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1. Optimized workflow for unknown screening using gas chromatography high‐resolution mass spectrometry expands identification of contaminants in silicone personal passive samplers

   https://doi.org/10.1002/rcm.9048  

   Travis, Steven C. ; Kordas, Katarzyna ; Aga, Diana S. ( February 2021 , Rapid Communications in Mass Spectrometry)

   Silicone wristbands have emerged as valuable passive samplers for monitoring of personal exposure to environmental contaminants in the rapidly developing field ofexposomics. Once deployed, silicone wristbands collect and hold a wealth of chemical information that can be interrogated using high‐resolution mass spectrometry (HRMS) to provide a broad coverage of chemical mixtures.

   Gas chromatography coupled to Orbitrap™ mass spectrometry (GC/Orbitrap™ MS) was used to simultaneously perform suspect screening (using in‐house database) and unknown screening (using vendor databases) of extracts from wristbands worn by volunteers. The goal of this study was to optimize a workflow that allows detection of low levels of priority pollutants, with high reliability. In this regard, a data processing workflow for GC/Orbitrap™ MS was developed using a mixture of 123 environmentally relevant standards consisting of pesticides, flame retardants, organophosphate esters, and polycyclic aromatic hydrocarbons as test compounds.

   The optimized unknown screening workflow using a search index threshold of 750 resulted in positive identification of 70 analytes in validation samples, and a reduction in the number of false positives by over 50%. An average of 26 compounds with high confidence identification, 7 level 1 compounds and 19 level 2 compounds, were observed in worn wristbands. The data were further analyzed via suspect screening and retrospective suspect screening to identify an additional 36 compounds.

   This study provides three important findings: (1) a clear evidence of the importance of sample cleanup in addressing complex sample matrices for unknown analysis, (2) a valuable workflow for the identification of unknown contaminants in silicone wristband samplers using electron ionization HRMS data, and (3) a novel application of GC/Orbitrap™ MS for the unknown analysis of organic contaminants that can be used in exposomics studies.

    

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2. Combining Gas Chromatography-Mass Spectrometry and Principal Component Analysis to Facilitate Complete Detection and Identification of Ignitable Liquids

   Sedwick, V. ( May 2022 , The chemical educator)

   Henry Charlier (Ed.)

   This paper reports an approach that developed instrumental parameters with two different GC-MS instruments. Data from the two devices were combined with principal component analysis (PCA) to analyze genuinely and ignited ignitable liquid residues (ILR). We simulate the field samples by burning seasoned pinewood soaked with each ignitable liquid (IL). Enough unburnt components from an IL remained on the burnt wood. These components were enough to reveal the chromatographic fingerprint of an IL. Most importantly, the chromatographic profile from a pure IL and IL poured onto a wooden substrate and ignited was identical. The chromatographic profiles reported from each instrument for each IL were reproducible to within 3% RSD. The MS data from both GC-MS instruments showed similar m/z peaks from all ILs, indicating similar hydrocarbon(s) and or fragmentation cluster patterns in the ILs studied ingredients. The PCA data showed characteristic differences giving rise to the separation between incendiaries, albeit some were overshadowed by clustering. In some cases, ILs that showed similar components in their mass spectra profile grouped as a class on the PCA display. We demonstrate an approach using direct headspace injection to individualize ILs recovered from crime scenes. Direct headspace injection and GC-MS combined with PCA are shown as promising facile methods for the qualitative determination of specific ILs in real-world arson samples. Initially, our project started as an undergraduate instrumental analysis guided-inquiry (GI) project. Such labs have been reported to enhance student learning and improve students' critical and problem-solving abilities. We plan to incorporate this approach in both an undergraduate instrumental analysis class and a graduate-level analytical chemistry class. 

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3. Differentiation and identification of fentanyl analogues using GC-IRD

   https://doi.org/doi.org/10.1016/j.forc.2020.100255  

   Winokur, Agnes ; Kaufman, Lindsay ; Almirall, Jose ( June 2020 , Forensic chemistry)

   Fentanyl analogues and their positional isomers have similar chemical structural configurations making them difficult to identify and differentiate. Gas chromatography coupled to a gas-phase infrared detector (GC-IRD) is a useful and powerful tool for the unambiguous identification of fentanyl compounds where traditional analytical techniques such as gas chromatography–mass spectrometry (GC–MS) offer limited information for this class of compounds. In this study, we demonstrate the utility of GC-IRD and show how this complementary information enables the identification of fentanyl analogues (2- and 3- furanylfentanyl, 2-furanylbenzylfentanyl, croto- nylfentanyl, cyclopropylfentanyl, methoxyacetylfentanyl, carfentanil, meta-fluoroisobutyryl fentanyl, para- fluoroisobutyryl fentanyl and ortho-fluoroisobutyryl fentanyl) when combined with GC–MS data. A description of the operating conditions including how the optimization of GC-IRD parameters can enhance the spectral resolution and unambiguous identification of these fentanyl analogues is presented, for the first time. In par- ticular, the effects of light pipe temperatures, acquisition resolution, the use of a programmed temperature vaporizing (PTV) inlet, and the analytical concentration of the sample were evaluated. A real-world case ex- ncountered in casework and how the implementation of GC- of these challenges in fentanyl differentiation and identification. 

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4. Volatile Organic Compound Profiling from Postmortem Microbes using Gas Chromatography–Mass Spectrometry

   https://doi.org/10.1111/1556-4029.14173  

   Cernosek, Terezie ; Eckert, Kevin E. ; Carter, David O. ; Perrault, Katelynn A. ( September 2019 , Journal of Forensic Sciences)

   Volatile organic compounds (VOCs) are by‐products of cadaveric decomposition and are responsible for the odor associated with decomposing remains. The direct link betweenVOCproduction and individual postmortem microbes has not been well characterized experimentally. The purpose of this study was to profileVOCs released from three postmortem bacterial isolates (Bacillus subtilis, Ignatzschineria indica, I. ureiclastica)using solid‐phase microextraction arrow (SPMEArrow) and gas chromatography–mass spectrometry (GC‐MS). Species were inoculated in headspace vials on Standard Nutrient Agar and monitored over 5 days at 24°C. Each species exhibited a differentVOCprofile that included common decompositionVOCs.VOCs exhibited upward or downward temporal trends over time.Ignatzschineria indicaproduced a large amount of dimethyldisulfide. Other compounds of interest included alcohols, aldehydes, aromatics, and ketones. This provides foundational data to link decomposition odor with specific postmortem microbes to improve understanding of underlying mechanisms for decompositionVOCproduction.

    

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5. Examining the mass loss and thermal properties of 3D printed models produced by fused deposition modeling and stereolithography under elevated temperatures

   https://doi.org/10.1108/RPJ-01-2022-0007  

   Hsieh, Shu-An ; Anderson, Jared L. ( June 2022 , Rapid Prototyping Journal)

   Purpose This paper aims to study the mass loss of three-dimensional (3D) printed materials at high temperatures. A preconcentration and analysis technique, static headspace gas chromatography-mass spectrometry (SHS-GC-MS), is demonstrated for the analysis of volatile compounds liberated from fused deposition modeling (FDM) and stereolithography (SLA) 3D printed models under elevated temperatures. Design/methodology/approach A total of seven commercial 3D printing materials were tested using the SHS-GC-MS approach. The printed model mass and mass loss were examined as a function of FDM printing parameters including printcore temperature, model size and printing speed, and the use of SLA postprocessing procedures. A high temperature resin was used to demonstrate that thermal degradation products can be identified when the model is incubated under high temperatures. Findings At higher printing temperatures and larger model sizes, the initial printed model mass increased and showed more significant mass loss after thermal incubation for FDM models. For models produced by SLA, the implementation of a postprocessing procedure reduced the mass loss at elevated temperatures. All FDM models showed severe structural deformation when exposed to high temperatures, while SLA models remained structurally intact. Mass spectra and chromatographic retention times acquired from the high temperature resin facilitated identification of eight compounds (monomers, crosslinkers and several photoinitiators) liberated from the resin. Originality/value The study exploits the high sensitivity of SHS-GC-MS to identify thermal degradation products emitted from 3D printed models under elevated temperatures. The results will aid in choosing appropriate filament/resin materials and printing mechanisms for applications that require elevated temperatures. 

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