Organic Compounds In Air Samples Research Articles

MOF-199-based coatings as SPME fiber for measurement of volatile organic compounds in air samples: Optimization of in situ deposition parameters

In this study MOF-199-based solid-phase microextraction coating was synthesized using an in situ solvothermal method on a stainless steel substrate. The effects of solvent, metal salt, chemical modulator, and batch composition on the physicochemical characteristics of the MOF-199 coating were studied. The thickness of the MOF-199 coating increased by 18% when 15.2 mmol of acetic acid was used as an additive. Using 99.9% butanol as the solvent improved homogeneity (smaller crystallite size) of the MOF coating and decreased coating thickness by 7.5 times compared to those of 75% ethanol. Using Cu(OAc)2·H2O as the metal precursor did not lead to the growth of the MOF-199 layer on stainless steel cores. Whilst the use of Cu(NO3)2·3H2O allowed to obtain 6-, 21-, 34-, 62-, 94- and 105 µm MOF-199 SPME coatings. Responses of 7 volatile organic compounds by 34-µm and 62-µm MOF-199-based fibers were 1.2–8.5 times higher than those of commercial PDMS/DVB. The method developed for the quantification of BTEX in the air was characterized by high linearity (R2 = 0.9909–0.9993), low limits of detection (0.03–0.09 μg/m3), and quantification (0.09–0.31 μg/m3), high repeatability (1.0–6.4%) and reproducibility (4.5–8.0%). The spike recoveries ranged from 73% to 108%.

A portable gas chromatograph for real-time monitoring of aromatic volatile organic compounds in air samples

We describe the design and performance evaluation of a portable gas chromatograph suitable for the analysis of volatile organic and odorous compounds at trace levels. The system comprises a carbon nanotube sponge preconcentrator, an electronic pressure control (EPC) unit, a temperature-programmable column module, and a fast-response photoionization detector. A built-in tablet computer controls instrumental parameters and chromatogram display functions. The compact GC with dimensions of 35 cm (l) × 26 cm (w) × 15 cm (h) is self-contained, weighing less than 5 kg without a battery pack, and uses no auxiliary compressed gases. Our design has three main advantages over conventional portable GCs: recharging configuration of ambient air as the carrier gas using a miniature diaphragm pump, precise control of column flow by the built-in canister and EPC system, and rapid thermal desorption of the preconcentrator facilitated by intrinsic resistivity of the carbon nanotube sponge. A 30 m, 0.28 mm I.D. capillary column operated at a head pressure of 14 psi provided a peak capacity of 55 for a 10 min isothermal analysis. The temperature-programmability feature could decrease the analysis time of less than 5 min for vapor mixture of benzene, toluene, ethylbenzene, and o-xylene. More than a 100-fold increase in sensitivity by preconcentrating a sample adsorption volume of 90 mL resulted in improved detection limits of 0.13 (benzene), 0.20 (toluene), 0.23 (ethylbenzene), and 0.28 (o-xylene) ppb (v/v). Our instrument displayed good stability and reproducibility of retention times (< 0.14% RSD) and intensities (< 4.5% RSD) for continuous measurements using the preconcentrator over 10 h. Thus, continuous and on-site determinations of trace volatile organic compounds in air samples with this instrument appear feasible.

Comparison of multiple calibration approaches for the determination of volatile organic compounds in air samples by solid phase microextraction Arrow and in-tube extraction

Several calibration approaches were evaluated for the quantitation of volatile organic compounds in air using miniaturized exhaustive and non-exhaustive sampling techniques, such as in-tube extraction (ITEX) and solid phase microextraction (SPME) Arrow. Eleven compounds, 2-ethyl-hexanol, hexanal, nonanal, toluene, ethyl-benzene, methyl isobutyl ketone, acetophenone, p-cymene, α-pinene, trimethylamine and triethylamine, all them found in the natural air samples, were selected as model analytes. Liquid injection, liquid standard addition to the sorbent bed and gas phase standards provided by an automatic permeation system, were evaluated in the case of ITEX packed with laboratory-made 10% polyacrylonitrile (PAN) material. Two different approaches, based on sampling of gas phase compounds from the permeation system and from sample vial containing gas phase standards, were evaluated for SPME Arrow with two different coatings, commercial divinylbenzene-poly(dimethylsiloxane) (DVB-PDMS) and laboratory-made mesoporous Mobil Composition of Matter No. 41 (MCM-41). In addition, interface model approach was used for the calculation of the real concentration of the target analytes in the sample from the total amount of analytes injected into the GC–MS in the case of SPME Arrow. Similar results were obtained with the different approaches used for the quantitation by ITEX and SPME Arrow. However, the use of gas phase standards with sample matrix similar to the natural samples, allowed the permeation system to provide the most reliable results for the quantitation of the target analytes. For this approach, linearity (expressed as r2 values) ranged between 0.991 and 0.999. The limit of detection ranged from 0.5 µg/m3 (trimethylamine, MCM-41) to 2.2 × 10−4 µg/m3 (methyl isobutyl ketone, MCM-41). In addition, the use of the fully automated permeation system provided good reproducibility values that were between 1.4% (acetophenone, MCM-41) and 7.8% (methyl isobutyl ketone, 10% PAN). The linear ranges were at least 3 order of magnitude for all the studied analytes with the exception of the calibration curve developed for trimethylamine with SPME Arrow (linear ranges between LOQ and 4.9 µg/m3 (DVB-PDMS) and LOQ and 9.8 µg/m3 (MCM-41)).

Partitioning sample collection/solvent extraction cartridge packed with octadecyl-derivatized macroporous silica particles for the analysis of sesquiterpenes in air samples.

A novel sampling device based on the partition of target analytes to the extraction medium was developed for the determination of sesquiterpenes in air samples. The extraction medium was prepared by the chemical derivatization of a specially prepared macroporous silica, with a specific surface area of 2.0 m2 /g. Taking advantage of the sample extraction, which was mainly based on the partition of sesquiterpenes between air and a C18 -bonded phase, the extracted analytes were rapidly and quantitatively desorbed just by passing a small amount of desorption solvent for subsequent analysis by gas chromatography with mass spectrometry. Several experimental conditions, such as the sampling volume and temperature, were systematically evaluated. Under optimized conditions, desorption of the extracted analytes was completed within 1 min with a desorption efficiency of more than 99.9%, achieved using 5 mL of acetone for all the evaluated sesquiterpenes. The applicability of the developed device was confirmed by the determination of several sesquiterpenes from coniferous trees. Although further improvements of the device are required for collecting large volumes or high-temperature air samples, the potential of the developed sampling device was confirmed by determining traces of semivolatile organic compounds in air samples.

A Pre-Concentrator for Explosive Vapor Detection

INTRODUCTION In recent years, the use of improvised explosive devices (IEDs) have become the preferred vehicle for terrorist attacks since they can be easily fabricated from readily available materials. This has raised concerns for the travelling public and prompted the need for a cost-effective, continuous monitoring system for explosives detection [1]. Recent works have been published regarding sensors and their ability to detect trace level explosives. Although these sensors address some of the needs for DHS, there is a limit to the modifications that can be made to these sensors in order to decrease the limit of detection. In this work, a pre-concentrator was developed as a means to increase the sensitivity of sensors used to detect vapor-phase explosives. Pre-concentrators employ sorbents that possess critical adsorption/desorption properties, thus allowing the delivery of a highly concentrated pulse of explosive vapor to the sensor. An order of magnitude improvement in detection limit was demonstrated for 2, 6-DNT and our pre-concentration approach shows considerable promise for the detection of other explosives at trace levels. EXPERIMENTAL Two microheaters were employed in our dynamically controlled sensor platform; one microheater was coated with a metal-oxide catalyst and a second microheater was left uncoated. The pre-concentrator, located upstream employed a spin-coated polystyrene film, which was deposited onto a third microheater, as shown in Figure 1. A carrier gas delivered the target molecules to the pre-concentrator for 180 seconds allowing time for collection of the explosive vapor. The pre-concentrator was then heated to desorb the explosive molecules, delivering a high concentration burst of 2, 6-DNT to both microheaters downstream. RESULTS Figure 2 illustrates the difference in signals after the thermal desorption of explosive molecules from the polymer. The response (signal) due to the pre-concentrator was nearly double that of the sensor alone. The results suggest an increase in power, signifying that an endothermic reaction occurs between the analyte and the catalyst. Figure 3 shows the detection limit obtained using the dual sensor (dynamically controlled) platform for TATP, which provides the baseline for comparison purposes; i.e. enhanced response due to pre-concentration. Further experiments were conducted to determine a gas flow that optimizes signal response, collection time and polymer film thickness and their role in the adsorption/desorption kinetics. CONCLUSION AND FUTURE WORK We have demonstrated that the addition of a polystyrene pre-concentrator to our sensor platform lowered the detection limit of 2, 6-DNT by an order of magnitude. Upon thermal desorption, there was an approximate 47% increase in sensor response. Future work will focus on developing other polymer pre-concentrators that will decrease the detection limit of other vapor phase explosives of interest. REFERENCES [1] Ras, M. R., F. Borrull, and R. M. Marcé. "Sampling and Preconcentration Techniques for Determination of Volatile Organic Compounds in Air Samples." TrAC Trends in Analytical Chemistry, 28.3 (2009): 347-61. Figure 1

Sample Preparation of Volatile Organic Compounds in Air Samples with a Novel Polyimide-Packed Cartridge Designed for the Subsequent Analysis in Capillary Gas Chromatography

Sample Preparation of Volatile Organic Compounds in Air Samples with a Novel Polyimide-Packed Cartridge Designed for the Subsequent Analysis in Capillary Gas Chromatography

Development of a method for the monitoring of odor-causing compounds in atmospheres surrounding wastewater treatment plants

This study describes the development of an analytical method based on active collection in a multisorbent Tenax TA/Carbograph 1TD tube, followed by thermal desorption and GC-MS for the determination of 16 volatile organic compounds in air samples. The analyzed compounds include ozone precursors and odor-causing compounds belonging to different chemical families (sulfur- and nitrogen-containing compounds, aldehydes, and terpenes). Two types of sorbents were tested and desorption conditions (temperature, time, and sampling, and desorption flow) were evaluated. External calibration was carried out using the multisorbent bed. Method detection limits in the range 0.2-2.0 μg m(-3) for 1 L samples were obtained. The method was applied for determining the target compounds in air samples from two different wastewater treatment plants. Most compounds were detected and toluene, limonene, and nonanal were found in particularly high concentrations with maximum values of 438, 233, and 382 μg m(-3), respectively.

Investigation of the source composition and temporal distribution of volatile organic compounds (VOCs) in a suburban area of the northwest of Spain using chemometric methods

Data sets obtained from the quantitative analysis of 43 volatile organic compounds in air samples acquired every hour in 50 different sampling days (covering the different seasons) during the years 2005 and 2006 in a suburban area of the NW Spain have been investigated by different chemometric methods including matrix augmentation principal component analysis (MA-PCA) and parallel factor analysis (PARAFAC). The application of these two chemometric methods allowed the estimation of the chemical profiles of the main pollution sources operating over the investigated location and also unravelling their main temporal patterns. Using PCA, it was possible to identify four main different sources related to different VOC families (aromatic, aliphatic, halogenated and biogenic). However, the temporal emission patterns could not be properly resolved when the data of each individual sampling day were considered separately. When VOC emissions during the same week and for the whole year (50 sampling days) were simultaneously analysed by a new matrix augmentation PCA (MA-PCA) strategy and by PARAFAC, a better recovery and description of the daily and hourly temporal trends were achieved. In fact, the combination of MA-PCA with the score rearrangement followed by the first singular value decomposition allowed the extraction of daily cyclical emission trends that were subjacent in the original non-trilinear data matrix by means of a very simple methodology facilitating the interpretation of these complex data sets.

Sampling and preconcentration techniques for determination of volatile organic compounds in air samples

Because air is complex and heterogeneous, continuously evolving in time and space and being influenced by atmospheric and geographical conditions, sampling is crucial in air analysis. Moreover, due to the low levels of pollutants present in the atmosphere, enrichment is often required. This review deals with the most common techniques for sampling and preconcentration of volatile organic compounds (VOCs) in air samples (e.g., whole-air collection in containers, which is usually combined with preconcentration step, and solid-sorbent enrichment methods). We also describe solid sorbents used to trap VOCs in air, and subsequent desorption techniques. In recent years, there have been many efforts to improve on-line analysis methods, which offer real-time data and are useful in providing rapid results. We examine the application of sorbent trapping to on-line analysis and other techniques for on-line analysis (e.g., membrane extraction and selected-ion-flow-tube mass spectrometry).

Characterization of sorption mechanisms of solid-phase microextraction with volatile organic compounds in air samples using a linear solvation energy relationship approach

The linear solvation energy relationship (LSER) model was used to characterize interactions responsible for sorption of volatile organic compounds (VOCs) in air samples on six different solid-phase microextraction (SPME) fibers at 296 K and zero relative humidity. The polydimethylsiloxane and polyacrylate fibers sorption data were also modeled at different relative humidities in the range of 10–90% and influence of water vapors on the extraction process is discussed. The LSER equations were obtained by a multiple regression of the distribution coefficients of 14 probe solutes on an appropriate SPME fiber against the solvation parameters of the solutes. The derived LSER equations successfully predicted the VOC distribution coefficients and the selectivity of individual SPME fibers for the various volatile solutes. The LSER approach coupled with SPME is a relatively simple and reliable tool to rapidly characterize the sorption mechanism of VOCs with various stationary phases and may potentially be applied to design and test new chromatographic materials for sampling or separation of VOCs.

Genotoxicity associated to exposure to Prestige oil during autopsies and cleaning of oil-contaminated birds

After the accident involving the oil tanker Prestige in November 2002 near 63,000 tons of heavy oil reached Galician coast (Northwest of Spain). This unleashed a large movement of volunteers to collaborate in several cleaning tasks. The aim of this study was to determine whether handling of Prestige oil-contaminated birds during autopsies and cleaning may have resulted in genotoxic damage. We have also evaluated the possible influence of DNA repair genetic polymorphisms (XRCC1 codons 194 and 399, XRCC3 codon 241 and APE1 codon 148) on susceptibility to the genotoxic effects evaluated. Exposure levels were analysed by determining volatile organic compounds in air samples. Peripheral blood samples were obtained from 34 exposed and 35 controls, and comet assay and micronucleus (MN) test were carried out. Genotyping was performed following PCR-RFLP procedures. Results obtained have shown significantly higher DNA damage, but not cytogenetic damage, in exposed individuals than in controls, related to time of exposure. Among exposed individuals, carriers of the variant alleles XRCC1 399Gln and APE1 148Glu have shown altered DNA damage with regard to wild-type homozygotes, suggesting exposure–genotype interactions. No effect of the DNA repair genetic polymorphisms analysed was observed in the MN test.

Temperature-programmed desorption for membrane inlet mass spectrometry

We present a novel technique for analyzing volatile organic compounds in air samples using a solid adsorbent together with temperature-programmed desorption and subsequent detection by membrane inlet mass spectrometry (TPD-MIMS). The new system has the advantage of a fast separation of compounds prior to the detection by MIMS. The gaseous sample is simply adsorbed on the adsorbent, which is then rapidly heated from 30 °C to 250 °C at a rate of 50 °C/min. Trapped organic compounds are released from the adsorbent into a helium stream at different temperatures depending on the strength of the interaction between the individual compound and the adsorbent. The helium stream carries the desorbed compounds to a membrane inlet (90 °C) equipped with a thin (25 μm) silicone membrane. The thin membrane and the high temperature of the membrane inlet allows most volatile compounds to diffuse through the membrane into the mass spectrometer in a few seconds. In this fashion we could completely separate many similar volatile compounds, for example toluene from xylene and trichloroethene from tetrachloroethene. Typical detection limits were at low or sub-nanogram levels, the dynamic range was 3 orders of magnitude, and the analysis time for a mixture was about 3–4 minutes. © 1998 John Wiley & Sons, Ltd.

Evaluation of gas chromatography coupled with ion mobility spectrometry for monitoring vinyl chloride and other chlorinated and aromatic compounds in air samples

AbstractThe objective of this research was to evaluate, in the laboratory, the potential of gas chromatography/ion mobility spectrometry (GC/IMS) for monitoring vinyl chloride and other organic compounds in air samples in the field. It was determined that GC/IMS has the potential to directly detect vinyl chloride in air at the 2 ppbv level, and when concentrated on an adsorbent trap from a 1 L sample of air, detection could be lowered to the 0.02 ppbv level. From a comparative investigation of 18 EPA priority pollutants and 34 common vapor‐phase organic compounds, many compounds were found to provide a more sensitive response in IMS than vinyl chloride, indicating that GC/IMS would be broadly applicable to the direct detection of vapor‐phase organics in air.Operating parameters including drift gas, spectrometer temperature, and sample‐inlet position were evaluated and discussed with respect to sensitivity and resolution. High temperature dramatically increased sensitivity to vinyl chloride. Vinyl chloride was shown to produce both negative and positive ion mobility spectra, with the negative‐mode spectra resulting from electron‐capture dissociation of the vinyl chloride. The limit of detection for vinyl chloride was found to be 7 pg/s. Limits of detection for 18 EPA priority pollutants were determined and compared to vinyl chloride. The responses of 34 other vapor‐phase organic compounds were also compared to that of vinyl chloride. Non‐selective, positive‐ion detection of 30 of the 34 compounds was demonstrated along with selective, electron‐capture‐type detection of 29 of them. Chloride‐specific and bromide‐specific detection illustrated the advantages of selected‐ion monitoring in IMS.

Capillary columns in series for GC analysis of volatile organic pollutants in atmospheric and alveolar air

AbstractAnalysis of volatile organic compounds in air samples requires high resolution capillary gas chromatography. When the sample contains both polar and non‐polar compounds, use of only one type of stationary phase can be unsuitable if it leads to the preferential separation of one kind of component having the same polarity at the expense of the separation of other classes of component.This paper describes the coupling of fused silica capillary columns of different polarity and length in order to achieve the separation of such complex mixtures. The combination is evaluated with a 42 component standard mixture and then applied to various atmospheric air samples and alveolar air of exposed subjects to demonstrate the capabilities of the complete sampling and separation technique.