricarboxylate modified by multilayer fluorinated graphene as a stationary phase

A composite material was synthesized at room temperature by performing modification of the copper benzene-1,3,5-tricarboxylate (HKUST-1) metal-organic framework material by multilayer fluorinated graphene (FG). The FG-HKUST-1 composite was used as a stationary phase for a micro gas chromatography column (μGCC) fabricated using micro-electro-mechanical system (MEMS) technology. The separation results showed that the μGCC with the FG-HKUST-1 composite stationary phase achieved a baseline separation of C1-C4 in 8 min. The retention factors for C2-C4 were 2.13, 7.14, and 12.04, respectively. The maximum relative standard deviation (RSD) of the retention times was 0.14 %. The difference in the retention time between methane and ethane was 1.11 min, with a resolution of 9.2 for methane and ethane. The retention factor of ethane and the resolution of methane and ethane were increased by 166 % and 114 %. Therefore, this μGCC is promising for separating light hydrocarbons with widely differing concentrations.

Comprehensive two-dimensional gas chromatography- A discussion on recent innovations

Although comprehensive 2-D GC is an established and often applied analytical method, the field is still highly dynamic thanks to a remarkable number of innovations. In this review, we discuss a number of recent developments in comprehensive 2-D GC technology. A variety of modulation methods are still being actively investigated and many exciting improvements are discussed in this review. We also review interesting developments in detection methods, retention modeling, and data analysis.

A Simple High-Flux Switchable VUV Lamp Based on an Electrodeless Fluorescent Lamp for SPI/PAI Mass Spectrometry

Single-photon ionization (SPI) is a unique soft ionization technique for organic analysis. A convenient high-flux vacuum ultraviolet (VUV) light source is a key precondition for wide application of SPI techniques. In this study, we present a novel VUV lamp by simply modifying an ordinary electrodeless fluorescent lamp. By replacing the glass bulb with a stainless steel bulb and introducing 5% Kr/He (v/v) as the excitation gas, an excellent VUV photon flux over 4.0 × 1014 photons s-1 was obtained. Due to its rapid glow characteristics, the VUV lamp can be switched on and off instantly as required by detection, ensuring the stability and service life of the lamp. To demonstrate the performance of the new lamp, the switchable VUV lamp was coupled with an SPI-mass spectrometer, which could be changed to photoinduced associative ionization (PAI) mode by doping gaseous CH2Cl2 to initiate an associative ionization reaction. Two types of volatile organic compounds sensitive to SPI and PAI, typically benzene series and oxygenated organics, respectively, were selected as samples. The instrument exhibited a high detection sensitivity for the tested compounds. With a measurement time of 11 s, the 3σ limits of detection ranged from 0.33 to 0.75 pptv in SPI mode and from 0.03 to 0.12 pptv in PAI mode. This study provides an extremely simple method to assemble a VUV lamp with many merits, e.g., portability, robustness, durability, low cost, and high flux. The VUV lamp may contribute to the development of SPI-related highly sensitive detection technologies.

A simple soft ionization approach for GC-MS assisted by capillary array

Electron ionization (EI) is the most widely used ionization method in gas chromatography/mass spectrometry (GC-MS). This method possesses a lot of advantages including versatility for various classes of volatile and semi volatile organic compounds, high sensitivity, structure informativity and reproducibility, production of database searchable mass spectra. On the other hand there are a number of compounds, which molecular ions are not stable enough to produce corresponding peaks in EI mass spectra, making it difficult to determine structures of compounds not presented in databases. A new approach allowing easy implementation of EI in a molecular beam formed by a capillary assembly is proposed for discussion in this communication. Primary experimental results achieved using this approach demonstrate its possibility to produce suitable for database search mass spectra with increased intensity of molecular ion peak.

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.

Determination of Barbiturates by Femtosecond Ionization Mass Spectrometry

Barbiturates are highly susceptible to dissociation in mass spectrometry (MS) because of their long side chains combined with a nonaromatic ring consisting of several carbonyl and amine groups. As a result, they exhibit extensive α-cleavage and subsequent rearrangement, making the identification of these compounds difficult. Although a library of electron ionization MS (EIMS) is available, most barbiturates have very similar fragment patterns. Accordingly, it would be desirable to develop a technique for soft ionization, providing a molecular ion and large fragment ions as well. In this study, a molecular ion was clearly observed, in addition to large fragment ions, for a variety of barbiturates based on multiphoton ionization MS (MPIMS) using a tunable ultraviolet femtosecond laser as the ionization source (fs-LIMS). This favorable result was achieved when the optimal laser wavelength for minimizing the excess energy remaining in the ionic state was used. An examination of the photofragmentation pathways suggested that an H atom in the side chain was abstracted by an oxygen atom in the carbonyl group in the ring structure thus initiating fragmentation and subsequent rearrangement. Barbiturates that are substituted with alkyl groups (amobarbital and pentobarbital) had narrower spectral regions for optimal ionization than the other barbiturates with alkyl and alkenyl groups (butalbital and secobarbital) and more with alkyl and phenyl groups (phenobarbital). All of the barbiturates studied provided unique mass spectral patterns in fs-LIMS, which was useful for the reliable identification of these compounds in practical trace analysis.

UPLC-Q-TOF-MS/MS Analysis of Seco-Sativene Sesquiterpenoids to Detect New and Bioactive Analogues From Plant Pathogen Bipolaris sorokiniana

Seco-sativene sesquiterpenoids are an important member of phytotoxins and plant growth regulators isolated from a narrow spectrum of fungi. In this report, eight seco-sativene sesquiterpenoids (1-8) were first analyzed using the UPLC-Q-TOF-MS/MS technique in positive mode, from which their mass fragmentation pathways were suggested. McLafferty rearrangement, 1,3-rearrangement, and neutral losses were considered to be the main fragmentation patterns for the [M+1]+ ions of 1-8. According to the structural features (of different substitutes at C-1, C-2, and C-13) in compounds 1-8, five subtypes (A-E) of seco-sativene were suggested, from which subtypes A, B/D, and E possessed the diagnostic daughter ions at m/z 175, 189, and 203, respectively, whereas subtype C had the characteristic daughter ion at m/z 187 in the UPLC-Q-TOF-MS/MS profiles. Based on the fragmentation patterns of 1-8, several known compounds (1-8) and two new analogues (9 and 10) were detected in the extract of plant pathogen fungus Bipolaris sorokiniana based on UPLC-Q-TOF-MS/MS analysis, of which 1, 2, 9, and 10 were then isolated and elucidated by NMR spectra. The UPLC-Q-TOF-MS/MS spectra of these two new compounds (9 and 10) were consistent with the fragmentation mechanisms of 1-8. Compound 1 displayed moderate antioxidant activities with IC50 of 0.90 and 1.97 mM for DPPH and ABTS+ scavenging capacity, respectively. The results demonstrated that seco-sativene sesquiterpenoids with the same subtypes possessed the same diagnostic daughter ions in the UPLC-Q-TOF-MS/MS profiles, which could contribute to structural characterization of seco-sativene sesquiterpenoids. Our results also further supported that UPLC-Q-TOF-MS/MS is a powerful and sensitive tool for dereplication and detection of new analogues from crude extracts of different biological origins.

Deeper investigation of oxygen-containing compounds in oleaginous feedstock (animal fat) by preparative column chromatography and comprehensive two-dimensional gas chromatography coupled with high-resolution time-of-flight mass spectrometry

The production of renewable fuels as biodiesel and bio-jet fuel is usually originated by the transformation and processing of oleaginous feedstocks, mainly composed of triacylglycerols. Currently, a significant part of the triacylglycerol production relies on grassy oil crops or other woody oil plants, representing more than 120 million metric tons every year. Considering that the worldwide triacylglycerol demand is expected to rise in the future, alternative routes are necessary to ensure a sustainable biodiesel industry and limit diesel price volatility. In this context, the use of animal fats could be an interesting alternative for biodiesel production as the production of animal byproducts represents nearly 17 million tons per year in the European Union only (2020). Animal fats, however, contain large amounts of no-esterified fatty acids and other oxygen compounds, reducing the yield of biodiesel. Therefore, a specific pretreatment is needed before the trans-esterification process. The setup of such appropriate pretreatments requires detailed upstream characterization of the minor components present in the feedstock. For this purpose, the minor component profile of animal fat was investigated by comprehensive two-dimensional gas chromatography coupled with high-resolution time-of-flight mass spectrometry. This was preceded by an innovative sample fractionation and focalization of these minor components by a preparative liquid chromatographic column method. The overall method permitted to extract different levels of information from the two-dimensional chromatograms, leading to a tentative identification of more than 150 compounds, mainly oxygenated, belonging to different chemical classes.

Two-Dimensional Gas Chromatographic and Mass Spectrometric Characterization of Lipid-Rich Biological Matrices-Application to Human Cerumen (Earwax)

Earwax is a readily accessible biological matrix that has the potential to be used in disease diagnostics. However, its semisolid nature and high chemical complexity have hampered efforts to investigate its potential to reveal disease markers. This is because more conventional methods of analysis such as gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry yield unsatisfactory results due to the presence of many nonvolatile and/or coeluting compounds, which in some cases have very similar mass spectrometric profiles. In addition, these routine methods often require the sample to be saponified, which dramatically increases the complexity of the analysis and makes it difficult to determine which compounds are actually present versus those that are produced by saponification. In this study, two-dimensional GC mass spectrometry (GC × GC-MS) was successfully applied for the characterization of the chemical components of earwax from healthy donors using nonpolar (primary) and midpolar (secondary) columns without saponification. Over 35 of the compounds that were identified are reported for the first time to be detected in unsaponified earwax. The resulting GC × GC-MS contour plots revealed visually recognizable compound class clusters of previously reported groups including alkanes, alkenes, fatty acids, esters, triglycerides, and cholesterol esters, as well as cholesterol and squalene. The application of GC × GC-MS revealed results that provide a foundation upon which future studies aimed at comparing healthy donor earwax to that from individuals exhibiting various disease states can be accomplished.

Breathomics to diagnose systemic sclerosis using thermal desorption and comprehensive two-dimensional gas chromatography high-resolution time-of-flight mass spectrometry

Systemic sclerosis is a rare autoimmune disease associated with rapidly evolving interstitial lung disease, responsible for the disease severity and mortality. Specific biomarkers enabling the early diagnosis and prognosis associated with the disease progression are highly needed. Volatile organic compounds in exhaled breath are widely available and non-invasive and have the potential to reflect metabolic processes occurring within the body. Comprehensive two-dimensional gas chromatography coupled to high-resolution mass spectrometry was used to investigate the potential of exhaled breath to diagnose systemic sclerosis. The exhaled breath of 32 patients and 30 healthy subjects was analyzed. The high resolving power of this approach enabled the detection of 356 compounds in the breath of systemic sclerosis patients, which was characterized by an increase of mainly terpenoids and hydrocarbons. In addition, the use of 4 complementary statistical approaches (two-tailed equal variance t-test, fold change, partial least squares discriminant analysis, and random forest) resulted in the identification of 16 compounds that can be used to discriminate systemic sclerosis patients from healthy subjects. Receiver operating curves were generated that provided an accuracy of 90%, a sensitivity of 92%, and a specificity of 89%. The chemical identification of eight compounds predictive of systemic sclerosis was validated using commercially available standards. The analytical variations together with the volatile composition of room air were carefully monitored during the timeframe of the study to ensure the robustness of the technique. This study represents the first reported evaluation of exhaled breath analysis for systemic sclerosis diagnosis and provides surrogate markers for such disease.

Unraveling the Complex Olefin Isomer Mixture Using Two-Dimensional Gas Chromatography-Photoionization-Time of Flight Mass Spectrometry

Commercial dodecenes are a complex chemical mixture with a majority of C₁₂ olefins and minority of C_8-18 olefins. Structurally, dodecene products may consist of straight-chain alkenes, branched alkenes, as well as cyclic hydrocarbons. Due to the difference of feeds and catalysts used in the oligomerization reaction, the composition of the dodecenes is complex and their properties are very different. Knowing the complex composition of dodecenes can help tune the production process and select the appropriate products according to their end use. To reveal the complex profile of dodecenes, an analytical method using two-dimensional gas chromatography (GC×GC) coupled photoionization (PI) - time of flight mass spectrometry (TOFMS) was developed in this study. A conventional (nonpolar × polar) column combination (non-polar column as 1^st dimension and mid-polar column as 2^nd dimension) was selected. The analytical condition of GC was optimized using fractional factorial experimental design (DoE). Olefin congener grouping by carbon chain length and double bond equivalent (DBE) was achieved based on the detection of molecular ions by PI-TOFMS. Grouping of dodecenes by linear, mono-branched, di- and tri-branched subgroups was achieved based on branching index (BI) under the assumption of no retention time (RT) overlap among subgroups. Certain dodecene isomers were identified by retention index (RI) and further confirmed by PI mass spectra. The information altogether provided a multimodal characterization possibility to be used with statistical tools. Principal component analysis (PCA) and hierarchical clustering analysis (HCA) of seventeen dodecene samples explained the composition variance between catalysts solid phosphoric acid and zeolite, as well as between feeds with C₄ and without C₄.

A unique data analysis framework and open source benchmark data set for the analysis of comprehensive two-dimensional gas chromatography software

Comprehensive two-dimensional gas chromatography (GC × GC) is amongst the most powerful separation technologies currently existing. Since its advent in early 1990, it has become an established method which is readily available. However, one of its most challenging aspects, especially in hyphenation with mass spectrometry is the high amount of chemical information it provides for each measurement. The GC × GC community agrees that there, the highest demand for action is found. In response, the number of software packages allowing for in-depth data processing of GC × GC data has risen over the last couple of years. These packages provide sophisticated tools and algorithms allowing for more streamlined data evaluation. However, these tools/algorithms and their respective specific functionalities differ drastically within the available software packages and might result in various levels of findings if not appropriately implemented by the end users. This study focuses on two main objectives. First, to propose a data analysis framework and second to propose an open-source dataset for benchmarking software options and their specificities. Thus, allowing for an unanimous and comprehensive evaluation of GC × GC software. Thereby, the benchmark data includes a set of standard compound measurements and a set of chocolate aroma profiles. On this foundation, eight readily available GC × GC software packages were anonymously investigated for fundamental and advanced functionalities such as retention and detection device derived parameters, revealing differences in the determination of e.g. retention times and mass spectra.

Multimodal combination of GC × GC-HRTOFMS and SIFT-MS for asthma phenotyping using exhaled breath

Chronic inflammatory lung diseases impact more than 300 million of people worldwide. Because they are not curable, these diseases have a high impact on both the quality of life of patients and the healthcare budget. The stability of patient condition relies mostly on constant treatment adaptation and lung function monitoring. However, due to the variety of inflammation phenotypes, almost one third of the patients receive an ineffective treatment. To improve phenotyping, we evaluated the complementarity of two techniques for exhaled breath analysis: full resolving comprehensive two-dimensional gas chromatography coupled to high-resolution time-of-flight mass spectrometry (GC × GC-HRTOFMS) and rapid screening selected ion flow tube MS (SIFT-MS). GC × GC-HRTOFMS has a high resolving power and offers a full overview of sample composition, providing deep insights on the ongoing biology. SIFT-MS is usually used for targeted analyses, allowing rapid classification of samples in defined groups. In this study, we used SIFT-MS in a possible untargeted full-scan mode, where it provides pattern-based classification capacity. We analyzed the exhaled breath of 50 asthmatic patients. Both techniques provided good classification accuracy (around 75%), similar to the efficiency of other clinical tools routinely used for asthma phenotyping. Moreover, our study provides useful information regarding the complementarity of the two techniques.

GC-MS with photoionization of cold molecules in supersonic molecular beams-Approaching the softest ionization method

A new type of photoionization ion source was developed for the ionization of cold molecules in supersonic molecular beams (named Cold PI). The system was based on a GC-MS with supersonic molecular beams and its fly-through EI of cold molecules ion source (Cold EI) plus quadrupole mass analyzer. A continuously operated deuterium VUV photoionization lamp was added and placed above and between the supersonic nozzle and skimmer whereas the Cold EI ion source served only as a portion of the ion transfer ion optics. The supersonic nozzle and skimmer were voltage biased and the VUV light crossed the supersonic expansion about 10 mm from the nozzle. We obtained over three orders of magnitude enhancement in the relative abundance of the molecular ion of squalane in Cold PI versus in photoionization of this compound as a thermal compound. Accordingly, we also proved that standard photoionization is not as soft ionization method as previously perceived for large compounds. We found that Cold PI is as soft as and possibly softer than field ionization; thus, it could be the softest known ionization method. The ionization yield was about 200-300 times weaker than with Cold EI yet our limit of detection was about 200 femtogram in SIM mode for cholesterol and pyrene which is reasonable. Practically, all hydrocarbons gave only molecular ions with rather uniform response whereas alcohols gave some molecular ions plus major fragment ions particularly with a loss of water (similarly to field ionization). We tested Cold PI in the GC-MS analysis of diesel fuels and analyzed the time averaged data for group type information. We also found that we can analyze the diesel fuels by fast under 20-s flow injection analysis in which the generated averaged mass spectrum of molecular ions only could serve for the characterization of fuels.

Real time monitoring of slow pyrolysis of polyethylene terephthalate (PET) by different mass spectrometric techniques

In the context of waste upgrading of polyethylene terephthalate (PET) by pyrolysis, this study presents three on-line mass spectrometric techniques with soft ionization for monitoring the emitted decomposition products and their thermal dependent evolution profiles. Pyrolysis experiments were performed using a thermogravimetric analyzer (TGA) under nitrogen atmosphere with a heating rate of 5 °C/min from 30 °C to 600 °C. Single-photon ionization (SPI at 118 nm/10.5 eV) and resonance enhanced multiple photon ionization (REMPI at 266 nm) were used with time-of-flight mass spectrometry (TOF-MS) for evolved gas analysis (TGA-SPI/REMPI-TOFMS). Additionally, the chemical signature of the pyrolysis products was investigated by atmospheric pressure chemical ionization (APCI) ultra high resolution Fourier Transform ion cyclotron resonance mass spectrometry (FT-ICR MS) which enables assignment of molecular sum formulas (TGA-APCI FT-ICR MS). Despite the soft ionization by SPI, the fragmentation of some compounds with the loss of the [O-CH = CH2] fragment is observed. The major compounds were acetaldehyde (m/z 44), benzoic acid (m/z 122) and a fragment of m/z 149. Using REMPI, aromatic species were selectively detected. Several series of pyrolysis products were observed in different temperature intervals, showing the presence of polycyclic aromatic hydrocarbons (PAHs), especially at high temperatures. FT-ICR MS data showed, that the CHO₄ class was the most abundant compound class with a relative abundance of 45.5%. The major compounds detected with this technique corresponded to m/z 193.0495 (C₁₀H₉O₄⁺) and 149.0233 (C₈H₅O₃⁺). Based on detailed chemical information, bulk reaction pathways are proposed, showing the formation of both cyclic monomer/dimer and linear structures.

Multi-capillary column high-pressure photoionization time-of-flight mass spectrometry and its application for online rapid analysis of flavor compounds

High-pressure photoionization time-of-flight mass spectrometry (HPPI-TOFMS) is a versatile and highly sensitive analytical technique for online and real-time analysis of trace volatile organic compounds in complex mixtures. However, discrimination of isomers is usually a great challenge for the soft ionization method, and matrix effect is also inevitable under high pressure in the HPPI source. In this work, we describe a first attempt to develop a two-dimensional (2D) hyphenated instrument by coupling of a multi-capillary column (MCC) with a HPPI-TOFMS to overcome these problems. The capability of the MCC-HPPI-TOFMS for discrimination of isomeric compounds and elimination of the matrix effect was demonstrated by analyzing flavor mixtures. With the merits of fast separation, soft ionization and high detection sensitivity, satisfactory effects in the 2D analysis were achieved, despite the relatively low chromatographic resolution of MCC. As a result, three isomers, eucalyptol, l-menthone and linalool, in a flavor mixture were successfully categorized within 90 s, and the matrix effect caused by solvent ethanol was significantly eliminated as well. The limits of detection (LODs) down to sub-ppbv level were achieved for the investigated five flavor compounds without any enrichment process, and an excellent repeatability was obtained with the relative standard deviations (RSDs) of signal intensities ≤5%. The MCC-HPPI-TOFMS system was preliminarily applied for rapid and online analysis of flavor compounds in the exhaled gas of a volunteer after mouth rinsing with a gargle product. The rapid changes of the three flavor compounds, as well as the steady endogenous metabolite acetone, in the exhaled gas were successfully determined with a time-resolution of only 1.5 min.

Compositional elucidation of heavy petroleum base oil by GC × GC-EI/PI/CI/FI-TOFMS

Comprehensive two-dimensional gas chromatography (GC × GC) coupled to time-of-flight mass spectrometry is a powerful separation tool for complex petroleum product analysis. However, the most commonly used electron ionization (EI) technique often makes the identification of the majority of hydrocarbons impossible due to the exhaustive fragmentation and lack of molecular ion preservation, prompting the need of soft-ionization energies. In this study, three different soft-ionization techniques including photo ionization (PI), chemical ionization (CI), and field ionization (FI) were compared against EI to elucidate their relative capabilities to reveal different base oil hydrocarbon classes. Compared with EI (70 eV), PI (10.8 eV) retained significant molecular ion (M^+· ) information for a large number of isomeric species including branched-alkanes and saturated monocyclic hydrocarbons along with unique fragmentation patterns. However, for bicyclic/polycyclic naphthenic and aromatic compounds, EI played upper hand by retaining molecular as well as fragment ions to identify the species, whereas PI exhibited mainly molecular ion signals. On the other hand, CI revealed selectivity towards different base oil groups, particularly for steranes, sulfur-containing thiophenes, and esters, yielding protonated molecular ions (M + H)⁺ for unsaturated and hydride abstracted ions (M-H⁺ ) for saturated hydrocarbons. FI, as expected, generated intact molecular ions (M^+· ) irrespective to the base oil chemical classes. It allowed elemental composition by TOFMS with a mass resolving power up to 8000 (FWHM) and a mass accuracy of 1 mDa, leading to the calculation of heteroatomic content, double bond equivalency, and carbon number of the compounds. The qualitative and quantitative results presented herein offer a unique perspective into the detailed comparison of different ionization techniques corresponding to several hydrocarbon classes.

Comprehensive comparative compositional study of the vapour phase of cigarette mainstream tobacco smoke and tobacco heating product aerosol

A simple direct sample collection/dilution and introduction method was developed using quartz wool and Tenax/sulficarb sorbents for thermal desorption and comprehensive two-dimensional gas chromatography (TD-GC × GC) analyses of volatile organic compounds from vapour phase (VP) fractions of aerosol produced by tobacco heating products (THP1.0) and 3R4F mainstream tobacco smoke (MTS). Analyses were carried out using flame ionisation detection (FID) for semi-quantification and both low and high resolution time-of-flight mass spectrometry (LR/HR-TOFMS) for qualitative comparison and peak assignment. Qualitative analysis was carried out by combining identification data based on linear retention indices (LRIs) with a match window of ±10 index units, mass spectral forward and reverse library searches (from LR and HRTOFMS spectra) with a match factor threshold of >700 (both forward and reverse), and accurate mass values of ± 3 ppm for increased confidence in peak identification. Using this comprehensive approach of data mining, a total of 79 out of 85 compounds and a total of 198 out of 202 compounds were identified in THP1.0 aerosol and in 3R4F MTS, respectively. Among the identified analytes, a set of 35 compounds was found in both VP sample types. Semi-quantitative analyses were carried out using a chemical class-based external calibration method. Acyclic, alicyclic, aromatic hydrocarbons and ketones appeared to be prominent in 3R4F MTS VP, whereas larger amounts of aldehydes, ketones, heterocyclic hydrocarbons and esters were present in THP1.0 aerosol VP. The results demontsrate the capability and versatility of the method for the characterization and comparison of complex aerosol samples and highlighted the relative chemical simplicity of THP1.0 aerosol in comparison to MTS.