Gas Phase Detection Research Articles

Microwave Detection of Wet Triacetone Triperoxide (TATP): Non-Covalent Forces and Water Dynamics.

The water adducts of triacetone triperoxide (TATP) have been observed by using broadband rotational spectroscopy. This work opens a new way for the gas-phase detection of this improvised explosive. The observed clusters exhibit unusual water dynamics and rarely observed multicenter interactions. TATP-H2 O is formed from the D3 symmetry conformer of TATP with water lying close to the C3 axis. Water rotation around this axis with a very low barrier gives rise to the rotational spectrum of a symmetric top. The main interaction of the monohydrate is a four-center trifurcated donor Ow -H⋅⋅⋅O hydrogen bond, not observed previously in the gas phase, reinforced by a weak four-center trifurcated acceptor C-H⋅⋅⋅Ow interaction. Surprisingly, all structural signatures show the weakness of these interactions. The complex TATP-(H2 O)2 is formed from the monohydrated TATP by the self-association of water.

VECSEL-based virtually imaged phased array spectrometer for rapid gas phase detection in the mid-infrared.

We present a novel, to the best of our knowledge, system for high-resolution, time-resolved spectroscopy in the mid-wave infrared based on a modelocked vertical external cavity surface emitting laser (VECSEL) frequency comb coupled to a virtually imaged phased array (VIPA) spectrometer. The GHz level repetition rate of VECSEL-based systems coupled to VIPA spectrometers enables comb tooth resolved spectra without the use of additional filter cavities often required to increase comb tooth spacing. We demonstrate absorption spectroscopy on a methane (CH4) gas mixture at 2900cm-1 (3.4 µm) with over 35cm-1 spectral bandwidth in a single image. Rapid time-resolved measurements were made using a 300 µs exposure time with an acquisition rate limited to 125 Hz by the available camera. High-resolution absolute frequency measurements were performed by scanning the repetition rate of the VECSEL frequency comb.

A nanoscale optical biosensor based on peptide encapsulated SWCNTs for detection of acetic acid in the gaseous phase

Biosensors play a key role in almost every field of human activity – ranging from biomedical diagnosis and point-of-care health monitoring to environmental monitoring and forensics. Single-walled carbon nanotubes (SWCNTs) are one of the most promising materials for near-infrared (NIR) fluorescence-based biosensing. Herein, we develop a reusable, drop-casted, real-time optical biosensor based on peptide-encapsulated SWCNTs for the detection of low concentrations of acetic acid in the air, at room temperature. While detection of NIR signal usually requires expensive and bulky equipment, here we use the (6,5) SWCNTs chirality whose peak fluorescence lies within the range of 970 nm – 1050 nm, enabling the usage of low cost and compact silicon-based detectors. We demonstrate the detection of wine spoilage based on excess gaseous acetic acid using peptide-wrapped SWCNT sensors down to 0.05% (v/v) acetic acid concentrations. Our results open new avenues for gas phase detection using NIR fluorescent SWCNT nanosensors.

Nanophotonic supercontinuum-based mid-infrared dual-comb spectroscopy

High resolution and fast detection of molecular vibrational absorption is important for organic synthesis, pharmaceutical processes, and environmental monitoring, and is enabled by mid-infrared (mid-IR) laser frequency combs via dual-comb spectroscopy. Here, we demonstrate a novel and highly simplified approach to broadband mid-IR dual-comb spectroscopy via supercontinuum generation, achieved using unprecedented nanophotonic dispersion engineering that allows for ultra-broadband and flat-envelope mid-IR frequency combs. Our mid-IR dual-comb spectrometer has an instantaneous bandwidth covering the functional group region from 2800 – 3600 c m − 1 , comprising more than 100,000 comb lines, enabling parallel gas-phase detection with a high sensitivity, sub-Doppler spectral resolution, and a high speed. In addition to the traditional functional groups, their isotopologues are also resolved in this supercontinuum-based dual-comb spectroscopy. Our approach combines well established fiber laser combs, digital coherent data averaging, and integrated nonlinear photonics, each in itself a state-of-the-art technology, signaling the emergence of mid-IR dual-comb spectroscopy for use outside of the protected laboratory environment.

Room Temperature Gas-Phase Detection and Gibbs Energies of Water Amine Bimolecular Complex Formation.

We have detected the H2O·DMA and H2O·TMA (DMA, dimethylamine; TMA, trimethylamine) bimolecular complexes at room temperature in the gas phase using Fourier transform infrared spectroscopy. For both complexes, five vibrational bands associated with the H2O molecule are observed and assigned. Within a reduced dimensional local mode framework, we set up a six-dimensional model, including the three H2O vibrational modes and three of the six intermolecular modes, all described with internal curvilinear coordinates. The single points on the potential energy surface and Eckart corrected dipole moment surface are calculated with the CCSD(T)-F12a/cc-pVDZ-F12 method. Combining the measured and calculated transition intensities, we determine the Gibbs energy of complex formation of both complexes from each of the observed bands. The multiple determinations give similar Gibbs energies, for each complex, and increase the confidence in the combined experimental and theoretical approach, and improve the accuracy of the determined Gibbs energies. The average Gibbs energies of complex formation are found to be 5.0 ± 0.2 and 3.8 ± 0.2 kJ/mol for H2O·DMA and H2O·TMA, respectively. In addition to the experimental uncertainty, there is a potential error on the calculated intensities corresponding to 0.4 kJ/mol. However, the small spread among the four determinations suggests that this error is even less. The Gibbs energies of these complexes serve as accurate benchmarks for theoretical approaches that are prevalent in hydrogen bonding and nucleation studies.

Detection of fuel-oxidizer explosives utilizing portable capillary electrophoresis with wipe-based sampling.

Portable analytical instrumentation that can provide an alarm indication for the presence of explosives and related components is critical for the identification of explosives-based hazards and threats. Many explosives incident reports involve an inorganic oxidizer-fuel mixture which can include pyrotechnics, fireworks, flash powders, black powders, black powder substitutes, and improvised or homemade explosives. A portable CE instrument with targeted analysis of common inorganic oxidizer ions, for example, chlorate, perchlorate, and nitrate, was used here as a rapid detection platform. Unlike frequently used gas-phase separation and detection instrumentation such as ion mobility spectrometry (IMS), an automated liquid extraction mechanism is required for CE separation using acetate paper sample collection wipes. Target inorganic oxidizers were inkjet-printed onto sample wipes to investigate instrument response relative to the collected analyte spatial distribution. Overall, analyte signal intensities increased with off-center sample deposition due to improved sample extraction from wipes and no change in response was observed for varied array distributions across wipes. The system demonstrated sub 200ng detection limits for all target analytes, with further improvement when normalizing to an internal standard.

Ultrasonic Detection of the Intravascular Free Gas Phase in Research on Diving

Abstract The article presents a unique atypical application of the sonography technique and a methodological description of the introduction of this technique to research. The Bayesian approach applied to validation of the Doppler method for intravascular detection of the free gas phase instead of typical statistical inference has been demonstrated in the article. It describes the place of this method in the diving research work conducted in the Polish Naval Academy without any detailed analysis of the results achieved in the studies on decompression supported by ultrasonic detection of the free gas phase in venous vessels. It is a commonly held opinion that Doppler ultrasonic detection of the intravascular free gas phase is not a procedure that can be particularly useful in decompression research. The main objection is that detection of the free gas phase in venous vessels is a weak function to predict the presence of the free gas phase in tissues and arterial blood, so this method is not suitable for assessing the risk of decompression. Only a few countries disagree with this commonly held view and use this method to assess the risk of decompression in decompression studies. France has introduced detection of the free gas phase in venous vessels for diving research and then, together with Canada, improved this method, and developed it to a standard form. Based on the published results of the Canadian research, the technique was evaluated at the Naval Academy using statistical methods. The Academy accepted and adopted the results of this research and started to use this method in its own research on decompression over 25 years ago and continues to use it to great effect.

Mechanism of droplet-formation in a supersonic microfluidic spray device

Spray drying is an approach employed in automotive, food, and pharmaceutical industries as a robust and cost efficient liquid atomization technique offering direct control over droplet dimensions. The majority of commercially available spray nozzles are designed for large throughput spray drying applications or uniform surface coating, but microfluidic nebulizers have recently been developed as small scale alternatives. Here, we explore the physical parameters that define the droplet size and formation under supersonic flow conditions commonly found in microfluidic spray drying systems. We examined the spray nozzle operation using high speed imaging and laser scattering measurements, which allowed us to describe the spray regimes and droplet size distributions. It was determined that by using this spray nozzle device, droplets with diameters of 4–8 μm could be generated. Moreover, we show that the supersonic de Laval nozzle model can be used to predict the average droplet size. Our approach can be used as a platform for interfacing fluid microprocessing with gas phase detection and characterization.

Improvement of sensitivity of surface plasmon resonance imaging for the gas-phase detection of volatile organic compounds

The analysis of volatile organic compounds (VOCs) is an important issue in various domains. For this, electronic noses (eN) are very promising as novel analytical tools that are portable, inexpensive, and efficient for reliable and rapid analyses. Recently, we have demonstrated that surface plasmon resonance imaging (SPRI) is especially interesting for the development of eNs dedicated for gas-phase analysis of VOCs. To further improve the performance of the eN based on SPRI, in this study, we investigated the influence of the LED wavelength on the sensitivity of the system. For this, a complete theoretical study together with a related experimental investigation for the validation were carried out. We have shown that the wavelength of the light source has an impact on the surface sensitivity of SPRI for the detection of VOCs. Indeed, in the studied wavelength range from 530 nm to 740 nm, both bulk sensitivity and surface sensitivity increase as the wavelength increases with good coherence between theoretical and experimental results. With the optimal LED wavelength, the detection limits of our eN reach low ppb range for VOC such as 1-butanol.

Lamellar nanoporous gold thin films with tunable porosity for ultrasensitive SERS detection in liquid and gas phase.

Lamellar nanoporous gold thin films, constituted of a stack of very thin layers of porous gold, are synthesized by chemical etching from a stack of successively deposited nanolayers of copper and gold. The gold ligament size, the pore size and the distance between lamellas are tunable in the few tens nanometer range by controlling the initial thickness of the layers and the etching time. The SERS activity of these lamellar porous gold films is characterized by their SERS responses after adsorption of probe bipyridine and naphtalenethiol molecules. The SERS signal is investigated as a function of the bipyridine concentration from 10-14 mol L-1 to 10-3 mol L-1. The higher SERS response corresponds to an experimental detection limit down to 10-12 mol L-1. These performance is mainly attributed to the specific nanoporous gold architecture and the larger accessible surface to volume ratio. The lamellar nanoporous gold substrate is explored for sensitive SERS detection of dimethyl methylphosphonate (DMMP), a surrogate molecule of the highly toxic G-series nerve agents. The resultant nanostructure facilitates the diffusion of target molecules through the nanopores and their localization at the enhancing metallic surface leading to the unequivocal Raman signature of DMMP at a concentration of 5 parts per million.

Ultra-sensitive gas phase detection of 2,4,6-trinitrotoluene by non-covalently functionalized graphene field effect transistors.

The high energy density (4.2 MJ kg-1) and low vapour pressure (7.2 × 10-9 atm) of chemical explosives such as TNT (2,4,6-trinitrotoluene) pose a grave security risk demanding immediate attention. Detection of such hazardous and highly challenging chemicals demands specific, ultra-sensitive and rapid detection platforms that can concomitantly transduce the signal as an electrical readout. Although chemo-sensitive strategies have been investigated, the majority of them are restricted to detecting TNT from solutions and are therefore not implementable in real-time, on-field situations. Addressing this demand, we report an ultra-sensitive (parts-per-billion) and rapid (∼40 s) detection platform for TNT based on non-covalently functionalized graphene field effect transistors (GFETs). This multi-parametric GFET detector exhibits a reliable and specific modulation in its Dirac point upon exposure to TNT in the vapour phase. The chemical specificity provided by 5-(4-hydroxyphenyl)-10,15,20-tri(p-tolyl) zinc porphyrin (ZnTTPOH) is synergistically combined with the high surface sensitivity of graphene through a non-covalent functionalization approach to realise p-doped GFETs (Zn-GFETs). Such a FET platform exhibits extremely sensitive shifts in Dirac point (ΔDP) that correlate with the number of nitro groups present in the analyte. Analytes with mono-, di-, and tri-nitro substituted aromatic molecules exhibit distinctly different ΔDP, leading to unprecedented specificity towards TNT. Additionally, the Dirac point of Zn-GFETs is invariant for common and potential interferons such as acetone and 2-propanol (perfume emulsifiers) thereby validating their practical applicability. Furthermore, the ΔDP is also manifested as changes in the contact potential of GFETs, indicating that sub-monolayer coverage of ZnTTPOH is sufficient to modulate the transfer characteristics of GFETs over an area 1000 times larger than the dopant dimensions. Specifically, ZnTTPOH-functionalized GFETs exhibit p-doped behaviour with positive ΔDP with respect to pristine GFETs. Such p-doped Zn-GFETs undergo selective charge-transfer mediated interactions with TNT resulting in enhanced electron withdrawal from Zn-GFETs. Thus the ΔDP shifts to a higher positive gate voltage leading to the dichotomous combination of the highest signal generation (1.2 × 1012 V mol-1) with ppb level molecular sensitivity. Significantly, the signal generated due to TNT is 105 times higher in magnitude compared to other potential interferons. The signal reliability is established in cross-sensitivity measurements carried out with a TNT-mDNB (1 : 10 molar ratio) mixture pointing to high specificity for immediate applications under atmospherically relevant conditions pertaining to homeland security and global safety.

From Gas Sensors to Detection of Etanol Vapour to Sensor of Bacteria Detection

Introduction. Metal oxide semiconductor sensors have many advantages. But their working temperature is still high and their sensitivities are frequently low. In the current work, I present the results from investigation of sensing ability of new kind of potentiometric solid state gas sensor.Aim. The main goal of this work is investigation of the temperature dependence in the flow of air and in ethanol vapour mixture of the investigated junction structures. Also, we investigated at fixed temperature the dependence of the thermoelectric force from the ethanol vapour concentration at possible low operation temperature. For the structure, which shows the lowest operation temperature to ethanol vapour, we investigate the ability to detect Pseudomonas putida suspension.Materials and methods. In this work, the sensitivity to ethanol vapour and Pseudomonas putida suspension were investigated by measuring the thermoelectric force (the voltage) appearing of the structures by standart voltmeters.Results. Two experimental installations for sensors have been developed. The first one is for detection of ethanol vapour by ZnO/ZnO:Cu, ZnO/ZnO:CuO, ZnO/ZnO:Fe junction structures. The second installation was for Pseudomonas putida suspension detection in gas phase by ZnO/ZnO:Fe junction structure. We discovered that ZnO/ZnO:Fe structure, has the lowest operation temperature of 200 °C to ethanol vapour. For this structure, the potential difference has a negative value and decreases with increasing the amount of the pulverized bacteria.Conclusion. We discovered that ZnO/ZnO:Fe structure, has the lowest operation temperature of 200 °C. This operation temperature is a bit higher than operation temperature of at which some very novel sensing structures shows the maximum sensitivity.

Gas phase detection of chemical warfare agents CWAs with portable Raman

The development of SERS substrates for chemical detection of specific analytes requires appropriate selection of plasmonic metal and the surface where it is deposited. Here we deposited Ag nanoplates on three substrates: i) conventional SiO2/Si wafer, ii) stainless steel mesh and iii) graphite foils. The SERS enhancement of the signal was studied for Rhodamine 6 G (R6 G) as common liquid phase probe molecule. We conducted a comprehensive study with λ = 532, 633 and 785 nm on all the substrates. The best substrate was investigated, at the optimum laser 785 nm, for gas phase detection of dimethyl methyl phosphonate (DMMP), simulant of the G-series nerve agents, at a concentration of 2.5 ppmV (14 mg/m3). The spectral fingerprint was clearly observed; with variations on the relative intensities of SERS Raman bands compared to bulk DMMP in liquid phase reflects the DMMP-Ag interactions. These interactions were simulated by Density Functional Theory (DFT) calculations and the simulated spectra matched with the experimental one. Finally, we were detected the characteristics DMMP fingerprint with hand-held portable equipment. These results open the way for the application of SERS technique on real scenarios where robust, light-weight, miniaturized and simple to use and cost-effective tools are required by first responders.

Sensing Nitrogen Mustard Gas Simulant at the ppb Scale via Selective Dual-Site Activation at Au/Mn3O4 Interfaces.

The efficient detection of chemical warfare agents (CWAs), putting at stake human life and global safety, is of paramount importance in the development of reliable sensing devices for safety applications. Herein, we present the fabrication of Mn3O4-based nanocomposites containing noble metal particles for the gas-phase detection of a simulant of vesicant nitrogen mustard, i.e., di(propylene glycol) monomethyl ether (DPGME). The target materials were fabricated by chemical vapor deposition of manganese oxide on Al2O3 substrates and subsequent functionalization with silver or gold via radio frequency sputtering. The obtained high purity composites, characterized by an intimate metal/oxide contact, yielded an outstanding efficiency in the detection of DPGME. In particular, sensing of the latter analyte with an ultralow detection limit of 0.6 ppb could be performed selectively with respect to other CWA simulants. In addition, the tuneability of selectivity patterns as a function of metal nanoparticle nature paves the way to the development of efficient and selective devices for practical end uses.

Quantitative analysis of gas phase molecular constituents using frequency-modulated rotational spectroscopy.

Rotational spectroscopy has been used for decades for virtually unambiguous identification of gas phase molecular species, but it has rarely been used for the quantitative analysis of molecular concentrations. Challenges have included the nontrivial reconstruction of integrated line strengths from modulated spectra, the correlation of pressure-dependent line shape and strength with partial pressure, and the multiple standing wave interferences and modulation-induced line shape asymmetries that sensitively depend on source-chamber-detector alignment. Here, we introduce a quantitative analysis methodology that overcomes these challenges, reproducibly and accurately recovering gas molecule concentrations using a calibration procedure with a reference gas and a conversion based on calculated line strengths. The technique uses frequency-modulated rotational spectroscopy and recovers the integrated line strength from a Voigt line shape that spans the Doppler- and pressure-broadened regimes. Gas concentrations were accurately quantified to within the experimental error over more than three orders of magnitude, as confirmed by the cross calibration between CO and N2O and by the accurate recovery of the natural abundances of four N2O isotopologues. With this methodology, concentrations of hundreds of molecular species may be quantitatively measured down to the femtomolar regime using only a single calibration curve and the readily available libraries of calculated integrated line strengths, demonstrating the power of this technique for the quantitative gas-phase detection, identification, and quantification.

Improved Gas-Phase Detection of Volatile Organic Compounds Using a Solid-State Conductive Polymer Electrolyte

Rapid screening of tuberculosis by evaluation of associated volatile organic compounds (VOCs) in breath has been shown to be a promising technology that is significantly faster and more convenient than traditional sputum culture tests. Methyl nicotinate and methyl p-anisate have been isolated as specific biomarkers for the mycobacterium tuberculosis, as they are not found in high concentrations in ambient air or the breath of healthy patients, but should be readily present in all patients with active TB. These VOCs can be electrochemically detected using a solid-state sensor based on metal-functionalized 3D titanium dioxide nanotube arrays (TNAs), as shown by Bhattacharyya et. al. [1]. This chronoamperometric method uses a two-electrode system, in which the pure titanium back of the sensor functioned as both the counter and reference electrode, meaning that the applied current is highly dependent on the resistance of the nanotubes and difficult to reproduce from sensor to sensor. This work will discuss two improvements to the current method: 1) a move to a three-electrode system using a solid electrolyte, and 2) potential scanning electrochemical methods used for detection. To improve reproducibility and specificity of the sensor, the platform has been modified to use a solid-state, conductive electrolyte in order to create a gas phase three-electrode system. A conductive polymer of known resistance is used to separate the functionalized TNA from the silver-painted counter and reference electrodes. Doing this ensures more consistent interactions with the analyte of interest between sensors. In addition to the electrode changes, new scanning potential methods such as cyclic voltammetry (CV) and square wave voltammetry (SWV) have shown promise in detecting the analytes more specifically than chronoamperometry. For example, running cyclic voltammetry using cobalt functionalized sensors shows a reduction peak at about -0.5 V vs a silver quasi-reference electrode when exposed to methyl nicotinate vapor. Results comparing different electrochemical methods and specific responses to the biomarkers will be presented. [1] D. Bhattacharyya, Y. R. Smith, S. K. Mohanty, and M. Misra, “Titania Nanotube Array Sensor for Electrochemical Detection of Four Predominate Tuberculosis Volatile Biomarkers,” J. Electrochem. Soc., vol. 163, no. 6, pp. B206–B214, 2016.

Gas-Phase Detection of Fluorotelomer Alcohols and Other Oxygenated Per- and Polyfluoroalkyl Substances by Chemical Ionization Mass Spectrometry.

Per- and polyfluoroalkyl substances (PFAS) are incorporated into an ever-increasing number of modern products and inevitably enter the environment and ultimately human bodies. Herein, we show that chemical ionization mass spectrometry with iodide reagent ion chemistry is a useful technique for the detection of fluorotelomer alcohols (FTOHs) and other oxygenated PFAS, including per- and polyfluoro carboxylic acids such as hexafluoropropylene oxide dimer acid. This technique offers direct, high-time resolution measurement capability with parts per trillion by volume (nanograms per cubic meter) gas-phase detection limits. Measurements were taken by direct volatilization of samples without prior processing, allowing for fast measurements and reduced sample treatment compared to established PFAS methods. We demonstrate the utility of this technique by sampling volatile and semivolatile PFAS from fluoro additives and fluoro products to quantify levels of FTOHs and identify additional fluorinated compounds for which standards were unavailable.

Vapor Pressure of Linear Nitrate Esters Determined by Transpiration Method in Combination with VO‐GC/MS

AbstractGas phase detection of explosives is an ongoing trend in the detection sciences. The conception of gas phase detection devices requires knowledge about gas phase concentration of the target analytes. Nitrate esters are well performing explosives with a high potential for misuse in improvised explosive devices that need to be detected at vulnerable infrastructures. With respect to this the six nitrate esters, ethyl nitrate (1), ethylene glycol dinitrate (2), glycerol trinitrate (3), meso‐erythritol tetranitrate (4), d‐mannitol hexanitrate (5) and pentaerythritol tetranitrate (6) were investigated in terms of detectability by vacuum outlet‐GC/MS as potential components in improvised explosive devices. All compounds besides 5 could be detected using vacuum outlet GC/MS and their limits of detection were determined according to DIN 32645 : 2008. The vapor pressure of 2–4 was measured using the transpiration method. It was observed that the introduction of a CHONO2 unit lowers the vapor pressure of the nitrate esters by about two orders of magnitude. For compound 4 the saturation concentration (73 ng L−1) was compared with a vapor pressure based estimation of its concentration in diffusion equilibrium (0.385 pg L−1).

First detection of a key intermediate in the oxidation of fuel + NO systems: HONO

This paper reports the first online gas phase detection of absolute concentrations of HONO under engine relevant conditions, during the oxidation of an alkane in the presence of NOx. The detection was achieved at laboratory scale thanks to the coupling of a jet-stirred reactor to a continuous-wave Cavity Ring-Down Spectroscopy cell. The evidence of the formation of HONO was obtained by comparing measured cw-CRDS spectra with a literature one. The formation of HONO was simultaneously observed with the appearance of another nitrogen compound: NO2. This confirms that HONO could also be formed from NO2 under engine conditions.

Gas phase detection and rotational spectroscopy of ethynethiol, HCCSH

ABSTRACTWe report the gas-phase detection and spectroscopic characterisation of ethynethiol (), a metastable isomer of thioketene () using a combination of Fourier-transform microwave and submillimetre-wave spectroscopies. Several a-type transitions of the normal species were initially detected below 40 GHz using a supersonic expansion-electrical discharge source, and subsequent measurement of higher-frequency, b-type lines using double resonance provided accurate predictions in the submillimetre region. With these, searches using a millimetre-wave absorption spectrometer equipped with a radio frequency discharge source were conducted in the range 280–660 GHz, ultimately yielding nearly 100 transitions up to and . From the combined data set, all three rotational constants and centrifugal distortion terms up to the sextic order were determined to high accuracy, providing a reliable set of frequency predictions to the lower end of the THz band. Isotopic substitution has enabled both a determination of the molecular structure of HCCSH and, by inference, its formation pathway in our nozzle discharge source via the bimolecular radical-radical recombination reaction , which is calculated to be highly exothermic (−477 kJ/mol) using the HEAT345(Q) thermochemical scheme.