Air sampling with porous solid-phase microextraction fibers

A new, rapid air sampling/sample preparation methodology was investigated using adsorptive solid-phase microextraction (SPME) fiber coatings and nonequilibrium conditions for volatile organic compounds (VOCs). This method is the fastest extraction technique for air sampling at typical airborne VOC concentrations. A theoretical model for the extraction was formulated based on the diffusion through the interface between the sampled (bulk) air and the SPME coating. Parameters that affect the extraction process including sampling time, air velocity, air temperature, and relative humidity were investigated with the porous (solid) PDMS/DVB and Carboxen/PDMS coatings. Very short sampling times from 5 s to 1 min were used to minimize the effects of competitive adsorption and to calibrate the extraction process in the initial linear extraction region. The predicted amounts of extracted mass compared well with the measured amounts of target VOCs. Findings presented in this study extend the existing fundamental knowledge related to sampling/sample preparation with SPME, thereby enabling the development of new sampling devices for the rapid sampling of air, headspace, water, and soil.     

Time-weighted average passive sampling with a solid-phase microextraction device

A modified Solid-Phase Microextraction (SPME) device has been used as a passive sampler to determine the time-weighted average (TWA) concentration of volatile organic compounds (VOCs) in air. Unlike conventional sampling with SPME, in which the fiber is extended outside its needle housing, during TWA passive sampling, the fiber is retracted a known distance into its needle housing. The SPME passive sampler collects the VOCs by the mechanism of molecular diffusion and sorption on to a coated fiber as collection medium. This process has been shown to be described by Fick's first law of diffusion, whereby determination of the amounts of analytes accumulated over time enable measurement of the TWA concentration to which the sampler was exposed. A series of fibers, 100-microm poly(dimethylsiloxane), 65-microm poly(dimethylsiloxane)/divinylbenzene, and 75-microm Carboxen/poly(dimethylsiloxane), were tested for their "zero sink", face velocity, and response time behavior. Of the fibers tested, that coated with 75-microm Carboxen/poly(dimethylsiloxane) was found to be an excellent passive sampler for VOCs. TWA passive sampling with a SPME device was shown to be almost independent of face velocity and to be more tolerant of high and low analyte concentrations and long and short sampling times, because of the ease with which the diffusion path length could be changed. It was found that environmental conditions, e.g., temperature, pressure, relative humidity, and ozone, have little or no effect on sampling. The 75-microm Carboxen/poly(dimethylsiloxane) fiber can retain VOCs for up to two weeks without significant loss. When the SPME device was tested in the field and the results were compared with those from National Institute of Occupational Health and Safety method 1501, good agreement was obtained.     

Development and application of a needle trap device for time-weighted average diffusive sampling

A simple, cost-effective analysis combining solventless extraction, thermal desorption, and determination of volatile organic compounds (VOCs) was developed and validated. A needle trap device (NTD) packed with the sorbent Carboxen1000 was used as a time-weighted average (TWA) diffusive sampler to collect target compounds by molecular diffusion and adsorption to the packed sorbent. This process can be described with derivations of Fick's first law of diffusion, which expresses the relation between the TWA concentrations to which the passive sampler is exposed and the mass of analytes adsorbed to the packed sorbent in the sampler. The effects of experimental factors such as temperature, pressure, humidity, and face velocity were taken into account in applying diffusive sampling under nonideal conditions. This study demonstrates that NTD is effective for air analysis of benzene, toluene, ethylbenzene, and o-xylene (BTEX), due to the good adsorption/desorption quality of Carboxen 1000 and to the special geometric shape of the needle with a small cross section avoiding the need for calibration. Storage tests showed good storage stability for BTEX. Verification of the theoretical model showed good agreement between theoretical and experimental sampling rates. Method validation done against NIOSH method 1501, SPME, and NTD active sampling revealed good agreement between those methods. Automated NTD sample introduction to a gas chromatograph facilitates the use of this technology for industrial hygiene applications.     

Sampling and analysis of airborne particulate matter and aerosols using in-needle trap and SPME fiber devices

A needle trap device (NTD) and commercial poly(dimethylsiloxane) (PDMS) 7-microm film thickness solid-phase microextraction (SPME) fibers were used for the sampling and analysis of aerosols and airborne particulate matter (PM) from an inhaler-administered drug, spray insect repellant, and tailpipe diesel exhaust. The NTD consisted of a 0.53-mm o.d. stainless steel needle having 5 mm of quartz wool packing section near the needle tip. Samples were collected by drawing air across the NTD with a Luertip syringe or via direct exposure of the SPME fiber. The mass loading of PM was varied by adjusting the volume of air pulled through the NTD or by varying the sampling time for the SPME fiber. The air volumes ranged from 0.1 to 50 mL, and sampling times varied from 10 s to 16 min. Particulates were either trapped on the needle packing or sorbed onto the SPME fiber. The devices were introduced to a chromatograph/mass spectrometer (GC/MS) injector for 5 min desorption. In the case of the NTD, 10 microL of clean air was delivered by a gas-tight syringe to aid the introduction of desorbed analytes. The compounds sorbed onto particles extracted by the SPME fiber or trapped in the needle device were desorbed in the injector and no carry-over was observed. Both devices performed well in extracting airborne polycyclic aromatic hydrocarbons (PAHs) in diesel exhaust, triamcinolone acetonide in a dose of asthma drug and DEET in a dose of insect repellant spray. Results suggest that the NTDs and PDMS 7-microm fibers can be used for airborne particulate sampling and analysis, providing a simple, fast, reusable, and cost-effective screening tool. The advantage of the SPME fiber is the open-bed geometry allowing spectroscopic investigations of particulates; for example, with Raman microspectroscopy.     

Theory and validation of solid-phase microextraction and needle trap devices for aerosol sample

Previous aerosol studies utilizing solid-phase microextraction (SPME) predominantly focused on volatile and semivolatile compounds in the gaseous phase. Difficulties were associated with quantitative analysis of these compounds when they were associated with atmospheric particles. The present study combines SPME technology with that of carboxen packed needles (needle trap, NT) for analysis of gaseous and particle-bound compounds in atmospheric samples. The NT device is constructed as a micro trap by placing some small sorbents in a needle. Aerosol samples are collected by drawing air through the NT device with a pump. The trapped components contain both gaseous chemical compounds as well as particulate matter present in the sample. The total concentration of analytes in an aerosol sample can be obtained on the basis of the exhaustive sampling mode of the NT device. Direct SPME is simultaneously used to determine gaseous compound in the aerosol sample. As a result, the SPME and NT devices, when used together, can provide a complete solution to highly efficient and accurate aerosol studies. The theoretical considerations of SPME and NT devices for aerosol sampling are validated by sampling seasalt aerosol, barbecue, and cigarette smoke. The concentrations of PAHs in the different phases of the samples are few ng/L. Result analysis shows that SPME and the NT device demonstrate several important advantages such as simplicity, convenience, and low costs under laboratory and on-site field sampling conditions.     

室内空气中VOC现场快速检测方法研究

对基于PID原理的VOC快速检测仪测定室内空气中总挥发性有机物进行了深入的研究,探讨了快检仪测定VOCs的特点和优势。分别采用已知组分的VOC标准气体和现场采样分析,对两种VOC测定方法的测定结果进行了比较研究,得出比值R的范围,提出VOCs表观浓度的概念,对进一步研究两种方法的可比性提供了可靠的依据。     

Evaluation of solid-phase microextraction for time-weighted average sampling of volatile sulfur compounds at ppb concentrations

The potential of solid-phase microextraction (SPME) for time-weighted average (TWA) sampling of volatile sulfur compounds in air at ppb concentrations was investigated. The target compounds (hydrogen sulfide, methanethiol (MeSH), ethanethiol (EtSH), dimethyl sulfide (Me2S), and dimethyl disulfide (Me2S2)) were extracted using SPME with a Carboxen-poly(dimethylsiloxane) fiber coating, and diffusion was controlled by keeping the fiber retracted within the needle of the sampling device. The effects of several important experimental variables (air velocity, direction of air flow, analyte concentration, humidity, temperature, extraction time) were studied. The uptake by the fiber was not affected by the direction of the air flow or the air velocity. The effects of concentration, humidity, temperature, and extraction time were examined in experiments with a central composite face design. The results showed that all or most of the investigated parameters had a significant impact on the uptake rates of H2S, MeSH, EtSH, and Me2S, which invalidated time-weighted average sampling of these compounds by SPME under the tested conditions. Moreover, reverse diffusion of H2S, MeSH, and EtSH occurred at 40% relative humidity. For Me2S2, the uptake rate had a variation of only 8% within the whole experimental domain, and the experimental value derived for the uptake rate was consistent with the theoretical value. This result was confirmed by comparative analyses of industrial samples by the standard addition method. Therefore, SPME appears to be a suitable technique for TWA sampling of Me2S2 using the Carboxen-poly(dimethylsiloxane) fiber coating. Finally, in an investigation of potential losses during storage of the fiber, no significant losses of the target compounds were detected after 3 days at -80 degrees C.     

室内空气中VOC全采样多项快速检测技术研究

采用硅烷化处理内壁的不锈钢采样罐采集室内空气样品,三级冷阱预浓缩,气相色谱-质谱仪联用分析室内空气中挥发性有机物(VOC)。选取100、50、25、10、52、ppb浓度点VOC标准气体绘制标准曲线,曲线的线性相关系数R≥0.99,每个浓度点重复测定的相对标准偏差RSD<5%(n=6),平均相对标准偏差MRSD<5%(n=6)。现场采样分析结果,平行样测定结果之差与平均值比较的相对偏差<10%。本检测方法的扩展不确定度10.6%。方法可实现对现场挥发性有机气体的全采样、全分析,避免了因吸附剂的选择吸附性所引起的采样、分析误差。     

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.     

Application of low-temperature glassy carbon-coated macrofibers for solid-phase microextraction analysis of simulated breath volatiles

With increasing interest in the detection of disease-related volatile organic compounds (VOCs) found in human breath, breath analysis could prove to be a very useful diagnostic tool, especially for the early detection of lung cancer. Solid-phase microextraction (SPME) is a technique well suited for breath analysis and has been applied to studying VOCs in the nanomolar concentration range. However, many compounds of interest in human breath are excreted at picomolar concentrations and may be unsuitable for analysis using conventional SPME sorbent phases. To extend the concentration range of conventional SPME, a novel 4-cm-long, low-temperature glassy carbon (LTGC) macrofiber was developed. The LTGC SPME macrofibers were used to extract five lung cancer-related VOCs (2-methylheptane, styrene, propylbenzene, decane, undecane) at conditions simulating human breath, and they were analyzed via gas chromatography/mass spectrometry. Results show that detection limits are lower using the SPME macrofibers compared to a conventional SPME fiber, in the low- to sub-picomolar range for the compounds of interest, which should be adequate for the analysis of these compounds in human breath. Also, the LTGC SPME macrofibers demonstrate significantly greater extraction efficiencies, sensitivity, and peak identification accuracy compared to that of commercial PDMS/DVB fibers without excessive chromatographic peak broadening. The use of SPME macrofibers broadens the potential range of application of SPME where the rapid extraction of very low levels of volatile compounds is required.     

Time-weighted average sampling with solid-phase microextraction device: implications for enhanced personal exposure monitoring to airborne pollutants

The solid-phase microextraction (SPME) device is used as a time-weighted average (TWA) sampler for gas-phase analytes by retracting the coated fiber a known distance into its needle housing during the sampling period. Unlike in conventional spot sampling with SPME, the TWA sampling approach does not allow the analytes to reach equilibrium with the fiber coating, but rather they diffuse through the opening in the needle to the location of the sorbent. The amount of analytes accumulated over time gives the measurement of the average concentration to which the device was exposed to. Depending on the sorbent used as the sink, TWA sampling for various analytes is possible with times ranging from 15 min to at least 16 h. Both the poly(dimethylsiloxane) (PDMS) and poly(dimethylsiloxane)/divinylbenzene (PDMS/DVB) fiber coating phases were tested, with the latter employing on-fiber derivatization for reactive carbonyl compounds, e.g., formaldehyde. Described herein are the theoretical and practical considerations for using the SPME device as a TWA sampler.     

Estimation of air/coating distribution coefficients for solid phase microextraction using retention indexes from linear temperature-programmed capillary gas chromatography. Application to the sampling and analysis of total petroleum hydrocarbons in air

The paper describes a method to quantify hydrocarbons in air exclusively on the basis of chromatographic parameters without the need for calibration. A simple technique is presented to estimate distribution coefficients (K) between air and the poly(dimethylsiloxane) solid phase microextraction (SPME) fiber coating using the linear temperature-programmed retention index system (LTPRI). There is a linear relationship (r(2) = 0.99989) between the log K for a series of n-alkanes and LTPRI, thus providing a means by which establishing a K for any peak in a chromatogram is possible given its published or experimentally determined LTPRI. This alternative approach to establishing K values significantly enhances and simplifies the use of SPME for sampling and analyzing air for quantification of compounds without the need for fiber calibration. Analysis of a group of 29 isoparaffinic compounds and a group of 33 aromatic compounds showed excellent agreement between their theoretical air to fiber distribution coefficients based on LTPRI and the experimentally obtained distribution coefficients. In addition, for a very complex mixture of organics such as gasoline, SPME can establish a total petroleum hydrocarbon in air level using LTPRI. This method was carefully evaluated, and the results were essentially identical between standard procedures and the proposed simple procedure described in the paper.     

Sampling and Raman confocal microspectroscopic analysis of airborne particulate matter using poly(dimethylsiloxane) solid-phase microextraction fibers

Commercial poly(dimethylsiloxane) (PDMS) 7-microm solid-phase microextraction (SPME) fibers were used for sampling and Raman spectroscopic analysis of a tailpipe diesel exhaust, candle smoke, cigarette smoke, and asbestos dust. Samples were collected via direct exposure of the SPME fiber to contaminated air. The mass loading for SPME fibers was varied by changing the sampling time. Results indicate that PDMS-coated fibers provide a simple, fast, reusable, and cost-effective air sampling tool for airborne particulates. The PDMS coating was stable; Raman bands of the PDMS coating were observed exactly at the same wavenumber positions before and after air sampling. Raman spectroscopic analysis resulted in identification of several characteristic bands allowing chemical speciation of particulates. The advantage of the SPME fiber is the open bed geometry allowing for application of various spectroscopic methods of particulate analysis. This paper describes the first-ever combined application of SPME technology with Raman confocal microspectroscopy for sampling and analysis of airborne particulates. Advantages of the combination of solid-phase microextraction and Raman microspectroscopy for airborne particulate analysis are discussed. Challenges associated with combined SPME sampling and Raman analysis of single particles are also described.     

Characterization of total volatile organic compound emissions from paints

 Recently, Homeswest in Western Australia and Murdoch University developed a project to construct low allergen houses (LAH) in a newly developed suburb. All potential volatile organic compound (VOC) emission materials used in LAH are required to be measured before the construction of LAH, to ensure they are low VOCs emission materials. To protect people sensitive to exposure to VOCs it is important to evaluate and select low VOCs emitting paints. In this paper, therefore, twelve different paints provided by local manufacturers were selected for analysis to characterize total volatile organic compounds (TVOC) emissions. Emissions of TVOCs from six organic solvent-soluble paints and six water-soluble paints were evaluated using a small test chamber under controlled temperature, relative humidity and air exchange rates. The major volatile organic compounds in these paints were also identified. The time dependence of TVOC emissions from paint products in the chamber was evaluated. TVOC emissions from organic solvent-soluble and water-soluble paints were compared. The influence of air exchange rate on the TVOC concentrations emitted from organic solvent-soluble and water-soluble paints was also investigated. A double-exponential equation was used to evaluate emission characteristics of TVOC from paint products. With this double-exponential model, the physical processes of TVOC emissions can be explained. A variety of emission parameters can be calculated and used to estimate real indoor TVOCs concentrations. Received: 13 July 1999 / Accepted: 27 September 1999     

Solid-phase microextraction field sampler

To facilitate the use of solid-phase microextraction (SPME) for field sampling, a new field sampler was designed and tested. The sampler was versatile and user-friendly. The SPME fiber can be positioned precisely inside the needle for time-weighted average sampling or exposed completely outside the needle for grab sampling. The needle is protected within a shield at all times, hereby eliminating the risk of operator injury and fiber damage. A replaceable Teflon cap is used to seal the needle to preserve sample integrity. Factors that affect the preservation of sample integrity (sorbent efficiency, temperature, sealing materials) were studied. The use of a highly efficient sorbent for the fiber is recommended as the first choice for the preservation of sample integrity. Teflon was a good material for sealing the fiber needle, had little memory effect, and could be used repeatedly. To address adsorption of high boiling point compounds on fiber needles, several kinds of deactivated needles were evaluated. RSC-2 fiber needles were the more effective. A preliminary field sampling investigation demonstrated the validity of the new SPME device for field applications.     

Cleaning air from multicomponent impurities of volatile organic compounds by pulsed corona discharge

The relative efficiency of the removal of impurities from airflow under the action of pulsed corona discharge has been studied by processing model mixtures of air with volatile organic compounds (VOCs). A method is proposed that allows the influence of the VOC structure on its reactivity to be directly determined. For this purpose, it is suggested to calculate a relative energy parameter characterizing the reactivity of a given impurity component in the framework of the method employed. This approach significantly intensifies the process of determination of the energy parameters of impurity removal and can be used as a criterion for comparative estimation of the efficiency of various methods employing nonequilibrium plasma for cleaning air from VOCs.     

Solvent vapour monitoring in work space by solid phase micro extraction

Solid phase micro extraction (SPME) is a fast, solvent-less alternative to conventional charcoal tube sampling/carbon disulfide extraction for volatile organic compounds (VOC). In this work, SPME was compared to the active sampling technique in a typical lab atmosphere. Two different types of fibre coatings were evaluated for solvent vapour at ambient concentration. A general purpose 100 microm film polydimethylsiloxane (PDMS) fibre was found to be unsuitable for VOC work, despite the thick coating. The mixed-phase carboxen/PDMS fibre was found to be suitable. Sensitivity of the SPME was far greater than charcoal sorbent tube method. Calibration studies using typical solvent such as dichloromethane (DCM), benzene (B) and toluene (T) showed an optimal exposure time of 5 min, with a repeatability of less than 20% for a broad spectrum of organic vapour. Minimum detectable amount for DCM is in the range of 0.01 microg/l (0.003 ppmv). Variation among different fibres was generally within 30% at a vapour concentration of 1 microg DCM/l, which was more than adequate for field monitoring purpose. Adsorption characteristics and calibration procedures were studied. An actual application of SPME was carried out to measure background level of solvent vapour at a bench where DCM was used extensively. Agreement between the SPME and the charcoal sampling method was generally within a factor of two. No DCM concentration was found to be above the regulatory limit of 50 ppmv.     

Quantitative in vivo microsampling for pharmacokinetic studies based on an integrated solid-phase microextraction system

An integrated microsampling approach based on solid-phase microextraction (SPME) was developed to provide a complete solution to highly efficient and accurate pharmacokinetic studies. The microsampling system included SPME probes that are made of poly(ethylene glycol) (PEG) and C18-bonded silica, a fast and efficient sampling strategy with accurate kinetic calibration, and a high-throughput desorption device based on a modified 96-well plate. The sampling system greatly improved the quantitative capability of SPME in two ways. First, the use of the C18-bonded silica/PEG fibers minimized the competition effect from analogues of the target analytes in a complicated sample matrix such as blood or plasma samples, which is a common problem associated with solid coating SPME fibers for quantitative analysis. Moreover, the C18-bonded silica/PEG fibers provide high sensitivity and a large dynamic range that covers the possible sample concentration range during diazepam administration and elimination. Second, the kinetic calibration method offers more accurate quantitation than the calibration curve method for in vivo SPME, because it compensates for convection and matrix effects during sampling. Therefore, it is especially suitable as a fast sampling technique for pre-equilibrium SPME. Furthermore, with the high-throughput desorption device, the integrated system offers compactness and high efficiency. Its feasibility for in vivo sampling was demonstrated by monitoring diazepam pharmacokinetics and validated by conventional chemical assays and equilibrium SPME. In addition, we propose a simple method to determine the apparent distribution constant between an SPME fiber and a blood matix (Kfs) and the distribution constant between an SPME fiber and a pure PBS buffer sample matrix (Kfb). As a result, both total and free concentrations of the drug and its metabolites can be detected simultaneously. Accordingly, the binding constants to the blood matrix can be obtained, which are of special significance for clinical diagnosis and drug discovery.     

In situ surface sampling of biological objects and preconcentration of their volatiles for chromatographic analysis

This report describes a rolling stir bar sampling procedure for volatile organic compounds (VOCs) present on various biological surfaces. In combination with thermal desorption/gas chromatography/mass spectrometry, this analytical technique was initially tested for quantitative profiling of human skin VOCs. It is also applicable to additional hydrophobic surfaces such as agricultural products, plant materials, and bird feathers. Use of embedded internal standards provides highly reproducible and quantitative results for a wide variety of sampled trace components. The samples of collected human skin VOCs and standards were found stable under cool storage conditions for at least 14 days, making this approach suitable for field biological and agricultural studies. Additionally, this methodology appears to have potential for forensic and toxicological investigations, as suggested through the analyses of VOC profiles of the human thumb prints recovered from a nonbiological smooth surface.