Air-cooled cold trap channel integrated in a microfluidic device for monitoring airborne BTEX with an improved detection limit

We integrated an air-cooled cold trap (CT) channel in a microfluidic device for monitoring airborne benzene, toluene, ethylbenzene, and xylene (BTEX) gases and demonstrated its effect on improving the detection limit of the microfluidic device. The device consists of concentration and detection cells formed of 3 x 1 cm Pyrex plates. We first introduced a sample gas into the concentration cell, and the gas was adsorbed onto an adsorbent in the channel. We then raised the temperature using a thin-film heater and introduced the desorbed gas into the detection cell. To prevent dilution of the gas before detection, we propose an improvement to the concentration cell structure that involves the integration of the CT channel. We examined the CT effect by comparing three types of concentration cell with different channel structures. We found that we could detect a gas concentration about 2 orders of magnitude lower than in our previous work by optimizing the channel structure and integrating a CT channel. As an example of BTEX detection,we obtained a 0.05 ppm detection limit for toluene gas with a sampling time of 30 min.     

Separate detection of BTX mixture gas by a microfluidic device using a function of nanosized pores of mesoporous silica adsorbent

We achieved separate detection of the components of 10 ppm of a benzene, toluene, and o-xylene mixture gas by using mesoporous silica powder incorporated in our microfluidic device. The device consists of concentration and detection cells formed of 3 cm x 1 cm Pyrex plates. We first introduced the mixture gas into the concentration cell where it was adsorbed on an adsorbent in a channel formed in the cell. We then raised the temperature using a thin-film heater and introduced the desorbed gas into the detection cell. Here, we measured the changes in the absorption spectra of the mixture gas in the detection cell. We found that the mixture ratio of the compounds in the desorbed gas varies with time because the thermal desorption property of each compound is different from that of the adsorbent. We analyzed the thermal desorption mechanism by comparing two types of silica adsorbents with different pore structures. We found that an adsorbent that has pores with a periodic and uniform nanosized column shape provides better component separation. We concluded that the uniform pore structure might cause the adsorbate molecules to exhibit a homogeneous adsorption state thus revealing the desorption properties of the gas more clearly.     

Evaluation of persulfate oxidative wet scrubber for removing BTEX gases

Soil vapor extraction (SVE) coupled with air sparging of groundwater is a method commonly used to remediate soil and groundwater contaminated with volatile organic petroleum contaminants such as gasoline. These hazardous contaminants are mainly attributable to the compounds-benzene, toluene, ethylbenzene, and xylenes (known collectively as BTEX). Exhaust gas from SVE may contain BTEX, and therefore must be treated before being discharged. This study evaluated the use of iron-activated persulfate chemical oxidation in conjunction with a wet scrubbing system, i.e., a persulfate oxidative scrubber (POS) system, to destroy BTEX gases. The persulfate anions can be activated by citric acid (CA) chelated Fe(2+) to generate sulfate radicals (SO(4)(*-), E degrees =2.4V), which may rapidly degrade BTEX in the aqueous phase and result in continuous destruction of the BTEX gases. The results show that persulfate activation occurred as a result of continuous addition of the citric acid chelated Fe(2+) activator, which readily oxidized the dissolved BTEX. Based on initial results from the aqueous phase, a suitable Fe(2+)/CA molar ratio of 5/3 was determined and used to initiate activation in the subsequent POS system tests. In the POS system, using persulfate as a scrubber solution and with activation by injecting Fe(2+)/CA activators under two testing conditions, varying iron concentrations and pumping rates, resulted in an approximate 50% removal of BTEX gases. During the course of the tests which in corporate activation, a complete destruction of BTEX was achieved in the aqueous phase. It is noted that no removal of BTEX occurred in the control tests which did not include activation. The results of this study would serve as a reference for future studies into the practical chemical oxidation of waste gas streams.     

Quantitative Analysis of Trace Moisture in N(2) and NH(3) Gases with Dual-Cell Near-Infrared Diode Laser Absorption Spectroscopy

This paper demonstrates our optical measurement system based on near-infrared tunable diode laser absorption spectrometry and reports the results of trace moisture determination in nitrogen and ammonia gases. A near-infrared InGaAsP distributed feedback diode laser operating at room temperature was employed as the optical source. We used a dual-cell detection strategy to cancel common mode noise from the diode laser and remove the effect of the residual moisture absorption in the beam path outside the sample cell. We also used this method to successfully eliminate the interfering absorption of matrix gas molecules such as NH(3). The detection limit of H(2)O absorption of 4 ppb in nitrogen and 12 ppb in ammonia was obtained using a single-pass absorption cell of only 92 cm in length and the average results of 10 scan measurements. This system has characteristics of both the high sensitivity and capability of in situ and real-time measurement.     

Nafion film/K(+)-exchanged glass optical waveguide sensor for BTX detection

An optical waveguide (OWG) sensor for the detection of BTX gases is reported. The highly sensitive element of this sensor was made by coating the copper Nafion film over a single-mode potassium ion exchanged glass OWG. We used the OWG sensor to detect toluene gas as a typical example BTX gas. The sensor exhibits a linear response to toluene in the range of 0.25-4250 ppm with response and recovery times less than 25 s. The sensor has a short response time, high sensitivity, and good reversibility.     

Nitrogen dioxide monitoring using a blue LED

We report on a monitoring technique for nitrogen dioxide based on broadband absorption spectroscopy using a blue light-emitting diode (LED) operating around 465 nm. The technique is suited for real-time measurements of nitrogen dioxide due to the use of a straightforward data evaluation method, limited interference from other gases, and a low degree of complexity compared with other real-time optical detection techniques having the same precision. Additionally, the use of a LED can reduce the cost of nitrogen dioxide monitoring. Real-time measurements of nitrogen dioxide concentration were demonstrated at atmospheric pressure, which is of great interest for industrial nitrogen dioxide emission monitoring; a detection limit of about 3 ppm using a 50-cm-long gas cell with 2 s integration time was achieved.     

Selective detection of volatile aromatic compounds using a compact laser ionization detector with fast gas chromatography

We report results for a new gas chromatography detector that is comparatively sensitive and far more selective for aromatic compounds than the traditional photoionization detector. The detection means is multiphoton ionization at atmospheric pressure. The ionization source in these experiments is a diode-pumped passively Q-switched microchip laser operating at 266 nm. Experiments were conducted with the detector interfaced to a fast gas chromatograph. For <20 s elution time, limits of detection were <1 pg for toluene, ethylbenzene, xylenes, and isopropylbenzene; the limit of detection for benzene is approximately 10 pg. Detector response was linear over 5 orders of magnitude, including these low levels. Negligible signals were observed for nonaromatic ketones, aldehydes, ethers, and cycloalkanes at levels as high as 0.1 microg (10 mg/L concentration). Detector efficiency after fast GC separation was 0.002% when using a detector cell with a radius of 1.1 cm and a purge gas flow of 500 mL/min. The advantages of this detector are further illustrated by the fast GC analysis of fuel samples.     

气体光学检测技术及其应用研究进展

气体的快速识别与检测已成为国内外研究者迫切解决的重大问题。随着光学技术的快速发展,气体光学检测技术以其高效率、多组分、高灵敏度等显著优势而成为气体检测领域的重要研究热点之一。本文介绍了气体光学检测技术的理论基础,并按主动式与被动式两大类综述了各种典型气体光学检测技术的工作原理及应用进展。运用这些气体检测技术,已经对几十种气体实现远距离、高灵敏度的连续实时监测,完成了多种场景下对气体成分、浓度、温度等参数的测量,有效减少了危险事故的发生。通过总结和分析现有气体光学检测技术仍存在的技术问题,对未来的发展趋势进行了展望。     

苯系物(BTEX)检测气敏材料研究进展

金属氧化物半导体传感器因具有体积小、成本低廉、使用方便等优点,越来越受到研究者的关注并被用于有毒有害气体的监测。传感材料是气敏传感器的核心,本文综述了近年来氧化物半导体BTEX气敏传感材料的研究进展,对传感材料的微结构、负载/掺杂改性、气敏性能、气敏机理及存在的问题进行了分析,并探讨了其下一步发展趋势。     

Experimental upgrades of membrane introduction mass spectrometry for water and air analysis

Some improvements to the membrane introduction mass spectrometry (MIMS) technique, resulting in low-ppt detection limits for volatile organohalogen compounds (CX) in water (namely, chloroform, bromoform, bromodichloromethane, chlorodibromomethane, tetrachloroethylene, trichloroethylene, 1,1,1-trichloroethane, and carbon tetrachloride) and low-microgram per cubic meter detection limits for benzene, toluene, ethylbenzene, and xylenes (BTEX) in gaseous samples, are shown. A static MIMS configuration was compared to a dynamic one, the former requiring longer time to obtain the analytical response. A cryotrapping preconcentration step is introduced and linearity of response, mixture effects, and detection limits are presented. The instrumental setup consists of a hollow fiber silicone membrane, a water or air container, a cryofocusing trap based on Tenax adsorbent, a Peltier cell, and a Varian ion trap benchtop mass spectrometer is described. This instrumental setup, which we named membrane extraction trap focusing mass spectrometry, allowed the detection of CX in water at a concentration as low as 8 ppt and of benzene in air at 0.1 microg/m3. The whole assembly shows great potential for on-site routine monitoring of drinking water resources and urban and indoor air under current EU and Italian regulations.     

Quantitative analysis of metabolic gases by multichannel Raman spectroscopy: use of a newly designed elliptic-spherical integration type of cell holder

We describe the quantitative analysis of some metabolic gases bymultichannel Raman spectroscopy. Raman spectra were measured forair, acetone, ammonia, carbon dioxide, and mixed gas consisting ofacetone, ammonia, and air. We designed a new elliptic-sphericalintegration type of cell holder to obtain the Raman spectra of gaseswith a high signal-to-noise ratio. Concentrations of acetone, ammonia, and carbon dioxide were determined by the peak intensities ofRaman bands at 2940, 3228, and 1385 cm(-1), respectively. To compensate for the fluctuations of Ramanintensities caused by several factors, such as the fluctuations oflaser power, the peak intensity of a band at 2324 cm(-1) dueto nitrogen gas was used as an internal intensity standard. Thecorrelation coefficient between the corrected Raman intensity at 2940cm(-1) and the concentration of acetone was calculated to be0.984 for a concentration range of 2-12 ppm. The detection limitof acetone gas was found to be 2 ppm.     

Absorption of a volatile organic compound by a jet loop reactor with circulation of a surfactant solution: performance evaluation

Biofiltration shows high efficiency for the removal of industrial waste gases and reliable operational stability at low investment and operating cost, especially when the VOC concentration is low, such as 100 ppmv (micro LL(-1)) or less. However, it has been reported that the abrupt change in VOC concentrations leads to the failure of the biofilter. Hence, the pretreatment of waste gases is necessary to ensure the stable operation of the biofilter. The objective of this study is to develop a jet loop reactor (JLR) with circulation of a surfactant solution to lower the concentration of VOCs, especially hydrophobic VOCs. Toluene and Tween 81 were used as a model industrial waste gas and a surfactant, respectively. Among several non-ionic surfactants tested, Tween 81 showed the most rapid dissolution of toluene. When a JLR is replaced with fresh Tween 81 solution (0.3% w/v) every hour, it successfully absorbed for 48 h over 90% of the toluene in an inlet gas containing toluene at 1000 ppmv (microL L(-1)) or less. Therefore, JLR with circulation of a surfactant solution is believed to ensure the stable operation of the biofilter even with the unexpected increase in the VOC concentrations.     

空芯光子晶体带隙光纤用于甲烷检测的研究

基于甲烷的光谱吸收理论,设计了一套利用空芯光子晶体带隙光纤(HC-PBGF)做传感气室的全光纤甲烷检测系统。根据HITRAN2012数据库和HAWKS软件确定甲烷的检测波长;利用气泵在HC-PBGF两端形成压力差来加快甲烷气体的扩散,利用反射镜延长光程至2倍;通过实验得到190s后气体扩散完成,0.5h内系统示值波动为0.012%,平均重复率为99.63%。最后配制0~2.5%浓度的甲烷气体进行浓度检测,得出甲烷浓度与相对吸收强度呈线性关系,线性度为99.92%。该系统成功实现了将HC-PBGF的空芯结构用于甲烷的吸收检测,加快了系统的响应速度,实现了仪器的小型化,使在线检测更加方便。     

Sensitive trace gas detection with near-infrared laser diodes and an integrating sphere

We describe a simple spectrometer for sensitive trace gas detection in the atmosphere. A communication laser diode is used as a light source, and a commercial integrating sphere is used as a multipass absorption cell. We developed a theoretical formulation of the relative absorption of the optical power by trace gases in the sphere and applied it to two kinds of experimental result: one that is concerned with a structureless broad absorption band of butane with the use of a 1.2-μm multimode laser diode, and one that is related to the study of an isolated and sharp rovibrational line of water vapor in air at atmospheric pressure with the use of an 830-nm single-mode laser diode. With equivalent path lengths of several meters obtained with a 10-cm-i.d. integrating sphere we can demonstrate the usefulness of such a device as a broadband multipass cell for the measurement of small absorptions.     

An analysis of synergistic and antagonistic behavior during BTEX removal in batch system using response surface methodology

The removal of benzene, toluene, ethylbenzene and xylene (BTEX) as quaternary mixtures were studied in batch systems using a well-defined mixed microbial culture. The synergistic and antagonistic effects of total BTEX removal (BTEXT-RE) due to the presence of mixed substrate was evaluated through experiments designed by response surface methodology (RSM). The low and high concentrations of individual BTEX were 15 and 75 mg l(-1), respectively. The results showed that, increasing the concentration of xylene increased the cumulative BTEX removal (BTEXT-RE), however the reverse occurred when benzene concentrations were increased from low to high levels. A mixed response of increasing and decreasing trend in the BTEXT-RE value was observed when either of toluene or ethylbenzene concentration was increased. When the concentrations of individual BTEX compounds were 30 mg l(-1), the BTEXT-RE was about 58%. Complete BTEXT-RE was achieved at optimal BTEX concentrations of 48.1, 45.6, 49.3 and 56.6 mg l(-1). The RSM approach was found efficient in explaining the main, squared and interaction effects among individual BTEX concentrations on the BTEXT-RE in a more statistically meaningful way.     

Simultaneous detection of molecular oxygen and water vapor in the tissue optical window using tunable diode laser spectroscopy

We report on a dual-diode laser spectroscopic system for simultaneous detection of two gases. The technique is demonstrated by performing gas measurements on absorbing samples such as an air distance, and on absorbing and scattering porous samples such as human tissue. In the latter it is possible to derive the concentration of one gas by normalizing to a second gas of known concentration. This is possible if the scattering and absorption of the bulk material is equal or similar for the two wavelengths used, resulting in a common effective pathlength. Two pigtailed diode lasers are operated in a wavelength modulation scheme to detect molecular oxygen ~760 nm and water vapor ~935 nm within the tissue optical window (600 nm to 1.3 mum). Different modulation frequencies are used to distinguish between the two wavelengths. No crosstalk can be observed between the gas contents measured in the two gas channels. The system is made compact by using a computer board and performing software-based lock-in detection. The noise floor obtained corresponds to an absorption fraction of approximately 6x10(-5) for both oxygen and water vapor, yielding a minimum detection limit of ~2 mm for both gases in ambient air. The power of the technique is illustrated by the preliminary results of a clinical trial, nonintrusively investigating gas in human sinuses.     

Liquid concentration sensor based on slot waveguide microresonators

A schematic diagram and operating principle are considered for an integrated optical concentration sensor based on slot waveguide microresonators, due to whose use the sensitivity of the sensor to a change in concentration may reach 0.001–0.01%. By means of this device, it is possible the concentration of both still gases and liquids and those flowing with a considerable velocity. The sensor may have a considerable number of sensing elements that makes it possible to monitor concentration simultaneously at different points of the volume of substance.     

Substrate interactions during anaerobic biodegradation of BTEX by the mixed cultures under nitrate reducing conditions

The enriched BTEX-degrading bacteria were used to investigate the substrate interactions during anaerobic biodegradation of all the possible BTEX binary combinations. Beneficial and detrimental substrate interactions were observed in comprehensive mixtures of benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene. The amendment of toluene or ethylbenzene could stimulate benzene degradation. Lower concentrations of m-xylene would enhance the degradation of benzene, whereas degradation of benzene was inhibited with higher concentrations of m-xylene. The simultaneous presence of toluene and ethylbenzene could stimulate the degradation of each other. The addition of toluene stimulated o-xylene degradation, whereas the amendment of ethylbenzene inhibited the degradation of o-xylene. Lower concentrations of toluene or ethylbenzene would enhance the degradation of m-xylene and p-xylene, whereas higher concentrations of toluene or ethylbenzene had a slight inhibitory effect on m-xylene and p-xylene degradation. The amendment of benzene, m-xylene or p-xylene would inhibit the degradation of other BTEX compounds. When the concentration of BTEX mixtures was over 150mg/l, the degradation of benzene, o-xylene, m-xylene and p-xylene was severely inhibited.     

一种用于从水中分离挥发性有机化合物的疏水性渗透汽化中空纤维复合膜

研制出一种名为VOC-SEP200新型中空纤维疏水性复合膜，并考察了这种复合膜从水中分离BTEX(苯、甲苯、乙苯和二甲苯)的性能．这4种芳香碳氢化合物是工业有机废水中的一组有代表性的污染物，本研究的最终目的是想从现实的工业废水中回收这些化合物．采用料液在纤维中孔流动的方式，系统考察了进料液流速、操作压力、温度和进料液浓度对膜分离效率及膜性能的影响．结果显示，随着进料液流速的提高，BTEX的通量随之增大．这是由于随着进料液流速的提高，浓度极化的影响会减少，同时BTEX和水的分离因子会有显著增大．结果还显示，膜的性能随膜横向的驱动力降低而提高，其最佳的渗透压范围是10．7～13．3kPa(即80～100mmHg)，此时BTEX通量达到最大平稳值，同时水的通量最小．提高渗透压可减少操作费用，同时可增强分离效果，和预期的情况一样，BTEX和水的渗透通量都随着温度和进料浓度的提高而增大，但再进一步提高浓度和温度，则对水通量不产生影响．水通量在初始阶段的增加可以归因于膜的溶胀，水通量不再随温度和浓度的进一步升高而增加，可以归因于水分子的聚集与膜的溶胀达到了平衡，     

Real-time monitoring of benzene, toluene, and p-xylene in a photoreaction chamber with a tunable mid-infrared laser and ultraviolet differential optical absorption spectroscopy

We describe the implementation of a mid-infrared laser-based trace gas sensor with a photoreaction chamber, used for reproducing chemical transformations of benzene, toluene, and p-xylene (BTX) gases that may occur in the atmosphere. The system performance was assessed in the presence of photoreaction products including aerosol particles. A mid-infrared external cavity quantum cascade laser (EC-QCL)-tunable from 9.41-9.88?μm (1012-1063?cm(-1))-was used to monitor gas phase concentrations of BTX simultaneously and in real time during chemical processing of these compounds with hydroxyl radicals in a photoreaction chamber. Results are compared to concurrent measurements using ultraviolet differential optical absorption spectroscopy (UV DOAS). The EC-QCL based system provides quantitation limits of approximately 200, 200, and 600 parts in 10(9) (ppb) for benzene, toluene, and p-xylene, respectively, which represents a significant improvement over our previous work with this laser system. Correspondingly, we observe the best agreement between the EC-QCL measurements and the UV DOAS measurements with benzene, followed by toluene, then p-xylene. Although BTX gas-detection limits are not as low for the EC-QCL system as for UV DOAS, an unidentified by-product of the photoreactions was observed with the EC-QCL, but not with the UV DOAS system.