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See detailTHE POTENTIAL OF SOFT IONIZATIONS FOR ANALYZING CHLORINATED PARAFFINS
Zou, Yun ULiege; Stefanuto, Pierre-Hugues ULiege; Focant, Jean-François ULiege

Conference (2021, August)

Introduction Chlorinated paraffins (CPs) are mixtures of polychlorinated n-alkanes containing over thousands of congeners and isomers. Due to the complexity of the composition, CPs are one of the most ... [more ▼]

Introduction Chlorinated paraffins (CPs) are mixtures of polychlorinated n-alkanes containing over thousands of congeners and isomers. Due to the complexity of the composition, CPs are one of the most challenging chemicals for the analytical scientists. In the instrumental point of view, gas chromatography (GC) is widely employed to separate organochlorines from CPs, especially short-chain and medium-chain CPs (SCCPs and MCCPs)1. Liquid chromatography (LC) is also applied to determine CPs, especially long-chain CPs (LCCPs)1. In order to separate SCCPs from MCCPs, two-dimensional GC (GC×GC) is a promising tool because of its superior separation power and peak capacity2-3. Electron capture detector (ECD), flame ionization detector (FID), and mass spectrometry (MS) are used as detectors in the CP analysis. MS is the most acceptable detector for CPs. Various ionization sources have been tested. They include electron ionization (EI), negative chemical ionization (NCI), electron capture negative ion (ECNI), Metastable atom bombardment (MAB) and positive chemical ionization (PCI) for GC-MS and GC×GC-MS, negative atmospheric pressure chemical ionization (APCI) and negative electro spray ionization (ESI) for LC-MS1. The standard EI with electron possessing 70 eV of kinetic energy is the most common ion source for GC-MS. However, it can only provide the information of total CPs. The information of individual congeners is hindered due to the nonspecific fragmentation pattern caused by high energy. NCI and ECNI are widely applied in the studies of CPs. The intensity of fragment ions [M-Cl]-, which present the information of the precursor congeners, are highly enhanced by NCI and ECNI. However, the discrimination of lower chlorine number congeners (below 5) is the disadvantage of these ionization sources. In recent years, other soft ionizations such as cold EI, low energy EI, field ionization (FI) and photoionization (PI) showed their advantages in the isomeric identification of hydrocarbons. In this study, state-of-the-art GC×GC-time of flight (TOF) MS coupled to soft ionizations PI and low energy EI was applied to analyze SCCPs. We aimed to explore the potential of the soft ionizations besides NCI or ECNI in the area of CPs. Materials and methods A SCCP standard mixture with chlorine content of 55% was used to exam the performance of different ion sources. Hexane was used as dilution solvent. The analyses were conducted on a GC (7890B, Agilent Technologies, Wilmington, DE, U.S.A.) equipped with Zoex thermal modulator (Zoex Corporation, Houston, U.S.A.). A TOFMS with a PI-EI combined ion source (JMS-T200GC “AccuTOF GCx-plus”, JEOL Ltd., Tokyo, Japan) was coupled to GC×GC. The PI, 15 eV, 20 eV, and 25 eV EI were employed in this study. A normal column set (non-polar as 1st dimension, polar as 2nd dimension) was used. The instrument condition was described in our previous work3. Data acquisition was controlled on msAxel ver. 2.1 (JEOL Ltd.). The data were processed using GC Image ver. 2.5 (Zoex Corporation, Houston, U.S.A.). Results and discussion The different dilutions of SCCP standard mixture were measured under the same GC×GC condition with PI, standard (70 eV) EI, and low energy (15 eV, 20 eV, 25 eV) EI, respectively. The chromatograms obtained with PI, 70 eV EI and 15 eV EI were shown in Fig. 1. The chromatograms of 15 eV, 20 eV, and 25 eV EI did not show significant difference. Therefore, they are not presented in Fig. 1. As can be seen from the chromatograms, standard EI has the highest sensitivity, while PI has the lowest sensitivity. In general, the sensitivity of standard EI and low energy EI are acceptable for the SCCPs in the environment samples. Besides the difference on sensitivity, the fragmentation pattern and the dominant fragment ions by PI and EI also show difference (Table 1). The dominant fragment ions in PI are [M-C5H9Cl3]. While the predominant fragment ions in 15 eV EI are [M-C5H9Cl4]. As seen from the mass spectrum of congener C11H17Cl7 (Fig. 1), the quantifier fragment ions m/z 185 in 15 eV EI is much enhanced than in the standard EI. While, the nonspecific fragments such as m/z 41 and 55 are much weakened in 15 eV EI. The mass spectrum of PI is the tidiest with significantly improved intensity of quantifier fragment ion m/z 220. Moreover, the fragment pattern can assist us to understand the fragmentation pathway and further predict the isomeric structures. Using the specific quantifiers of 24 congeners of SCCPs, the congener distribution is calculated. The congener patterns are constant among the low energy EI with different energies (Fig. 2). However, PI mode showed significantly different congener patterns compared with low energy EI. To be specific, PI overestimated the contribution of C10-11 - Cl5-7 congeners and underestimated C10-13 - Cl8-10 congeners. In general, PI had discrimination of longer carbon chains (C13) and highly chlorinated congeners (Cl9-10). This could be caused by the low sensitivity of PI. Since C13 and Cl9-10 congeners do not contribute much in SCCPs, their intensities are also much lower. In summary, although the current technique of PI cannot reach to the same sensitivity level as EI and low energy EI, the tidy and informative mass spectrum reveal the potential and benefit that PI can bring to the analysis of CPs and possibly to the other organochlorines. Low energy EI, compared to standard EI, presented the enhanced intensity of the fragment ions which represent the precursor structure. To increase the sensitivity of soft ionization sources by the instrument vendors will benefit the analysis of CPs. [less ▲]

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See detailCharacterizing the olefin oligomerization products using two-dimensional gas chromatography-photoionization-time of flight mass spectrometry
Zou, Yun ULiege; Stefanuto, Pierre-Hugues ULiege; Maimone, Mariarosa et al

Conference (2021, August)

Commercial dodecenes are the products of light olefin oligomerization in the petrochemical industry. It is a complex mixture of C8-18 olefins with C12 olefins dominantly. The dodecene products may consist ... [more ▼]

Commercial dodecenes are the products of light olefin oligomerization in the petrochemical industry. It is a complex mixture of C8-18 olefins with C12 olefins dominantly. The dodecene products may consist of linear alkenes, branched alkenes, and cyclic hydrocarbons. The composition of the dodecene products and their properties are very different due to the different feedstocks and catalysts used in the production. Better understanding the composition of dodecene products can help tune the production process and select the appropriate products according to their end-use. In this study two-dimensional gas chromatography (GCGC) coupled photoionization (PI) - time of flight mass spectrometry (TOFMS) was applied to characterize the dodecene products. A conventional column combination (non-polar column as 1st dimension and mid-polar column as 2nd dimension) was selected. The GC condition was optimized using fractional factorial experimental design (DoE). Olefin congeners according to carbon chain length and double bond equivalent (DBE) can be separated based on the enhanced intensity of molecular ions by PI-TOFMS. The structural subgroups of dodecenes, namely linear, mono-branched, di- and tri-branched isomers, were separated based on branching index (BI). The dodecene isomers were identified by retention indices (RI) and confirmed by PI mass spectra. The global information of dodecene products enabled the multimodal characterization with statistical tools. The difference among seventeen dodecene products by different catalysts, solid phosphoric acid (SPA) and zeolite, and different feedstocks, with C4 and without C4 olefins, is explained by principal component analysis (PCA) and hierarchical clustering analysis (HCA). [less ▲]

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See detailVolatile fingerprinting of boar taint by GC×GC-TOFMS
Dubois, Lena ULiege; Delhaye, Myriam; Mayeres, Patrick et al

Scientific conference (2021, June 09)

As a response to growing ethical constraints, the meat production industry has agreed to abandon surgical castration of male piglets towards 2018. However, raising uncastrated male pigs increases the risk ... [more ▼]

As a response to growing ethical constraints, the meat production industry has agreed to abandon surgical castration of male piglets towards 2018. However, raising uncastrated male pigs increases the risk commercializing meat with an undesirable taste know as boar taint. The main compounds contributing to the fecal, urine, and sweat-like taste or smell are androstenone, skatole, and indole. Different analytical methods have been proposed and validated for their quantification in plasma or fat tissue [1]. However, the application of these methods is oftentimes not applicable directly in a slaughterhouse routine due to time constraints related to the high throughput of industrial meat production processes. Only a few on-site options exist but are still at testing stage [2]. Therefore, it is common practice to conduct olfactive screening based on so called ‘soldering iron sensory methods’ carried out by trained assessor. Tainted carcasses are then pushed aside from commercialization. This is currently the fastest and least onerous procedure to determine boar taint presence but it is believed to suffer from inter-individual variations and limited correlation to instrumental measurements. The incidence of boar taint at commercial slaughters in Belgium is estimated to between 3 and 7% [3]. In this study, back fat and in-vivo samples (saliva, hair, semen) were analyzed with comprehensive two-dimensional gas chromatography (GC×GC) coupled to time-of-flight mass spectrometry (TOFMS) for volatile fingerprinting. References: [1] Heyrman et al. (2017). Animal, 11(11), 2084-2093. [2] K. Verplanken, S. Stead, Renata Jandova, C. Van Poucke, J. Claereboudt, J. Vanden Busche, S. De Saeger, Z. Takats, J. Wauters, L. Vanheacke, Talanta, 169 (2017) 30-36. [3] E. Heyrman, S. Millet, F.A.M. Tuyttens, B. Ampe, S. Janssens, N. Buys, J. Wauters, L. Vanhaecke, M. Aluwé, Animal, 11 (2017), 2084-2093. [less ▲]

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See detailIn vitro modelling of lung inflammatory processes
Zanella, Delphine ULiege; HENKET, Monique ULiege; SCHLEICH, FLorence ULiege et al

Conference (2021, June)

Exhaled breath analysis has a high potential for early non-invasive diagnosis of lung conditions. The inflammation processes associated with oxidative stress yield to the conversion of membranes ... [more ▼]

Exhaled breath analysis has a high potential for early non-invasive diagnosis of lung conditions. The inflammation processes associated with oxidative stress yield to the conversion of membranes components into volatile organic compounds (VOC) secreted by the lungs. The characterization and understanding of the inflammatory metabolic pathways involved into VOC production is necessary to define proper medication. In this study, lung inflammation was simulated in-vitro on lung epithelial cells. We compared the VOC production following a conventional oxidative stress in-vitro using hydrogen peroxide (H2O2) with a biological model using inflammatory sputum from asthmatic patients. The VOC were extracted and analyzed by solid-phase microextraction comprehensive two-dimensional gas chromatography hyphenated to time-of-flight mass spectrometry. In the oxidative stress experiments, we exposed the epithelial cells to 0.1 mM H2O2 for 1 h. In the biological stress experiment, the epithelial cells were exposed to 50 % (v/v) inflammatory and non-inflammatory pool of sputum supernatants for 24 h. These optimal conditions were used to induce metabolic response, releasing specific metabolites, without causing significant cellular apoptosis. According to the type of inflammation induced, different VOCs were produced by the cells. For both chemical and biological challenges, an increase of carbonyl compounds and hydrocarbons was observed. However, 36% of the specific VOCs were produced only after a biological stress. Taken together, these results highlight that in-vitro VOC analysis is a very promising approach to characterize complex lung inflammatory mechanisms. The future implementation of multi-omics screening could reveal new information on the molecular mechanisms involved in lung inflammation. [less ▲]

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See detailInsights into olefin oligomerization products based on GC×GC-PI-TOFMS
Zou, Yun ULiege; Stefanuto, Pierre-Hugues ULiege; Maimone, Mariarosa et al

Conference (2021, June)

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See detailModeling approaches for temperature-programmed gas chromatographic retention times under vacuum outlet conditions
Gaida, Meriem ULiege; Franchina, Flavio ULiege; Stefanuto, Pierre-Hugues ULiege et al

in Journal of Chromatography. A (2021), 1651

This contribution evaluates the performance of two predictive approaches in calculating temperature-programmed gas chromatographic retention times under vacuum outlet conditions. In the first approach ... [more ▼]

This contribution evaluates the performance of two predictive approaches in calculating temperature-programmed gas chromatographic retention times under vacuum outlet conditions. In the first approach, the predictions are performed according to a thermodynamic-based model, while in the second approach the predictions are conducted by using the temperature-programmed retention time equation. These modeling approaches were evaluated on 47 test compounds belonging to different chemical classes, under different experimental conditions, namely, two modes of gas flow regulation (i.e., constant inlet pressure and constant flow rate), and different temperature programs (i.e., 7 °C/min, 5 °C/min, and 3 °C/min). Both modeling approaches gave satisfactory results and were able to accurately predict the elution profiles of the studied test compounds. The thermodynamic-based model provided more satisfying results under constant flow rate mode, with average modeling errors of 0.43%, 0.33%, and 0.15% across all the studied temperature programs. Nevertheless, under constant inlet pressure mode, lower modeling errors were achieved when using the temperature-programmed retention time equation, with average modeling errors of 0.18%, 0.18%, and 0.31% across the used temperature programs. [less ▲]

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See detailRecent Applications of Volatolomics
Stefanuto, Pierre-Hugues ULiege; Dubois, Lena ULiege; Zanella, Delphine ULiege et al

Scientific conference (2021, May)

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See detailRecent Applications of Volatolomics
Focant, Jean-François ULiege; Stefanuto, Pierre-Hugues ULiege

Scientific conference (2021, May)

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See detailBreathomics to diagnose systemic sclerosis using thermal desorption and comprehensive two-dimensional gas chromatography high-resolution time-of-flight mass spectrometry
Zanella, Delphine ULiege; GUIOT, Julien ULiege; Stefanuto, Pierre-Hugues ULiege et al

in Analytical and Bioanalytical Chemistry (2021)

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 ... [more ▼]

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 ttest, 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. [less ▲]

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See detailComparison of headspace solid-phase microextraction high capacity fiber coatings for untargeted analysis of beer volatiles using GC-MS/VUV
Zanella, Delphine ULiege; Anderson, Hailee E.; Selby, Talena et al

Poster (2021, March 12)

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See detailModeling the GCxGC separation as individual subsystems under vacuum outlet conditions: First dimension retention time predictions
Gaida, Meriem ULiege; Franchina, Flavio ULiege; Focant, Jean-François ULiege

Poster (2021, February 02)

In light of the wide applicability of multidimensional GC techniques in the analysis of complex samples, method development and optimization have become more challenging and time-consuming (1). Therefore ... [more ▼]

In light of the wide applicability of multidimensional GC techniques in the analysis of complex samples, method development and optimization have become more challenging and time-consuming (1). Therefore, a renewed interest in modeling GC separations has sprung. In fact, establishing accurate modeling procedures helps bypass demanding trial and error optimizations, thus significantly decreasing the number of runs preceding the actual chromatographic separation. Typically, the GC×GC run is modeled as a whole complex set. However, in this research, the comprehensive two-dimensional gas chromatography (GC×GC) separation is modeled as individual subsystems in which the primary and secondary columns are treated separately and the cryogenic modulator is considered as a consecutively second injection device. In this scheme, retention times are modeled using two predictive approaches. The first uses the general temperature-programmed retention time (2,3) and the second is based on thermodynamic modeling(4). Both approaches use retention data retrieved from isothermal runs and simulate the temperature-programmed GC runs as series of infinitesimal isothermal time intervals during which both the retention factor and the carrier gas velocity are considered constant. The performance of both approaches is evaluated using several standards and experimental conditions (two modes of gas flow regulation and different temperature programs). While the modeling error is considerably smaller for the thermodynamic model, predictions with both approaches are in good agreement with the experimental data. Additionally, both models provide accurate retention time predictions for different chromatographic conditions. References 1. Prebihalo, S. E.; Berrier, K. L.; Freye, C. E.; Bahaghighat, H. D.; Moore, N. R.; Pinkerton, D. K.; Synovec, R. E. Anal. Chem. 2018, 90, 505–532. 2. Habgood, H. W.; Harris, W. E. Anal. Chem. 1960, 32 (4), 450–453. 3. Calvin Giddings, J. J. Chromatogr. A 1960, 4, 11–20. 4. Karolat, B.; Harynuk, J. J. Chromatogr. A 2010, 1217, 4862–4867. [less ▲]

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See detailGC×GC-TOFMS for boar taint volatolomics
Dubois, Lena ULiege; Delhaye, Myriam; Mayeres, Patrick et al

Poster (2021, January)

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See detailImpact of the adsorbent material on volatile metabolites during in vitro and in vivo bio-sampling
Franchina, Flavio ULiege; Zanella, Delphine ULiege; Dejong, Thibaut ULiege et al

in Talanta (2021)

The increased attraction of biological volatile compounds has opened the route to a wide variety of sampling techniques, amongst which trap tubes packed with adsorbent materials are commonly used. Many ... [more ▼]

The increased attraction of biological volatile compounds has opened the route to a wide variety of sampling techniques, amongst which trap tubes packed with adsorbent materials are commonly used. Many types of adsorbent materials are available and the choice of the adsorbent can impact the obtained results in untargeted analysis. Therefore, a proper combination of the adsorbent material and the sample is necessary to increase the robustness and reproducibility of biological studies. In this study, the sampling performance of thermal desorption tubes with six common adsorbent material combinations, i.e., Tenax® TA, Tenax® TA/Carbopack™ B, Tenax® TA/Sulficarb, Tenax® TA/Carbograph™ 5TD, Tenax® TA/Carbograph™ 1TD/Carboxen® 1003, and Carboxen® 1013/Carbograph™ 5TD, was evaluated in two different setups: in vitro and in vivo sampling. The in vitro setup consisted of the headspace dynamic extraction of spiked serum, and a mixture of 19 standards was evaluated in terms of response and reproducibility. The in vivo setup consisted into two parts: the first one was based the evaluation of the standard mixture, which was flash-vaporised into Tedlar® bags containing exhaled breath; the second part was based on the longitudinal monitoring of breath metabolites originating from a beverage intake (i.e., brewed coffee), over a 90 min time period. The tubes were all desorbed and analysed in a comprehensive two-dimensional gas chromatography system coupled to a high-resolution time-of-flight mass spectrometer (GC×GC-HR ToF MS). In both sampling setups, the widest analytes coverage and the overall best extraction yield on the selected compounds were obtained using Tenax® TA, followed by Tenax® TA/Carbopack™ B. Tenax® TA provided the highest sampling reproducibility with 12 %RSD, 10 %RSD and < 5 %RSD of the response during the experiments using the in vitro setup, the in vivo setup, and during the longitudinal tracking, respectively. [less ▲]

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See detailUnraveling the Complex Olefin Isomer Mixture Using Two-Dimensional Gas Chromatography-Photoionization-Time of Flight Mass Spectrometry
Zou, Yun ULiege; Stefanuto, Pierre-Hugues ULiege; Maimone, Mariarosa et al

in Journal of Chromatography. A (2021), 1645

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See detail30th Anniversary of comprehensive two-dimensional gas chromatography: Latest advances
Zanella, Delphine ULiege; Focant, Jean-François ULiege; Franchina, Flavio ULiege

in Analytical Science Advances (2021), (2), 213-224

Detailed reference viewed: 45 (16 ULiège)