Evaluation of the pulsed discharge helium ionization detector for the analysis of hydrogen and methane in breath

Substrate-dependent strategies to mitigate sulfate inhibition on microbial reductive dechlorination of polychlorinated biphenyls

Sulfate widely co-exists with polychlorinated biphenyls (PCBs) at various concentrations in the subsurface environment. Previous studies have suggested that sulfate often hampers microbial degradation of aliphatic chlorinated solvents such as chloroethenes. However, the impact of sulfate on microbial reductive dechlorination of aromatic PCBs and the underlying mechanisms have received limited attention. Likewise, strategies to mitigate such inhibition remain scarce. Here we found that the mechanisms and mitigation strategies of sulfate inhibition on PCB dechlorination were substrate-dependent. Under electron donor-limiting conditions, even a low concentration of sulfate (2 mM) resulted in a decreased PCB dechlorination rate by 88.7% in a co-culture comprising Dehalococcoides mccartyi CG1 and the sulfate-reducing bacterium Desulfovibrio desulfuricans F1, an inhibition which was attributed to the competition for electron donor between sulfate reduction and PCB dechlorination. As expected, re-amendment of 5 mM lactate effectively re-initiated PCB dechlorination. However, in the presence of a higher concentration of sulfate (5 mM), the PCB dechlorination rate in the co-culture was 77.7% lower than in the control, even with excessive electron donor supply. This inhibition was linked to high concentration of sulfide (∼5 mM) produced from sulfate reduction, as suggested by high availability of electron donor, recovery of dechlorination activity after removal of sulfide, and negligible influence of sulfate on PCB dechlorination in the axenic culture of D. mccartyi CG1. Indeed, sulfide (>5 mM) was found to directly suppress expression of PCB-dechlorinating reductive dehalogenase gene. The highest transcriptional level of pcbA1 was 2.9 ± 0.3 transcripts·cell-1 in the presence of ∼5 mM sulfide, which was increased to 37.4 ± 5.0 transcripts·cell-1 when sulfide was removed. Under this scenario, introduction of ferrous salts (5 mM) efficiently alleviated sulfide inhibition on PCB dechlorination. Interestingly, the augmentation of methanogens in the co-culture was also effective in mitigating sulfide inhibition on PCB dechlorination, offering a new approach to protect Dehalococcoides under sulfide stress. Collectively, these findings deepen our understanding of the influence of sulfate on microbial reductive dechlorination of PCBs and contribute to developing appropriate strategies based on geochemical conditions to alleviate sulfate inhibition during bioremediation of PCB-contaminated sites.

Highly Sensitive and Selective Detection of Hydrogen Using Pd-Coated SnO2 Nanorod Arrays for Breath-Analyzer Applications

We report a breath hydrogen analyzer based on Pd-coated SnO₂ nanorods (Pd-SnO₂ NRs) sensor integrated into a miniaturized gas chromatography (GC) column. The device can measure a wide range of hydrogen (1–100 ppm), within 100 s, using a small volume of human breath (1 mL) without pre-concentration. Especially, the mini-GC integrated with Pd-SnO₂ NRs can detect 1 ppm of H₂, as a lower detection limit, at a low operating temperature of 152 °C. Furthermore, when the breath hydrogen analyzer was exposed to a mixture of interfering gases, such as carbon dioxide, nitrogen, methane, and acetone, it was found to be capable of selectively detecting only H₂. We found that the Pd-SnO₂ NRs were superior to other semiconducting metal oxides that lack selectivity in H₂ detection. Our study reveals that the Pd-SnO₂ NRs integrated into the mini-GC device can be utilized in breath hydrogen analyzers to rapidly and accurately detect hydrogen due to its high selectivity and sensitivity.

Recent advances on endogenous gasotransmitters in inflammatory dermatological disorders

•

Endogenous gasotransmitters nitric oxide (NO), carbon monoxide (CO), hydrogen sulfide (H₂S), and potential candidates sulfur dioxide (SO₂), methane (CH₄), hydrogen gas (H₂), ammonia (NH₃) and carbon dioxide (CO₂), are generated within the human body.

•

Endogenous and potential gasotransmitters regulate inflammation, vasodilation, and oxidation in inflammatory dermatological disorders.

•

Endogenous and potential gasotransmitters play potential roles in psoriasis, atopic dermatitis, acne, and chronic skin ulcers.

•

Further research should explore the function of these gases and gas donors and inhibitors in inflammatory dermatological disorders.

Background

Endogenous gasotransmitters are small gaseous mediators that can be generated endogenously by mammalian organisms. The dysregulation of the gasotransmitter system is associated with numerous disorders ranging from inflammatory diseases to cancers. However, the relevance of these endogenous gasotransmitters, prodrug donors and inhibitors in inflammatory dermatological disorders has not yet been thoroughly reviewed and discussed.

Aim of review

This review discusses the recent progress and will provide perspectives on endogenous gasotransmitters in the context of inflammatory dermatological disorders.

Key scientific concepts of review

Endogenous gasotransmitters nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H₂S) are signaling molecules that regulate several physiological and pathological processes. In addition, sulfur dioxide (SO₂), methane (CH₄), hydrogen gas (H₂), ammonia (NH₃), and carbon dioxide (CO₂) can also be generated endogenously and may take part in physiological and pathological processes. These signaling molecules regulate inflammation, vasodilation, and oxidative stress, offering therapeutic potential and attracting interest in the field of inflammatory dermatological disorders including psoriasis, atopic dermatitis, acne, rosacea, and chronic skin ulcers. The development of effective gas donors and inhibitors is a promising alternative to treat inflammatory dermatological disorders with controllable and precise delivery in the future.

CH3SH and H2S Sensing Properties of V2O5/WO3/TiO2 Gas Sensor

Resistive-type semiconductor-based gas sensors were fabricated for the detection of methyl mercaptan and hydrogen sulfide. To fabricate these sensors, V2O5/WO3/TiO2 (VWT) particles were deposited on interdigitated Pt electrodes. The vanadium oxide content of the utilized VWT was 1.5, 3, or 10 wt.%. The structural properties of the VWT particles were investigated by X-ray diffraction and scanning electron microscopy analyses. The resistance of the VWT gas sensor decreased with increasing methyl mercaptan and hydrogen sulfide gas concentrations in the range of 50 to 500 ppb. The VWT gas sensor with 3 wt.% vanadium oxide showed high methyl mercaptan and hydrogen sulfide responses and good gas selectivity against hydrogen at 300 °C.

The applicability of a large-volume injection (LVI) system for quantitative analysis of permanent gases O2 and N2 using a gas chromatograph/barrier discharge ionization detector

To develop accurate quantitation methods for two major permanent gases, N₂ and O₂, a series of calibration experiments were carried out using a gas chromatograph (GC)/barrier discharge ionization detector (BID) equipped with a large-volume injection (LVI) system. To this end, gaseous working standards (WSs) diluted with helium gas were prepared at ten different concentration levels representing three different concentration ranges (in ppm) in 1-L polyester aluminum (PEA) bags ((1) low, 209~2090 (O₂) and 791~7910 (N₂); (2) moderate, 2090 ~ 20,900 (O₂) and 7910~79,100 (N₂); and (3) high, 20,900~209,000 (O₂) and 79,100~791,000 (N₂)). Cross-calibration experiments for each individual WS were carried out using the loop injection system with four different capacities (0.01, 0.5, 1, and 10 mL). The calibration results were then evaluated with respect to key variables including loop capacity, concentration, and mass quantity. Accordingly, we observed the optimal performance of the BID in terms of sensitivity and linearity (R ² > 0.98) when the WS of the moderate concentration range was analyzed with the small loop (0.01 and 0.5 mL). The method detection limit (MDL) values of the four loop sizes (between 0.01 and 10 mL) were 7~500 ng for O₂ (38.4~557 ppm) and 24~2230 ng for N₂ (195~2105 ppm).

Mixed-Potential Gas Sensors Using an Electrolyte Consisting of Zinc Phosphate Glass and Benzimidazole

Mixed-potential gas sensors with a proton conductor consisting of zinc metaphosphate glass and benzimidazole were fabricated for the detection of hydrogen produced by intestinal bacteria in dry and humid air. The gas sensor consisting of an alumina substrate with platinum and gold electrodes showed good response to different hydrogen concentrations from 250 parts per million (ppm) to 25,000 ppm in dry and humid air at 100-130 °C. The sensor response varied linearly with the hydrogen and carbon monoxide concentrations due to mass transport limitations. The sensor responses to hydrogen gas (e.g., -0.613 mV to 1000 ppm H₂) was higher than those to carbon monoxide gas (e.g., -0.128 mV to 1000 ppm CO) at 120 °C under atmosphere with the same level of humidity as expired air.

Analysis of hydrogen and methane in seawater by "Headspace" method: Determination at trace level with an automatic headspace sampler

"Headspace" technique is one of the methods for the onboard measurement of hydrogen (H₂) and methane (CH₄) in deep seawater. Based on the principle of an automatic headspace commercial sampler, a specific device has been developed to automatically inject gas samples from 300ml syringes (gas phase in equilibrium with seawater). As valves, micro pump, oven and detector are independent, a gas chromatograph is not necessary allowing a reduction of the weight and dimensions of the analytical system. The different steps from seawater sampling to gas injection are described. Accuracy of the method is checked by a comparison with the "purge and trap" technique. The detection limit is estimated to 0.3nM for hydrogen and 0.1nM for methane which is close to the background value in deep seawater. It is also shown that this system can be used to analyze other gases such as Nitrogen (N₂), carbon monoxide (CO), carbon dioxide (CO₂) and light hydrocarbons.

Sensing properties of Pd-loaded Co3O4 film for a ppb-level NO gas sensor

We prepared 0.1 wt%–30 wt% Pd-loaded Co₃O₄ by a colloidal mixing method and investigated the sensing properties of a Pd-loaded Co₃O₄ sensor element, such as the sensor response, 90% response time, 90% recovery time, and signal-to-noise (S/N) ratio, toward low nitric oxide (NO) gas levels in the range from 50 to 200 parts per billion. The structural properties of the Pd-loaded Co₃O₄ powder were investigated using X-ray diffraction analysis and transmission electron microscopy. Pd in the powder existed as PdO. The sensor elements with 0.1 wt%–10 wt% Pd content have higher sensor properties than those without any Pd content. The response of the sensor element with a 30 wt% Pd content decreased markedly because of the aggregation and poor dispersibility of the PdO particles. High sensor response and S/N ratio toward the NO gas were achieved when a sensor element with 10 wt% Pd content was used.

Thermal balance analysis of a micro-thermoelectric gas sensor using catalytic combustion of hydrogen

A thermoelectric gas sensor (TGS) with a combustion catalyst is a calorimetric sensor that changes the small heat of catalytic combustion into a signal voltage. We analyzed the thermal balance of a TGS to quantitatively estimate the sensor parameters. The voltage signal of a TGS was simulated, and the heat balance was calculated at two sections across the thermoelectric film of a TGS. The thermal resistances in the two sections were estimated from the thermal time constants of the experimental signal curves of the TGS. The catalytic combustion heat Q_catalyst required for 1 mV of ΔV_gas was calculated to be 46.1 μW. Using these parameters, we find from simulations for the device performance that the expected Q_catalyst for 200 and 1,000 ppm H₂ was 3.69 μW and 11.7 μW, respectively.

Diagnostic potential of the pulsed discharged helium ionization detector (PDHID) for pathogenic Mycobacterial volatile biomarkers

Pathogenic Mycobacteria cause diseases in animals and humans with significant economic and societal consequences. Current methods for Mycobacterial detection relies upon time- and labor-intensive techniques such as culturing or DNA analysis. Using gas chromatography and mass spectrometry, four volatile compounds (methyl phenylacetate, methyl p-anisate, methyl nicotinate and o-phenyl anisole) were recently proposed as potential biomarkers for Mycobacteria. We demonstrate for the first time the capabilities of a field-deployable, pulsed discharge helium ionization detector (PDHID) for sensing these volatiles. We determined the analytical performance of the PDHID toward these Mycobacterial volatiles. Detector performance was moderately affected over the temperature range of 150 to 350 °C. The linear dynamic range for all four analytes exceeded three orders of magnitude. The limits of detection (LOD) and quantitation (LOQ) were calculated as 150 and 450 pg respectively, for all compounds, except methyl phenylacetate (LOD and LOQ, 90 and 270 pg, respectively). Control charts revealed that the PDHID detection system was generally stable, and deviations could be traced to common causes and excluded special causes. Grob tests and ionization potential data suggest that the PDHID is capable of detecting Mycobacterial volatiles in a complex milieu such as culture headspace or breath samples from tuberculosis patients. The diagnostic potential of the PDHID is critical to our goal of a handheld, field-deployable 'sniffer' system for biological pathogens and chemical warfare agents.

Pulsed discharge helium ionization detector with multiple combined bias/collecting electrodes for gas chromatography

A pulsed discharge ionization detector (PDHID) with multiple combined bias/collecting electrodes (MC-PDHID) has been developed. Unlike most ionization detector designs with only one collecting electrode, the MC-PDHID builds multiple electrodes inside the detector cell. Each electrode serves as both a bias and a collecting electrode, thus gathering more information from the detector cell and improving PDHIP performance. The advantages of the MC-PDHID are: (1) sensitivity is increased by a factor of 2-3 times as compared with a single collecting electrode PDHID; (2) peak symmetry is improved, especially for narrow peaks; (3) it is possible to use a lower helium flow rate without compromising peak tailing; (4) linear dynamic range is increased by an order of magnitude through the calibration of electron and ion response factors; (5) certain groups of compounds can be identified. For example, if a trace amount of water is used as a dopant, the detector can identify alcohols and compounds with a hydrogen bond, since these compounds interact with the water coated on the wall in the detector cell which makes them stay in the detector cell longer than other compounds. In this research, the detector is characterized with different detector temperatures, flow rates, bias electrical potential arrangements, and bias potential polarities.

Designing a reliable leak bio-detection system for natural gas pipelines

Monitoring of natural gas (NG) pipelines is an important task for economical/safety operation, loss prevention and environmental protection. Timely and reliable leak detection of gas pipeline, therefore, plays a key role in the overall integrity management for the pipeline system. Owing to the various limitations of the currently available techniques and the surveillance area that needs to be covered, the research on new detector systems is still thriving. Biosensors are worldwide considered as a niche technology in the environmental market, since they afford the desired detector capabilities at low cost, provided they have been properly designed/developed and rationally placed/networked/maintained by the aid of operational research techniques. This paper addresses NG leakage surveillance through a robust cooperative/synergistic scheme between biosensors and conventional detector systems; the network is validated in situ and optimized in order to provide reliable information at the required granularity level. The proposed scheme is substantiated through a knowledge based approach and relies on Fuzzy Multicriteria Analysis (FMCA), for selecting the best biosensor design that suits both, the target analyte and the operational micro-environment. This approach is illustrated in the design of leak surveying over a pipeline network in Greece.

Exhaled breath analysis: The new interface between medicine and engineering

Exhaled breath testing is becoming an increasingly important non-invasive diagnostic method that can be used in the evaluation of health and disease states in the lung and beyond. Potential advantages of breath tests over other conventional medical tests include their non-invasive nature, low cost, and safety. To advance in this area further, however, there has to be a close collaboration between technical experts and engineers who have devices looking for clinical application(s), the medical experts who have the clinical problems looking for a test/biomarker that can be helpful in diagnosis or monitoring, and industry/commercial experts who can build and commercialize the final product.

Mid-infrared trace gas analysis with single-pass fourier transform infrared hollow waveguide gas sensors

A hollow core optical fiber gas sensor has been developed in combination with a Fourier transform infrared (FT-IR) spectrometer operating in the spectral range of 4000-500 cm(-1), enabling continuous detection of small volume gas-phase analytes such as CH(4), CO(2), C(2)H(5)Cl, or their mixtures at trace levels. Ag/Ag-halide hollow core optical fibers simultaneously serve as an optical waveguide for broad-band mid-infrared radiation and as a miniaturized absorption gas cell. Specifically, carbon dioxide, methane, and ethyl chloride as well as binary mixtures in a carrier gas were analyzed during exponential dilution experiments. In the studies reported here, the integration of an optical gas sensor with FT-IR spectroscopy provides excellent detection limits for small gas volumes ( approximately 1.5 mL) of individual analytes at a few tens of parts per billion (ppb, vol/vol) for carbon dioxide and a few hundreds of ppb (vol/vol) for methane. Furthermore, the broad-band nature of the radiation source and of the hollow core optical waveguide provides the capability of multi-constituent analysis in mixtures.

Trace analysis of impurities in bulk gases by gas chromatography-pulsed discharge helium ionization detection with “heart-cutting” technique

A method has been developed for the detection of low-nL/L-level impurities in bulk gases such as H(2), O(2), Ar, N(2), He, methane, ethylene and propylene, respectively. The solution presented here is based upon gas chromatography-pulsed discharge helium ionization detection (GC-PDHID) coupled with three two-position valves, one two-way solenoid valve and four packed columns. During the operation, the moisture and heavy compounds are first back-flushed via a pre-column. Then the trace impurities (except CO(2) which is diverted to a separate analytical column for separation and detection) together with the matrix enter onto a main column, followed by the heart-cut of the impurities onto a longer analytical column for complete separation. Finally the detection is performed by PDHID. This method has been applied to different bulk gases and the applicability of detecting impurities in H(2), Ar, and N(2) are herewith demonstrated. As an example, the resulting detection limit of 100 nL/L and a dynamic range of 100-1000 nL/L have been obtained using an Ar sample containing methane.

Identification of gas emanated from human skin: methane, ethylene, and ethane

We investigated whether methane, ethylene and ethane gas can be detected in gas emanating from human skin, which is called skin gas. Skin gas was collected with a homemade stainless-steel trap system, which was cooled with liquid nitrogen, and analyzed with a gas chromatograph fitted with a flame ionization detector (FID). Skin-gas samples were obtained by covering a hand for 30 min with a polyfluorovinyl bag in which pure helium gas was introduced. The bag, the trap system and GC were set up online to avoid any contamination by air. Methane, ethylene and ethane in skin gas were successfully collected at an average amount emanated for 30 min (from ten subjects) of 150 +/- 63, 20 +/- 11 and 17 +/- 8 [mean +/- SD] pg/cm2, respectively.