Development of continuous on-line purge and trap analysis

An on-line purge and trap system for continuous monitoring of Volatile Organic Compounds (VOC) is presented. The purge chamber was designed for continuous extraction of VOC from water with nitrogen. The analytes were preconcentrated on a microtrap prior to analysis by GC with flame ionization detection. The microtrap served as a fast injection device for carrying out analysis at high frequency. Continuous monitoring was accomplished by performing injections at fixed intervals. This system showed high sensitivity, high precision, detection limits at the ppb level, and stable response over long periods of continuous operation. Factors affecting system performance were studied. A predictive model based on gas-liquid partitioning is also presented.     

Design of a portable gas chromatography with a conducting polymer nanocomposite detector device and a method to analyze a gas mixture

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. It has an air pump coupled to the inlet of a chromatographic column for pumping air and an injector coupled to the inlet of chromatographic column for feeding the sample using the air as a carrier gas. A detector is arranged downstream from and coupled to the outlet of the chromatographic column. The detector is a nanostructure semiconductive microfiber. The device further comprises an evaluation unit arranged and configured to evaluate each detected component to determine the concentration. The 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. Finally, the method was successfully applied to the extraction and determination of analytes in water samples.     

On-site monitoring of biogenic emissions from Eucalyptus dunnii leaves using membrane extraction with sorbent interface combined with a portable gas chromatograph system

Membrane extraction with sorbent interface, combined with a portable gas chromatograph system (MESI-Portable GC) for continuous on-line monitoring of biogenic volatile organic compounds (BVOCs) emissions (from leaves of Eucalytus dunnii in a greenhouse), is presented herein. A sampling chamber was designed to facilitate the extraction and identification of the BVOCs emitted by the Eucalytus dunnii leaves. Preliminary experiments, including; enrichment times, microtrap temperatures, stripping gas flow rates, and desorption temperatures were investigated to optimize experimental parameters. The main components of BVOCs released by the Eucalytus dunnii leaves were identified by comparing the retention times of peaks with those of authentic standard solutions. They were then confirmed with solid phase microextraction coupled with gas chromatography and mass spectrometry (SPME-GC-MS). BVOC emission profiles of [small alpha]-pinene, eucalyptol, and [gamma]-terpinene emitted by intact and damaged Eucalytus dunnii leaves were obtained. The findings suggest that the MESI-Portable GC system is a simple and useful tool for field monitoring changes in plant emissions as a function of time.     

Development of membrane extraction with a sorbent interface-micro gas chromatography system for field analysis

The commercially available portable gas chromatographs have a rather limited scope of applications, typically allowing analysis of gaseous samples only, and having relatively poor sensitivity. Combination of those instruments with modern sampling/sample preparation techniques can remedy these problems. A Chrompack micro-GC system equipped with a thermal conductivity detector has been coupled to membrane extraction with a sorbent interface (MESI). The sorbent trap has replaced the GC injector. The design of the trap was also modified in order to enhance the preconcentration of analytes. The use of a thin flat sheet membrane reduces the response time, and decreases the memory effect of the system. Rapid separation times were achieved, and the sensitivity was significantly improved. MESI enables semi-continuous monitoring of both gaseous and aqueous samples, owing to the selectivity of the membrane material. The system does not use moving parts, therefore being reliable. The sensitivity of the micro-GC system was increased by a factor of more than 100 by the addition of the MESI system, even with a preconcentration time as short as 1 min. Chloroform, having a concentration lower than 1 ppb, was detected in tap water. A cup system was used to allow headspace sampling of volatile organic compounds from aqueous matrices, keeping the membrane away from interfering species that could be present in water, and improving the mass transfer. A linear calibration line was obtained, and the estimated limit of detection was 60 ppt. This represents a great improvement for the sensitivity of the micro-GC system.     

Performance and characteristics of a trace gas analyzer for the determination of volatile organic compounds in air

An instrument has been developed and tested for the continuous measurement of volatile organic compounds (VOC) in air. The system consists of a gas chromatograph equipped with a dedicated sampling device that allows the sample to be transferred to a cooled microtrap via sampling loops (10, 100, 250 ml) or via a direct pump transfer to the trap. The microtrap is placed in the chromatographic oven just below a modified split-splitless injector, allowing direct liquid injection for calibration of the system; the injector is in communication with the sampling valve equipped with the loop and the sampling pump. The system allows 24-hour sampling and analysis of a large number of VOC (up to 25 individual hydrocarbons ranging from C2 C9) and also polar volatile organic compounds PVOC. Thanks to the particular trap geometry, a minimum consumption of liquid nitrogen (between 150 300 ml) is needed for each analytical run and no water managing system is normally required for humid air samples.     

Resistively heated temperature programmable silicon micromachined gas chromatography with differential mobility spectrometry

A microfabricated electromechanical system based on radio frequency modulated ion mobility spectrometry (MEMS-RFIMS), also known as differential ion mobility spectrometry (DMS) has been successfully interfaced to a custom-fabricated resistively heated temperature programmable micromachined gas chromatograph. In contrast to a conventional time-of-flight ion mobility spectrometer, the DMS uses the non-linear mobility dependence in strong radio frequency electric fields for ion filtering. Selective and sensitive detection of targeted analytes of interest can be achieved by using different transport gases, radio frequencies, and associated compensation voltages. In addition, the detection of both positive and negative ions, depending on the ionization mechanism favorable to the analytes involved is achieved. When compared to a stand-alone GC with a non spectrometric detector or a stand-alone DMS, GC-DMS as a hyphenated technique offers two competitive advantages; two orthogonal separating methods in a single analytical system and the resolving power of gas chromatography to minimize charge exchange in the ionization chamber of the detector. In this article, a portable, resistively heated temperature programmable silicon machined gas chromatograph with differential mobility detection is introduced. The performance of the instrument is illustrated with examples of difficult industrial applications.     

Integration of continuous-flow sampling with microchip electrophoresis using poly(dimethylsiloxane)-based valves in a reversibly sealed device

Here we describe a reversibly sealed microchip device that incorporates poly(dimethylsiloxane) (PDMS)-based valves for the rapid injection of analytes from a continuously flowing stream into a channel network for analysis with microchip electrophoresis. The microchip was reversibly sealed to a PDMS-coated glass substrate and microbore tubing was used for the introduction of gas and fluids to the microchip device. Two pneumatic valves were incorporated into the design and actuated on the order of hundreds of milliseconds, allowing analyte from a continuously flowing sampling stream to be injected into an electrophoresis separation channel. The device was characterized in terms of the valve actuation time and pushback voltage. It was also found that the addition of sodium dodecyl sulfate (SDS) to the buffer system greatly increased the reproducibility of the injection scheme and enabled the analysis of amino acids derivatized with naphthalene-2,3-dicarboxaldehyde/cyanide. Results from continuous injections of a 0.39 nL fluorescein plug into the optimized system showed that the injection process was reproducible (RSD of 0.7%, n = 10). Studies also showed that the device was capable of monitoring off-chip changes in concentration with a device lag time of 90 s. Finally, the ability of the device to rapidly monitor on-chip concentration changes was demonstrated by continually sampling from an analyte plug that was derivatized upstream from the electrophoresis/continuous flow interface. A reversibly sealed device of this type will be useful for the continuous monitoring and analysis of processes that occur either off-chip (such as microdialysis sampling) or on-chip from other integrated functions.     

Zero solvent emission process for sulfur dioxide recovery using a membrane contactor and ionic liquids

Selective absorption into a liquid is a widespread method to separate and concentrate sulfur dioxide from gas emissions, reducing air pollution and environmental risks. Process intensification can be performed first by the substitution of the equipment (e.g. scrubbers) for a membrane device to avoid drops dragging, and second by the substitution of the absorption solvent (e.g. N,N-dimethylaniline) for ionic liquids to avoid solvent volatilization. According to this intensification, a zero solvent emission process has been developed.The ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate is used as the absorption solvent and the results are compared to the N,N-dimethylaniline results. A ceramic hollow fibre module is the membrane device where the sulfur dioxide absorption takes place. A gas stream with a typical composition of roasting effluents flows through the shell side and the absorption liquid flows counter currently by the inside of the hollow fibres. The influence of carbon dioxide in the absorption is also evaluated and the overall mass transfer coefficients are calculated. The difference between the estimated mass transfer coefficients and the experimental results for both solvents is discussed assuming partial wetting of the membrane.     

Gas chromatography analysis of benzene, toluene, ethylbenzene and xylenes using newly designed needle trap device in aqueous samples

A newly designed needle trap device with Carbopack X as a sorbent material is used for sampling, preconcentration and injection of volatile analytes benzene, toluene, ethylbenzene and xylenes (BTEX) into gas chromatograph. The closed system of stripping the analytes from water samples was used. An injection port with a modified metal liner was used to desorb analytes trapped in needle trap device. The main advantage of needle trap device consists in the simple methodology and easiness and rapidity of the analysis. Needle trap device is suitable for sampling in field. The experimental parameters as breakthrough volume of stripping gas, linearity, repeatability and limit of detection (LOD) and quantification (LOQ) were investigated. LOD ranges from 0.05 to 0.07 microgL(-1) and relative standard deviation ranges from 0.5% to 11.6% at concentrations 5 and 0.1 microgL(-1), respectively.     

Mixing with bubbles: a practical technology for use with portable microfluidic devices

This paper demonstrates a methodology for micromixing that is sufficiently simple that it can be used in portable microfluidic devices. It illustrates the use of the micromixer by incorporating it into an elementary, portable microfluidic system that includes sample introduction, sample filtration, and valving. This system has the following characteristics: (i) it is powered with a single hand-operated source of vacuum, (ii) it allows samples to be loaded easily by depositing them into prefabricated wells, (iii) the samples are filtered in situ to prevent clogging of the microchannels, (iv) the structure of the channels ensure mixing of the laminar streams by interaction with bubbles of gas introduced into the channels, (v) the device is prepared in a single-step soft-lithographic process, and (vi) the device can be prepared to be resistant to the adsorption of proteins, and can be used with or without surface-active agents.     

Preliminary studies of using preheated carrier gas for on-line membrane extraction of semivolatile organic compounds

In this paper, we present results for the on-line determination of semivolatile organic compounds (SVOCs) in air using membrane extraction with a sorbent interface–ion mobility spectrometry (MESI-IMS) system with a preheated carrier (stripping) gas. The mechanism of the mass transfer of SVOCs across a membrane was initially studied. In comparison with the extraction of volatile analytes, the mass transfer resistance that originated from the slow desorption from the internal membrane surface during the SVOC extraction processes should be taken into account. A preheated carrier gas system was therefore built to facilitate desorption of analytes from the internal membrane surface. With the benefit of a temperature gradient existing between the internal and external membrane surfaces, an increase in the desorption rate of a specific analyte at the internal surface and the diffusion coefficient within the membrane could be achieved while avoiding a decrease of the distribution constant on the external membrane interface. This technique improved both the extraction rate and response times of the MESI-IMS system for the analysis of SVOCs. Finally, the MESI-IMS system was shown to be capable of on-site measurement by monitoring selected polynuclear aromatic hydrocarbons emitted from cigarette smoke. Figure Schematic of the MESI-IMS preheating carrier (stripping) gas system     

Sensitive Detection of Elemental Mercury Vapor by Gold Nanoparticle Decorated Carbon Nanotube Sensors

Low-cost, low power consumption gas sensors that can detect or quantify various gas analytes are of increasing interest for various applications ranging from mobile health, to environmental exposure assessment and homeland security. In particular miniature gas sensors based on nanomaterials that can be manufactured in the form of sensor arrays present great potential for the development of portable monitoring devices. In this study, we demonstrate that a chemiresistive nanosensor comprised of single walled carbon nanotubes decorated with gold nanoparticles has impressive sensitivity to elemental mercury (Hg) gas concentrations, with a lower detection limit as low as 2 ppb(v). Furthermore, this nanosensor was found to regenerate, though slowly, without any additional recovery steps. Finally, the mercury vapor sensing mechanism allowed for direct investigations into the origin of Surface Enhanced Raman Scattering (SERS) in carbon nanotubes decorated with Au nanoparticles.     

Ion chromatographic system with a novel switching suppression device

Ion chromatography (IC) has been a powerful tool for measuring ionic species in environmental samples such as tap, river and drain waters. Suppressor modules (membrane and disposable column types) have been used for reducing the background of a baseline. A new type of suppressor device, which has a suppressor resin and switching valve was developed. Fresh ionic resin is introduced into a groove for each analysis to perform the suppression of the working eluent. The eluent composition for obtaining higher sensitivity and better resolutions among ionic species and carbonate ion was also investigated. Although carbonate buffers are used for ion separation in general, the separation of carbonate ion from other ions was not achieved. A borate eluent resulted in good resolutions and higher sensitivity. A new column was also developed for obtaining higher column efficiency and resolution. The optimization of anion separation using a new IC system (IC-2001) that consists of a new suppressor device, an anion-exchange column (TSKgel SuperIC-Anion, 150x4.6 mm), an autosampler, a conductivity cell and a pump in a compact module is described.     

Automation of solid-phase microextraction on a 96-well plate format

Studies have been performed assessing the feasibility and characterizing the automation of solid-phase microextraction (SPME) on a multi-well plate format. Four polycyclic aromatic hydrocarbons (PAHs), naphthalene, fluorene, anthracene and fluoranthene, were chosen as test analytes to demonstrate the technique due to their favorable partition coefficients, K(fw), between polydimethylsiloxane (PDMS) extraction phases and water. Four different PDMS configurations were investigated regarding their suitability. These included (i) a PDMS membrane; (ii) a multi-fiber device containing lengths of PDMS-coated flexible wire; (iii) a stainless steel pin covered with silicone hollow fiber membrane and (iv) commercial PDMS-coated flexible metal fiber assemblies. Of these configurations, the stainless steel pin covered with silicone tubing was chosen as a robust alternative. An array of 96 SPME devices that can be placed simultaneously into a 96-well plate was constructed to demonstrate the high-throughput potential when performing multiple microextractions in parallel. Different agitation methods were assessed including magnetic stirring, sonication, and orbital shaking at different speeds. Orbital shaking whilst holding the SPME device in a stationary position provided the optimum agitation conditions for liquid SPME. Once the analytes had been extracted, desorption of the analytes into an appropriate solvent was investigated. Liquid-phase SPME and solvent desorption on the multi-well plate format is shown to be a viable alternative for automated high-throughput SPME analysis compatible with both gas- and liquid-chromatography platforms.     

Vertical-flow paper SERS system for therapeutic drug monitoring of flucytosine in serum

A number of life-saving drugs require therapeutic drug monitoring (TDM) for safe and effective use. Currently, however, TDM is performed using sophisticated analytical techniques relegated to central labs, increasing the cost per test and time to answer. Here, using a novel vertical flow membrane system with inkjet-printed surface enhanced Raman sensors, along with a portable spectrometer, we demonstrate a low cost and easy to use device to quantify levels of flucytosine, an antifungal that requires TDM for effective patient care, from undiluted human serum. To our knowledge, this work represents the first report of a passive vertical flow sample cleanup method with surface enhanced Raman detection. We first investigated and optimized the parameters of the vertical flow system for the detection of flucytosine in spiked serum samples. Then, using an optimized vertical-flow system utilizing nitrocellulose membranes and a paper SERS sensor, we achieved detection of down to 10 μg mL⁻¹ flucytosine in undiluted serum, with quantitative detection across the entire therapeutic range. This system reduces the assay time to about 15 min, far quicker than the current gold standards. We anticipate that this novel system will enable near-patient therapeutic drug monitoring, leading to the safe and effective administration of a number of life-saving drugs. Furthermore, it will spawn the development of SERS detection systems capable of separating target analytes from real-world biological matrices.     

便携式气相色谱仪共用开发平台中多功能一体化控制器模块的研制

基于整体便携式气相色谱仪共用开发平台的设计理念,研制出了多功能一体化控制器模块.模块包括控制器、功率驱动组件和信号采集组件,直接嵌入到便携式气相色谱仪中.经试验考核,色谱柱温度波动不高于±0.1℃,60℃/min速率升温波动的RSD低于0.15%,进样口和检测器温度波动不高于±0.1℃,柱压不高于±0.16 KPa.以浓度为1 mg/m3的苯标准样品连续6次自动抽取1 m L样品进样分析,定性和定量重复性偏差RSD分别为0.1%和4.6%(峰高),温湿度试验为0~40℃和95%,振动试验(无运输包装)位移为25.4 mm、加速度为1.5 g,以频率5~200~5 Hz正弦波振动与XYZ轴向振动,试验结果正常.模块应用到3种新型仪器中效果理想,满足现场及野外应用要求,具有通用、坚固、体积小和功耗低等特点.     

A Three‐Dimensional Origami Paper‐Based Device for Potentiometric Biosensing

Current paper‐based potentiometric ion‐sensing platforms are planar devices used for clinically relevant ions. These devices, however, have not been designed for the potentiometric biosensing of proteins or small molecule analytes. A three‐dimensional origami paper‐based device, in which a solid‐contact ion‐selective electrode is integrated with an all‐solid‐state reference electrode, is described for the first time. The device is made by impregnation of paper with appropriate bioreceptors and reporting reagents on different zones. By folding and unfolding the paper structures, versatile potentiometric bioassays can be performed. A USB‐controlled miniaturized electrochemical detector can be used for simple and in situ measurements. Using butyrylcholinesterase as a model enzyme, the device has been successfully applied to the detection of enzyme activities and organophosphate pesticides involved in the enzymatic system as inhibitors. The proposed 3D origami paper device allows the potentiometric biosensing of proteins and small molecules in a simple, portable, and cost‐effective way.     

Membrane-controlled reagent-delivery systems – a new approach for the continuous production of reagent and standard solutions

A new simple and robust system for the production of standard solutions, based on the mass-transfer of analytes through membranes, is described. The device consists of a cone-shaped reservoir vessel, filled with a concentrated solution of the analyte and separated from a liquid acceptor stream by a membrane. Mass-flow from donor to acceptor solution is controlled by the mass-transfer-affecting properties of the active membrane area, which is determined by the hole in a template (diameter 0.8 mm) placed between the membrane and the acceptor-channel. Using nitrate as model analyte and a track-etched membrane filter (pore size 0.1 μm) dilution factors up to 2,400,000 with long-term reproducible accuracy of < 2% have been achieved. Adjustment of a requested concentration is possible by varying either the flow rate of the acceptor stream or the concentration of the reservoir solution. Received: 22 November 2000 / Revised: 5 March 2001 / Accepted: 7 March 2001     

On-line monitoring trihalomethanes in chlorinated water by membrane introduction-fast gas chromatography mass-spectrometry

An analytical method based on membrane introduction and fast gas chromatography-mass spectrometry (GC-MS) has been developed for the on-line monitoring of trihatomethanes (THMs) in chlorinated drinking water. The coupling of membrane introduction with fast GC-MS offers the advantage of membrane introduction as an on-line sampling device and fast GC-MS as a separation and identification method. While maintaining the on-line monitoring characteristic of traditional membrane introduction mass spectrometry (MIMS), the difficulty of distinguishing CHCl3 and CHBrCl2 in MIMS was overcome by rapid GC separation and MS analysis. Water permeated across the membrane affected the analysis of CHBr2Cl and CHBr3. A method based on controlling the injection temperature and injection time has been developed to overcome the moisture problem. This method is simple and less time consuming than the conventional moisture removing method. Under typical operating conditions, the sampling rate was about 20 samples h(-1) capable of on-line monitoring THMs in chlorinated drinking water. The detection limits of this system were found to be about 2 ppt, 4 ppt, 4 ppt, and 8 ppt for CHCl3 CHBrCl2, CHBr2Cl, and CHBr3, respectively.     

Sensitivity of a planar micro-flame ionization detector

The sensitivity of a MEMS μFID with reduced fuel gas consumption for portable applications like mobile GC or THA is examined. It is shown that sensitivity depends on flame size and type of sample gas supply (either separate supply or premixed with the hydroxygen). In contrast to conventional FIDs, the sensitivity of the μFID increases with decreasing molecule size. The sensitivity to methane can be optimized up to conventional values. Measurements with the μFID as a second detector in a μGC module prove the additional functionality of such a system.