Volatile Organic Compounds Detector Research Articles

Species-Selective Detection of Volatile Organic Compounds by Ionic Liquid-Based Electrolyte Using Electrochemical Methods.

The detection of volatile organic compounds (VOCs) is an important topic for environmental safety and public health. However, the current commercial VOC detectors suffer from cross-sensitivity and low reproducibility. In this work, we present species-selective detection for VOCs using an electrochemical cell based on ionic liquid (IL) electrolytes with features of high selectivity and reliability. The voltammograms measured with the IL-based electrolyte absorbing different VOCs exhibited species-selective features that were extracted and classified by linear discriminant analysis (LDA). The detection system could identify as many as four types of VOCs, including methanol, ethanol, acetone, formaldehyde, and additional water. A mixture of methanol and formaldehyde was detected as well. The sample required for the VOCs classification system was 50 μL, or 1.164 mmol, on average. The response time for each VOC measurement is as fast as 24 s. The volume of VOCs such as formaldehyde in solution could also be quantified by LDA and electrochemical impedance spectroscopy techniques, respectively. The system showed a tunable detection range for 1.6 and 16% (w/v) CH2O solution by adjusting the composition of the electrolyte. The limit of detection was as low as 1 μL. For the 1.6% CH2O solution, the linearity calibration range was determined to be from 5.30 to 53.00 μmol with a limit of detection at 0.53 μmol. The mechanisms for VOCs determination and quantification are also thoroughly discussed. It is expected that this work could provide a new insight into the concept of electrochemical detection of VOCs with machine learning analysis and be applied to both VOCs gas monitoring and fluid detection.

Effect of heating history on the emission of volatile organic compounds from asphalt materials

Asphalt binders release hazardous fumes during high-temperature heating that severely endanger human health and pollute the environment. In this study, a volatile organic compound (VOC) generation and detection device comprising a portable VOC detector was developed, and two heating modes (intermittent and continuous heating) were established to explore the influence of heating history on the VOC emission behavior of five asphalt samples. The changes in the VOC species and content, as determined by the heating history, were analyzed via gas chromatography–mass spectrometry (GC–MS). Finally, the key factors affecting the emission of VOCs from asphalt are discussed based on the four components of asphalt materials. The results indicated that the emission of VOCs from asphalt materials under intermittent heating conditions decreased significantly with increasing heating history (significantly fewer VOCs, including 13 common components such as alkanes, benzenes, and hydrocarbon derivatives, were emitted under this condition than under continuous heating conditions at the same temperature point). Compared with continuous heating, intermittent heating is more conducive for studying asphalt VOCs. Under intermittent heating, different asphalt materials exhibited similar VOC emission curves; the VOCs were mainly emitted during the first two heating stages (200 and 180 °C, respectively). Thus, it can be deduced that asphalt VOC emissions were induced by the synchronized actions of the four components of asphalt materials. Therefore, different components can contribute to the emission of several VOCs of the same composition. The heavy and light components mainly facilitate the emission of common components with carbon atomic numbers <18 and > 18, respectively.

Unique Photoactivated Time-Resolved Response in 2D GeS for Selective Detection of Volatile Organic Compounds.

Volatile organic compounds (VOCs) sensors have a broad range of applications including healthcare, process control, and air quality analysis. There are a variety of techniques for detecting VOCs such as optical, acoustic, electrochemical, and chemiresistive sensors. However, existing commercial VOC detectors have drawbacks such as high cost, large size, or lack of selectivity. Herein, a new sensing mechanism is demonstrated based on surface interactions between VOC and UV-excited 2D germanium sulfide (GeS), which provides an effective solution to distinguish VOCs. The GeS sensor shows a unique time-resolved electrical response to different VOC species, facilitating identification and qualitative measurement of VOCs. Moreover, machine learning is utilized to distinguish VOC species from their dynamic response via visualization with high accuracy. The proposed approach demonstrates the potential of 2D GeS as a promising candidate for selective miniature VOCs sensors in critical applications such as non-invasive diagnosis of diseases and health monitoring.

Hollow microspheres formed by nanograins of Cr[formula omitted]Ti[formula omitted]O[formula omitted] synthesized by ultrasonic spray pyrolysis for acetone detection

The (Cr,Ti)2O3+z system, with corundum structure, has been studied due its technological application as gas or volatile compound detector. In this work we studied Cr1.8Ti0.2O3+z (CTO) particles grown by ultrasonic spray pyrolysis technique. The sample consists on hollow microspheres with a mean diameter of 12.8 μm, and the walls of the spheres are constituted by nanograins. Magnetic susceptibility studies and electron spin resonance spectroscopy showed a para- to antiferromagnetic transition at (306 ± 1) K. The acetone detection experiments were performed on compressed CTO forming a porous pellet. The CTO fabricated by spray pyrolysis detected very well acetone vapours with a linear response with the acetone concentration. This demonstrates that CTO particles produced by ultrasonic spray pyrolysis technique present high potentiality as volatile organic compounds detector. This synthesis route is economical and allows producing a great quantity of material in a short time, making this method adequate for large scale production.

A portable negative pressure unit reduces bone cement fumes in a simulated operating room

In this report, we demonstrate a versatile method for the removal of bone cement fumes from the vicinity of health care workers in a simulated operating room. The mixing of two component bone cement in the perimeter of an operating room releases volatile organic compounds (VOCs). The use of localized negative pressure within proximity of the mixing vessel is expected to reduce the concentration of VOCs dispersed near the airway of operating room personnel. A standard two component bone cement formulation was mixed in the perimeter of a simulated operating room. A median VOC concentration of 19 ppm was detected with a portable VOC detector. When a portable negative pressure unit was stationed near the mixing area at distances of 8 and 36 cm from the mixing vessel, the median VOC rise was reduced by approximately 97% and 83%, respectively, relative to the control. The use of a portable negative pressure unit provides a potential increase in the safety for all staff when working with materials that give off VOCs in the operating room.

VOCs gas sensor based on MOFs derived porous Au@Cr2O3-In2O3 nanorods for breath analysis

Breath analysis is a promising disease monitoring approach in medical diagnosis with the advantages of non-invasive, point-of-care testing, and much low cost than traditional medical analysis. Human exhaled contains hundreds of volatile organic compounds (VOCs), and its concentration variations can be used as the characteristic biomarkers for specific diseases. To achieve the trace detection of VOCs, the MOFs derived porous Au@Cr2O3-In2O3 nanorods composite material for isoprene, ethanol, and formaldehyde gas sensing applications was reported. The characterization results show that the special porous nanorods structure is conducive to a high specific surface area (67.3 m2/g of Au@Cr2O3-In2O3) and the modification by Cr2O3 and Au improves the oxygen components and smaller the crystallite size. The gas testing results show that the prepared Au@Cr2O3-In2O3 sensor exhibits the reliable detection ability of typical VOCs biomarkers at a ppb-level concentration, while the working temperature is as low as 180 ℃. The responses of Au@Cr2O3-In2O3 sensor as low as 50 ppb for isoprene, 200 ppb for ethanol, and 200 ppb for formaldehyde in the study concentrations. Furthermore, the sensor exhibits superior response over other typical non-VOCs breathing biomarkers (NH3, CO, H2, and NO2), which shows excellent selectivity as a VOCs detector. The sensor still has a good long-term stability and performs at high humidity. The heterojunction effect (Cr2O3) and electron sensitization (Au) synthetically improve the gas sensing performance of the sensor. Thus, we believe that the prepared porous Au@Cr2O3-In2O3 nanorod is a promising gas sensing material for the breath VOCs gas detection in related diseases diagnosis.

A breath of fresh air - the potential for COVID-19 breath diagnostics.

A breath of fresh air - the potential for COVID-19 breath diagnostics.

Gas concentrator with an activated carbon adsorbent for breath analysis

Abstract The detection of volatile organic compounds (VOCs) in respired breath is important because it can serve as a non-invasive means for obtaining information regarding an individual’s health status and for diagnosing diseases. However, it is difficult to detect respired VOCs because the concentration is very low, i.e., on the order of ppt to sub-ppm. Current commercially available small-sized VOC detectors are unable to detect sub-ppm-level VOCs; thus, large-scale analytical equipment, such as gas chromatography systems and mass spectrometers, are required for breath analysis research. To realize practical application of the breath analysis method, performance measures, such as the selectivity and sensitivity of a small-sized VOC detector, must be improved. Here, we propose a gas concentrator for breath analysis and evaluate its adsorption and desorption performance. The gas concentrator concentrates the low level of VOCs in exhaled breath to a level that is detectable by commercial VOC detectors. In this study, we also considered the practicability of our proposed device in terms of collection convenience, storability, and transportability of the exhaled sample. We experimentally demonstrated that the gas concentrator could capture gas molecules without reducing the pressure of the gas. Furthermore, we demonstrated that the process of collecting the target gas molecules from a large amount of initially injected gas and subsequently transferring it to a small volume of carrier gas increased the gas concentration by at least 25 times. Consequently, the adsorption and desorption rates of the gas concentrator were found to reach approximately 90% and 70%, respectively. It is expected that the proposed gas concentrator can be combined with a gas analyzer or detector for breath analysis-based disease diagnosis.

High Sensitive Detection of Volatile Organic Compounds Using Tin Oxide Semiconductor Sensors with Hot-Wire-Type Structures

Introduction Detection of VOCs (volatile organic compounds) has been required because it is detrimental to human health. In particular, in working environment with organic solvents, the need for VOC detectors has grown to reduce the damage to workers. For this purpose, we have developed SnO2 semiconductor sensors with hot-wire-type structures.The hot-wire-type semiconductor sensor can detect ppm concentration gas with a simple structure suitable for mass-production, resulting in practical use in various applications [1]. In this work, we have achieved high sensitivity and selectivity for VOCs by optimizing SnO2 loaded with several metal oxides. Moreover, the newly developed VOC sensor has excellent durability against the poisonous siloxane, leading to commercial products thanks to these advantageous characteristics.To improve convenience for portable use of VOC detectors, we have developed VOC sensors fabricated by micro electro mechanical systems (MEMS) technology to save power consumption [2]. The power consumption of the MEMS VOC sensor was greatly reduced in comparison with conventional hot-wire-type sensors, without sacrificing high sensitivity to VOCs. The low power consumption of the MEMS sensor makes it possible to extend the battery life, which would lead to further spread use of the VOC detectors. Experimental Figure 1 shows the structure of a hot wire semiconductor sensor, which consists of a platinum wire coil and a sintered SnO2 bead. A solution containing several metals was dropped and immersed in the sintered SnO2. Thereafter, metal oxides were supported on SnO2 by current heating to fabricate a hot-wire semiconductor VOC sensor. The coil served as both a heater and electrodes for the semiconductor bead; the total resistance of the sensor (Rs) was approximated by a parallel electric circuit consisting of the coil resistance and the semiconductor one (Fig.2). For the evaluation of the characteristics, the sensor output voltage (V s) was obtained by incorporating the sensor into a bridge circuit and applying a voltage. The operating temperature of the VOC sensor was controlled to be approximately 450 ℃. The sample gas sensitivity was calculated as difference between V s in mixture of air and sample gas (V s gas) and V s in clean air (V s air).Figure 3 shows a cross-sectional schematic of the MEMS VOC sensor. In the MEMS sensor, a Pt micro-heater/electrodes, patterned by using photolithography, was constructed on about 100 μm square insulating membrane cross-linked to the Si substrate. A sensitive layer of SnO2 with thickness of a few tens µm was deposited on the Pt micro-heater by thick film technology. After sintering the SnO2 thick film on the platinum pattern, several metal oxides were added. Results and Conclusions Figure 4 shows the typical gas sensitivity characteristics of the fabricated hot-wire-type semiconductor sensor to various VOCs. The sensor showed high sensitivity for vapors such as acetone, ethyl acetate, and toluene in a concentration range that affects human health. On the other hand, the sensor showed low sensitivity to interfering gases such as methane and hydrogen. These results demonstrate that the sensors have sufficient selectivity for practical use. Optimization of loaded metal oxides successfully controlled oxidation activity of SnO2 optimally, resulting in improved VOC sensitivity and further reduced interfering gas sensitivity. Furthermore, the sensor showed significantly better durability against toxic siloxane gas than the conventional one, resulting in long-life use in real field. The improved durability against siloxane poisoning is attributable to the controlled oxidation activity of SnO2 by loaded metal oxides. The developed sensor is useful for monitoring VOC as a practical detector that can measure in real time.Next, we investigated the MEMS VOC sensors. Quick thermal response owing to the miniaturized structure enabled us to achieve working temperatures (~500 °C) of the sensor only in 30 milliseconds. Thus, we could operate the MEMS sensor in a pulsed voltage mode, in which averaged power consumption was less than 1 mW. We confirmed that the MEMS sensors, even with the pulsed voltage operation, reproduced high sensitivity to VOCs obtained in the conventional sensor. In addition, the MEMS sensor exhibited long term stability for more than two years. The MEMS VOC sensor would contribute to the improvement of working environment with the spread use of VOC detectors.In conclusion, we have successfully developed hot-wire-type semiconductor VOC sensors ready for commercial use. We have also developed VOC sensors fabricated by MEMS technology to save power consumption.

Formaldehyde and Total VOC (TVOC) Commercial Low-Cost Monitoring Devices: From an Evaluation in Controlled Conditions to a Use Case Application in a Real Building

Formaldehyde and volatile organic compounds (VOCs) are major indoor pollutants with multiple origins. Standard methods exist to measure them that require analytical expertise and provide, at best, an average value of their concentrations. There is a need to monitor them continuously during periods of several days, weeks, or even months. Recently, portable devices have become available. Two categories of portable devices are considered in this research paper: connected objects for the general public (price &lt;500 €) and monitoring portable devices for professional users (price in the range &gt;500 to 5000 €). The ISO method (ISO 16000-29) describes the standard for VOC detector qualification. It is quite complex and is not well adapted for a first qualitative evaluation of these low-cost devices. In this paper, we present an experimental methodology used to evaluate commercial devices that monitor formaldehyde and/or total volatile organic compounds (TVOC) under controlled conditions (23 °C, 50–65% relative humidity (RH)). We conclude that none of the connected objects dedicated to the general public can provide reliable data in the conditions tested, not even for a qualitative evaluation. For formaldehyde monitoring, we obtained some promising results with a portable device dedicated to professional users. In this paper, we illustrate, with a real test case in an office building, how this device was used for a comparative analysis.

Compact devices for generation of reference trace VOC mixtures: a new concept in assuring quality at chemical and biochemical laboratories.

Volatile organic compounds (VOCs) in gas mixtures at trace level (nmol/mol) are routinely measured by chemical and biochemical laboratories as climate indicators, indoor air quality pollutants from building materials emissions, contaminants in food and beverages, and biomarkers in body fluids (blood, urine, breath) of occupational exposure or human diseases. Current analytical instruments used for measurements are gas chromatographs equipped with various injector and detector configurations. The assurance of measurement quality is done by using a huge amount of certified liquid VOC standard solutions (or gaseous VOC standard cylinders) with multiple dilutions to reach the required trace level. This causes high standard uncertainty in instrument calibrations, high cost, and high consumption of analysis and laboratory personal time. In this paper, we present the implementation of portable generators producing VOC gas standards at trace level for automatic and direct calibration of VOC detectors employed in various contexts, removing the need for preparation of matrix calibration standards in cylinders. Two compact devices in-house developed by two national metrology institutes-the Istituto Nazionale di Ricerca Metrologica (INRIM) and the Federal Institute of Metrology (METAS)-are here used to dynamically generate reference gas mixtures in an SI traceable way. The two devices are based on different technologies: diffusion and permeation, for INRIM and METAS, respectively. A metrological characterization is given and the practical implementation at chemical and biochemical laboratories is discussed. Graphical abstract Onsite calibration with transportable generation system with similar performances to primary laboratory devices.

Zeolite based microconcentrators for volatile organic compounds sensing at trace-level: fabrication and performance

A novel 6-step microfabrication process is proposed in this work to prepare microfluidic devices with integrated zeolite layers. In particular, microfabricated preconcentrators designed for volatile organic compounds (VOC) sensing applications are fully described. The main novelty of this work is the integration of the pure siliceous MFI type zeolite (silicalite-1) polycrystalline layer, i.e. 4.0 ± 0.5 μm thick, as active phase, within the microfabrication process just before the anodic bonding step. Following this new procedure, Si microdevices with an excellent distribution of the adsorbent material, integrated resistive heaters and Pyrex caps have been obtained. Firstly, the microconcentrator performance has been assessed by means of the normal hexane breakthrough curves as a function of sampling and desorption flowrates, temperature and micropreconcentrator design. In a step further, the best preconcentrator device has been tested in combination with downstream Si based microcantilevers deployed as VOC detectors. Thus, a preliminar evaluation of the improvement on detection sensitivity by silicalite-1 based microconcentrators is presented.

A Portable Micro Gas Chromatography System for Lung Cancer Associated Volatile Organic Compound Detection

With the help of micro-electromechanical systems (MEMS) and complementary metal-oxide-semiconductor (CMOS) technology, a portable micro gas chromatography ( $\upmu {\text{GC}}$ ) 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 $0.35\;\upmu {\text{m}}$ 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 ${{\text{R}}^{2}} = 0.985$ and the detection sensitivity is up to 15 ppb with 1,3,5-trimethylbenzene.

A proto-type sensor for volatile organic compounds based on magnesium porphyrin molecular films

An inexpensive portable sensor which can detect volatile organic compounds (VOCs) has been developed. The system consists of a commercial blue LED which emits light that is detected by a phototransistor. The phototransistor is coated with a few thin layers of a gas sensing porphyrin. Porphyrins have a highly conjugated molecular structure that displays strong absorption in the visible region of the spectrum. The porphyrin layer undergoes a subtle shift in its absorbance characteristics upon exposure to specific volatile organic compounds. This varies the light intensity received by the phototransistor and results in a change in the voltage across the phototransistor when the analyte is detected. This sensor design can be applied to any available porphyrin–analyte pairing to develop a wide range of VOC detectors. Presented here is an alcohol sensor based upon the interaction of various alcohols with a magnesium porphyrin.

Emission characteristics of VOCs from three fixed-roof p-xylene liquid storage tanks

This study evaluates emission characteristics of volatile organic compounds (VOCs) caused by standing loss (L S) and working loss (L W) of three vertical fixed-roof p-xylene (p-X) liquid tanks during 1-year storage and filling operation. The annual net throughput of the tanks reached 70,446t, resulting in 9,425kg of p-X vapor emission including 5,046kg of L S (53.54%) and 4,379kg of L W (46.46%). The estimated L W of AP-42 displayed better agreement with the measured values of a VOC detector than the estimated L S of AP-42. The L S was best correlated with the liquid height of the tanks, while the L W was best correlated with the net throughput of the tanks. As a result, decreasing vapor space volume of the tanks and avoiding high net throughput of the tanks in a high ambient temperature period were considered as effective means to lessen VOC emission from the fixed-roof organic liquid storage tank.

A Wireless Sensor Network for Precise Volatile Organic Compound Monitoring

A variety of methods have been developed to monitor VOC concentration in hazardous sites. The methods range from calculation to measurement, point measuring to remote sensing. Some are suited for leak detection, others for estimation of the annual emission or both. None of the following available methods comes close to the ideal method. A distributed instrument providing precise monitoring of Volatile Organic Compound (VOC) concentration in a petrochemical plant is described; it consists of a Wireless Sensor Network (WSN) platform whose nodes are equipped with meteorological/climatic sensors and VOC detectors. Internet connectivity is provided in real time at a one-minute sampling rate, thus providing environmental authorities and plant management with an unprecedented tool for immediate warning in case of critical events. The paper describes the WSN platform, detailing various units (gateways, nodes, detectors) and shows the features of scalability and reconfigurability, with minimal intrusiveness or obtrusiveness. Environmental and process data are forwarded to a remote server and made available to the authenticated users through a rich user interface that provides data rendering in various formats and worldwide access to data. A survey of the VOC detector technologies involved is also provided.

Application of an array sensor based on plasma-deposited organic film coated quartz crystal resonators to monitoring indoor volatile compounds

The basic response ability of an array sensor based on plasma-deposited organic film-coated quartz crystal resonators (QCRs) was investigated with a view to their use for indoor air monitoring. The array of plasma-deposited organic film-coated QCRs was applied to detect and separate volatile organic compounds (VOCs) including alkanes, aromatic carbons, chlorocarbons, ketones, and alcohols. Continuous monitoring tests were tried in a real room environment (a refreshment area and a smoking area) with an array of plasma-deposited organic film-coated QCRs along with commercial sensors for indoor monitoring, a relative humidity/temperature sensor, a carbon dioxide sensor, and a three-dimensional micro-ultrasonic airflow meter. To provide a comparison commercial VOC detectors based on a photo-ionization detector and a semiconductor for indoor monitoring tests were used. The plasma-deposited organic film-coated QCRs exhibited fast pulse responses to volatile compounds in the room air along the baseline shift correlated with relative humidity changes and more sensitive responses compared with commercial organic gas detectors.