Gas Preconcentrator Research Articles

The detection of acetone in exhaled breath using gas Pre-Concentrator by modified Metal-Organic framework nanoparticles

Volatile organic compounds (VOCs) from exhaled breath are promising indicators for the diagnostics of human health conditions. However, the composition of breath is rather complex, including water vapors and various tiny amounts of gases and biomarkers. Pre-concentrator plays a significant role in capturing and concentrating target gas in the gas mixture. In this work, the MIL-101 (Cr) nanoparticles are coated with polydimethylsiloxane (PDMS) through physical vapor deposition process to concentrate acetone under high humidity and room temperature. Experimentally, the newly developed material exhibits significant improvement in signal intensity that is 76.3 times greater than a commercial reference material under relative humility of 80 %. The detection range is also proven to be desirable (from 100 ppb to 2500 ppb), capturing the spectrum of acetone concentrations typically found in human exhaled breath. Moreover, following a thermal desorption process, the device demonstrates a high degree of linearity with a coefficient of 0.9956. The modified metal–organic framework materials are made into a flexible thin-film-shape device, that could be embedded in a facemask. The proposed device could meet the critical requirements for sampling, concentrating and detecting of exhaled breath biomarkers, thereby opening a new opportunity as part of the flexible electronic systems on face masks to facilitate quantitative breath analyses.

Metal-organic framework-based high-performance column chip for micro gas chromatography: hybrid function for simultaneous preconcentration and separation of volatile organic compounds.

Numerous attempts have been made to replace commercial bulky gas chromatography (GC) systems with compact GC systems for monitoring volatile organic compounds in indoor air. However, recently developed compact GC systems are still too bulky in terms of user convenience, portability, and on-site analysis. Hence, an advanced miniaturization of compact GC systems is needed. Importantly, the small and high-performance gas pretreatment chip devices should be developed for compact GC systems. This paper reports the development of a metal-organic framework (MOF)-coated hybrid micro gas chromatography column chip (hybrid GC chip) capable of preconcentration and separation on harmful volatile organic compounds at low-concentration in one single chip device. The hybrid GC chip, 2 cm × 2 cm in size, was fabricated using a microelectromechanical systems process. The synthesized MOF-5 particles were coated on the inner wall of the fabricated hybrid GC chip and acted as an adsorbent and a stationary phase. The developed hybrid GC chip afforded high preconcentration factors with 1033-1237 and high separation resolutions with 3.8-13.3. The developed column showed good performance as a gas preconcentrator and separation column, and is the first device to perform both roles in one single chip device.

Composition Characteristics of VOCs in the Atmosphere of the Beibei Urban District of Chongqing: Insights from Long-Term Monitoring

Reducing anthropogenic volatile organic compounds (VOCs) is the most effective way to mitigate O3 pollution, which has increased over the past decades in China. From 2012 to 2017, special stainless-steel cylinders were used to collect ambient air samples from the urban area of Beibei district, Chongqing. Three-step pre-concentration gas chromatography–mass spectrometry was used to detect the collected air samples. The composition, concentration, photochemical reactivity, and sources of VOCs in Beibei were analyzed. During the observation period, the annual average VOC concentration was 31.3 ppbv, which was at an intermediate range compared to other cities in China. Alkanes (36.8%) and aromatics (35.6%) were the most abundant VOC groups, followed by halo-hydrocarbons (14.4%) and alkenes (12.6%). The overall trend of seasonal distribution of VOC concentration was high in summer and autumn, and low in winter and spring, with a statistically significant difference between summer and winter concentrations. The ozone formation potential (OFP) showed that alkenes were the most active species, followed by aromatics and alkanes, and summer was the season with the highest OFP (131.6 ppbv). Three major emission sources were identified through principal component analysis (PCA), i.e., vehicle exhaust emissions (66.2%), fuel oil evaporation (24.8%), and industrial sources (9.0%). To ameliorate the air quality within the study area, concerted efforts should be directed towards curtailing traffic emissions and mitigating the release of alkenes, particularly emphasizing more stringent interventions during the summer season.

Porous silica preconcentrator for selective ambient volatile organic compounds detection: Effects of surface functionalization and humidity

With the increased demand for hand-held and ambient gas sensors, it is imperative to develop sensors that can offer both selective and sensitive detection. Gas preconcentration is a widely tried and tested method to increase the sensitivity of gas detectors. While it effectively lowers the limit of detection, it does not impact the selectivity of the detector. Therefore, preconcentrator materials have mostly been used in conjunction with selective detectors. In this work, we use the preconcentration method with a nonselective small and portable photoionization detector to introduce selectivity. For this purpose, we use a relatively slow heating rate, that allows for gradual desorption and analytes from the preconcentrator material–nanoporous silica. The characteristic desorption temperature of the volatile organic compounds (VOC) from the preconcentrator allows selective detection of the VOC. In this work, we study the effect of surface functionalization, to make it hydrophobic, and observe the adsorption–desorption behavior of polar (isopropyl alcohol) and non-polar (octane) gas molecules. The hydrophobic silica surface was found to improve the adsorption of non-polar octane, while it reduced the adsorption of polar isopropyl alcohol. The desorption temperature for isopropanol remained unchanged for both functionalized and non-functionalized preconcentrators; however, the desorption temperature for octane increased by 10 °C when the functionalized hydrophobic pSiO2 was used. We also observed the presence of humidity, a known interferent, did not heavily impact the sensing performance. These results are promising evidence that functionalized porous silica integrated with a photoionization detector can be used for selective gas detection in the ambient atmosphere.

Online Real-Time Detection of the Degradation Products of Lithium Oxygen Batteries

Since the decomposition of electrolyte is one of the most important issues in the development of lithium–air batteries (LABs), which are considered to be promising energy storage devices for the future sustainable society, we examined the molecules produced during discharge/charge of a tetraethylene glycol dimethyl ether (TEGDME)-based LAB, or a lithium oxygen battery (LOB), as we used pure oxygen as an active material, in real time by using a newly developed online cold-trap pre-concentrator–gas chromatography/mass spectroscopy system. A total of 37 peaks were detected, and 27 of them were assigned to specific molecules. Several molecules were present as impurities in TEGDME, and a few molecules were generated during discharge, but most of the molecules were generated during charge. Some of the molecules generated at the end of charge were also generated without discharge, indicating that these molecules were formed by direct electrochemical oxidation without involvement of active oxygen.

Analysis of continuous flow through trace gas Pre-concentrator modified with polycarbonate membranes

Analysis of continuous flow through trace gas Pre-concentrator modified with polycarbonate membranes

On-chip monitoring of toxic gases: capture and label-free SERS detection with plasmonic mesoporous sorbents.

The detection of the spread of toxic gas molecules in the air at low concentration in the field requires a robust miniaturized system combined with an analytical technique that is portable and able to detect and identify the molecules, as is the case with surface enhanced Raman scattering (SERS). This work aims to address capability gaps faced by first responders in real-time detection, identification and monitoring of neurotoxic gases by developing robust, reliable and reusable SERS microfluidic chips. Thus, the key performance attributes of a portable SERS detection system that must be addressed in detail are its limit of detection, response time and reusability. To this purpose, we integrate a 3D plasmonic architecture based on closely packed mesoporous silica (MCM48) nanospheres decorated with Au nanoparticle arrays, denoted as MCM48@Au, into a Si microfluidic chip designed and used for preconcentration and label-free detection of gases at a trace concentration level. The SERS performance of the plasmonic platform is thoroughly analyzed using DMMP as a model neurotoxic simulant over a 1 cm2 SERS active area and over a range of concentrations from 100 ppbV to 2.5 ppmV. The preconcentration-based SERS signal amplification by the mesoporous silica moieties is evaluated against dense silica counterparts, denoted as Stöber@Au. To assess the potential for applications in the field, the microfluidic SERS chip has been interrogated with a portable Raman spectrometer, evaluated with temporal and spatial resolution and subjected to several gas detection/regeneration cycles. The reusable SERS chip shows exceptional performance for the label-free monitoring of 2.5 ppmV gaseous DMMP.

Carbon-nanotube-based Gas Preconcentration for Breath Analysis

Carbon-nanotube-based Gas Preconcentration for Breath Analysis

A Review of Preconcentrator Materials, Flow Regimes and Detection Technologies for Gas Adsorption and Sensing (Adv. Mater. Interfaces 20/2022)

Gas Preconcentrators Gas preconcentrators are used to lower the detection limit of gas sensors. In article number 2200632, Aminur Chowdhury, Tanya Hutter, and co-workers review the progress in gas preconcentrators focusing on porous materials. Detection technologies, integration, current limitations and improvement opportunities are also presented.

A Review of Preconcentrator Materials, Flow Regimes and Detection Technologies for Gas Adsorption and Sensing

AbstractA preconcentrator is a device used to lower the detection limit of a gas sensor, often integrated upstream of the sensor. Gas preconcentrators have attracted great research interest because of their wide range applications including atmospheric pollution detection, breath analysis, and homeland security. Nanoporous materials, such as carbonaceous adsorbents, metal‐organic frameworks, metallic adsorbents, and oxides, are used to preconcentrate gases for improving detection capability. In this review, preconcentrator materials, detection technologies, and integration with detector configurations are surveyed. Current limitations and future improvement opportunities are also discussed.

Polymeric micro gas preconcentrators based on graphene oxide and carbon nanopowder adsorbents for gas detection application

In this study, an application of novel polymer-based microfluidic channels for preconcentration and detection of methane gas is investigated. Poly (methyl methacrylate) (PMMA) microfluidic channel is filled by graphene oxide (GO) as a new adsorbent for thermal preconcentration and carbon nanopowder is loaded into a polydimethylsiloxane (PDMS) microfluidic channel. The effective microfluidic channels area is 14 mm × 10 mm. The laser cutting and etching followed by thermally-solvent bonding process are used for PMMA microfluidic channel fabrication. Also, PDMS microfluidic channel is fabricated by SU-8 molding technique, lithography process, and oxygen plasma bonding on glass. SEM, Raman spectroscopy, and FTIR characterizations are carried out for investigation of the synthesized GO. The amount of electrical power consumption of devices is also investigated by simulation and experiment. The performance of both micro preconcentrators (μPCs) are compared through the similar experimental tests which exhibit the suitable performance of fabricated μPCs with proper repeatability for preconcentration purposes. The effect of gas flow rate, heating rate, gas exposure time, and gas concentration are investigated for both microfluidic channels and their optimized values were obtained. According to the lower desorption temperature of GO, despite its slightly lower response (10.41) compared to carbon nanopowder μPCs (12.34), due to its almost half power consumption (0.375 W in comparison with 0.8 W), it can be an appropriate candidate for preconcentration applications. PMMA and PDMS-based microfluidic channels show promising choices in the preconcentration application for the adsorbents with low desorption temperatures. As a result, PMMA as a low-cost material with a simple fabrication process in microchannels and GO as the novel adsorbent material can be suitable candidates in low working temperature and rapid preconcentration devices. • Microfluidic channels are fabricated based on poly (methyl methacrylate) (PMMA), and polydimethylsiloxane (PDMS) • Graphene oxide (GO) and carbon nanopowder are used as the adsorbent materials for PMMA and PDMS microfluidic channels, respectively. • The effect of gas flow rate, heating rate, gas exposure time, and gas concentration are investigated to achieve the optimized values. • The power consumption and temperature distribution of heater are studied through the simulation.

Pollution Characteristics and Health Risk Assessment of VOCs in Jinghong

In order to investigate the seasonal variation in chemical characteristics of VOCs in the urban and suburban areas of southwest China, we used SUMMA canister sampling in Jinghong city from October 2016 to June 2017. Forty-eight VOC species concentrations were analyzed using atmospheric preconcentration gas chromatography–mass spectrometry (GC–MS), Then, regional VOC pollution characteristics, ozone formation potentials (OFP), source identity, and health risk assessments were studied. The results showed that the average concentration of total mass was 144.34 μg·m−3 in the urban area and 47.81 μg·m−3 in the suburban area. Alkanes accounted for the highest proportion of VOC groups at 38.11%, followed by olefins (36.60%) and aromatic hydrocarbons (25.28%). Propane and isoprene were the species with the highest mass concentrations in urban and suburban sampling sites. The calculation of OFP showed that the contributions of olefins and aromatic hydrocarbons were higher than those of alkanes. Through the ratio of specific species, the VOCs were mainly affected by motor vehicle exhaust emissions, fuel volatilization, vegetation emissions, and biomass combustion. Combined with the analysis of the backward trajectory model, biomass burning activities in Myanmar influenced the concentration of VOCs in Jinghong. Health risk assessments have shown that the noncarcinogenic risk and hazard index of atmospheric VOCs in Jinghong were low (less than 1). However, the value of the benzene cancer risk to the human body was higher than the safety threshold of 1 × 10−6, showing that benzene has carcinogenic risk. This study provides effective support for local governments formulating air pollution control policies.

Application of Metal-Organic Frameworks in Gas Pre-concentration, Pre-separation and Detection

Application of Metal-Organic Frameworks in Gas Pre-concentration, Pre-separation and Detection

(Invited) Miniaturized Gas Analysis Platform for Non-Invasive Disease Detection

Recently, non-invasive diagnosis of human diseases using gas samples from human has become increasingly important due to its simple way to make a person less reluctant. The exhaled breath or urine vapors from patients can contain VOCs, which have been reported to be clinically meaningful biomarkers. However, it is difficult to make a diagnosis accurately due to very low gas concentration level of disease related VOCs, which is 1~100 ppb level. To overcome the detection limit of various commercialized gas sensors or detectors, the preconcentration of gas samples from human is required. On the other hand, gas chromatography (GC), which is extensively applied for gas mixture analysis, is necessary to separate and identify the gas components.A miniaturized gas analysis platform for the analysis of the low concentration and multiple disease related VOCs has been developed using a micro gas preconcentrator chip, a micro gas chromatography chip, a thermal conductivity detector chip, etc. Its design and fabrication process will be introduced and its basic performance will be presented for various clinically important VOCs.

Recent developments and trends in miniaturized gas preconcentrators for portable gas chromatography systems: A review

In the last years, a growing number of fields such as air quality monitoring, breath analysis or explosives and chemical warfare agents detection requiring fast, on-site, sensitive analysis has led to the development of portable gas chromatography systems. In most cases, these systems integrate a miniaturized gas preconcentrator, which provides a significant enhancement of the sensitivity enabling quantification of analytes present in the sample at trace levels. In this review, the authors have focused on recent developments in these preconcentrators integrated in portable gas chromatography systems. The main materials and fabrication techniques, designs, heating technologies, fluidic connections, adsorbents, and applications are discussed. In addition, an analysis of some factors affecting preconcentration performance is presented. A new figure of merit called Normalized Preconcentration Efficacy (NPE) is proposed to evaluate the performance of these devices in a standardized manner, making possible a more straightforward comparison between different devices.

Easy-to-manufacture micro gas preconcentrator integrated in a portable GC for enhanced trace detection of BTEX

Air pollution is a current environmental and global public health issue, which requires technological developments to monitor airborne pollutants such as Volatile Organic Compounds (VOCs). These organic species are dangerous for humans even at trace levels.In this regard, an analytical device can be advantageously coupled with a preconcentration system to improve its sensitivity. In this context, a novel preconcentrator was conceived, manufactured, and tested inside an existing portable gas chromatograph (GC). With a very limited gas sample of 20 mL, the limits of detection achieved are 0.057, 0.150, 0.368, 0.396, 0.418 ppb for benzene, toluene, ethylbenzene, m-/p-xylenes and o-xylene, respectively. These values enable the system to monitor air quality even in the environments with the strictest regulation (0.6 ppb for benzene). Besides, the comparison with the literature demonstrates that the present analytical device is from two to three orders of magnitude more sensitive than the previous ones when detection limit is expressed in pg.The repeatability and reproducibility experiments show that the measurements are reliable and stable over time, while maintaining a reasonable time resolution of 19 min which can be easily reduced to 15 min by a full automation. Moreover, the average power consumption of the system was limited to 61 W allowing the system to work autonomous and battery powered. Finally, this preconcentrator can be conveniently fabricated without the need for a cleanroom and the simplicity of the design provides an easy way to replace the adsorbent broadening the range of VOC that can be detected.

Comparative Study of Various Methods for Trace SF6 Measurement Using GC-µECD: Demonstration of Lab-Pressure-Based Drift Correction by Preconcentrator

AbstractThis study presents a high-precision method, using a preconcentrator–gas chromatograph with microelectron capture detector (GC-μECD), to measure SF6 at ambient levels. Carboxen 1000 was used as an adsorbent for the preconcentrator and exhibited a high adsorption efficiency for N2O and SF6 and low adsorption efficiency for O2. This enabled the selective removal of atmospheric O2 from analytes and improved repeatability of the SF6 peak that followed the O2 peak, in a separation column of activated alumina F1. In addition, the increased sensitivity resulting from preconcentrated SF6 improved the signal-to-noise ratio. This led to better analytical precision in comparison with other measurement methods including the conventional and forecut–backflush (FCBF) methods. The precision-to-drift ratios of the conventional, FCBF, and preconcentration methods were 0.11, 0.10, and 0.03, respectively. Analytical precision of the preconcentration method was 0.08% for 10 consecutive injections; this was the best among the three methods. The long-term drift of the SF6 response was inversely proportional to the laboratory pressure. Based on this finding, room pressure can be used to correct for ECD signal drift, with an uncertainty of 0.14% over a 48-h period, using the preconcentration method. Another advantage of the preconcentration method was the excellent linearity of the SF6 response to a wide range of concentrations, including its ambient concentration.

Recognizing lung cancer using a homemade e-nose: A comprehensive study

In recent years, breath analysis has been used as a tool for lung cancer detection and many gas sensors were developed for this purpose. Although they are fabricated with advanced materials, for now, gas sensors are still limited in their medical application due to their unfavorable performance. Here, we hypothesized that a combination of diverse types of sensors could aid in improving the detection performance. We fabricated an e-nose based on 10 gas sensors of 4 types and directly tested it using samples from 153 healthy participants and 115 lung cancer patients, without gas pre-concentration. Additionally, we studied and compared five feature extraction algorithms. The extracted features were then used in 2 optimized clustering algorithms and 3 supervised classification strategies, and their performance was investigated. As a result, “breath-prints” for all subjects were successfully obtained. The combined features extracted by LDA and Fast ICA formed the best feature space. Within this feature space, both clustering algorithms grouped all “breath-prints” into exactly 2 clusters with an Adjusted Rand Index greater than 0.95. Among the 3 supervised classification strategies, random forest with 3-fold cross validation showed the best performance with 86.42% of mean classification accuracy and 0.87 of AUC, which was somewhat better than many recently reported sensor arrays. It can be concluded that, the diversity of sensors may play a role in improving the performance of the e-nose though to what extent still requires evaluation.

Micro gas preconcentrator using metal organic framework embedded metal foam for detection of low-concentration volatile organic compounds

Analysis of volatile organic compounds (VOCs) is essential for on-site environmental monitoring and toxic chemicals detection. However, quantitatively detecting VOC gases is difficult because of their low gas concentration (<100 ppb), and preconcentration is necessary to overcome the detection limitations of various gas sensors. Many studies on micro preconcentrators (μ-PC) have been reported, however, these devices suffer from high desorption temperatures and significant pressure drops, which degrade sensing ability and increase operating costs, respectively. Due to these disadvantages, such devices are not yet commercially available. In this study, a μ-PC was developed using metal organic framework embedded metal foam (MOFM) as an adsorbent. The preconcentration performance of the μ-PC was evaluated based on several key parameters, such as desorption temperature, adsorption time, and initial sample concentration. In addition, the MOFM and commercial adsorbents were each packed in the same μ-PC chip, respectively, to compare their preconcentration and pressure drop performances. The MOFM-adsorbent-packed μ-PC demonstrated the preconcentration factors were 2.6 and 4 times higher, and the pressure drops were 4 and 3 times lower than those of the commercial adsorbents under the same conditions owing to the high specific surface area and the efficient flow distribution of the MOFM adsorbent.

Micro-fabricated packed metal gas preconcentrator for enhanced monitoring of ultralow concentration of isoprene

A novel non-silicon-based micro-preconcentration device, as a pretreatment component in a portable gas chromatography system, was developed for the preconcentration one of the trace volatile organic compounds (VOCs) in the exhaled gases, which is one typical biomarker for the chronic liver disease (CLD). The device was designed as an array of manifold-shaped rectangular metal micro-channels with flat dimensions of 16 mm × 12.6 mm and the internal empty volume is 14.4 μL on the copper substrate. Instead of the non-silicon fabrication process, the traditional laser etching technology (LET) was optimized to etch micro-channels, and vacuum diffusion welding (VDW) was applied to form internal channels. The fabricated chip was filled with Carbopack X adsorbent. In the testing, the metal gas preconcentrator (MGP) was installed in a commercial GC (gas chromatography) and nitrogen was used as carrier gas and desorbed gas. With the MPG, up to 352 of concentration factor can be achieved for 10 ppb isoprene. The developed MGP, which has advantages of high strength, low cost, good thermal conductivities, can potentially be used for non-invasive screening of advanced liver fibrosis by monitoring isoprene concentrations in exhaled breath.