Air sampling and analysis of volatile organic compounds with solid phase microextraction

Solid phase microextraction (SPME) presents many advantages over conventional analytical methods by combining sampling, preconcentration, and direct transfer of the analytes into a standard gas chromatograph (GC). Since its commercial introduction in the early 1990s, SPME has been successfully applied to the sampling and analysis of environmental samples. This paper presents an overview of the current methods for air sampling and analysis with SPME using both grab and time-weighted average (TWA) modes. Methods include total volatile organic compounds (TVOCs), formaldehyde, and several target volatile organic compounds (VOCs). Field sampling data obtained with these methods in indoor air were validated with conventional methods based on sorbent tubes. The advantages and challenges associated with SPME for air sampling are also discussed. SPME is accurate, fast, sensitive, versatile, and cost-efficient, and could serve as a powerful alternative to conventional methods used by the research, industrial, regulatory, and academic communities.     

热解析-固相微萃取-气相色谱法测定空气样品中挥发性有机化合物

建立了热解析-固相微萃取-气相色谱法测定空气样品中挥发性有机化合物的分析方法,并对色谱分离条件、玻璃针筒保存样品的稳定性、固相微萃取萃取纤维、萃取时间、色谱进样时间等条件进行了优化,9种挥发性有机化合物的峰面积与其质量浓度在所测范围内有较好的线性关系,相对标准偏差＜8.8%,检出限为0.05～0.75 μg/100 mL,满足实际空气样品测定需要。     

Comments on the NAS Report: Odors From Stationary and Mobile Sources

ABSTRACT

Solid phase microextraction (SPME) presents many advantages over conventional analytical methods by combining sampling, preconcentration, and direct transfer of the analytes into a standard gas chromatograph (GC). Since its commercial introduction in the early 1990s, SPME has been successfully applied to the sampling and analysis of environmental samples. This paper presents an overview of the current methods for air sampling and analysis with SPME using both grab and time-weighted average (TWA) modes. Methods include total volatile organic compounds (TVOCs), formaldehyde, and several target volatile organic compounds (VOCs). Field sampling data obtained with these methods in indoor air were validated with conventional methods based on sorbent tubes. The advantages and challenges associated with SPME for air sampling are also discussed. SPME is accurate, fast, sensitive, versatile, and cost-efficient, and could serve as a powerful alternative to conventional methods used by the research, industrial, regulatory, and academic communities.     

Dynamic air sampling of volatile organic compounds using solid phase microextraction

A new dynamic air sampling system was devised and evaluated in conjunction with solid phase microextraction (SPME) fiber materials for extracting odor-causing volatile organic compounds (VOCs) present in swine building environments. Utilizing a standard solution consisting of 11 compounds (i.e., volatile fatty acids, indoles, and phenol), sampling times, volumes, and flow rates were adjusted to establish optimal extraction conditions. Results indicated that the sampling system was effective with the Carboxen/Polydimethylsiloxane (CAR/PDMS) fiber in extracting all 11 standard compounds. The best sampling conditions for the extraction were a 100-mL sampling vial subjected to a continuous flow of 100 mL/min for 60 min. The gas chromatographic analysis showed that the reproducibility was within acceptable ranges for all compounds (RSD=4.24-17.26% by peak areas). In addition, field tests revealed that the sampling system was capable of detecting over 60 VOCs in a swine house whose major components were identified by gas chromatography-mass spectrometry (GC-MS) and by their retention times as volatile fatty acids, phenols, indole, and skatole. The field tests also showed that considerably different levels of VOCs were present in various parts of the swine building.     

Chemical-sensory characterization of dairy manure odor using headspace solid-phase microextraction and multidimensional gas chromatography mass spectrometry-olfactometry

Livestock operations are associated with emissions of odor, gases, and particulate matter. The majority of previous livestock odor studies focused on swine operations whereas relatively few relate to dairy cattle. Identifying the compounds responsible for the primary odor impact is a demanding analytical challenge because many critical odor components are frequently present at very low concentrations within a complex matrix of numerous insignificant volatiles. The objective of this study was to describe a chemical-sensory profile of dairy manure odor using headspace solid-phase microextraction (HS-SPME) and multidimensional gas chromatography-mass spectrometry-olfactometry (MDGC-MS-O). Two analytical approaches were used: (1) HS-SPME time-series extractions (from seconds up to 20 hr) followed by gas chromatography-mass spectrometry-olfactometry (GC-MS-O) analyses, and (2) relatively short HS-SPME extractions (30 min) followed by MDGC-MS-O analyses on selected chromatogram heart-cuts. Dairy manure was collected at research dairy farms in the United States and Israel. Volatile organic compounds (VOCs) resolved from multiple analyses included sulfur-containing compounds, volatile fatty acids, ketones, esters, and phenol/indole derivatives. A total of 86 potential odorants were identified. Of them, 17 compounds were detected by the human nose only. A greater number of VOCs and odorous compounds were detected, as well as higher mass loading, on solid-phase microextraction (SPME) fibers observed for longer extractions with SPME. However, besides sulfur-containing compounds, other selected compounds showed no apparent competition and displacement on the SPME fiber. The use of MDGC-MS-O increased chromatographic resolution even at relatively short extractions and revealed 22 additional odorants in one of the regions of the chromatogram. The two analytical approaches were found to be parallel to some extent whereas MDGC-MS-O can also be considered as a complementary approach by resolving more detailed chemical-sensory odor profiles.     

A laboratory technique for investigation of diffusion and transformation of volatile organic compounds in low permeability media

A laboratory diffusion cell technique that permits spatial and temporal estimates of porewater concentrations over short intervals suitable for estimation of effective diffusion coefficients (De) and degradation rate constants (k) of volatile organic compounds (VOCs) in saturated low permeability media is presented. The diffusion cell is a sealed cylinder containing vapour reservoirs for sampling, including a vapour reservoir source and an array of vapour-filled "mini-boreholes", which are maintained water- and sediment-free by slightly negative porewater pressures. The vapour reservoirs were sampled by Solid Phase Micro-Extraction (SPME), resulting in minimal disturbance to the experimental system. Porewater concentrations are estimated from the measured vapour concentrations. Experiments were conducted using a non-reactive medium and five VOCs with a range in partitioning properties. Calibration experiments showed that equilibrium partition coefficients could be used for calculating concentrations in the vapour reservoir source from concentrations in the SPME coating after a 1-min microextraction and that the reservoir concentration was insignificantly affected by sampling. However, equilibrium was not reached during the one-min extraction of the boreholes; the microextraction reduced the borehole vapour concentrations, leading to diffusion of VOCs from porewater into the vapour-filled borehole. Thus, empirical partitioning coefficients were required for the determination of porewater VOC concentrations. The experimental data and numerical modelling indicate masses extracted by SPME extraction are relatively small, with minimal perturbation on processes studied in diffusion experiments. This technique shows promise for laboratory investigation of diffusion and transformation processes in low permeability media.     

Analysis of volatile and semivolatile organic compounds in municipal wastewater using headspace solid-phase microextraction and gas chromatography.

The aim of this work was to develop a simple and fast analytical method for the determination of a wide range of organic compounds (volatile and semivolatile compounds) in municipal wastewater. The headspace-solid-phase microextraction (HS-SPME) and gas chromatography (with mass spectroscopy) was used for determination of the organic compounds. In this study, 39 organic compounds were determined, including 3 sulfur compounds, 28 substituted benzenes, and 8 substituted phenols. The extraction parameters, such as types of SPME fiber, extraction temperature, extraction time, desorption time, salt effect, and magnetic stirring, were investigated. The method had very good repeatability, because the relative standard deviations ranged from 0.5 to 12%. The detection limit of each compound was at or below the microgram-per-liter level. This method was applied for determination of the organic compounds in raw wastewater, primary effluent, secondary effluent, and chlorinated secondary effluent samples from the Chania Municipal Wastewater Treatment Plant (Crete, Greece).     

Organic compounds in indoor air—their relevance for perceived indoor air quality?

It is generally believed that indoor air pollution, one way or another may cause indoor air complaints. However, any association between volatile organic compounds (VOCs) concentrations and increase of indoor climate complaints, like the sick-building syndrome symptoms, is not straightforward. The reported symptom rates of, in particular, eye and upper airway irritation cannot generally be explained by our present knowledge of common chemically non-reactive VOCs measured indoors. Recently, experimental evidence has shown those chemical reactions between ozone (either with or without nitrogen dioxide) and unsaturated organic compounds (e.g. from citrus and pine oils) produce strong eye and airway irritating species. These have not yet been well characterised by conventional sampling and analytical techniques. The chemical reactions can occur indoors, and there is indirect evidence that they are associated with eye and airway irritation. However, many other volatile and non-volatile organic compounds have not generally been measured which could equally well have potent biological effects and cause an increase of complaint rates, and posses a health/comfort risk. As a consequence, it is recommended to use a broader analytical window of organic compounds than the classic VOC window as defined by the World Health Organisation. It may include hitherto not yet sampled or identified intermediary species (e.g., radicals, hydroperoxides and ionic compounds like detergents) as well as species deposited onto particles. Additionally, sampling strategies including emission testing of building products should carefully be linked to the measurement of organic compounds that are expected, based on the best available toxicological knowledge, to have biological effects at indoor concentrations.     

Models for estimating organic emissions from building materials: Formaldehyde example

One important source of chronic exposure to low levels of organic compounds in the indoor environment is emissions from building materials. Because removal of offending products may be costly or otherwise impractical, it is important that the emissions of organic pollutants be understood prior to incorporation of these materials into buildings. Once the organic pollutants of concern are identified, based on potential health effects and emission potential from the building material, it is necessary that an emission model be developed to predict the behavior of emission rates under various indoor conditions. Examples of the type of requirements that must be addressed in developing models for estimating organic emissions from building materials into the indoor environment are presented. Important factors include the products' characteristic source strengths at standard test conditions, impact of variations in environmental conditions (such as temperature and humidity), concentrations of the modeled organic pollutants in indoor environments and product ages. Ideally, emission models should have physical/chemical bases so that the important physical factors can be identified and their relative importance quantified. Although a universal model describing organic emissions from all building materials may not be feasible due to the tremendous variety of organic products and building materials in use, the most studied of the volatile organic compounds from building materials, formaldehyde, is used to illustrate an approach to the development of a specific model for organic emissions.     

Matrix effect on the performance of headspace solid phase microextraction method for the analysis of target volatile organic compounds (VOCs) in environmental samples

Solid phase microextraction (SPME) is a fast, cheap and solvent free methodology widely used for environmental analysis. A SPME methodology has been optimized for the analysis of VOCs in a range of matrices covering different soils of varying textures, organic matrices from manures and composts from different origins, and biochars. The performance of the technique was compared for the different matrices spiked with a multicomponent VOC mixture, selected to cover different VOC groups of environmental relevance (ketone, terpene, alcohol, aliphatic hydrocarbons and alkylbenzenes). VOC recovery was dependent on the nature itself of the VOC and the matrix characteristics. The SPME analysis of non-polar compounds, such as alkylbenzenes, terpenes and aliphatic hydrocarbons, was markedly affected by the type of matrix as a consequence of the competition for the adsorption sites in the SPME fiber. These non-polar compounds were strongly retained in the biochar surfaces limiting the use of SPME for this type of matrices. However, this adsorption capacity was not evident when biochar had undergone a weathering/aging process through composting. Polar compounds (alcohol and ketone) showed a similar behavior in all matrices, as a consequence of the hydrophilic characteristics, affected by water content in the matrix. SPME showed a good performance for soils and organic matrices especially for non-polar compounds, achieving a limit of detection (LD) and limit of quantification (LQ) of 0.02 and 0.03 ng g⁻¹ for non-polar compounds and poor extraction for more hydrophilic and polar compounds (LD and LQ higher 310 and 490 ng g⁻¹). The characteristics of the matrix, especially pH and organic matter, had a marked impact on SPME, due to the competition of the analytes for active sites in the fiber, but VOC biodegradation should not be discarded in matrices with active microbial biomass.     

Sources and Source Strengths of Volatile Organic Compounds in a New Office Building

This study was conducted at a newly constructed federal office building in Portland, Oregon. The primary objectives were to identify the major sources of volatile organic compounds (VOC) in the building and to measure both long-term (one year) and short-term (several day) variations in concentrations and source strengths. Samples for VOC were collected on four occasions over a period of 14 months starting with the first month of occupancy. During the final sampling period, samples were collected over four days (Friday - Monday). The samples were analyzed for individual compounds and for total VOC (TVOC). The results were expressed as specific source strengths, as well as concentrations, to facilitate comparisons of measurements made under different ventilation conditions.

The primary source of VOC in the building was identified as liquid-process photocopiers and plotters which emitted a characteristic mixture of C10-Cn isoparaffinic hydrocarbons. The specific source strength of TVOC, which was dominated by the emissions from these office machines, remained relatively constant over the course of the study. Motor vehicles in the below-ground parking garage were implicated as another major source of hydrocarbons in the building. Over the final four-day sampling period, the specific source strength of TVOC varied by about a factor of five, predominantly reflecting occupant use of office machines.     

Volatile metabolites from mold growth on building materials and synthetic media

Mold species which were isolated from damp buildings were grown on sterile building materials and some synthetic media in order to study the microbial volatile organic compounds produced. Patterns of the microbial volatile organic compounds (MVOC) were very media dependent but media which favor terpene biosynthesis may give patterns unique enough for identification of dominant indoor molds.     

Analysis of volatile fatty acids in wastewater collected from a pig farm by a solid phase microextraction method

The main purpose of this study is to develop a reliable Solid Phase Microextraction (SPME) method for monitoring the concentration of volatile fatty acid (VFA) in the wastewater collected from pig farms. Ten volatile fatty acid species were spiked in 2 ml of swine wastewater and extracted with a carbowax coated extraction fiber to evaluate the accuracy and precision of the method. The fiber was introduced into a gas chromatography system by thermal desorption and detected by a mass spectrometer detector. The estimated method detection limits ranged from 11.5 mM/L for formic acid to 0.03 mM/L for heptanoic acid. The method is more sensitive than the sample direct injection method. The percentage recovery of analytes ranged from 77.3 for propanoic acid to 114.1 for formic acid at the spike level of 19.09 mM/L. The compound absorption rate varied significantly with the fiber absorption time for n-Valeric, isocaproic, n-caproic and heptanoic acids. An SPME method with twenty minutes fiber absorption and three minutes thermal desorption was tested in this study and resulted in good reproducibility for analyzing VFAs in swine wastewater. The method may be applied for scanning a wide spectrum of polar organic compounds in environmental samples.     

Gas chromatographic analysis of organic marker compounds in fine particulate matter using solid-phase microextraction

A gas chromatographic method that uses solid-phase microextraction for analysis of organic marker compounds in fine particulate matter (PM2.5) is reported. The target marker compounds were selected for specificity toward emission from wood smoke, diesel or gasoline combustion, or meat cooking. Temperature-programmed volatilization analysis was used to characterize the thermal stabilities and volatile properties of the compounds of interest. The compounds were thermally evaporated from a quartz filter, sorbed to a solid phase microextraction (SPME) fiber, and thermally desorbed at 280 degrees C in a gas chromatograph injection port connected via a DB 1701 capillary separating column. Various experimental parameters (fiber type, time, and temperature of sorption) were optimized. It was found that high extraction yield could be achieved using a polyacrylate fiber for polar substances, such as levoglucosan, and a 7-microm polydimethylsiloxane (PDMS)-coated fiber for nonpolar compounds, such as hopanes and polyaromatic hydrocarbon. A compromise was made by selecting a carboxen/PDMS fiber, which can simultaneously extract all of the analytes of interest with moderate-to-high efficiency at 180 degrees C within a 30-min accumulation period. The optimized method was applied to the determination of levoglucosan in pine wood combustion emissions. The simplicity, rapidity, and selectivity of sample collection with a polymer-coated SPME coupled to capillary gas chromatography (GC) made this method potentially useful for atmospheric chemistry studies.     

A mass transfer model for simulating VOC sorption on building materials

The sorption of volatile organic compounds (VOCs) by different building materials can significantly affect VOC concentrations in indoor environments. In this paper, a new model has been developed for simulating VOC sorption and desorption rates of homogeneous building materials with constant diffusion coefficients and material–air partition coefficients. The model analytically solves the VOC sorption rate at the material–air interface. It can be used as a “wall function” in combination with more complex gas-phase models that account for non-uniform mixing to predict sorption process. It can also be used in conjunction with broader indoor air quality studies to simulate VOC exposure in buildings.     

Solid-phase microextraction coupled with atomic emission spectroscopy--rapid screening for volatile chlorinated compounds

Solid-phase microextraction (SPME) coupled with atomic emission spectroscopy was evaluated as a rapid screening tool for volatile halogenated compounds in water samples. After extraction, the SPME fiber was introduced to the injector where the analytes were rapidly and efficiently desorbed. The analytes entered the detector over a short period of time and produced one well-defined analyte signal. Element selective responses were measured to confirm the presence and to roughly estimate the content of volatile compounds. The total time for extraction and detection was approximately 5 min, which makes this method a rapid and promising technique for determination of total amount of volatile halogenated compounds. The proposed technique may prove useful as a screening test in order to pinpoint the samples that need further assessment by capillary gas chromatography.     

Evaluation of sample recovery of malodorous livestock gases from air sampling bags, solid-phase microextraction fibers, Tenax TA sorbent tubes, and sampling canisters

Odorous gases associated with livestock operations are complex mixtures of hundreds if not thousands of compounds. Research is needed to know how best to sample and analyze these compounds. The main objective of this research was to compare recoveries of a standard gas mixture of 11 odorous compounds from the Carboxen/PDMS 75-microm solid-phase microextraction fibers, polyvinyl fluoride (PVF; Tedlar), fluorinated ethylene propylene copolymer (FEP; Teflon), foil, and polyethylene terephthalate (PET; Melinex) air sampling bags, sorbent 2,b-diphenylene-oxide polymer resin (Tenax TA) tubes, and standard 6-L Stabilizer sampling canisters after sample storage for 0.5, 24, and 120 (for sorbent tubes only) hrs at room temperature. The standard gas mixture consisted of 7 volatile fatty acids (VFAs) from acetic to hexanoic, and 4 semivolatile organic compounds including p-cresol, indole, 4-ethylphenol, and 2'-aminoacetophenone with concentrations ranging from 5.1 ppb for indole to 1270 ppb for acetic acid. On average, SPME had the highest mean recovery for all 11 gases of 106.2%, and 98.3% for 0.5- and 24-hr sample storage time, respectively. This was followed by the Tenax TA sorbent tubes (94.8% and 88.3%) for 24 and 120 hr, respectively; PET bags (71.7% and 47.2%), FEP bags (75.4% and 39.4%), commercial Tedlar bags (67.6% and 22.7%), in-house-made Tedlar bags (47.3% and 37.4%), foil bags (16.4% and 4.3%), and canisters (4.2% and 0.5%), for 0.5 and 24 hr, respectively. VFAs had higher recoveries than semivolatile organic compounds for all of the bags and canisters. New FEP bags and new foil bags had the lowest and the highest amounts of chemical impurities, respectively. New commercial Tedlar bags had measurable concentrations of N,N-dimethyl acetamide and phenol. Foil bags had measurable concentrations of acetic, propionic, butyric, valeric, and hexanoic acids.     

室内空气中挥发性有机物采样方法进展

介绍了近年来室内空气中挥发性有机物的各种采样方法及适用范围，其中重点介绍了美国环保署最新版的TO－17方法和J.Pawliszyn发明的固相微萃取法（SPME），并对一系列的采样方法进行了比较，阐述了这些方法在国内外的应用及研究进展，同时讨论了这些方法的局限性。     

A comparison of exposure methods for SPME-based bioavailability estimates

The ability of polydimethlysiloxane coated solid phase microextraction (SPME) fibers to predict bioavailability has been documented for a number of species and compounds. There are also a variety of established methods for establishing SPME-based bioavailability estimates; however, factors such as time until equilibrium and exposure regimen could affect fiber concentrations and have not yet been thoroughly tested. Exposure time may influence SPME fiber concentrations at equilibrium. Co-exposure of the fibers with different animals or the invertebrate species used could yield different estimates than those acquired using a shaker table system to achieve equilibrium between the sediment and SPME fibers. The current study examined the effects of time and exposure method (shaker table versus co-exposure with test species) on SPME fiber concentrations for two hydrophobic compounds: permethrin and p,p′-dichlorodiphenyldichloroethylene (DDE). An additional experiment with permethrin determined whether animal densities or fiber number influenced fiber concentrations. There were significant differences between the time required for SPME fibers to reach equilibrium when co-exposed with different species or separately, but fiber concentrations at equilibrium among treatments for both compounds were similar. Furthermore, among the 12 variations in species and fiber densities, there were no significant differences among treatments indicating that neither the route of exposure, animal density, nor fiber volume influenced SPME fiber estimates. This demonstrated that SPME fiber concentrations at equilibrium were not affected by exposure conditions, increasing their versatility in environmental assessments.     

Comparison of analytical techniques for the determination of aldehydes in test chambers

The level of carbonyl compounds in indoor air is crucial due to possible health effects and the high prevalence of their potential sources. Therefore, selecting a convenient and rapid analytical technique for the reliable detection of carbonyl compound concentrations is important. The acetyl acetone (acac) method is a widely used standard procedure for detecting gaseous formaldehyde. For measuring formaldehyde along with other carbonyl compounds, the DNPH-method is commonly applied. The recommended procedure for measuring volatile organic compounds (VOCs) is sampling on Tenax TA, followed by thermal desorption and GC/MS analysis. In this study, different analytical techniques for the quantification of formaldehyde, pentanal, and hexanal are critically compared. It was found that the acac- and DNPH-method are in very good agreement for formaldehyde. In contrast, the DNPH-method significantly underestimates indoor air concentrations of the higher aldehydes in comparison to sampling on Tenax TA, although both methods are strongly correlated. The reported results are part of the EURIMA-WKI study on levels of indoor air pollutants resulting from construction, building materials and interior decoration.