Chemical Specificity Research Articles

Evaluation of the efficiency of dry anaerobic digester in the production of biogas and fertilizer using activated sludge and plant waste.

The process of dry anaerobic digestion (DAD) is an effective economic and environmentally friendly method due to its features such as reducing the volume of waste, destroying pathogens, consuming less energy, and producing biogas rich in energy and fertilizer. This study was conducted on a pilot scale with a reactor volume of 24L in 30 days for three ratios of C/N: 30, 25, and 20 separately using a mixture of activated sludge and plant waste. During the process, the temperature, pH, and ratio of C/N were measured at certain times, and the percentage of gases produced by the Gas chromatography (GC) device was also measured. The results were compared with the National standard of Iran (Compost, Physical, and Chemical Specifications) at the end of the process. The results showed that the average volume of biogas produced in ratios of C/N: 30, 25, 20 is 1.7, 2.5, and 1.5L. d-1, respectively. The results showed that in the C/N ratio of 20, and 25, the amount of, C/N ratio and NO3 are in the range the standard of class 1, and the amount of Phosphorus pentoxide (P2O5) is in the range the standard of class 2. The results showed that the average microbial parameters in ratios of C/N: 30, 25, and 20 are lower than the national standard of Iran. The dry digester is an efficient method in waste treatment, methane gas production, and quality fertilizer close to the national standard of Iran.

Weaker neuroligin 2 - neurexin 1β interaction tethers membranes and signal synaptogenesis through clustering.

Single-pass transmembrane proteins neuroligin (NL) and neurexin (NRX) constitute a pair of synaptic adhesion molecules (SAMs) that are essential for the formation of functional synapses. Binding affinities vary by ∼ 1000 folds between arrays of NL and NRX subtypes, which contribute to chemical and spatial specificities. Current structures are obtained with truncated extracellular domains of NL and NRX and are limited to the higher-affinity NL1/4-NRX complexes. How NL-NRX interaction leads to functional synapses remains unknown. Here we report structures of full-length NL2 alone, and in complex with NRX1β in several conformations, which has the lowest affinity among major NL-NRX subtypes. We show how conformational flexibilities may help in adapting local membrane geometry, and reveal mechanisms underlying variations in NL-NRX affinities modulation. We further show that, despite lower affinity, NL2-NRX1β interaction alone is capable of tethering different lipid membranes in total reconstitution, and that NL2 and NRX1β cluster at inter-cellular junctions without the need of other synaptic components. In addition, NL2 combines with the master post-synaptic scaffolding protein gephyrin and clusters neurotransmitter receptors at cellular membrane. These findings suggest dual roles of NL2 - NRX1β interaction - both as mechanical tether, and as signaling receptors, to ensure correct spatial and chemical coordination between two cells to generate function synapses.

Accelerated Prediction of Phase Behavior for Block Copolymer Libraries Using a Molecularly Informed Field Theory.

Solution formulations involving polymers are the basis for a wide range of products spanning consumer care, therapeutics, lubricants, adhesives, and coatings. These multicomponent systems typically show rich self-assembly and phase behavior that are sensitive to even small changes in chemistry and composition. Longstanding computational efforts have sought techniques for predictive modeling of formulation structure and thermodynamics without experimental guidance, but the challenges of addressing the long time scales and large length scales of self-assembly while maintaining chemical specificity have thwarted the emergence of general approaches. As a consequence, current formulation design remains largely Edisonian. Here, we present a multiscale modeling approach that accurately predicts, without any experimental input, the complete temperature-concentration phase diagram of model diblock polymers in solution, as established postprediction through small-angle X-ray scattering. The methodology employs a strategy whereby atomistic molecular dynamics simulations is used to parametrize coarse-grained field-theoretic models; simulations of the latter then easily surmount long equilibration time scales and enable rigorous determination of solution structures and phase behavior. This systematic and predictive approach, accelerated by access to well-defined block copolymers, has the potential to expedite in silico screening of novel formulations to significantly reduce trial-and-error experimental design and to guide selection of components and compositions across a vast range of applications.

Mid-infrared hyperspectral microscopy with broadband 1-GHz dual frequency combs

Mid-infrared microscopy is an important tool for biological analyses, allowing a direct probe of molecular bonds in their low energy landscape. In addition to the label-free extraction of spectroscopic information, the application of broadband sources can provide a third dimension of chemical specificity. However, to enable widespread deployment, mid-infrared microscopy platforms need to be compact and robust while offering high speed, broad bandwidth, and high signal-to-noise ratio. In this study, we experimentally showcase the integration of a broadband, high-repetition-rate dual-comb spectrometer (DCS) in the mid-infrared range with a scanning microscope. We employ a set of 1-GHz mid-infrared frequency combs, demonstrating their capability for high-speed and broadband hyperspectral imaging of polymers and ovarian tissue. The system covers 1000 cm−1 at νc = 2941 cm−1 with 12.86 kHz spectra acquisition rate and 5 µm spatial resolution. Taken together, our experiments and analysis elucidate the trade-off between bandwidth and speed in DCS as it relates to microscopy. This provides a roadmap for the future advancement and application of high-repetition-rate DCS hyperspectral imaging.

Construction of Yolk@shell Nanocomposite Particles with Controlled Multisized Pore Structures by Monomicelle Confined Assembly.

Hollow nanoparticles with tunable structures and spatial and chemical specificity are considered as promising carriers. However, it remains a formidable challenge to endow hollow nanomaterials with precisely controlled multisized macro/mesoporous structures up to now. This paper demonstrates a "polydopamine (PDA) expansion-shrinkage" strategy combined with a monomicelle interfacial confined assembly method to achieve the highly controllable preparation of a series of yolk@shell PDA@SiO2 composite nanoparticles with structural asymmetry and a tunable multisized pore in the shell. The strategy allows systematic manipulation of the average pore size of large slit pores in the range of 15.4-86.5 nm by adjusting the reaction temperature. Benefiting from advantages such as an asymmetric structure and multilevel porosity, they exhibit excellent performance in the applications of on-demand loading of dual-sized cargoes, dual-propelled nanomotors, and particle size-selected encapsulation and separation. These findings provide inspiration for the construction of asymmetric yolk@shell structures with tunable multisized pores for a wide range of biological and chemical applications.

The surface tension of Martini 3 water mixtures.

The Martini model, a coarse-grained forcefield for biomolecular simulations, has experienced a vast increase in popularity in the past decade. Its building-block approach balances computational efficiency with high chemical specificity, enabling the simulation of organic and inorganic molecules. The modeling of coarse-grained beads as Lennard-Jones particles poses challenges for the accurate reproduction of liquid-vapor interfacial properties, which are crucial in various applications, especially in the case of water. The latest version of the forcefield introduces refined interaction parameters for water beads, tackling the well-known artifact of Martini water freezing at room temperature. In addition, multiple sizes of water beads are available for simulating the solvation of small cavities, including the smallest pockets of proteins. This work focuses on studying the interfacial properties of Martini water, including surface tension and surface thickness. Employing the test-area method, we systematically compute the liquid-vapor surface tension across various combinations of water bead sizes and for temperatures from 300 to 350K. These findings are of interest to the Martini community as they allow users to account for the low interfacial tension of Martini water by properly adjusting observables computed via coarse-grained simulations to allow for accurate matching against all-atom or experimental results. Surface tension data are also interpreted in terms of local enrichment of the various mixture components at the liquid-vapor interface by means of Gibbs' adsorption formalism. Finally, the critical scaling of the Martini surface tension with temperature is reported to be consistent with the critical exponent of the 3D Ising universality class.

Martini 3 OliGo̅mers: A Scalable Approach for Multimers and Fibrils in GROMACS.

Martini 3 is a widely used coarse-grained simulation method for large-scale biomolecular simulations. It can be combined with a Go̅ model to realistically describe higher-order protein structures while allowing the folding and unfolding events. However, as of today, this method has largely been used only for individual monomers. In this article, we describe how the Go̅ model can be implemented within the framework of Martini 3 for a multimer system, taking into account both intramolecular and intermolecular interactions in an oligomeric protein system. We demonstrate the method by showing how it can be applied to both structural stability maintenance and assembly/disassembly of protein oligomers, using aquaporin tetramer, insulin dimer, and amyloid-β fibril as examples. We find that addition of intermolecular Go̅ potentials stabilizes the quaternary structure of proteins. The strength of the Go̅ potentials can be tuned so that the internal fluctuations of proteins match the behavior of atomistic simulation models, however, the results also show that the use of too strong intermolecular Go̅ potentials weakens the chemical specificity of oligomerization. The Martini-Go̅ model presented here enables the use of Go̅ potentials in oligomeric molecular systems in a computationally efficient and parallelizable manner, especially in the case of homopolymers, where the number of identical protein monomers is high. This paves the way for coarse-grained simulations of large protein complexes, such as viral protein capsids and prion fibrils, in complex biological environments.

The application of vibrational spectroscopy in forensic analysis of biological evidence.

Vibrational spectroscopy is a powerful analytical domain, within which Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy stand as exemplars, offering high chemical specificity and sensitivity. These methodologies have been instrumental in the characterization of chemical compounds for an extensive period. They are particularly adept at the identification and analysis of minute sample quantities. Both FTIR and Raman spectroscopy are proficient in elucidating small liquid samples and detecting nuanced molecular alterations. The application of chemometrics further augments their analytical prowess. Currently, these techniques are in the research phase within forensic medicine and have yet to be broadly implemented in examination and identification processes. Nonetheless, studies have indicated that a combined classification model utilizing FTIR and Raman spectroscopy yields exceptional results for the identification of biological fluid-related information and the determination of causes of death. The objective of this review is to delineate the current research trajectory and potential applications of these two vibrational spectroscopic techniques in the detection of body fluids and the ascertainment of causes of death within the context of forensic medicine.

Spatial Distribution of Wells in the Eastern Side of Nineveh Governorate – Iraq

Groundwater is an important resource, especially in areas where water resources do not meet the requirements of life. Therefore, population centers in areas far from rivers are linked to the quantity and quality of groundwater available. The study area represents a large part of the eastern part of Nineveh Governorate, which is dotted with small cities and villages with population and agricultural activity. The quantity and quality of groundwater are related to the nature of the reservoir rocks in the region, which are mainly represented by the Pila Spi Formation, composed of dolomite limestone, the Fat’ha Formation, composed of periodic successions of marl, limestone, and gypsum, and the Injana Formation, composed of periodic successions of sandstone, siltstone, and clay. The quality of the rocks exposed in the study area, especially at the feet of the Bashiqa and Ain Al-Safra mountains, and the ability of the minerals that make up them to dissolve in conditions of weathering and erosion also affect the water content of dissolved salts. The water quality index (WQI) was calculated to determine its suitability for civil use based on the physical (pH, E.C, T.D.S and T.H) and chemical (Ca2+, Mg2+, Na+, K+, HCO3-, SO42-, Cl- and NO3-) specifications. In light of this, the distribution of wells was determined according to their specifications. In general, there were six regions; The first in the northern part has excellent water, the second in the south has good water, the third in the south has unsuitable water, and the fourth area, which represents the area confined between the city of Mosul and Mount Bashiqa, has poor water quality, while the area adjacent to Ain Al-Sufra Mountain is classified as having good water quality, while The area located to the southwest towards the Tigris River is of very poor quality. There are sites for wells whose specifications vary according to the type of activity there.

In vitro and in vivo analyses of eFAP: a novel FAP-targeting small molecule for radionuclide theranostics and other oncological interventions

BackgroundFibroblast activation protein (FAP), a transmembrane serine protease overexpressed by cancer-associated fibroblasts in the tumor stroma, is an interesting biomarker for targeted radionuclide theranostics. FAP-targeting radiotracers have demonstrated to be superior to [18F]FDG PET/CT in various solid cancers. However, these radiotracers have suboptimal tumor retention for targeted radionuclide therapy (TRT). We aimed to develop a novel FAP-targeting pharmacophore with improved pharmacokinetics by introducing a substitution at the 8-position of (4-quinolinoyl)-glycyl-2-cyanopyrrolidine, which allows for conjugation of a chelator, dye, or other payloads.ResultsHere we showed the synthesis of DOTA-conjugated eFAP-6 and sulfo-Cyanine5-conjugated eFAP-7. After chemical characterization, the uptake and specificity of both tracers were determined on FAP-expressing cells. In vitro, [111In]In-eFAP-6 demonstrated a superior affinity and a more rapid, although slightly lower, peak uptake than gold standard [111In]In-FAPI-46. Confocal microscopy demonstrated a quick FAP-mediated internalization of eFAP-7. Studies with HT1080-huFAP xenografted mice confirmed a more rapid uptake of [177Lu]Lu-eFAP-6 vs. [177Lu]Lu-FAPI-46. However, tumor retention at 24 h post injection of [177Lu]Lu-eFAP-6 was lower than that of [177Lu]Lu-FAPI-46, hereby currently limiting its use for TRT.ConclusionThe superior affinity and faster tumor accumulation of eFAP-6 over FAPI-46 makes it a suitable compound for radionuclide imaging. After further optimization, the eFAP series has great potential for various oncological interventions, including fluorescent-guided surgery and effective targeted radionuclide theranostics.

New hybrid nano- and bio-based phase change material containing graphene-copper particles hosting beeswax-coconut oil for solar thermal energy storage: Predictive modeling and evaluation using machine learning

Although utilizing phase change materials (PCMs) for thermal energy storage and management has remarkably grown, the reliance on petroleum-based PCMs has raised concerns about their sustainability. Hence, in this study, the mixture of beeswax (BW) and coconut oil (CO) as a new biological-based PCM (bio-PCM) was developed. Also, the effect of 0.5, 1, and 2 wt% of graphene-copper (Gr-Cu) hybrid nanoparticles on the bio-PCM's ability in thermal energy storage (TES) was scrutinized. Thermal, chemical, physical, and stability specifications of BW-CO/Gr-Cu nano- and bio-based PCMs (bio-nPCMs) were examined by Differential Scanning Calorimeter (DSC), Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Also, the thermal conductivity of bio-PCM and bio-nPCMs were explored in a range of temperatures from 25 to 60 °C. FTIR indicated no chemical reactions or new synthesis materials in the final composite. Also, all the used materials were recognized by XRD. DSC analysis showed that melting and solidification of bio-PCM start at 51 and 56 °C while adding 2 wt% Gr-Cu nanoparticles reduced the temperatures to 49.9 °C and 53.8 °C, respectively. In addition, bio-PCM had latent heats of 172.3 kJ/kg and 173.11 kJ/kg for melting and solidification, whereas 2 wt% Gr-Cu nanoparticles shifted them to 160.75 kJ/kg and 167.45 kJ/kg, in respect. On the other hand, the higher the concentration of Gr-Cu in the base PCM, the higher the thermal conductivity of bio-nPCMs maximally about 604 % higher than that of the base bio-PCM at T = 25 °C. Furthermore, a new model was proposed for the thermal conductivity that had an average error of 5 %. Machine learning was employed to estimate the thermal conductivity and latent heat. The former with R-squared, mean error (MSE), and average absolute relative deviation (%AARD) of 0.9996, 1.1253 × 10−4, 1.871, and the latter with 1, 4.7 × 10−10, and 0.01, respectively. The outcomes of this study present a procedure to develop future bio-PCMs and hybrid nanoparticles to pave the way to reaching net-zero carbon.

Oxidation Kinetics of Fluorescent Membrane Lipid Peroxidation Indicators.

The oxidation of the cellular membrane through lipid peroxidation (LPO) is linked to aging and disease. Despite the physiological importance, the chemical mechanisms underlying LPO and oxidative reactions in membranes in general remain incompletely understood, and challenges exist in translating LPO inhibitor efficacies from in vitro to in vivo. The complexity of LPO, including multiple oxidation reactions in complex membrane environments and the difficulty in quantifying reaction kinetics, underlies these difficulties. In this work, we developed a robust and straightforward method for quantifying the oxidation rate kinetics of fluorescent molecules and determined the oxidation kinetics of widely fluorophores used as indicators of membrane LPO, diphenylhexatriene (DPH), BODIPY-C11, and Liperfluo. The measurement is initiated by lipoxygenase, which provides chemical specificity and enables a straightforward interpretation of oxidation kinetics. Our results reveal that the membrane composition significantly impacts the observed kinetics oxidation in DPH and BODIPY-C11 but not Liperfluo. Reaction mechanisms for their lipid peroxide-induced oxidation are proposed. This work provides a foundation for the quantitative analysis of LPO with fluorescence and extricating the complexity of oxidation reactions within membranes.

Unpacking Alternative Features of the Bacterial Chemotaxis System.

The bacterial chemotaxis system is one of the best-understood cellular pathways and serves as the model for signal transduction systems. Most chemotaxis research has been conducted with transmembrane chemotaxis systems from Escherichia coli and has established paradigms of the system that were thought to be universal. However, emerging research has revealed that many bacteria possess alternative features of their chemotaxis system, demonstrating that these systems are likely more complex than previously assumed. Here, we compare the canonical chemotaxis system of E. coli with systems that diverge in supramolecular architecture, sensory mechanisms, and protein composition. The alternative features have likely evolved to accommodate chemical specificities of natural niches and cell morphologies. Collectively, these studies demonstrate that bacterial chemotaxis systems are a rapidly expanding field that offers many new opportunities to explore this exceedingly diverse system.

Enhancing Spatial Resolution in Tandem Mass Spectrometry Ion/Ion Reaction Imaging Experiments through Image Fusion.

We have recently developed a charge inversion ion/ion reaction to selectively derivatize phosphatidylserine lipids via gas-phase Schiff base formation. This tandem mass spectrometry (MS/MS) workflow enables the separation and detection of isobaric lipids in imaging mass spectrometry, but the images acquired using this workflow are limited to relatively poor spatial resolutions due to the current time and limit of detection requirements for these ion/ion reaction imaging mass spectrometry experiments. This trade-off between chemical specificity and spatial resolution can be overcome by using computational image fusion, which combines complementary information from multiple images. Herein, we demonstrate a proof-of-concept workflow that fuses a low spatial resolution (i.e., 125 μm) ion/ion reaction product ion image with higher spatial resolution (i.e., 25 μm) ion images from a full scan experiment performed using the same tissue section, which results in a predicted ion/ion reaction product ion image with a 5-fold improvement in spatial resolution. Linear regression, random forest regression, and two-dimensional convolutional neural network (2-D CNN) predictive models were tested for this workflow. Linear regression and 2D CNN models proved optimal for predicted ion/ion images of PS 40:6 and SHexCer d38:1, respectively.

Effect of Adding Vitamin to Cooking Oil on Peroxide Value

The aim of this research is to reduce the number of peroxides in two frying oil samples by using one of the natural antioxidants which is vitamin E, one of the chemical specifications that assess the oil is the peroxide number, which is the number of free radicals formed in the oil and the number of peroxides increases during exposure to heat, moisture, oxygen, bad storage conditions, light or other conditions. These peroxides have a harmful effect on the consumer health (Carcinogenic substances). The vitamin E had a clear impact on the peroxide value, as when conducting the experiment and using oil to fry potato slices, the number of peroxides was high before adding vitamin E which score approximately (Peroxide number is 5.6 for 15 minutes, 9.8 for 30 minutes, and 11.6 for 45 minutes). After using vitamin E in amount of 10 microgram per 100 ml of oil, the effect was clear of vitamin E on the number of peroxide as it decreased significantly. Which scored (5 for 15 minutes, 8.1 for 30 minutes, 8.9 for 45 minutes), When vitamin E added by 20 microgram the result was (4.8 for 15 minutes, 5.5 for 30 minutes, 6.5 for 45 minutes). 50 micrograms per 100 oils shown to have no significant effect on the peroxide value. it was found that the best concentration is 20 micrograms for a sample of 100 ml of oil.

Overtone photothermal microscopy for high-resolution and high-sensitivity vibrational imaging

Photothermal microscopy is a highly sensitive pump-probe method for mapping nanostructures and molecules through the detection of local thermal gradients. While visible photothermal microscopy and mid-infrared photothermal microscopy techniques have been developed, they possess inherent limitations. These techniques either lack chemical specificity or encounter significant light attenuation caused by water absorption. Here, we present an overtone photothermal (OPT) microscopy technique that offers high chemical specificity, detection sensitivity, and spatial resolution by employing a visible probe for local heat detection in the C-H overtone region. We demonstrate its capability for high-fidelity chemical imaging of polymer nanostructures, depth-resolved intracellular chemical mapping of cancer cells, and imaging of multicellular C. elegans organisms and highly scattering brain tissues. By bridging the gap between visible and mid-infrared photothermal microscopy, OPT establishes a new modality for high-resolution and high-sensitivity chemical imaging. This advancement complements large-scale shortwave infrared imaging approaches, facilitating multiscale structural and chemical investigations of materials and biological metabolism.

Selective Termination of Autophagy-Dependent Cancers.

The goal of cancer research is to identify characteristics of cancer cells that allow them to be selectively eliminated without harming the host. One such characteristic is autophagy dependence. Cancer cells survive, proliferate, and metastasize under conditions where normal cells do not. Thus, the requirement in cancer cells for more energy and macromolecular biosynthesis can evolve into a dependence on autophagy for recycling cellular components. Recent studies have revealed that autophagy, as well as different forms of cellular trafficking, is regulated by five phosphoinositides associated with eukaryotic cellular membranes and that the enzymes that synthesize them are prime targets for cancer therapy. For example, PIKFYVE inhibitors rapidly disrupt lysosome homeostasis and suppress proliferation in all cells. However, these inhibitors selectively terminate PIKFYVE-dependent cancer cells and cancer stem cells with not having adverse effect on normal cells. Here, we describe the biochemical distinctions between PIKFYVE-sensitive and -insensitive cells, categorize PIKFYVE inhibitors into four groups that differ in chemical structure, target specificity and efficacy on cancer cells and normal cells, identify the mechanisms by which they selectively terminate autophagy-dependent cancer cells, note their paradoxical effects in cancer immunotherapy, and describe their therapeutic applications against cancers.

Chemical specificity in polyzwitterion-polyelectrolyte coacervates: polycations vs polyanions

Aqueous solutions containing polyzwitterions and polyelectrolytes were studied to probe the effects of chemical specificity on the complexation among different types of chains and resulting liquid–liquid phase separation (coacervation). Two kinds of blends were studied. A polyzwitterion, poly(sulfobetaine methacrylate) (PSBMA), was blended with either (1) a polycation, poly(diallydimethylammonium chloride) (PDADMAC), or (2) a polyanion, sodium poly(styrene sulphonate) (NaPSS). Coacervation was observed in both blends after equilibration, while the freshly prepared blend solutions exhibited distinct behavior dependent on the mixing protocols. Mixing solutions of the polyzwitterions and the polycations led to coacervation almost instantaneously. In contrast, the blends containing the same polyzwitterions and the polyanions exhibited no such coacervation by following the same mixing protocol. However, blends prepared after dissolving a solid mixture containing the same polyzwitterions and the polyanions in water exhibited coacervation. Based on the small-angle X-ray scattering (SAXS), cryo-electron microscopy, and rheology measurements, complexation and coacervation in the polyzwitterion-polyelectrolyte blends is rationalized in terms of the entropy change associated with reorganization of solvent (water), which appears to be larger in the polyzwitterion-polycation case in comparison with the polyzwitterion-polyanion blends. These results highlight the importance of chemical specificity and mixing protocols leading to metastable structures in designing a new class of materials based on macromolecular complexation of polyzwitterions.

Exploring the potential of textile effluent sludge as a construction material through comprehensive characterization and analysis

This study primarily focused on assessing the feasibility of utilizing textile effluent sludge (TES) in the creation of sustainable building materials, demonstrating the possibility of using this material and eventually generating new market opportunities. The physical, chemical, and mineralogical characterization of textile sludge was carried out after preliminary crushing and grain-size sorting. Five samples collected from the effluent treatment facility of textile industries situated in the Vidarbha region of Maharashtra, India, underwent characterization to explore their potential innovative applications in the construction sector. Various physical tests, such as specific gravity, density, water absorption, and sieve analysis, were performed on these samples. Chemical characterization was carried out using x-ray diffraction, x-ray fluorescence, a field emission scanning electron microscope coupled with energy-dispersive x-ray spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetry/differential thermal analysis. The results obtained demonstrate the potential of TES in the creation of sustainable building materials. In addition, the mix proportion of TES was further optimized using LINGO software to meet the chemical specifications required for cement.

Chemical Analysis of Exhaled Vape Emissions: Unraveling the Complexities of Humectant Fragmentation in a Human Trial Study.

Electronic cigarette smoking (or vaping) is on the rise, presenting questions about the effects of secondhand exposure. The chemical composition of vape emissions was examined in the exhaled breath of eight human volunteers with the high chemical specificity of complementary online and offline techniques. Our study is the first to take multiple exhaled puff measurements from human participants and compare volatile organic compound (VOC) concentrations between two commonly used methods, proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) and gas chromatography (GC). Five flavor profile groups were selected for this study, but flavor compounds were not observed as the main contributors to the PTR-ToF-MS signal. Instead, the PTR-ToF-MS mass spectra were overwhelmed by e-liquid thermal decomposition and fragmentation products, which masked other observations regarding flavorings and other potentially toxic species associated with secondhand vape exposure. Compared to the PTR-ToF-MS, GC measurements reported significantly different VOC concentrations, usually below those from PTR-ToF-MS. Consequently, PTR-ToF-MS mass spectra should be interpreted with caution when reporting quantitative results in vaping studies, such as doses of inhaled VOCs. Nevertheless, the online PTR-ToF-MS analysis can provide valuable qualitative information by comparing relative VOCs in back-to-back trials. For example, by comparing the mass spectra of exhaled air with those of direct puffs, we can conclude that harmful VOCs present in the vape emissions are largely absorbed by the participants, including large fractions of nicotine.