Selected ion flow tube mass spectrometry (SIFT-MS) for on-line trace gas analysis

Volatile organic compounds (VOCs) in terrestrial extreme environments: implications for life detection beyond Earth

Covering: 1961 to 2024Discovering and identifying unique natural products/biosignatures (signatures that can be used as evidence for past or present life) that are abundant, and complex enough that they indicate robust evidence of life is a multifaceted process. One distinct category of biosignatures being explored is organic compounds. A subdivision of these compounds not yet readily investigated are volatile organic compound (VOCs). When assessing these VOCs as a group (volatilome) a fingerprint of all VOCs within an environment allows the complex patterns in metabolic data to be unravelled. As a technique already successfully applied to many biological and ecological fields, this paper explores how analysis of volatilomes in terrestrial extreme environments could be used to enhance processes (such as metabolomics and metagenomics) already utilised in life detection beyond Earth. By overcoming some of the complexities of collecting VOCs in remote field sites, a variety of lab based analytical equipment and techniques can then be utilised. Researching volatilomics in astrobiology requires time to characterise the patterns of VOCs. They must then be differentiated from abiotic (non-living) signals within extreme environments similar to those found on other planetary bodies (analogue sites) or in lab-based simulated environments or microcosms. Such an effort is critical for understanding data returned from past or upcoming missions, but it requires a step change in approach which explores the volatilome as a vital additional tool to current 'Omics techniques.

The impact of surfaces on indoor air chemistry following cooking and cleaning

Cooking and cleaning are common sources of indoor air pollutants, including volatile organic compounds (VOCs). The chemical fate of VOCs indoors is determined by both gas-phase and multi-phase chemistry, and can result in the formation of potentially hazardous secondary pollutants. Chemical interactions at the gas-surface boundary play an important role in indoor environments due to the characteristically high surface area to volume ratios (SAVs). This study first characterises the VOC emissions from a typical cooking and cleaning activity in a semi-realistic domestic kitchen, using real-time measurements. While cooking emitted a larger amount of VOCs overall, both cooking and cleaning were sources of chemically reactive monoterpenes (peak mixing ratios 7 ppb and 2 ppb, respectively). Chemical processing of the VOC emissions from sequential cooking and cleaning activities was then simulated in a kitchen using a detailed chemical model. Results showed that ozone (O3) deposition was most effective onto plastic and soft furnishings, while wooden surfaces were the most effective at producing formaldehyde following multi-phase chemistry. Subsequent modelling of cooking and cleaning emissions using a range of measured kitchen SAVs revealed that indoor oxidant levels and the subsequent chemistry, are strongly influenced by the total and material-specific SAV of the room. O3 mixing ratios ranged from 1.3-7.8 ppb across 9 simulated kitchens, with higher concentrations of secondary pollutants observed at higher O3 concentration. Increased room volume, decreased total SAV, decreased SAVs of plastic and soft furnishings, and increased wood SAV contributed to elevated formaldehyde and total peroxyacetyl nitrates (PANs) mixing ratios, of up to 1548 ppt and 643 ppt, respectively, following cooking and cleaning. Therefore, the size and material composition of indoor environments has the potential to impact the chemical processing of VOC emissions from common occupant activities.

Advanced analytical techniques for authenticity identification and quality evaluation in Essential oils: A review

Essential oils (EO), secondary metabolites of plants are fragrant oily liquids with antibacterial, antiviral, anti-inflammatory, anti-allergic, and antioxidant effects. They are widely applied in food, medicine, cosmetics, and other fields. However, the quality of EOs remain uncertain owing to their high volatility and susceptibility to oxidation, influenced by factors such as the harvesting season, extraction, and separation techniques. Additionally, the huge economic value of EOs has led to a market marked by widespread and varied adulteration, making the assessment of their quality challenging. Therefore, developing simple, quick, and effective identification techniques for EOs is essential. This review comprehensively summarizes the techniques for assessing EO quality and identifying adulteration. It covers sensory evaluation, physical and chemical property evaluation, and chemical composition analysis, which are widely used and of great significance for the quality evaluation and adulteration detection of EOs.

Recent advances in mass spectrometry techniques for atmospheric chemistry research on molecular-level

The Earth's atmosphere is composed of an enormous variety of chemical species associated with trace gases and aerosol particles whose composition and chemistry have critical impacts on the Earth's climate, air quality, and human health. Mass spectrometry analysis as a powerful and popular analytical technique has been widely developed and applied in atmospheric chemistry for decades. Mass spectrometry allows for effective detection, identification, and quantification of a broad range of organic and inorganic chemical species with high sensitivity and resolution. In this review, we summarize recently developed mass spectrometry techniques, methods, and applications in atmospheric chemistry research in the past several years on molecular-level. Specifically, new developments of ion-molecule reactors, various soft ionization methods, and unique coupling with separation techniques are highlighted. The new mass spectrometry applications in laboratory studies and field measurements focused on improving the detection limits for traditional and emerging volatile organic compounds, characterizing multiphase highly oxygenated molecules, and monitoring particle bulk and surface compositions.

Volatile organic compounds in exhaled breath of newborns: a pilot study

OBJECTIVE

To assess volatile organic compounds (VOCs) in breath samples collected non-invasively from preterm and full-term infants.

METHODS

This was a pilot study included preterm and full-term infants who were not intubated or suspected or diagnosed with metabolic or gastrointestinal disorders. The samples were analyzed for VOCs using a selected-ion flow-tube mass spectrometer.

RESULTS

Twenty infants were included; ten preterm and ten full-term infants. Twenty-two VOCs were detected and measurable in all samples. There was a significant difference between preterm and full-term infants for the 2-propanol, acetaldehyde, acetone, acetonitrile, benzene, ethanol, isoprene, pentane, 3-methylhexane, 2-nonene, ethane, triethylamine, and trimethylamine compounds.

CONCLUSION

It is feasible to measure VOCs in breath samples of preterm and full-term non-intubated infants. Full-term infants express different concentrations than preterm infants. Further studies are needed to examine the utility and reproducibility of measuring VOCs to identify neonatal diseases and predict outcomes.

High and low pathogenicity avian influenza virus discrimination and prediction based on volatile organic compounds signature by SIFT-MS: a proof-of-concept study

High and low pathogenicity avian influenza viruses (HPAIV, LPAIV) are the primary causes of poultry diseases worldwide. HPAIV and LPAIV constitute a major threat to the global poultry industry. Therefore, early detection and well-adapted surveillance strategies are of the utmost importance to control the spread of these viruses. Volatile Organic Compounds (VOCs) released from living organisms have been investigated over the last decades as a diagnostic strategy. Mass spectrometry instruments can analyze VOCs emitted upon viral infection. Selected ion flow tube mass spectrometry (SIFT-MS) enables direct analysis of cell headspace in less than 20 min. As a proof-of-concept study, we investigated the ability of a SIFT-MS coupled sparse Partial Least Square-Discriminant Analysis analytical workflow to discriminate IAV-infected cells. Supernatants of HPAIV, LPAIV, and control cells were collected from 1 to 72 h post-infection and analyzed using our analytical workflow. At each collection point, VOCs' signatures were first identified based on four independent experiments and then used to discriminate the infectious status of external samples. Our results indicate that the identified VOCs signatures successfully discriminate, as early as 1-h post-infection, infected cells from the control cells and differentiated the HPAIV from the LPAIV infection. These results suggest a virus-dependent VOCs signature. Overall, the external samples' status was identified with 96.67% sensitivity, 100% specificity, and 97.78% general accuracy.

Femtosecond Laser Ionization Mass Spectrometry for Online Analysis of Human Exhaled Breath

A variety of organic compounds in human exhaled breath were measured online by mass spectrometry using the fifth (206 nm) and fourth (257 nm) harmonic emissions of a femtosecond ytterbium (Yb) laser as the ionization source. Molecular ions were enhanced significantly by means of resonance-enhanced, two-color, two-photon ionization, which was useful for discrimination of analytes against the background. The limit of detection was 0.15 ppm for acetone in air. The concentration of acetone in exhaled breath was determined for three subjects to average 0.31 ppm, which lies within the range of normal healthy subjects and is appreciably lower than the range for patients with diabetes mellitus. Many other constituents, which could be assigned to acetaldehyde, ethanol, isoprene, phenol, octane, ethyl butanoate, indole, octanol, etc., were observed in the exhaled air. Therefore, the present approach shows potential for use in the online analysis of diabetes mellitus and also for the diagnosis of various diseases, such as COVID-19 and cancers.

Biofiltration of gaseous mixtures of dimethyl sulfide, dimethyl disulfide and dimethyl trisulfide: Effect of operational conditions and microbial analysis

The efficient removal of volatile sulfur compounds (VSCs), such as dimethyl sulfide (DMS), dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS), is crucial due to their foul odor and corrosive potential in sewer systems. Biofilters (BFs) offer promise for VSCs removal, but face challenges related to pH control and changing conditions at full scale. Two BFs, operated under acidophilic conditions for 78 days, were evaluated for their performance at varying inlet concentrations and empty bed residence times (EBRTs). BF1, incorporating 4-6 mm marble limestone for pH control, outperformed BF2, which used NaHCO3 in the nutrient solution. BF1 displayed better resilience, maintained a stable pH of 4.6 ± 0.6, and achieved higher maximum elimination capacities (ECmax, 41 mg DMS m-3 h-1 (RE 38.3%), 146 mg DMDS m-3 h-1 (RE 83.1%), 47 mg DMTS m-3 h-1 (RE 93.1%)) at an EBRT of 56 s compared to BF2 (9 mg DMS m-3 h-1 (RE 7.1%), 9 mg DMDS m-3 h-1 (RE 4.8%) and 11 mg DMTS m-3 h-1 (RE 26.6%)). BF2 exhibited pH stratification and decreased performance after feeding interruptions. The biodegradability of VSCs followed the order DMTS > DMDS > DMS, and several microorganisms were identified contributing to VSCs degradation in BF1, including Bacillus (14%), Mycobacterium (11%), Acidiphilium (7%), and Acidobacterium (3%).

Geographic information system-based determination of priority monitoring areas for hazardous air pollutants in an industrial city

Industrial cities are hotspots for many hazardous air pollutants (HAPs), which are detrimental to human health. We devised an identification method to determine priority HAP monitoring areas using a comprehensive approach involving monitoring, modeling, and demographics. The methodology to identify the priority HAP monitoring area consists of two parts: (1) mapping the spatial distribution of selected categories relevant to the target pollutant and (2) integrating the distribution maps of various categories and subsequent scoring. The identification method was applied in Ulsan, the largest industrial city in South Korea, to identify priority HAP monitoring areas. Four categories related to HAPs were used in the method: (1) concentrations of HAPs, (2) amount of HAP emissions, (3) the contribution of industrial activities, and (4) population density in the city. This method can be used to select priority HAP monitoring areas for intensive monitoring campaigns, cohort studies, and epidemiological studies.

Does green mean clean? Volatile organic emissions from regular versus green cleaning products

Cleaning products emit a range of volatile organic compounds (VOCs), including some which are hazardous or can undergo chemical transformations to generate harmful secondary pollutants. In recent years, "green" cleaners have become increasingly popular, with an implicit assumption that these are better for our health and/or the environment. However, there is no strong evidence to suggest that they are better for indoor air quality compared to regular products. In this study, the VOC composition of 10 regular and 13 green cleaners was examined by headspace analysis. Monoterpenes were the most prevalent VOCs, with average total monoterpene concentrations of 8.6 and 25.0 mg L-1 for regular and green cleaners, respectively. Speciated monoterpene emissions were applied to a detailed chemical model to investigate the indoor air chemistry following a typical cleaning event. Green cleaners generally emitted more monoterpenes than regular cleaners, resulting in larger increases in harmful secondary pollutant concentrations following use, such as formaldehyde (up to 7%) and PAN species (up to 6%). However, emissions of the most reactive monoterpenes (α-terpinene, terpinolene and α-phellandrene), were observed more frequently from regular cleaners, resulting in a disproportionately large impact on the concentrations of radical species and secondary pollutants that were formed after cleaning occurred.

Exhaled breath is found to be better than blood samples for determining propofol concentrations in the brain tissues of rats

The correlation between propofol concentration in exhaled breath (CE) and plasma (CP) has been well-established, but its applicability for estimating the concentration in brain tissues (CB) remains unknown. Given the impracticality of directly sampling human brain tissues, rats are commonly used as a pharmacokinetic model due to their similar drug-metabolizing processes to humans. In this study, we measuredCE,CP, andCBin mechanically ventilated rats injected with propofol. Exhaled breath samples from the rats were collected every 20 s and analyzed using our team's developed vacuum ultraviolet time-of-flight mass spectrometry. Additionally, femoral artery blood samples and brain tissue samples at different time points were collected and measured using high-performance liquid chromatography mass spectrometry. The results demonstrated that propofol concentration in exhaled breath exhibited stronger correlations with that in brain tissues compared to plasma levels, suggesting its potential suitability for reflecting anesthetic action sites' concentrations and anesthesia titration. Our study provides valuable animal data supporting future clinical applications.

Simulation study of three new quadrupole ion funnels to improve low-mass ion transmission

RATIONALE

By applying radio frequency (RF) and direct current (DC) voltages to corresponding ring electrodes, ion funnel (IF) can efficiently focus and transmit ions. However, IF has an inherent mass discrimination problem that will greatly limit low mass-to-charge (m/z) ion focusing and transmission. To improve the transmission efficiency (TE) of the IF, this paper explores three new profile quadrupole ion funnels (QIF).

METHODS

Computer simulations of the potential field distributions of QIFs and conventional IFs were performed to assess their focusing characteristics. To compare the TE, ion optics simulation programs SIMION and AXSIM were used to perform a series of simulations. Three QIF types (toroidal, cylindrical, and hyperbolic configurations) were used to improve ion TE, and their transmission and focus performance were also compared with conventional IF.

RESULTS

By simulating the trajectories of ions in the IF, the optimum electrical parameters for three new QIFs were obtained and compared with conventional IFs, with TE improvements recorded for m/z < 100 of 16%, 20%, and 13%.

CONCLUSIONS

The results indicate that studying these three new IF configurations has great research significance for improving sensitivity to low m/z ions in mass spectrometer instruments.

Robust Automated SIFT-MS Quantitation of Volatile Compounds in Air Using a Multicomponent Gas Standard

Selected ion flow tube mass spectrometry, SIFT-MS, has been widely used in industry and research since its introduction in the mid-1990s. Previously described quantitation methods have been advanced to include a gas standard for a more robust and repeatable analytical performance. The details of this approach to calculate the concentrations from ion-molecule reaction kinetics based on reaction times and instrument calibration functions determined from known concentrations in the standard mix are discussed. Important practical issues such as the overlap of product ions are outlined, and best-practice approaches are presented to enable them to be addressed during method development. This review provides a fundamental basis for a plethora of studies in broad application areas that are possible with SIFT-MS instruments.

Detection technologies of volatile organic compounds in the breath for cancer diagnoses

Although there are new approaches in both cancer treatment and diagnosis, overall mortality is a major concern. New technologies have attempted to look at breath volatile organic compounds (VOCs) detection to diagnose cancer. Gas Chromatography and Mass Spectrometry (GC - MS) have remained the gold standard of VOC analysis for decades, but it has limitations in differentiating VOCs between cancer subtypes. To increase efficacy and accuracy, new methods to analyze these breath VOCs have been introduced, such as Solid Phase Microextraction/Gas Chromatography-Mass Spectrometry (SPME/GC-MS), Selected Ion Flow Tube - Mass Spectrometry (SIFT-MS), Proton Transfer Reaction - Mass Spectrometry (PRT-MS), Ion Mobility Spectrometry (IMS), and Colorimetric Sensors. This article highlights new technologies that have been studied and applied in the detection and quantification of breath VOCs for possible cancer diagnoses.

Novel Models for Accurate Estimation of Air-Blood Partitioning: Applications to Individual Compounds and Complex Mixtures of Neutral Organic Compounds

The air-blood partition coefficient (Kab) is extensively employed in human health risk assessment for chemical exposure. However, current Kab estimation approaches either require an extensive number of parameters or lack precision. In this study, we present two novel and parsimonious models to accurately estimate Kab values for individual neutral organic compounds, as well as their complex mixtures. The first model, termed the GC×GC model, was developed based on the retention times of nonpolar chemical analytes on comprehensive two-dimensional gas chromatography (GC×GC). This model is unique in its ability to estimate the Kab values for complex mixtures of nonpolar organic chemicals. The GC×GC model successfully accounted for the Kab variance (R2 = 0.97) and demonstrated strong prediction power (RMSE = 0.31 log unit) for an independent set of nonpolar chemical analytes. Overall, the GC×GC model can be used to estimate Kab values for complex mixtures of neutral organic compounds. The second model, termed the partition model (PM), is based on two types of partition coefficients: octanol to water (Kow) and air to water (Kaw). The PM was able to effectively account for the variability in Kab data (n = 344), yielding an R2 value of 0.93 and root-mean-square error (RMSE) of 0.34 log unit. The predictive power and explanatory performance of the PM were found to be comparable to those of the parameter-intensive Abraham solvation models (ASMs). Additionally, the PM can be integrated into the software EPI Suite, which is widely used in chemical risk assessment for initial screening. The PM provides quick and reliable estimation of Kab compared to ASMs, while the GC×GC model is uniquely suited for estimating Kab values for complex mixtures of neutral organic compounds. In summary, our study introduces two novel and parsimonious models for the accurate estimation of Kab values for both individual compounds and complex mixtures.

Exhaled Breath Analysis Using Selected Ion Flow Tube Mass Spectrometry and Disease Severity in Heart Failure

Exhaled breath volatile organic compounds (VOCs) are elevated in heart failure (HF). The ability of VOCs to predict long term cardiovascular mortality and morbidity has not been independently verified. In 55 patients admitted with acute decompensated heart failure (ADHF), we measured exhaled breath acetone and pentane levels upon admission and after 48 h of diuresis. In a separate cohort of 51 cardiac patients undergoing cardiopulmonary exercise testing (CPET), we measured exhaled breath acetone and pentane levels before and at peak exercise. In the ADHF cohort, admission acetone levels correlated with lower left ventricular ejection fraction (LVEF, r = -0.297, p = 0.035). Greater weight loss with diuretic therapy correlated with a greater reduction in both acetone levels (r = -0.398, p = 0.003) and pentane levels (r = -0.309, p = 0.021). In patients with above-median weight loss (≥4.5 kg), patients demonstrated significantly greater percentage reduction in acetone (59% reduction vs. 7% increase, p < 0.001) and pentane (23% reduction vs. 2% reduction, p = 0.008). In the CPET cohort, admission acetone and pentane levels correlated with higher VE/VCO2 (r = 0.39, p = 0.005), (r = 0.035, p = 0.014). However, there were no significant correlations between baseline or peak exercise acetone and pentane levels and peak VO2. In longitudinal follow-up with a median duration of 33 months, patients with elevated exhaled acetone and pentane levels experienced higher composite adverse events of death, ventricular assist device implantation, or orthotopic heart transplantation. In patients admitted with ADHF, higher exhaled breath acetone levels are associated with lower LVEF and poorer outcomes, and greater reductions in exhaled breath acetone and pentane tracked with greater weight loss. Exhaled acetone and pentane may be novel biomarkers in heart failure worthy of future investigation.

State-of-the-art and challenges in the analysis of renewable gases

The development of renewable and low-carbon gases for injection into the gas grid obtained by different processes such as anaerobic digestion, pyrogasification, hydrothermal gasification, and methanation, followed by upgrading steps, increases the demand for analysis and characterization in order to fully manage their integration into the gas value chain. If the analysis of the main compounds (methane, carbon dioxide, hydrogen, and carbon monoxide) is well described, the analysis of impurities in renewable gases remains more challenging due to their various natures and quantities. After a brief description of renewable and low-carbon methane production processes, the review focuses on the methods used for the analysis of the different compounds in renewable gases, from the main ones to impurities at ppbv levels. Gas chromatography (GC), coupled with different detectors, is the preferred technique, enabling the analysis and quantification of siloxanes, terpenes, oxygenates, and sulfur compounds. Recently, comprehensive two-dimensional GC has been applied to renewable gases, increasing the number of compounds detected. Non-chromatographic techniques are also reviewed. As sampling is of major importance in the search for reliable analyses, a whole section is devoted to this aspect. Among the available methods, pre-concentration on adsorbent tubes emerges as the most relevant solution.

A measurement and modelling investigation of the indoor air chemistry following cooking activities

Domestic cooking is a source of indoor air pollutants, including volatile organic compounds (VOCs), which can impact on indoor air quality. However, the real-time VOC emissions from cooking are not well characterised, and similarly, the resulting secondary chemistry is poorly understood. Here, selected-ion flow-tube mass spectrometry (SIFT-MS) was used to monitor the real-time VOC emissions during the cooking of a scripted chicken and vegetable stir-fry meal, in a room scale, semi-realistic environment. The VOC emissions were dominated by alcohols (70% of total emission), but also contained a range of aldehydes (14%) and terpenes (5%), largely attributable to the heating of oil and the preparation and heating of spices, respectively. The direct cooking-related VOC emissions were then simulated using the Indoor Chemical Model in Python (INCHEM-Py), to investigate the resulting secondary chemistry. Modelling revealed that VOC concentrations were dominated by direct emissions, with only a small contribution from secondary products, though the secondary species were longer lived than the directly emitted species. Following cooking, hydroxyl radical concentrations reduced by 86%, while organic peroxy radical levels increased by over 700%, later forming secondary organic nitrates, peroxyacylnitrates (PANs) and formaldehyde. Monoterpene emissions were shown to drive the formation of secondary formaldehyde, albeit to produce relatively modest concentrations (average of 60 ppt). Sensitivity analysis of the simulation conditions revealed that increasing the outdoor concentrations of ozone and NOx species (2.9× and 9×, respectively) resulted in the greatest increase in secondary product formation indoors (≈400%, 200% and 600% increase in organic nitrates, PANs and formaldehyde production, respectively). Given the fact that climate change is likely to result in increased ozone concentrations in the future, and that increased window-opening in response to rising temperatures is also likely, higher concentrations of indoor oxidants are likely in homes in the future. This work, therefore, suggests that cooking could be a more important source of secondary pollutants indoors in the future.

Volatile Methylsiloxanes in Complex Samples: Recent Updates on Pretreatment and Analysis Methods

Volatile methylsiloxanes (VMSs) are massively produced chemicals having applications in industry and home because of their physical and chemical characteristics. They are used in personal care products such as cosmetics, household coatings, cleaners, skin care products, and others. Resultantly, large number of VMSs are discharged into air where they can be subjected to atmospheric migrations over long distances causing toxic and estrogenic effects, persistence, and bioaccumulations. Many institutions have taken measures to control VMSs. They require accurate, rapid, and sensitive pretreatment and analysis methods for diverse samples. Herein, the pretreatment and determination methods of VMSs as reported in recent years are reviewed and summarized. Pretreatments include commonly methods such as membrane-assisted solvent extraction, liquid-liquid extraction, and others, while novel methods are solid phase extraction, solid phase microextraction, diverse liquid phase microextraction and others. Analyses are made through gas chromatography-based methods. In addition, the advantages, and disadvantages of techniques are compared, and the prospects of pretreatment and analysis methods are discussed.

Identification of Corrosive Volatile Compounds Found in the Headspace of Chicken Noodle Soup Retorted in Metal Cans

This study investigated the development of volatile compounds in the headspace of canned chicken noodle soup (and sought to develop appropriate testing methods). The primary objective of this study was to identify compounds in the soup that were responsible for the initiation of the corrosion in the cans. The long-term goal of these studies is to develop an efficient method to investigate how headspace volatile compounds in foods could cause corrosion defects in metal cans and how these could be corrected without undermining the quality and safety of the food. To determine and to evaluate the volatile compounds in the canned soups, selected ion flow tube-mass spectrometry (SIFT-MS) was used. The coatings of the tested cans were carefully stripped off and analyzed using this SIFT-MS method. High levels of sulfur-containing volatile compounds and organic acids were detected in both the soups and the coatings. It was concluded that during the retorting of the sealed cans filled with chicken soup, sulfur-containing volatile compounds formed and entered the headspace of the tested cans and interacted with the coating, leading to the formation of blackened stains.

Direct mass spectrometry analysis of exhaled human breath in real-time

The molecular composition of exhaled human breath can reflect various physiological and pathological conditions. Considerable progress has been achieved over the past decade in real-time analysis of exhaled human breath using direct mass spectrometry methods, including selected ion flow tube mass spectrometry, proton transfer reaction mass spectrometry, extractive electrospray ionization mass spectrometry, secondary electrospray ionization mass spectrometry, acetone-assisted negative photoionization mass spectrometry, atmospheric pressure photoionization mass spectrometry, and low-pressure photoionization mass spectrometry. Here, recent developments in direct mass spectrometry analysis of exhaled human breath are reviewed with regard to analytical performance (chemical sensitivity, selectivity, quantitative capabilities) and applications of the developed methods in disease diagnosis, targeted molecular detection, and real-time metabolic monitoring.

Proton-transfer rate constants for the determination of organic indoor air pollutants by online mass spectrometry

Proton transfer reaction mass spectrometry (PTR-MS) has become an indispensable analytical tool for indoor related sciences. With high-resolution techniques not only is the online monitoring of the selected ions in the gas phase possible, but also, with some limitations, the identification of substance mixtures without chromatographic separation. The quantification is carried out with the help of kinetic laws, which require knowledge of the conditions in the reaction chamber, the reduced ion moblilities and the reaction rate constant k_PT under these conditions. Ion-dipole collision theory can be used to calculate k_PT. One approach is an extension of Langevin's equation and is known as average dipole orientation (ADO). In a further development, the analytical solution of ADO was replaced by trajectory analysis, which resulted in capture theory. The calculations according to ADO and capture theory require precise knowledge of the dipole moment and the polarizability of the respective target molecule. However, for many relevant indoor related substances, these data are insufficiently known or not known at all. Consequently, the dipole moment μ_D and polarizability α of 114 organic compounds that are frequently found in indoor air had to be determined using advanced quantum mechanical methods. This required the development of an automated workflow that performs conformer analysis before computing μ_D and α using density functional theory (DFT). Then the reaction rate constants with the H₃O⁺ ion are calculated according to the ADO theory (k_ADO), capture theory (k_cap) and advanced capture theory for different conditions in the reaction chamber. The kinetic parameters are evaluated with regard to their plausibility and critically discussed for their applicability in PTR-MS measurements.

Impact of shipping emissions regulation on urban aerosol composition changes revealed by receptor and numerical modelling

Various shipping emissions controls have recently been implemented at both local and national scales. However, it is difficult to track the effect of these on PM2.5 levels, owing to the non-linear relationship that exists between changes in precursor emissions and PM components. Positive Matrix Factorisation (PMF) identifies that a switch to cleaner fuels since January 2020 results in considerable reductions in shipping-source-related PM2.5, especially sulphate aerosols and metals (V and Ni), not only at a port site but also at an urban background site. CMAQ sensitivity analysis reveals that the reduction of secondary inorganic aerosols (SIA) further extends to inland areas downwind from ports. In addition, mitigation of secondary organic aerosols (SOA) in coastal urban areas can be anticipated either from the results of receptor modelling or from CMAQ simulations. The results in this study show the possibility of obtaining human health benefits in coastal cities through shipping emission controls.

Detecting Hexafluoroisopropanol Using Soft Chemical Ionization Mass Spectrometry and Analytical Applications to Exhaled Breath

Here we explore the potential use of proton transfer reaction/selective reagent ion-time-of-flight-mass spectrometry (PTR/SRI-ToF-MS) to monitor hexafluoroisopropanol (HFIP) in breath. Investigations of the reagent ions H₃O⁺, NO⁺, and O₂^+• are reported using dry (relative humidity (rH) ≈ 0%) and humid (rH ≈ 100%)) nitrogen gas containing traces of HFIP, i.e., divorced from the complex chemical environment of exhaled breath. HFIP shows no observable reaction with H₃O⁺ and NO⁺, but it does react efficiently with O₂^+• via dissociative charge transfer resulting in CHF₂⁺, CF₃⁺, C₂HF₂O⁺, and C₂H₂F₃O⁺. A minor competing hydride abstraction channel results in C₃HF₆O⁺ + HO₂^• and, following an elimination of HF, C₃F₅O⁺. There are two issues associated with the use of the three dominant product ions of HFIP, CHF₂⁺, CF₃⁺, and C₂H₂F₃O⁺, to monitor it in breath. One is that CHF₂⁺ and CF₃⁺ also result from the reaction of O₂^+• with the more abundant sevoflurane. The second is the facile reaction of these product ions with water, which reduces analytical sensitivity to detect HFIP in humid breath. To overcome the first issue, C₂H₂F₃O⁺ is the ion marker for HFIP. The second issue is surmounted by using a Nafion tube to reduce the breath sample's humidity prior to its introduction into drift tube. The success of this approach is illustrated by comparing the product ion signals either in dry or humid nitrogen gas flows and with or without the use of the Nafion tube, and practically from the analysis of a postoperative exhaled breath sample from a patient volunteer.

Recent developments and applications of selected ion flow tube mass spectrometry (SIFT-MS)

Selected ion flow tube mass spectrometry (SIFT-MS) is now recognized as the most versatile analytical technique for the identification and quantification of trace gases down to the parts-per-trillion by volume, pptv, range. This statement is supported by the wide reach of its applications, from real-time analysis, obviating sample collection of very humid exhaled breath, to its adoption in industrial scenarios for air quality monitoring. This review touches on the recent extensions to the underpinning ion chemistry kinetics library and the alternative challenge of using nitrogen carrier gas instead of helium. The addition of reagent anions in the Voice200 series of SIFT-MS instruments has enhanced the analytical capability, thus allowing analyses of volatile trace compounds in humid air that cannot be analyzed using reagent cations alone, as clarified by outlining the anion chemistry involved. Case studies are reviewed of breath analysis and bacterial culture volatile organic compound (VOC), emissions, environmental applications such as air, water, and soil analysis, workplace safety such as transport container fumigants, airborne contamination in semiconductor fabrication, food flavor and spoilage, drugs contamination and VOC emissions from packaging to demonstrate the stated qualities and uniqueness of the new generation SIFT-MS instrumentation. Finally, some advancements that can be made to improve the analytical capability and reach of SIFT-MS are mentioned.

On-Site Detection of Volatile Organic Compounds (VOCs)

Volatile organic compounds (VOCs) are of interest in many different fields. Among them are food and fragrance analysis, environmental and atmospheric research, industrial applications, security or medical and life science. In the past, the characterization of these compounds was mostly performed via sample collection and off-site analysis with gas chromatography coupled to mass spectrometry (GC-MS) as the gold standard. While powerful, this method also has several drawbacks such as being slow, expensive, and demanding on the user. For decades, intense research has been dedicated to find methods for fast VOC analysis on-site with time and spatial resolution. We present the working principles of the most important, utilized, and researched technologies for this purpose and highlight important publications from the last five years. In this overview, non-selective gas sensors, electronic noses, spectroscopic methods, miniaturized gas chromatography, ion mobility spectrometry and direct injection mass spectrometry are covered. The advantages and limitations of the different methods are compared. Finally, we give our outlook into the future progression of this field of research.

Breath VOC analysis and machine learning approaches for disease screening: a review

Early disease detection is often correlated with a reduction in mortality rate and improved prognosis. Currently, techniques like biopsy and imaging that are used to screen chronic diseases are invasive, costly or inaccessible to a large population. Thus, a non-invasive disease screening technology is the need of the hour. Existing non-invasive methods like gas chromatography-mass spectrometry, selected-ion flow-tube mass spectrometry, and proton transfer reaction-mass-spectrometry are expensive. These techniques necessitate experienced operators, making them unsuitable for a large population. Various non-invasive sources are available for disease detection, of which exhaled breath is preferred as it contains different volatile organic compounds (VOCs) that reflect the biochemical reactions in the human body. Disease screening by exhaled breath VOC analysis can revolutionize the healthcare industry. This review focuses on exhaled breath VOC biomarkers for screening various diseases with a particular emphasis on liver diseases and head and neck cancer as examples of diseases related to metabolic disorders and diseases unrelated to metabolic disorders, respectively. Single sensor and sensor array-based (Electronic Nose) approaches for exhaled breath VOC detection are briefly described, along with the machine learning techniques used for pattern recognition.

Current Limitations of Staph Infection Diagnostics, and the Role for VOCs in Achieving Culture-Independent Detection

Staphylococci are broadly adaptable and their ability to grow in unique environments has been widely established, but the most common and clinically relevant staphylococcal niche is the skin and mucous membranes of mammals and birds. S. aureus causes severe infections in mammalian tissues and organs, with high morbidities, mortalities, and treatment costs. S. epidermidis is an important human commensal but is also capable of deadly infections. Gold-standard diagnostic methods for staph infections currently rely upon retrieval and characterization of the infectious agent through various culture-based methods. Yet, obtaining a viable bacterial sample for in vitro identification of infection etiology remains a significant barrier in clinical diagnostics. The development of volatile organic compound (VOC) profiles for the detection and identification of pathogens is an area of intensive research, with significant efforts toward establishing breath tests for infections. This review describes the limitations of existing infection diagnostics, reviews the principles and advantages of VOC-based diagnostics, summarizes the analytical tools for VOC discovery and clinical detection, and highlights examples of how VOC biomarkers have been applied to diagnosing human and animal staph infections.

Real-Time Monitoring of Miniaturized Thermal Food Processing by Advanced Mass Spectrometric Techniques

Mass spectrometry is a popular and powerful analytical tool to study the effects of food processing. Industrial sampling, real-life sampling, or challenging academic research on process-related volatile and aerosol research often demand flexible, time-sensitive data acquisition by state-of-the-art mass analyzers. Here, we show a laboratory-scaled, miniaturized, and highly controllable setup for the online monitoring of aerosols and volatiles from thermal food processing based on dielectric barrier discharge ionization (DBDI) mass spectrometry (MS). We demonstrate the opportunities offered by the setup from a foodomics perspective to study emissions from the thermal processing of wheat bread rolls at 210 °C by Fourier transformation ion cyclotron resonance MS. As DBDI is an emerging technology, we compared its ionization selectivity to established atmospheric pressure ionization tools: we found DBDI preferably ionizes saturated, nitrogenous compounds. We likewise identified a sustainable overlap in the selectivity of detected analytes with APCI and electrospray ionization (ESI). Further, we dynamically recorded chemical fingerprints throughout the thermal process. Unsupervised classification of temporal response patterns was used to describe the dynamic nature of the reaction system. Compared to established tools for real-time MS, our setup permits one to monitor chemical changes during thermal food processing at ultrahigh resolution, establishing an advanced perspective for real-time mass spectrometric analysis of food processing.

A gas-phase standard delivery system for direct breath analysis

Applications for direct breath analysis by mass spectrometry (MS) are rapidly expanding. One of the more recent mass spectrometry-based approaches is secondary electrospray ionization coupled to high-resolution mass spectrometry (SESI-HRMS). Despite increasing usage, the SESI methodology still lacks standardization procedures for quality control and absolute quantification. In this study, we designed and evaluated a custom-built standard delivery system tailored for direct breath analysis. The system enables the simultaneous introduction of multiple gas-phase standard compounds into ambient MS setups in the lower parts-per-million (ppm) to parts-per-billion (ppb) range. To best mimic exhaled breath, the gas flow can be heated (37 °C-40 °C) and humidified (up to 98% relative humidity). Inter-laboratory comparison of the system included various SESI-HRMS setups, i.e. an Orbitrap and a quadrupole time-of-flight mass spectrometer (QTOF), and using both single- as well as multi-component standards. This revealed highly stable and reproducible performances with between-run variation <19% and within-run variation <20%. Independent calibration runs demonstrated high accuracy (96%-111%) and precision (>95%) for the single-compound standard acetone, while compound-specific performances were obtained for the multi-component standard. Similarly, the sensitivity varied for different compounds within the multi-component standard across all SESI-Orbitrap and -QTOF setups, yielding limits of detections from 3.1 ppb (forp-xylene) to 0.05 ppb (for 1,8-cineol). Routinely applying the standard system throughout several weeks, allowed us to monitor instrument stability and to identify technical outliers in exhaled breath measurements. Such routine deployment of standards would significantly improve data quality and comparability, which is especially important in longitudinal and multi-center studies. Furthermore, performance validation of the system demonstrated its suitability for reliable absolute quantification while it illustrated compound-dependent behavior for SESI.

An integrated instrument of a tandem quadrupole mass spectrometer for cluster reaction and soft-landing deposition

We have developed an integrated instrument system of a multiple-ion laminar flow tube (MIFT) reactor combined with a tandem quadrupole mass spectrometer (TQMS) and soft-landing deposition (SD) apparatus. A customized water-cooling magnetron sputtering (MagS) source is designed, by which we are able to attain a highly efficient preparation of metal clusters of 1-30 atoms with tunable size distributions. Following the MagS source, a laminar flow tube reactor is designed, allowing for sufficient gas-collision reactions of the as-prepared metal clusters, which is advantageous for probing magic clusters and minimizing wall effects when probing the reaction dynamics of such clusters. The customized TQMS analyzer involves a conical octupole, two linear octupoles, a quadruple ion deflector, and a 19 mm quadruple mass analyzer, allowing to decrease the pressure stepwise (from ∼5 to ∼10^-9 Torr), thus ensuring high sensitivity and high resolution of the mass spectrometry analysis. In addition, we have designed a dual SD apparatus for the mass-selected deposition of clusters and their reaction products. For the whole system, abbreviated as MagS-MIFT-TQMS-SD, we have performed a detailed ions-fly simulation and quantitatively estimated the ions transfer efficiency under vacuum conditions determined by real experiments. Taking these advantages, well-resolved Pb_n ⁺, Ag_n ⁺, and Nb_n ⁺ clusters have been produced, allowing for meticulous studies of cluster reactions under sufficient gas-phase collisions free of electric field trapping. Also, we have tested the efficiency of the dual SD.

Volatile Organic Compound Fragmentation in the Afterglow of Pulsed Glow Discharge in Ambient Air

Glow discharge (GD) source gained an increased level of attention in relation to the analysis of volatile organic compounds (VOCs) since past work showed that this soft ionization method allowed direct analysis of VOCs with minimal fragmentation, however, the issue of fragmentation was not previously studied in detail. The aim of the present work was to investigate the effect of discharge conditions on VOC fragmentation in the system consisting of the cell with pulsed glow discharge and a time-of-flight mass spectrometer. Ionization of VOCs of different classes (hydrocarbons, alcohols, esters, and carboxylic acids) was investigated. A copper cathode with flat geometry was used. VOCs were ionized in the afterglow of short pulse glow discharge in the air. The use of discharge afterglow significantly reduces or eliminates the effects of ionization mechanisms other than Penning process, in particular, electron ionization. This significantly reduced VOC fragmentation and provided rather low limits of detection. Specific cluster formation was observed for alcohols and esters, which may facilitate their identification.

OH Radical and Chlorine Atom Kinetics of Substituted Aromatic Compounds: 4-chlorobenzotrifluoride (p-ClC6H4CF3)

The mechanisms for the OH radical and Cl atom gas-phase reaction kinetics of substituted aromatic compounds remain a topic of atmospheric and combustion chemistry research. 4-Chlorobenzotrifluoride (p-chlorobenzotrifluoride, p-ClC₆H₄CF₃, PCBTF) is a commonly used substituted aromatic volatile organic compound (VOC) in solvent-based coatings. As such, PCBTF is classified as a volatile chemical product (VCP) whose release into the atmosphere potentially impacts air quality. In this study, rate coefficients, k₁, for the OH + PCBTF reaction were measured over the temperature ranges 275-340 and 385-940 K using low-pressure discharge flow-tube reactors coupled with a mass spectrometer detector in the ICARE/CNRS (Orléans, France) laboratory. k₁(298-353 K) was also measured using a relative rate method in the thermally regulated atmospheric simulation chamber (THALAMOS; Douai, France). k₁(T) displayed a non-Arrhenius temperature dependence with a negative temperature dependence between 275 and 385 K given by k₁(275-385 K) = (1.50 ± 0.15) × 10^-14 exp((705 ± 30)/T) cm³ molecule^-1 s^-1, where k₁(298 K) = (1.63 ± 0.03) × 10^-13 cm³ molecule^-1 s^-1 and a positive temperature dependence at elevated temperatures given by k₁(470-950 K) = (5.42 ± 0.40) × 10^-12 exp(-(2507 ± 45) /T) cm³ molecule^-1 s^-1. The present k₁(298 K) results are in reasonable agreement with two previous 296 K (760 Torr, syn. air) relative rate measurements. The rate coefficient for the Cl-atom + PCBTF reaction, k₂, was also measured in THALAMOS using a relative rate technique that yielded k₂(298 K) = (7.8 ± 2) × 10^-16 cm³ molecule^-1 s^-1. As part of this work, the UV and infrared absorption spectra of PCBTF were measured (NOAA; Boulder, CO, USA). On the basis of the UV absorption spectrum, the atmospheric instantaneous UV photolysis lifetime of PCBTF (ground level, midlatitude, Summer) was estimated to be 3-4 days, assuming a unit photolysis quantum yield. The non-Arrhenius behavior of the OH + PCBTF reaction over the temperature range 275 to 950 K is interpreted using a mechanism for the formation of an OH-PCBTF adduct and its thermochemical stability. The results from this study are included in a discussion of the OH radical and Cl atom kinetics of halogen substituted aromatic compounds for which only limited temperature-dependent kinetic data are available.

Focusing on Volatile Organic Compounds of Natural Resins by Selected-Ion Flow Tube-Mass Spectrometry

The analysis of archeological artifacts, due to the high value of antique objects, is preferably performed by nondestructive, noninvasive, and in situ techniques. At present, the most common in situ protocols used for the analysis of organic materials are spectroscopic approaches. In this work, we tested selected-ion flow tube-mass spectrometry (SIFT-MS), a transportable mass spectrometry system for the characterization and discrimination of natural resins by the analysis of their volatile organic compounds profiles. We chose diterpenoid, triterpenoid, and aromatic resins as reference materials, focusing on the most identified in archeological artifacts. This work aims to create a SIFT-MS database of mass spectra suitable for characterizing archeological samples. The spectral data obtained by SIFT-MS were interpreted with the aid of chromatograms and mass spectra obtained by head space-gas chromatography/mass spectrometry (HS-GC/MS). Finally, principal components analysis (PCA) was used to further underline the differences among the different materials and to investigate the possibility of discriminating different classes of resins based on their SIFT spectra.

Authentication of extra virgin Argan oil by selected-ion flow-tube mass-spectrometry fingerprinting and chemometrics

Recognized for its nutritional and therapeutic use, extra-virgin Argan Oil (EVAO) is frequently adulterated. Selected-Ion Flow-Tube Mass Spectrometry (SIFT-MS) spectra were applied to quantify adulterants (i.e., Argan oil of lower quality (LQAO), olive oil (OO), and sunflower oil (SO)) in EVAO. Four data sets, i.e., using H₃O⁺, NO⁺, O₂⁺ reagent ions, and the combined data were considered. Soft independent modelling of class analogy (SIMCA), and partial least squares discriminant analysis (PLS-DA) were assessed to distinguish adulterated- from pure EVAO. The effectiveness of SIFT-MS associated with PLS and support vector machine (SVM) regression to quantify trace adulterants in EVAO was evaluated. Variable Importance in Projection (VIP), and interval-PLS (iPLS) were also investigated to extract useful features. Different models were built to predict the EVAO authenticity and the degree of adulteration. High accuracy was achieved. SIFT-MS spectra handled with the appropriate chemometric tools were found suitable for the quality evaluation of EVAO.

Capture Theory Models: An overview of their development, experimental verification, and applications to ion-molecule reactions

Since Arrhenius first proposed an equation to account for the behaviour of thermally activated reactions in 1889, significant progress has been made in our understanding of chemical reactivity. A number of capture theory models have been developed over the past several decades to predict the rate coefficients for reactions between ions and molecules-ranging from the Langevin equation (for reactions between ions and non-polar molecules) to more recent fully quantum theories (for reactions at ultra-cold temperatures). A number of different capture theory methods are discussed, with the key assumptions underpinning each approach clearly set out. The strengths and limitations of these capture theory methods are examined through detailed comparisons between low-temperature experimental measurements and capture theory predictions. Guidance is provided on the selection of an appropriate capture theory method for a given class of ion-molecule reaction and set of experimental conditions-identifying when a capture-based model is likely to provide an accurate prediction. Finally, the impact of capture theories on fields such as astrochemical modelling is noted, with some potential future directions of capture-based approaches outlined.

Influence of Sample Gas Humidity on Product Ion Formation in High Kinetic Energy Ion Mobility Spectrometry (HiKE-IMS)

High Kinetic Energy Ion Mobility Spectrometers (HiKE-IMS) chemically ionize gaseous samples via reactant ions and separate the generated ions by their motion in a neutral gas under the influence of an electric field. Operation at reduced pressures of 10-40 mbar allows for reaching high reduced electric field strengths (E/N) of up to 120 Td. At these high E/N, the generated ions gain the namesake high kinetic energies, leading to a decrease in cluster size of the reactant ions by increasing the reaction rate of collision-induced cluster dissociation of hydrates. In positive ion polarity and in purified air, H₃O⁺(H₂O)_n, NO⁺(H₂O)_n, and O₂^+•(H₂O)_p are the most abundant reactant ions. In this work, we investigate the effect of varying sample gas humidity on product ion formation for several model substances. Results show that increasing the sample gas humidity at high E/N of 120 Td shifts product ion formation from a charge transfer dominated reaction system to a proton transfer dominated reaction system. For HiKE-IMS operated at high E/N, the reduction in cluster size of reactant ions allows ionization of analytes with low proton affinity even at high relative humidity in the sample gas of RH = 75% at 303.15 K and 1013.25 hPa. In contrast to conventional IMS, where increasing the sample gas humidity inhibits ionization for various analytes, increasing sample gas humidity in HiKE-IMS operated at 120 Td is actually beneficial for ionization yield of most analytes investigated in this work as it increases the number of H₃O⁺(H₂O)n.

The need for multicomponent gas standards for breath biomarker analysis

Exhaled breath is a non-invasive, information-rich matrix with the potential to diagnose or monitor disease, including infectious disease. Despite significant effort dedicated to biomarker identification in case control studies, very few breath tests are established in practice. In this topical review, we identify how gas standards support breath analysis today and what is needed to support further expansion and translation to practice. We examine forensic and clinical breath tests and discuss how confidence has been built through unambiguous biomarker identification and quantitation supported by gas calibration standards. Based on this discussion, we identify a need for multicomponent gas standards with part-per-trillion to part-per-million concentrations. We highlight National Institute of Standards and Technology (NIST) gas standards developed for atmospheric measurements that are also relevant to breath analysis and describe investigations of long-term stability, chemical reactions, and interactions with gas cylinder wall treatments. An overview of emerging online instruments and their need for gas standards is also presented. This review concludes with a discussion of our ongoing research to examine the feasibility of producing multicomponent gas standards at breath-relevant concentrations. Such standards could be used to investigate interference from ubiquitous endogenous compounds and as a starting point for standards tailored to specific breath tests.

Study of the Chemical Ionization of Organophosphate Esters in Air Using Selected Ion Flow Tube-Mass Spectrometry for Direct Analysis

Organophosphate esters are an emerging environmental concern since they spread persistently across all environmental compartments (air, soil, water, etc.). Measurements of semivolatile organic compounds are important but not without challenges due to their physicochemical properties. Selected ion flow tube-mass spectrometry (SIFT-MS) can be relevant for their analysis in air because it is a direct analytical method without separation that requires little preparation and no external calibration. SIFT-MS is based on the chemical reactivity of analytes with reactant ions. For volatile and semivolatile organic compound analysis in the gas phase, knowledge of ion-molecule reactions and kinetic parameters is essential for the utilization of this technology. In the present work, we focused on organophosphate esters, semivolatile compounds that are now ubiquitous in the environment. The ion-molecule reactions of eight precursor ions that are available in SIFT-MS (H₃O⁺, NO⁺, O₂^•+, OH^-, O^•-, O₂^•-, NO₂^-, and NO₃^-) with six organophosphate esters were investigated. The modeling of ion-molecule reaction pathways by calculations supported and complemented the experimental work. Organophosphate esters reacted with six of the eight precursor ions with characteristic reaction mechanisms, such as protonation with hydronium precursor ions and association with NO⁺ ions, while nucleophilic substitution occurred with OH^-, O^•-, and O₂^•-. No reaction was observed with NO₂^- and NO₃^- ions. This work shows that the direct analysis of semivolatile organic compounds is feasible using SIFT-MS with both positive and negative ionization modes.

Reference materials for MS-based untargeted metabolomics and lipidomics: a review by the metabolomics quality assurance and quality control consortium (mQACC)

INTRODUCTION

The metabolomics quality assurance and quality control consortium (mQACC) is enabling the identification, development, prioritization, and promotion of suitable reference materials (RMs) to be used in quality assurance (QA) and quality control (QC) for untargeted metabolomics research.

OBJECTIVES

This review aims to highlight current RMs, and methodologies used within untargeted metabolomics and lipidomics communities to ensure standardization of results obtained from data analysis, interpretation and cross-study, and cross-laboratory comparisons. The essence of the aims is also applicable to other 'omics areas that generate high dimensional data.

RESULTS

The potential for game-changing biochemical discoveries through mass spectrometry-based (MS) untargeted metabolomics and lipidomics are predicated on the evolution of more confident qualitative (and eventually quantitative) results from research laboratories. RMs are thus critical QC tools to be able to assure standardization, comparability, repeatability and reproducibility for untargeted data analysis, interpretation, to compare data within and across studies and across multiple laboratories. Standard operating procedures (SOPs) that promote, describe and exemplify the use of RMs will also improve QC for the metabolomics and lipidomics communities.

CONCLUSIONS

The application of RMs described in this review may significantly improve data quality to support metabolomics and lipidomics research. The continued development and deployment of new RMs, together with interlaboratory studies and educational outreach and training, will further promote sound QA practices in the community.

Real-Time Monitoring of Volatile Organic Compounds in Ambient Air Using Direct-Injection Mass Spectrometry

Exposure to volatile organic compounds (VOCs) at low parts per billion (ppb) concentrations (by volume, ppbV) in ambient air is increasingly being recognized as a health risk. Furthermore, VOCs contribute to the formation of photochemical smog and particulate matter, which are hazardous and negatively impact the environment. Although most urban VOCs are anthropogenic in origin, some are produced by living organisms, especially trees. Gas chromatography (GC) is conventionally applied to VOC analysis of air, but it generally has a time resolution of tens of minutes and detection at low ppbV levels, frequently requiring sample preconcentration (such as using thermal desorption tubes (TDTs) or canister sampling with cryotrapping prior to analysis). Newer direct-injection mass spectrometry (DIMS) techniques can address the challenge of time resolution (seconds to tens of seconds) and eliminate the need for sampling via TDTs or canisters while still providing sufficient specificity. In this article, the results of a DIMS air monitoring campaign in Auckland, New Zealand, are described. Real-time selected ion flow tube mass spectrometry (SIFT–MS) measurements were obtained at three sites over a period of several weeks each: (i) adjacent to a freeway, (ii) in a residential area, and (iii) at a rural location. There were 13 compounds that were targeted in the study, covering various sources: fugitive emissions and incomplete combustion (benzene, toluene, and ethylbenzene, along with the xylene isomers, styrene, and ethanol), incomplete combustion (1,3-butadiene, formaldehyde, acetaldehyde, acrolein, benzaldehyde, and acetone), and biogenic origin (isoprene and monoterpenes (total of all isomers). At each site, SIFT–MS provided effective on-site analysis to sub-ppbV levels with better than 1-min time resolution.

Particulate Matter in Swine Barns: A Comprehensive Review

Particulate matter (PM) represents an air quality management challenge for confined swine production systems. Due to the limited space and ventilation rate, PM can reach relatively high concentrations in swine barns. PM in swine barns possesses different physical, chemical, and biological characteristics than that in the atmosphere and other indoor environments. As a result, it exerts different environmental and health effects and creates some unique challenges regarding PM measurement and mitigation. Numerous research efforts have been made, generating massive data and information. However, relevant review reports are sporadic. This study aims to provide an updated comprehensive review of swine barn PM, focusing on publications since 1990. It covers various topics including PM characteristics, sources, measurement methods, and in-barn mitigation technologies. As PM in swine barns is primarily of biological origins, bioaerosols are reviewed in great detail. Relevant topics include bacterial/fungal counts, viruses, microbial community composition, antibiotic-resistant bacteria, antibiotic resistance genes, endotoxins, and (1→3)-β-D-glucans. For each topic, existing knowledge is summarized and discussed and knowledge gaps are identified. Overall, PM in swine barns is complicated in chemical and biological composition and highly variable in mass concentrations, size, and microbial abundance. Feed, feces, and skins constitute the major PM sources. Regarding in-barn PM mitigation, four technologies (oil/water sprinkling, ionization, alternation of feed and feeders, and recirculating air filtration) are dominant. However, none of them have been widely used in commercial barns. A collective discussion of major knowledge gaps and future research needs is offered at the end of the report.

Build, Share and Remix: 3D Printing for Speeding Up the Innovation Cycles in Ambient Ionisation Mass Spectrometry (AIMS)

Ambient ionisation mass spectrometry (AIMS) enables studying biological systems in their native state and direct high-throughput analyses. The ionisation occurs in the physical conditions of the surrounding environment. Simple spray or plasma-based AIMS devices allow the desorption and ionisation of molecules from solid, liquid and gaseous samples. 3D printing helps to implement new ideas and concepts in AIMS quickly. Here, we present examples of 3D printed AIMS sources and devices for ion transfer and manipulation. Further, we show the use of 3D printer parts for building custom AIMS sampling robots and imaging systems. Using 3D printing technology allows upgrading existing mass spectrometers with relatively low cost and effort.

Untargeted selected ion flow tube mass spectrometry headspace analysis: High-throughput differentiation of virgin and recycled polyethylene pellets

RATIONALE

Recycled plastics are increasingly used for packaging of fast-moving consumer goods (FMCG). Compared with packaging made from virgin polymers, there is greater risk of taints entering products due to prior use of the polymers and incomplete cleaning. Increased quality assurance testing of polymer feedstock is required for recycled packaging. Selected ion flow tube mass spectrometry (SIFT-MS) analysis coupled with multivariate statistical data processing can provide high-throughput untargeted screening of recycled polymers at low cost per sample.

METHODS

SIFT-MS is a direct-injection MS technique that provides high-throughput automated headspace analysis of polymer samples when coupled with a syringe-injection autosampler (12 incubated samples per hour). Full-scan SIFT-MS data were processed using multivariate statistical analysis (specifically, the soft independent modeling by class analogy (SIMCA) algorithm).

RESULTS

SIFT-MS full-scan data were acquired for ten replicates each of ten recycled and four virgin high-density polyethylene (HDPE) pellet products from multiple manufacturers. The samples varied approximately 20-fold in terms of total volatile residue, while showing very high repeatability across replicates. SIFT-MS scan data were dominated by aliphatic and monoterpene hydrocarbon residues, and - to a lesser extent - alcohols. Application of the SIMCA algorithm to the data resulted in successful classification by both individual samples and manufacturers.

CONCLUSIONS

Automated, untargeted SIFT-MS analysis coupled with multivariate statistical data analysis has the potential to provide rapid, effective screening of recycled polymer products, which would provide increased quality assurance of recycled polymers used for FMCG.

Theoretical Investigation of Charge Transfer from NO+ and O2+ Ions to Wine-Related Volatile Compounds for Mass Spectrometry

Density-functional theory (DFT) is used to obtain the molecular data essential for predicting the reaction kinetics of chemical-ionization-mass spectrometry (CI-MS), as applied in the analysis of volatile organic compounds (VOCs). We study charge-transfer reactions from NO⁺ and O₂⁺ reagent ions to VOCs related to cork-taint and off-flavor in wine. We evaluate the collision rate coefficients of ion-molecule reactions by means of collision-based models. Many NO⁺ and O₂⁺ reactions are known to proceed at or close to their respective collision rates. Factors affecting the collision reaction rates, including electric-dipole moment and polarizability, temperature, and electric field are addressed, targeting the conditions of standard CI-MS techniques. The molecular electric-dipole moment and polarizability are the basic ingredients for the calculation of collision reaction rates in ion-molecule collision-based models. Using quantum-mechanical calculations, we evaluate these quantities for the neutral VOCs. We also investigate the thermodynamic feasibility of the reactions by computing the enthalpy change in these charge-transfer reactions.

Volatile fingerprint of food products with untargeted SIFT-MS data coupled with mixOmics methods for profile discrimination: Application case on cheese

Volatile organic compounds (VOCs) emitted by food products are decisive for the perception of aroma and taste. The analysis of gaseous matrices is traditionally done by detection and quantification of few dozens of characteristic markers. Emerging direct injection mass spectrometry technologies offer rapid analysis based on a soft ionisation of VOCs without previous separation. The recent increase of selectivity offered by the use of several precursor ions coupled with untargeted analysis increases the potential power of these instruments. However, the analysis of complex gaseous matrix results in a large number of ion conflicts, making the quantification of markers difficult, and in a large volume of data. In this work, we present the exploitation of untargeted SIFT-MS volatile fingerprints of ewe PDO cheeses in a real farm model, using mixOmics methods allowing us to illustrate the typicality, the manufacturing processes reproducibility and the impact of the animals' diet on the final product.

Taking leads out of nature, can nano deliver us from COVID-like pandemics?

The COVID-19 crisis has alerted the research community to re-purpose scientific tools that can effectively manage emergency pandemic situations. Researchers were never so desperate to discover a 'magic bullet' that has significant clinical benefits with minimal or no side effects. At the beginning of the pandemic, due to restricted access to traditional laboratory techniques, many research groups delved into computational screening of thousands of lead molecules that could inhibit SARS-CoV-2 at one or more stages of its infectious cycle. Several in silico studies on natural derivatives point out their potency against SARS-CoV-2 proteins. However, theoretical predictions and existing knowledge on related molecules reflect their poor oral bioavailability due to biotransformation in the gut and liver. Nanotechnology has evolved into a key field for precise and controlled delivery of various drugs that lack aqueous solubility, have low oral bioavailability and possess pronounced toxicity in their native form. In this review, we discuss various nanoformulations of natural products with favorable ADME properties, and also briefly explore nano-drug delivery to lungs, the primary site of SARS-CoV-2 infection. Natural products are also envisioned to augment nanotechnology-based 1) personnel protective equipment for ex vivo viral inactivation and 2) wearable sensors that perform rapid and non-invasive analysis of volatile organic compounds in exhaled breath of the infected person after therapeutic food consumption.

The potential of NO+ and O2 +• in switchable reagent ion proton transfer reaction time-of-flight mass spectrometry

Selected ion flow tube mass spectrometry (SIFT-MS) and proton transfer reaction mass spectrometry with switchable reagent ion capability (PTR+SRI-MS) are analytical techniques for real-time qualification and quantification of compounds in gas samples with trace level concentrations. In the detection process, neutral compounds-mainly volatile organic compounds-are ionized via chemical ionization with ionic reagents or primary ions. The most common reagent ions are H₃ O⁺ , NO⁺ and O₂ ^+• . While ionization with H₃ O⁺ occurs by means of proton transfer, the ionization via NO⁺ and O₂ ^+• offers a larger variety on ionization pathways, as charge transfer, hydride abstraction and so on are possible. The distribution of the reactant into various reaction channels depends not only on the usage of either NO⁺ or O₂ ^+• , but also on the class of analyte compounds. Furthermore, the choice of the reaction conditions as well as the choice of either SIFT-MS or PTR+SRI-MS might have a large impact on the resulting products. Therefore, an overview of both NO⁺ and O₂ ^+• as reagent ions is given, showing differences between SIFT-MS and PTR+SRI-MS as used analytical methods revealing the potential how the knowledge obtained with H₃ O⁺ for different classes of compounds can be extended with the usage of NO⁺ and O₂ ^+• .