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Recent advances in micro detectors for micro gas chromatography

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Abstract

Micro gas chromatography (μGC) has been continuously gaining attention since the last century owing to multiple favorable characteristics, such as its small size, low power consumption and minimal production and maintenance costs. μGC has the potential to provide practical solutions to emerging analytical challenges in security, health, and environment. In this review, we summarize recent advances in micro detectors for μGC, including the study of the miniaturization of conventional detectors and the development of novel detectors for μGC chromatography.

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... The deep reactive-ion etching (DRIE) in such a case was used for miniaturization of the sensor [91]. The layered deposition of the SOI technique enabled fabrication at 400 to 600C with lowering the leakage current [92][93][94]. The most recent work [95] in Mar 2020 by Yiang et al. is the state of the art in the entire generation [96][97][98][99][100] of CMOS nanofabrication based on nano-wires and nano-electrode deposition. ...
... Process of DRIE based SOI Fabrication of Monolithic GS by CMOS technology[92][93][94] Preprints (www.preprints.org) | NOT PEER-REVIEWED ...
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... The deep reactive-ion etching (DRIE) in such a case was used for miniaturization of the sensor [91]. The layered deposition of the SOI technique enabled fabrication at 400 to 600C with lowering the leakage current [92][93][94]. ...
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... Significant improvements have been occurring, driven by the need for analytical tools that can analyze target and non-target components from complex samples, from a sensitive and/or selective point of view. Thus, several advances have been performed, namely the development of new stationary phases of GC columns, improvements of chromatographic equipment (e.g., development of pneumatics, microfluidic devices, and modulators, among others) and detection systems (selective and/or high-sensitivity detectors, with increasingly compact configuration and more user-friendly maintenance), improvements in the hardware and software (Wong et al., 2013), and also the recent advances in micro-GC systems (Qu and Duan, 2019). Consequently, the improvement on resolution and limits of detection (LOD), and reduction on the time of instrumental analysis and data processing have been contributing to the deeper characterization of samples. ...
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... Recent advances in chromatography have shown potential for the use of commercial micro-GC for VOC detection (Ho et al., 2001). However, its application in situ is still under development and thus has not been widely used for in-process monitoring (Qu and Duan, 2019). Rapid detection using commercially available sensors for detection of VOCs has been evaluated for in-process control as an alternative to bench-top based conventional laboratory methods (Szulczyński and Gę). ...
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... The detectors for μGC need to be small in size and fitted to the small flow dimension within the microfluidic channel. Recently, an interesting review on miniaturization of conventional GC detectors and the developments of novel detectors for μGC chromatography has been published [57]. The basic principle of several microdetectors based on silicon technology is briefly discussed in this section. ...
... The further miniaturisation is possible by using nanoelectromechanical (NEMS) technology. Recently, an interesting review on miniaturisation of conventional GC detectors and the developments of novel detectors for micro GC chromatography has been published [3]. ...
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Recent research trends now offer new opportunities for developing the next generations of label-free biochemical sensors using graphene and other two-dimensional materials. While the physics of graphene transistors operated in electrolyte is well grounded, important chemical challenges still remain to be addressed, namely the impact of the chemical functionalizations of graphene on the key electrical parameters and the sensing performances. In fact, graphene - at least ideal graphene - is highly chemically inert. The functionalizations and chemical alterations of the graphene surface - both covalently and non-covalently - are crucial steps that define the sensitivity of graphene. The presence, reactivity, adsorption of gas and ions, proteins, DNA, cells and tissues on graphene have been successfully monitored with graphene. This review aims to unify most of the work done so far on biochemical sensing at the surface of a (chemically functionalized) graphene field-effect transistor and the challenges that lie ahead. The authors are convinced that graphene biochemical sensors hold great promise to meet the ever-increasing demand for sensitivity, especially looking at the recent progresses suggesting that the obstacle of Debye screening can be overcome.
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In this paper, we have modeled and analyzed affinities and kinetics of volatile organic compounds (VOCs) adsorption (and desorption) on various surface chemical groups using multiple self-assembled monolayers (SAMs) functionalized film bulk acoustic resonator (FBAR) array. The high-frequency and micro-scale resonator provides improved sensitivity in the detections of VOCs at trace levels. With the study of affinities and kinetics, three concentration-independent intrinsic parameters (monolayer adsorption capacity, adsorption energy constant and desorption rate) of gas-surface interactions are obtained to contribute to a multi-parameter fingerprint library of VOC analytes. Effects of functional group's properties on gas-surface interactions are also discussed. The proposed sensor array with concentration-independent fingerprint library shows potential as a portable electronic nose (e-nose) system for VOCs discrimination and gas-sensitive materials selections.
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Alignment of NWs (NWs) is the core issue for integrating NWs into nanodevices in future. This review made a concise retrospect on reported assembling methods and mainly emphasized on the electrospinning method and its developments, as well as the following applications of the aligned nanowire array (NWA) in electronics and optoelectronics. First, we classified reported assembling methods into three categories: “grow then place”, “place then grow” and “grow and place” (electrospinning method). Then, we focused on the electrospinning method and its modified method including field assisted method, rotating collector assisted method and near-field assisted methods, as well as their merits and defects, respectively. Next, we illustrated the applications of the NWs arrays fabricated by electrospinning in field effect transistors (FET), gas sensors, piezoelectric sensors and photodetectors. Finally, we made a short conclusion and prospection on electrospinning method. As an easy and cheap nanowire fabrication and alignment method, electrospinning has a bright future in one-dimensional materials based electronics and optoelectronics.
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A vapor sensor comprising a nanoparticle-coated microfabricated optofluidic ring resonator (µOFRR) is introduced. A multilayer film of polyether functionalized thiolate monolayer protected gold nanoparticles (MPN) was solvent cast on the inner wall of the hollow cylindrical SiOx µOFRR resonator structure, and whispering gallery mode (WGM) resonances were generated with a 1550-nm tunable laser via an optical fiber taper. Reversible shifts in the WGM resonant wavelength upon vapor exposure were detected with a photodetector. The μOFRR chip was connected to a pair of upstream etched-Si chips containing PDMS-coated separation μcolumns and calibration curves were generated from the peak-area responses to five volatile organic compounds (VOCs). Calibration curves were linear, and the sensitivities reflected the influence of analyte volatility and analyte-MPN functional group affinity. Sorption-induced changes in film thickness apparently dominate over changes in the refractive index of the film as the determinant of responses for all VOCs. Peaks from the MPN-coated µOFRR were just 20-50% wider than those from a flame ionization detector for similar μcolumn separation conditions, reflecting the rapid response of the sensor for VOCs. The five VOCs were baseline separated in < 1.67 min, with detection limits as low as 38 ng.
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This paper reports a novel miniaturized detector for gas chromatography based on film bulk acoustic resonator (FBAR) sensor array. Polymer coated FBAR demonstrated detection limit of parts per million (ppm) concentrations for several volatile organic vapors. Orthogonal selectivity between n-pentane and acetone is achieved by integrating different polymer coated FBARs as sensor array. A prototype of chromatographic instrument using FBAR sensor array as detector was demonstrated by facile hyphenation of the device with commercial separation column. Such GC system is used to quantitative identification of dual gas mixture by employing principal component analysis (PCA). This MEMS chemical sensor technology offers high sensing performance, miniaturized size, and low power consumption, which are critical for development of portable gas chromatography.
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Almost four decades of investigations have opened up many avenues to explore the production and utilization of planar (i.e., microchip) gas chromatographic columns. However, there remain many practical constraints that limit their widespread commercialization and use. The main challenges arise from non-ideal column geometries, dead volume issues and inadequate interfacing technologies, which all affect both column performance and range of applications. This review reflects back over the years on the extensive developments in the field, with the goal to stimulate future creative approaches and increased efforts to accelerate microchip gas chromatography development toward reaching its full potential.
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A sensitive GC–MS method is reported for the determination of twelve polycyclic aromatic hydrocarbons (PAHs) in baby food. The sample preparation involves QuEChERS extraction combined with low-density solvent dispersive liquid–liquid microextraction (LDS-DLLME) and ultra-low temperature (−80 °C). Plackett–Burman screening design was employed to identify the main sample preparation variables that affect the extraction efficiency, such as the volume of toluene used in LDS-DLLME. The suitability of proposed method was verified by analytical selectivity, linearity in solvent and matrix-matched calibration curves and adequate recoveries (72–112%) and precision (RSD values ≤11%), under repeatability and within-laboratory reproducibility conditions. High analytical sensitivity was achieved for the monitoring of PAHs at the strict limit of 1 µg kg⁻¹ fixed by the European Commission for baby foods. The validated method was applied to thirty-two commercial baby food samples, and the investigated PAHs were not detected in any sample.
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In this work, a novel detector of gaseous analytes for monitoring of low levels of BTEX (benzene, toluene, ethylbenzene and o-xylene) is discussed. The detector is based on SnO2 thin (30nm) films functionalized with gold-palladium (9:1 molar ratio) bimetal nanoparticles. The detector consists of four independent sensing elements thermally activated by an internal heater. The performance of Au/[email protected]2 sensing elements was evaluated in comparison with some other gas sensitive materials, such as: pure SnO2, SnO2 decorated with gold (Au), and SnO2 decorated with palladium (Pd) nanoparticles. The superiority of the gas sensing performance of the Au/[email protected]2 nanocomposite structure was demonstrated based on its response to low concentrations (12.5-500 ppb) of benzene or toluene. A more complex analysis of gaseous mixtures with different concentrations (0.3-20ppb) of BTEX mixture was accomplished by incorporating the novel detector into the portable gas chromatograph (GC) PAC R1120. High sensitivity of the detector in combination with fast response and recovery time allowed us to obtain fine gas chromatograms and to perform a complete analysis of a gas sample in less than 11min. Ultra-low concentrations of BTEX components at sub-ppb level (0.3 ppb) were identified and detected by the GC analysis. Besides the experimental data, the theoretical validation of the detector's high performance was provided based on high catalytic activity of Au/Pd nanoparticles and electronic interaction of bimetal nanoclusters with SnO2 support.
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Flexible and wearable sensors have drawn extensive concern due to their wide potential applications in wearable electronics and intelligent robots. Flexible sensors with high sensitivity, good flexibility, and excellent stability are highly desirable for monitoring human biomedical signals, movements and the environment. The active materials and the device structures are the keys to achieve high performance. Carbon nanomaterials, including carbon nanotubes (CNTs), graphene, carbon black and carbon nanofibers, are one of the most commonly used active materials for the fabrication of high-performance flexible sensors due to their superior properties. Especially, CNTs and graphene can be assembled into various multi-scaled macroscopic structures, including one dimensional fibers, two dimensional films and three dimensional architectures, endowing the facile design of flexible sensors for wide practical applications. In addition, the hybrid structured carbon materials derived from natural bio-materials also showed a bright prospect for applications in flexible sensors. This review provides a comprehensive presentation of flexible and wearable sensors based on the above various carbon materials. Following a brief introduction of flexible sensors and carbon materials, the fundamentals of typical flexible sensors, such as strain sensors, pressure sensors, temperature sensors and humidity sensors, are presented. Then, the latest progress of flexible sensors based on carbon materials, including the fabrication processes, performance and applications, are summarized. Finally, the remaining major challenges of carbon-based flexible electronics are discussed and the future research directions are proposed.
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The analysis of exhaled volatile organic compounds (VOCs) related to lung cancer is a very promising way in medical diagnosis because it is non-invasive and much less expensive than traditional medical analysis used so far. In that sense, a silicon micro-analytical platform consisting of a micro-preconcentrator coupled to a silicon spiral gas chromatographic micro‐column was built, and a metal oxide-based gas sensor was used as a miniaturized gas detector. This micro-fabricated device was successfully tested to selectively detect low concentrations of VOCs considered as lung cancer biomarkers, within a few minutes even in presence of high concentrations of water vapor and carbon dioxide.
Book
The bible of gas chromatography-offering everything the professional and the novice need to know about running, maintaining, and interpreting the results from GCAnalytical chemists, technicians, and scientists in allied disciplines have come to regard Modern Practice of Gas Chomatography as the standard reference in gas chromatography. In addition to serving as an invaluable reference for the experienced practitioner, this bestselling work provides the beginner with a solid understanding of gas chromatographic theory and basic techniques.This new Fourth Edition incorporates the most recent developments in the field, including entirely new chapters on gas chromatography/mass spectrometry (GC/MS); optimization of separations and computer assistance; high speed or fast gas chromatography; mobile phase requirements: gas system requirements and sample preparation techniques; qualitative and quantitative analysis by GC; updated information on detectors; validation and QA/QC of chromatographic methods; and useful hints for good gas chromatography.As in previous editions, contributing authors have been chosen for their expertise and active participation in their respective areas. Modern Practice of Gas Chromatography, Fourth Edition presents a well-rounded and comprehensive overview of the current state of this important technology, providing a practical reference that will greatly appeal to both experienced chomatographers and novices.
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Cannabis products have recently regained much attention due to the high pharmacological potential of their cannabinoid content. In this review, the most widely used sample preparation strategies for the extraction of cannabinoids are described for the specific application to either plant materials or biological matrices. Several analytical techniques are described pointing out their respective advantages and drawbacks. In particular, chromatographic methods, such as TLC, GC and HPLC, are discussed and compared in terms of selectivity and sensitivity. Various detection methods are also presented based on the specific aim of the cannabinoids analysis. Lastly, critical considerations are mentioned with the aim to deliver useful suggestions for the selection of the optimal and most suitable method of analysis of cannabinoids in either biomedical or cannabis derived samples.
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Lung cancer (LC) is the leading cause of cancer death in men and the second leading cause in women worldwide. The use of low-dose computed tomography in early diagnosis was shown to reduce mortality by 20% with a median follow-up time of 6.5 years. In order to increase profitability and reduce radiation risks and costs, exhaled biomarkers could serve to help establish narrower inclusion criteria. The aim of this study was to identify new, well-founded volatile organic compounds in exhaled breath which distinguish LC patients from chronic obstructive pulmonary disease (COPD) patients and healthy subjects. There were 210 subjects enrolled and divided into three groups: control group (n = 89), COPD group (n = 40 stable COPD patients) and LC group (n = 81 with histological confirmation). Exhaled breath samples were collected using BioVOC® breath sampler devices. The analytical technique used was thermal desorption-gas chromatography-mass spectrometry. The compounds studied were hexanal, heptanal, octanal, nonanal, propanoic and nonanoic acids. Nonanoic acid showed statistically significant differences between the LC group and the other groups. It is 2.5 times and almost 9 times more likely to be found in the LC group than in the control group or COPD group, respectively. It is independent of histology but depends on tumour stage.
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A portable chromatography device and a method were developed to analyze a gas mixture. The device comprises a chromatographic column for separating components of a sample of the gas mixture. The device further comprises an air pump coupled to the inlet of a chromatographic column for pumping an air to the chromatographic column and an injector coupled to the inlet of chromatographic column for feeding the sample through the chromatographic column via the air as a carrier gas. A detector is arranged downstream from the chromatographic column and coupled to the outlet of the chromatographic column. The detector is a nanostructure semi-conductive microfiber. The device further comprises an evaluation unit arranged and configured to evaluate each detected component so as to determine a concentration of each detected component. Designed portable system was used for simultaneous detection of amines. The possibility of applying dispersive liquid–liquid microextraction for the determination of analytes in trace levels is demonstrated. The reproducibility of this method is acceptable, and good standard deviations were obtained. The relative standard deviation value is less than 6% for all analytes. The method was successfully applied to the extraction and determination of analytes in water samples. This article is protected by copyright. All rights reserved
Article
We developed a fully automated portable 2-dimensional (2-D) gas chromatography (GC x GC) device, which had a dimension of 60 cm × 50 cm × 10 cm and weight less than 5 kg. The device incorporated a micropreconcentrator/injector, commercial columns, micro-Deans switches, microthermal injectors, microphotoionization detectors, data acquisition cards, and power supplies, as well as computer control and user interface. It employed multiple channels (4 channels) in the second dimension ((2)D) to increase the (2)D separation time (up to 32 s) and hence (2)D peak capacity. In addition, a nondestructive flow-through vapor detector was installed at the end of the (1)D column to monitor the eluent from (1)D and assist in reconstructing (1)D elution peaks. With the information obtained jointly from the (1)D and (2)D detectors, (1)D elution peaks could be reconstructed with significantly improved (1)D resolution. In this Article, we first discuss the details of the system operating principle and the algorithm to reconstruct (1)D elution peaks, followed by the description and characterization of each component. Finally, 2-D separation of 50 analytes, including alkane (C6-C12), alkene, alcohol, aldehyde, ketone, cycloalkane, and aromatic hydrocarbon, in 14 min is demonstrated, showing the peak capacity of 430-530 and the peak capacity production of 40-80/min.
Article
This paper presents the design, fabrication, and characterization of a microhelium dielectric barrier discharge photoionization detector (μHDBD-PID) on chip with dimensions of only ∼15 mm × ∼10 mm × ∼0.7 mm and weight of only ∼0.25 g. It offers low power consumption (<400 mW), low helium consumption (5.8 mL/min), rapid response (up to ∼60 ms at a flow rate of 1.5 mL/min), quick warm-up time (∼5 min), an excellent detection limit (a few picograms), a large linear dynamic range (>4 orders of magnitude), and maintenance-free operation. Furthermore, the μHDBD-PID can be driven with a miniaturized (∼5 cm × ∼2.5 cm × ∼2.5 cm), light (22 g), and low cost (∼$2) power supply with only 1.5 VDC input. The dependence of the μHDBD-PID performance on bias voltage, auxiliary helium flow rate, carrier gas flow rate, and temperature was also systematically investigated. Finally, the μHDBD-PID was employed to detect permanent gases and a sublist of the EPA 8260 standard reagents that include 51 analytes. The μHDBD-PID developed here can have a broad range of applications in portable and microgas chromatography systems for in situ, real-time, and sensitive gas analysis.
Article
A generic method to reduce the in-line flow dependence of thermal conductivity detectors (TCDs) is presented. The principle is based on a dual-MEMS device configuration. Two thin-film sensors on membranes in parallel in the gas stream on the same chip are differentially operated. Both micro-TCDs are designed to be identical in terms of contact with the main gas flow, however a different depth of the detection chamber results in a different response to the thermal conductivity of the sample gas. Static and dynamic simulations have been performed to characterize the design of the fabricated structures. Devices have been fabricated in a MEMS process using a combined surface- and bulk micromachining process. The devices have been characterized statically and dynamically. Measurements on prototypes show that depending on the range of gases, device size and flow range device the effect of flow on the thermal conductivity can be reduced by a factor 4-15.
Article
A photoionization detector (PID) is widely used as a gas chromatography (GC) detector. By virtue of its non-destructive nature, multiple PIDs can be used in multi-dimensional GC. However, different PIDs have different responsivities towards the same chemical compound with the same concentration or mass due to different aging conditions of the PID lamps and windows. Here, we carried out a systematic study regarding the response of 5 Krypton μPIDs in a 1 × 4-channel 2-dimensional μGC system to 7 different volatile organic compounds (VOCs) with the ionization potential ranging from 8.45 eV to 10.08 eV and the concentration ranging from ∼1 ng to ∼2000 ng. We used one of the PIDs as the reference detector and calculated the calibration factor for each of the remaining 4 PIDs against the first PID, which we found is quite uniform regardless of the analyte, its concentration, or chromatographic peak width. Based on the above observation, we were able to quantitatively reconstruct the coeluted peaks in the first dimension using the signal obtained with a PID array in the second dimension. Our work will enable rapid and in situ calibration of PIDs in a GC system using a single analyte at a single concentration. It will also lead to the development of multi-channel multi-dimensional GC where multiple PIDs are employed.
Article
With the help of micro-electromechanical systems (MEMS) and complementary metal-oxide-semiconductor (CMOS) technology, a portable micro gas chromatography ([Formula: see text]) system for lung cancer associated volatile organic compounds (VOCs) detection is realized for the first time. The system is composed of an MEMS preconcentrator, an MEMS separation column, and a CMOS system-on-chip (SoC). The preconcentrator provides a concentration ratio of 2170. The separation column can separate more than seven types of lung cancer associated VOCs. The SoC is fabricated by a TSMC [Formula: see text] 2P4M process including the CMOS VOCs detector, sensor calibration circuit, low-noise chopper instrumentation amplifier (IA), 10 bit analog to digital converter, and the microcontrol unit (MCU). Experimental results show that the system is able to detect seven types of lung cancer associated VOCs (acetone, 2-butanone, benzene, heptane, toluene, m-xylene, 1,3,5-trimethylbenzene). The concentration linearity is [Formula: see text] and the detection sensitivity is up to 15 ppb with 1,3,5-trimethylbenzene.
Article
To establish adequate on-site solvent trapping of volatile chemical warfare agents (CWAs) from air samples, we measured the breakthrough volumes of CWAs on three adsorbent resins by an elution technique using direct electron ionization mass spectrometry. The trapping characteristics of Tenax(®) TA were better than those of Tenax(®) GR and Carboxen(®) 1016. The latter two adsorbents showed non-reproducible breakthrough behavior and low VX recovery. The specific breakthrough values were more than 44 (sarin) L/g Tenax(®) TA resin at 20°C. Logarithmic values of specific breakthrough volume for four nerve agents (sarin, soman, tabun, and VX) showed a nearly linear correlation with the reciprocals of their boiling points, but the data point of sulfur mustard deviated from this linear curve. Next, we developed a method to determine volatile CWAs in ambient air by thermal desorption-gas chromatography (TD-GC/MS). CWA solutions that were spiked into the Tenax TA(®) adsorbent tubes were analyzed by a two-stage TD-GC/MS using a Tenax(®) TA-packed cold trap tube. Linear calibration curves for CWAs retained in the resin tubes were obtained in the range between 0.2pL and 100pL for sarin, soman, tabun, cyclohexylsarin, and sulfur mustard; and between 2pL and 100pL for VX and Russian VX. We also examined the stability of CWAs in Tenax(®) TA tubes purged with either dry or 50% relative humidity air under storage conditions at room temperature or 4°C. More than 80% sarin, soman, tabun, cyclohexylsarin, and sulfur mustard were recovered from the tubes within 2 weeks. In contrast, the recoveries of VX and Russian VX drastically reduced with storage time at room temperature, resulting in a drop to 10-30% after 2 weeks. Moreover, we examined the trapping efficiency of Tenax TA(®) adsorbent tubes for vaporized CWA samples (100mL) prepared in a 500mL gas sampling cylinder. In the concentration range of 0.2-2.5mg/m(3), >50% of sarin, soman, tabun, cyclohexylsarin, and HD were recovered, whereas <1% of VX and Russian VX were recovered in the same concentration range. The results indicate that CWA vapors, with the exception of VX and Russian VX, can be measured by an on-site collection procedure using the Tenax(®) TA resin tubes, followed by a subsequent TD-GC/MS analysis. Copyright © 2015 Elsevier B.V. All rights reserved.
Article
This paper describes the detection of volatile organic compounds (VOCs) using an e-nose type integrated microfabricated sensor array, in which each resonator is coated with different supramolecular monolayers: p-tert-butyl calix[8]arene (Calix[8]arene), 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine (Porphyrin), beta-cyclodextrin (β-CD) and cucurbit[8]uril (CB[8]). Supramolecular monolayers fabricated by Langmuir-Blodgett techniques work as specific sensing interface for different VOCs recognition which increase the sensor selectivity. Microfabricated ultra-high working frequency transducers (4.4 GHz) enable their high sensitivity towards monolayer sensing which facilitate the analyses of VOCs adsorption isotherms and kinetics. Two affinity constants (K1, K2) are obtained for each VOC, which indicate the gas molecule adsorption happen inside and outside of the supramolecular cavities. Additional kinetic information (adsorption/desorption rate constants (ka, kd)) are obtained, thus enrich the sensing matrix (△f, K1, K2, ka, kd) which can be used as fingerprint patterns for highly specific detection and discrimination of VOCs.
Article
A highly sensitive and fast responsive semiconductor metal oxide detector based on In2O3 nanoparticle film was developed and evaluated. The mechanical structure of the detector was properly designed to obtain a small chamber volume in order to well fit to a commercial gas chromatographic capillary column. The detector was constructed by coating In2O3 nanoparticle film onto a small ceramic plate. Results indicate that the proposed semiconductor metal oxide detector in this study shows a fast response (several seconds) and a high sensitivity. Moreover, the detector can be operated at ambient condition, which largely simplifies the design of portable gas chromatograph. The fabricated detector was also used to detect gas mixtures with a detection limit down to several ppb. It is concluded that the semiconductor metal oxide detector based on nanostructured materials possesses great potential for constructing portable gas chromatograph.
Article
In recent years, the need of measurement and detection of samples in situ or with very small volume and low concentration (low sub parts per billion) is a cause for going to miniaturize systems via micro electromechanical system (MEMS) technology. Gas chromatography (GC) is a common technique that is widely used for separating and measuring the semi volatile and volatile compounds. Conventional GCs are bulky and cannot be used for in situ analysis, hence in the last decades many studies have been reported with the aim of designing and developing chip-based GC. The focus of this review is to follow and investigate the development and the achievements in the field of chip-based GC and its components from beginning up to now.
Conference Paper
We have developed a portable gas analyzer that consists of a micro-flame ionization detector (micro-FID) and a micro-gas chromatograph (micro-GC). Both components are being integrated in a lunchbox sized housing with all the peripherals to operate the micro-GC/FID without an external power and gas supply. The total size of the micro-GC/FID lunch box is currently 24x20x10 cm3 with 4 kg mass. The micro-FID currently has 40 mC/gC of sensitivity, which is twice as sensitive as the best performing micro-FID reported so far. An electrolyzer in the lunchbox produces pure hydrogen and oxygen for the micro-FID, eliminating the need for gas tanks on board. Cbana's gas analyzer succeeded in separating 17 compounds at the nanogram level, including alcohols, aldehydes, ketones, halogenated hydrocarbons and BTEX (benzene, toluene, ethylbenzene, and xylenes). The lunchbox gas analyzer performance, small size, and fast analysis time may enable NASA to significantly reduce the cost of analysis in planetary exploration missions, cabin air monitoring in spacecraft or the international space station (ISS). © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
Article
The characterization of a miniaturized helium discharge ionization detector (μHDID) for micro gas chromatography through a number of parameterized experimental measurements is presented. The response of the detector is directly related to the He discharge voltage, bias electrode-to-discharge distance, and collector-to-bias distance by a simple mathematical expression. The effect of the bias voltage and the bias and collector electrode spacings relative to the He discharge were found to improve the detector response as much as 12-fold depending on the design and various operational parameters. The detection of octane from a headspace injection was performed over 24 h of continuous operation with no noticeable degradation. Finally, a sensitivity test for octane in air was conducted using the design and parameters with the best response to obtain an absolute limit of detection of 60 pg for octane in air at 3.3 mW.
Article
We report on a small (20 × 10 mm) micromachined device for the detection of gases in micro-gas chromatography (GC). It incorporates a micro-discharge across a 20-μm gap, and a remote electrode in the micro cavity that generates an electrical signal corresponding to the photo-ionization of gaseous analytes in a stream of carrier gas. Multi-component mixtures were detected and the results compared to those obtained with a flame ionization detector. The minimum detectable limit is 350 pg.μL−1 of n-octane in air when applying a 1.4 mW discharge. The combination of wet etching of glass (as used for microfluidic channels) with a lift-off process for detector electrodes by a robust batch process results in a universal, non-destructive, and sensitive microdetector for micro-GC. Figure ᅟ
Article
Nearly all existing nanoelectronic sensors are based on charge detection, where molecular binding changes the charge density of the sensor and leads to sensing signal. However, intrinsically slow dynamics of interface-trapped charges and defect-mediated charge-transfer processes significantly limit those sensors' response to tens to hundreds of seconds, which has long been known as a bottleneck for studying the dynamics of molecule-nanomaterial interaction and for many applications requiring rapid and sensitive response. Here we report a fundamentally different sensing mechanism based on molecular dipole detection enabled by a pioneering graphene nanoelectronic heterodyne sensor. The dipole detection mechanism is confirmed by a plethora of experiments with vapour molecules of various dipole moments, particularly, with cis- and trans-isomers that have different polarities. Rapid (down to ~\n0.1 s) and sensitive (down to ~\n1 ppb) detection of a wide range of vapour analytes is achieved, representing orders of magnitude improvement over state-of-the-art nanoelectronics sensors.
Article
This paper reports a microfabricated 2×4 cm gas chromatography chip to separate and detect gases in a two-port structure by embedding a microthermal conductivity detector (μTCD) within a separation column. A circular on-chip heater is placed on the backside of the monolithic device enabling temperature programming and consequently faster analysis of the heavier components. A unique process enhanced by reactive ion etching lag (RIE lag) is used to achieve multiple etch depths in silicon and restrict the process flow to just three masks. The silicon substrate contains the separation column, the heater, and the tunnels for the TCD electric feed throughs. A Pyrex wafer containing the TCD elements is anodically bonded to the silicon substrate to seal the structure. Performance of a standalone μTCD fabricated in the same process and integrated in a hybrid fashion is also described. The single-chip design demonstrates successful separation and identification of multi-component gas mixtures with a performance comparable to that obtained through a flame ionization detector connected in series. Further, on-chip temperature programming capability was utilized to elevate the column temperature to 75 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C to exhibit analysis in less than a minute.
Article
We developed a monolithic subsystem that integrates a microgas chromatography (μGC) separation column and on-column, nondestructive Fabry-Pérot (FP) vapor sensors on a single silicon chip. The device was fabricated using deep reactive ion etching of silicon to create fluidic channels and polymers were deposited on the same silicon chip to act as a stationary phase or an FP sensor, thus avoiding dead volumes caused by the interconnects between the column and sensor traditionally used in μGC. Two integration designs were studied. In the first design, a 25-cm long μGC column was coated with a layer of polymer that served as both the stationary phase and the FP sensor, which has the greatest level of integration. This design was capable of sub-second response times and detection limits under 10 ng. In the second design, an FP sensor array spray coated with different vapor sensing polymers was integrated with a 30-cm long μGC column, which significantly improves the system flexibility and detection sensitivity. With this design, we show that the FP sensors have a detection limit on the order of tens of picograms or ~500 ppb with a sub-second response time. Furthermore, the FP sensor array are shown to respond to a mixture of analytes separated by the integrated separation channel, allowing for the construction of response patterns, which, along with retention time, can be used as a basis of analyte identification.
Article
In this work, a comprehensive, predictive and quantitative model of a whole gas analyzer is provided in order to facilitate the design of such high performance devices. All the pre-analytical (gas separation) and analytical (detection and readout) stages have been modeled and experimentally calibrated. Heterogeneous simulations have been used to quantify the impact of the whole architecture on the output characteristic of the gas analyzer. Finally, the model of the NEMS sensor and the chromatography micro-column assembly has been experimentally validated with TEOX (toluene, ethylbenzene, octane, and xylene) gases.
Article
A prototype microfabricated gas chromatograph (μGC) adapted specifically for the rapid determination of selected gas-phase marker compounds of the explosive 2,4,6-trinitrotoluene (TNT) at sub-parts-per-billion (ppb) concentrations in complex mixtures is described. Si-microfabricated focuser, separation column, and sensor array components are integrated with a high-volume sampler of conventional construction to reduce analysis time and limits of detection (LOD). The primary markers selected as target analytes were 2,4-dinitrotoluene (2,4-DNT; a persistent impurity of TNT) and 2,3-dimethyl-2,3-dinitrobutane (DMNB; a taggant), with 2,6-dinitrotoluene (2,6-DNT; a less prominent impurity) also included in numerous tests. Selective preconcentration, on-column focusing, temperature-programmed chromatographic separation, and sensor array detection/recognition facilitate determinations of the primary markers in the presence of 20 (or more) interferences in 2 min under laptop control. Estimated LODs are 2.2, 0.48, and 0.86 ng for DMNB, 2,6-DNT, and 2,4-DNT, respectively, which correspond to 0.30, 0.067, and 0.12 ppb in each 1-L air sample collected.
Article
A micro-flame ionization detector (micro-FID) design is presented that is targeted for use in a portable gas sensor. Our micro-FID is based on a diffusion flame and features a folded flame structure that is more sensitive than a counter-flow flame designs. Unlike conventional FIDs that use a premixed or open diffusion flame, an air–hydrogen diffusion flame is employed and tested in an encapsulated structure of Quartz–Macor–Quartz layers. Diffusion flames are generally known to be more controllable and stable than premixed flames, where the stability of the micro-FID plays an important role for portable gas sensors. Various channel designs for oxidant and fuel flows meeting with different angles at the burner cavity are tested to obtain a stable flame and high output sensitivity over methane test samples. To verify the empirically designed microchannel, we simulate the temperature distribution in the microchannel by using computational fluid dynamics (CFD) software. To gauge the sensitivity of the device, the collected electric charges per mole (C/mol) is calculated and taken as a reference value of ionization efficiency. The result of the folded flame design is 1.959 × 10−2 C/mol for methane that is about 34 times higher than the result using a counter-flow flame, which is 5.73 × 10−4 C/mol for methane, while one of the commercial macro FIDs’ is 10−1 C/mol. This result shows that the micro-FID using the folded flame structure has higher ionization efficiency with less leakage of the analytes than of the classical counter-flow flame design.
Article
In this paper the combination and application of a silicon based miniaturised gas chromatography (GC) column packed with Carboxen 1000 and a gas detector based on a commercial SnO2 metal oxide sensor are described. Target analytes are gas mixtures containing hydrocarbons with low molecular weight from C1 and C2 and ethylene as main target gas. The detector achieved a resolution of at least 1 ppmv related to ethylene gas. The combination of the detector with the miniaturised GC-column provides a linear behaviour between the injected ethylene gas volume and the related peak area in the chromatogram with a resolution of 2 nl. Examination of the GC-performance gave HEPT-values of about 0.7 mm and chromatographic resolutions of 100% in most cases using a gas mixture containing CO2, nitrogen, acetylene, ethylene, methane and ethane with synthetic air as carrier gas.
Article
We report the instrumentation of a μ-GC system that was capable of performing real-time analysis of sub-ppb-levels of organic mixture vapors. This system consists of a multi-stage preconcentrator/injector, a capillary column with at-column heater configuration and a photo ionization detector (PID). A tablet computer was embedded inside the instrument case to form a stand-alone system that can provide both instrument control and chromatogram data handling without an external computer. Through the compact design of fluidic system, this fully functional GC measured 30 (l) × 17(w) × 8(h) cm and the weight was less than 3 kg. This system could be powered by either a 12 V DC adapter or batteries. Mixtures of 10 organic compounds were tested to demonstrate the performance of this system. Separation of the 10 compounds took only 2 min due to the rapid temperature programming ability of at-column heater. The detection limit ranged from 0.02 to 0.36 ppb can be achieved with 1.0 L sample volume. The analytical cycle including sampling, separation and cooling required only 15 min. The stability of this μ-GC was evaluated by analyzing VOCs at ~ 3 ppb vapor concentration through continuous operation over 24 h. The retention time varied less than 1.2% (RSD, n = 120). The variation in peak areas ranged from 2.2% (benzene) to 5.2% (m-xylene).
Article
We fabricated and characterized on-chip Fabry–Pérot (FP) vapor sensors for the development of on-column micro-gas chromatography (μGC) detectors. The FP sensors were made by coating a thin layer of polymer on a silicon wafer. The air–polymer and polymer–silicon interfaces form an FP cavity, whose resonance wavelengths change in response to the vapor absorption/desorption, thus allowing for rapid detection and quantification of vapors. For proof-of-concept, two polymers (PDMS and SU-8) were used independently and placed in an array in a microfluidic channel, and showed different sensitivities for different vapors. A sub-nano-gram detection limit and sub-second response time were achieved, representing orders of magnitude improvement over those previously reported. This on-chip design will enable the unprecedented integration of optical vapor sensors with μGC systems.
Article
This paper describes the design, modeling, fabrication, and characterization of a novel micro thermal conductivity detector (μTCD). To maximize the detection response, highly isolated thermistors and a four-filament Wheatstone bridge circuit were designed. To enhance the reliability, these thermistors were supported by a multi-layer structure beam formed by a diffusion of silicon layer, a silicon oxidation layer, and a silicon nitride layer. A polydimethylsiloxane (PDMS) membrane instead of a glass was used to seal the μTCD at the room temperature with a good sealing effect. Moreover this method could avoid the resistance variation of thermistors affected by the high temperature during the bonding step. From the pressure and the hermetic tests, the μTCD could withstand 0.5MPa pressure without leakage and destroying the chip. Then the μTCD was used to detect the CH4 with a detection response of 500ppm and a short response time of 30s.