Development of a versatile,easy and rapid atmospheric monitor for benzene,toluene, ethylbenzene and xylenes determination in air

A new procedure for the passive sampling in air of benzene, toluene, ethylbenzene and xylene isomers (BTEX) is proposed. A low-density polyethylene layflat tube filled with a mixture of solid phases provided a high versatility tool for the sampling of volatile compounds from air. Several solid phases were assayed in order to increase the BTEX absorption in the sampler and a mixture of florisil and activated carbon provided the best results. Direct head-space-gas chromatography–mass spectrometry (HS-GC–MS) measurement of the whole deployed sampler was employed for a fast determination of BTEX. Absorption isotherms were used to develop simple mathematical models for the estimation of BTEX time-weighted average concentrations in air. The proposed samplers were used to determine BTEX in indoor air environments and results were compared with those found using two reference methodologies: triolein-containing semipermeable membrane devices (SPMDs) and diffusive Radiello samplers. In short, the developed sampling system and analytical strategy provides a versatile, easy and rapid atmospheric monitor (VERAM).     

Headspace-mass spectrometry determination of benzene, toluene and the mixture of ethylbenzene and xylene isomers in soil samples using chemometrics

A simple and fast method has been developed for the determination of benzene, toluene and the mixture of ethylbenzene and xylene isomers (BTEX) in soils. Samples were introduced in 10 mL standard glass vials of a headspace (HS) autosampler together with 150 μL of 2,6,10,14-tetramethylpentadecane, heated at 90 °C for 10 min and introduced in the mass spectrometer by using a transfer line heated at 250 °C as interface. The volatile fraction of samples was directly introduced into the source of the mass spectrometer which was scanned from m/z 75 to 110. A partial least squares (PLS) multivariate calibration approach based on a classical 3³ calibration model was build with mixtures of benzene, toluene and o-xylene in 2,6,10,14-tetramethylpentadecane for BTEX determination. Results obtained for BTEX analysis by HS-MS in different types of soil samples were comparables to those obtained by the reference HS-GC-MS procedure. So, the developed procedure allowed a fast identification and prediction of BTEX present in the samples without a prior chromatographic separation.     

Determination of benzene, toluene, ethylbenzene and xylenes in soils by multiple headspace solid-phase microextraction

Multiple headspace-solid phase microextraction (MHS-SPME) is a recently developed technique for the quantification of analytes in solid samples that avoids the matrix effect. This method implies several consecutive extractions from the same sample. In this way, the total area corresponding to complete extraction can be directly calculated as the sum of the areas of each individual extraction when the extraction is exhaustive, or through a mathematical equation when it is not exhaustive. In this paper, the quantitative determination of benzene, toluene, ethylbenzene and xylene isomers (BTEX) in a certified soil (RTC-CRM304, LGC Promochem) and in a contaminated soil by multiple HS-SPME coupled to a gas chromatography-flame ionisation detector (GC-FID) is presented. BTEX extraction was carried out using soil suspensions in water at 30 degrees C with a 75 microm carboxen-polydimethylsiloxane (CAR-PDMS) fibre and calibration was carried out using aqueous BTEX solutions at 30 degrees C for 30 min with the same fibre. BTEX concentration was calculated by interpolating the total peak area found for the soils in the calibration graphs obtained from aqueous solutions. The toluene, ethylbenzene, o-xylene and m,p-xylene concentrations obtained were statistically equal to the certified values.     

Phenylacetylene as a new surrogate standard for the determination of BTEX by GC/FID

Benzene, toluene, ethylbenzene, xylene (short form: BTEX) and other monoaromatic compounds are environmental contaminants which are often analyzed by GC/FID. For the calculation of BTEX concentrations in water samples normally external quantification with defined BTEX solutions is sufficient. However, for accurate quantification of BTEX in complex matrices it is necessary to use internal standards, e.g. ¶1-chlorohexane. Isotopes of BTEX are usually the best alternative but they are only applicable to GC/MS, because their retention times are similar to the original BTEX. 1-Chlorohexane and phenylacetylene were compared with respect to their quality as internal standards. Good results were obtained with ¶the monoaromatic phenylacetylene as a surrogate standard. The physical properties of phenylacetylene are very similar to BTEX species and it normally does not occur in environmental samples. 1-Chlorohexane was more strongly adsorbed on the used soil than BTEX during sample preparation. This fact suggests that the single aromatic rings of BTEX and phenylacetylene are mainly responsible for the adsorption behavior.     

Phenylacetylene as a new surrogate standard for the determination of BTEX by GC/FID

Benzene, toluene, ethylbenzene, xylene (short form: BTEX) and other monoaromatic compounds are environmental contaminants which are often analyzed by GC/FID. For the calculation of BTEX concentrations in water samples normally external quantification with defined BTEX solutions is sufficient. However, for accurate quantification of BTEX in complex matrices it is necessary to use internal standards, e.g. 1-chlorohexane. Isotopes of BTEX are usually the best alternative but they are only applicable to GC/MS, because their retention times are similar to the original BTEX. 1-Chlorohexane and phenylacetylene were compared with respect to their quality as internal standards. Good results were obtained with the monoaromatic phenylacetylene as a surrogate standard. The physical properties of phenylacetylene are very similar to BTEX species and it normally does not occur in environmental samples. 1-Chlorohexane was more strongly adsorbed on the used soil than BTEX during sample preparation. This fact suggests that the single aromatic rings of BTEX and phenylacetylene are mainly responsible for the adsorption behavior.     

Fullerenes as sorbent materials for benzene, toluene, ethylbenzene, and xylene isomers preconcentration

A simple and novel SPE system for benzene, toluene, ethylbenzene, and xylene isomers (BTEX) compounds in water is proposed in which samples are directly propelled from a 15 mL glass vial through a sorbent column by means of a needle, thereby avoiding evaporative losses and the sorption of BTEX on the manifold materials. Following elution with 150 microL of ethyl acetate, 1 microL of extract is injected into a gas chromatograph-mass spectrometer system. A comparative study of various sorbent materials (C60 fullerene, Tenax TA, and RP-C18) revealed C60 fullerene to be the best choice in terms of sensitivity (a likely result of its increased sample breakthrough volume), precision (the surfactant medium used to prepare samples minimizes evaporative losses), selectivity (C60 fullerene only interacts with nonpolar aromatic compounds), and reusability (columns containing 60 mg of C60 fullerene remain serviceable for at least 6 months). This C60 fullerene-based method exhibits a linear range of 0.1-100 microg/L, a detection limit of 0.04 microg/L, and an RSD of ca. 3%. It was applied to the determination of BTEX in various types of water including sea and waste water with good precision.     

Comparative analysis of bias in the collection of airborne pollutants: Tests on major aromatic VOC using three types of sorbent-based methods

This study was undertaken to establish one of the most reliable sampling methods and to precisely evaluate the bias involved in the collection of airborne pollutant samples. For the purpose of our study, we investigated the performance of three different types of sampling techniques by measuring major aromatic volatile organic compounds (VOC) in outdoor air; the target analytes specifically include benzene, toluene, ethylbenzene, and xylene (commonly called BTEX). As the first step of our approach, we designed and developed a multi-channel sampling system consisting of a six-port mass flow controller (SJU-MFC) system. Because this system allowed the collection of up to six replicate samples, our measurement results were analyzed and screened statistically for the derivation of high-quality BTEX data. The feasibility of this sampling system was further tested through a comparison with concurrent measurement data sets obtained by two additional, but independent, sampling techniques: (1) automatic continuous sampler (ACS) and (2) on-line GC (O-GC) system. Based on the data sets collected concurrently by three different sampling methods, we attempted to evaluate the compatibility of sampling techniques. Although the results obtained by SJU-MFC system were not statistically different from those of the O-GC system, they were moderately distinguishable from those of ACS. Such patterns were seen consistently, when examined by correlation analysis. The overall results of our study thus generally point out that the compatibility of data sets, when the proper caution is taken, improve significantly among different sampling methodologies.     

Field analysis of benzene, toluene, ethylbenzene and xylene in water by portable gas chromatography-microflame ionization detector combined with headspace solid-phase microextraction

In this work, portable gas chromatography-microflame ionization detection (portable GC-μFID) coupled to headspace solid-phase microextraction (HS-SPME) was developed for the field analysis of benzene, toluene, ethylbenzene and xylene (BTEX) in water samples. The HS-SPME parameters such as fiber coating, extraction times, stirring rate, the ratio of headspace volume to sample volume, and sodium chloride concentration were studied. A 65 μm poly(dimethylsiloxane)-divinylbenzene (PDMS-DVB) SPME fiber, 900 rpm, 3.0 ml of headspace (1.0 ml water sample in 4.0 ml vial), and 35% sodium chloride concentration (w/v) were respectively chosen for the best extraction response. An extraction time of 1.0 min was enough to extract BTEX in water samples. The relative standard deviation (R.S.D.) for the procedure varied from 5.4% to 8.3%. The method detection limits (MDLs) found were lower than 1.5 μg/l, which was enough sensitive to detect the BTEX in water samples. The optimized method was applied to the field analysis of BTEX in wastewater samples. These experiment results show that portable GC-μFID combined with HS-SPME is a rapid, simple and effective tool for field analysis of BTEX in water samples.     

Large Volume Headspace Analysis Using Solid-Phase Microcolumn Extraction

A rapid and simple large volume headspace (HS) sampling technique termed headspace solid-phase microcolumn extraction (HS-SPMCE) is described. HS gas above a liquid or solid sample is aspirated by attaching a gas-tight syringe onto a glass thermal desorption tube filled with Tenax sorbent. The trapped analytes are recovered by thermal desorption for gas chromatography–mass spectrometry (GC–MS) analysis. Benzene, toluene, ethylbenzene and the xylene isomers (BTEX) are used as model compounds to demonstrate the application of the extraction procedure for water samples. The results of the tests of the effect of agitation time and aspiration rate on recovery of the analytes show a good robustness of the method. BTEX are determined in the linear range from 0.5 to 50.0 μg L^?1 with limits of detection (3 σ) ranging within 0.09–0.14 μg L^?1 (MS was in scan mode). The method provides a good repeatability (RSD < 9%) and only a negligible carryover effect was observed ( ≤0.05%) when analysing BTEX at concentration 50.0 μg L^?1.     

The evaluation of a tenax GR diffusive sampler for the determination of benzene and other volatile aromatics in outdoor air

The applicability of a tube-type diffusive sampler as an environmental monitor for benzene, toluene, ethylbenzene and xylene (BTEX) is reported. Uptake rates have been experimentally determined for a novel type adsorbent, Tenax GR, and compared to theoretical values. It is shown, that the uptake rates are virtually independent of environmental parameters within the experimental conditions studied. The response of the sampler to transient changes in concentrations has been determined in the laboratory. It is found that the sampler is capable of following an extreme concentration profile. Field comparisons with pumped samplers have been performed and good agreement is observed between the results of the two independent methods. The samplers have also been applied as environmental monitors at different locations.     

Simultaneous determination of methyl tert.-butyl ether and its degradation products,other gasoline oxygenates and benzene,toluene, ethylbenzene and xylenes in Catalonian groundwater by purge-and-trap-gas chromatography-mass spectrometry

In Catalonia (northeast Spain), a monitoring program was carried out to determine methyl tert.-butyl ether (MTBE), its main degradation products, tert.-butyl alcohol (TBA), tert.-butyl formate (TBF), and other gasoline additives, the oxygenate dialkyl ethers ethyl tert.-butyl ether, tert.-amyl methyl ether and diisopropyl ether and the aromatic compounds benzene, toluene, ethylbenzene and xylene (BTEX) in 21 groundwater wells that were located near different gasoline point sources (a gasoline spill and underground storage tank leakage). Purge-and-trap coupled to gas chromatography-mass spectrometry was optimised for the simultaneous determination of the above mentioned compounds and enabled to detect concentrations at ng/l or sub-microg/l concentrations. Special attention was given to the determination of polar MTBE degradation products, TBA and TBF, since not much data on method performance and environmental levels are given on these compounds in groundwater. All samples analysed contained MTBE at levels between 0.3 and 70 microg/l. Seven contaminated hot spots were identified with levels up to US Environmental Protection Agency drinking water advisory (20-40 microg/l) and a maximum concentration of 670 microg/l (doubling the Danish suggested toxicity level of 350 microg/l). Samples with high levels of MTBE contained 0.1-60 microg/l of TBA, indicating (but not proving) in situ degradation of parent compound. In all cases, BTEX was at low concentrations or not detected showing less solubility and persistence than MTBE. This fact confirms the suitability of MTBE as a tracer or indicator of long-term gasoline contamination than the historically used BTEX.     

Direct screening of water samples for benzene hydrocarbon compounds by headspace liquid-phase microextraction-gas chromatography

The applicability of headspace liquid-phase microextraction and gas chromatography is evaluated for the expeditious and reliable screening of tap and drinking water samples for selected volatile organic compounds (viz., benzene, toluene, ethylbenzene, and xylene isomers, BTEX). The method uses 3.5 microL of n-hexadecane as extraction solvent, 10 min extraction time with stirring at 1250 rpm, at 20 degrees C and 0.38 g/mL salt addition. The enrichment factors of this method are from 135 to 213. Limits of detection are in the range of 4.1-23.5 ng/L. The relative standard deviations at 0.05, 50, 200, and 400 microg/L of spiking levels are in the range of 0.61%-4.01%. Recoveries of six BTEX from drinking water at these spiking levels are between 95.4% and 104.4%.     

固相微萃取涂层的制备及其在水体和气态基质中的应用

采用物理涂渍的方法制备了γ-Al2O3固相微萃取涂层。通过γ-Al2O3固相微萃取（SPME）-气相色谱（GC）联用技术,对水中痕量苯系物苯、甲苯、乙苯、二甲苯异构体(BTEXs)进行萃取分析,结果表明该涂层具有热稳定性强(最高使用温度可达350 ℃)、灵敏度高(检测限为1~10 μg/L)以及制备重复性好（相对标准偏差为8.3%）的特点;同时该涂层对气态基质中的污染物亦可进行萃取分析。     

Isomeric identification by laser control mass spectrometry

The influence shaped femtosecond laser pulses have on molecular photofragmentation and ionization, coupled with the intrinsic sensitivity of mass spectrometry, results in a powerful tool for fast, accurate, reproducible and quantitative isomeric identification. Complex phase functions are introduced to enhance differences during the laser-molecule interactions, which depend on geometric structure, resulting in different fragmentation fingerprints. A full account is given on the setup and results leading to a technique that can be used to distinguish between compounds normally indistinguishable by conventional electron ionization mass spectrometry. We demonstrate geometric and structural isomer identification of cis-/trans-3-heptene, cis-/trans-4-methyl-2-pentene, o-/p-cresol and o-/p-xylene. For the positional isomers of xylene we present a complete dataset consisting of 1024 different phases to explore phase complexity. A selection of two phases from that data can then be used to achieve quantitative identification in mixtures of xylene isomers. Finally, we evaluate receiver operational curves obtained from our experimental data to demonstrate the reliability that can be achieved by femtosecond laser control mass spectrometry.     

Optimisation of solid-phase microextraction of volatiles

The results of a systematic study on the precision and repeatability of measurements of the headspace solid phase micro-extraction (SPME) with open-cap vials in combination with capillary gas chromatography in comparison with septum-sealed vials are reported. Benzene, toluene, ethylbenzene, and xylene isomers (BTEX) were used as the target analytes in the investigation of spiked water samples at concentration levels of 42.5 μg l⁻¹. The dependence of a sample volume versus peak area showed maximum SPME recovery. The influence of sample volume on the precision and the time of taking the sample on the losses of volatile analytes was examined.     

Cobalt oxide nanoparticles as a novel high-efficiency fiber coating for solid phase microextraction of benzene,toluene, ethylbenzene and xylene from aqueous solutions

In this work cobalt oxide nanoparticles were introduced for preparation of a novel solid phase microextraction (SPME) fiber coating. Chemical bath deposition (CBD) technique was used in order for synthesis and immobilization of the Co₃O₄ nanomaterials on a Pt wire for fabrication of SPME fiber. The prepared cobalt oxide coating was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The fiber was evaluated for the extraction of benzene, toluene, ethylbenzene and xylene (BTEX) in combination with GC–MS. A simplex optimization method was used to optimize the factors affecting the extraction efficiency. Under optimized conditions, the proposed fiber showed extraction efficiencies comparable to those of a commercial polydimethylsiloxane (PDMS) fiber toward the BTEX compounds. The repeatability of the fiber and its reproducibility, expressed as relative standard deviation (RSD), were lower than about 11%. No significant change was observed in the extraction efficiency of the new SPME fiber after over 50 extractions. The fiber was successfully applied to the determination of BTEX compounds in real samples. The proposed nanostructure cobalt oxide fiber is a promising alternative to the commercial fibers as it is robust, inexpensive and easily prepared.     

Improved detection of toxic chemicals using bioluminescent bacteria

A sensitive, rapid and simple bioluminescent (BL) assay using bioluminescent bacteria to detect the toxic activity of several chemicals is described. This assay is based on the measurement of inhibition of light production of a bioluminescent bacterial strain, isolated from seawater, in the presence of different toxins like heavy metals, organic chemicals, such as benzene, toluene, ethylbenzene, xylene (BTEX) and a wide range of pesticides in environmental samples. The improvement with respect to other commercial and non-commercial bioluminescent assays consists of the possibility to work at room temperature without the need to thermostat, thus allowing the use of simpler and low cost instruments, or to improve the assay using a microplate format, which makes it possible to analyse several samples also continuously for several hours. Using lyophilised bacteria, the assay is performed in less than an hour, without any bacterial cultivation, which makes the test suitable for rapid and sensitive evaluation of chemical pollutants in environmental samples.     

Analysis of organic compounds in environmental samples by headspace solid phase microextraction

The analysis of samples contaminated by organic compounds is an important aspect of environmental monitoring. Because of the complex nature of these samples, isolating target organic compounds from their matrices is a major challenge. A new isolation technique, solid phase microextraction, or SPME, has recently been developed in our laboratory. This technique combines the extraction and concentration processes into one step; a fused silica fiber coated with a polymer is used to extract analytes and transfer them into a GC injector for thermal desorption and analysis. It is simple, rapid, inexpensive, completely solvent-free, and easily automated. To minimize matrix interferences in environmental samples, SPME can be used to extract analytes from the headspace above the sample. The combination of headspace sampling with SPME separates volatile and semi-volatile analytes from non-volatile compounds, thus greatly reducing the interferences from non-target compounds. This paper reports the use of headspace SPME to isolate volatile organic compounds from various matrices such as water, sand, clay, and sludge. By use of the technique, benzene, toluene, ethyl-benzene, and xylene isomers (commonly known as BTEX), and volatile chlorinated compounds can be efficiently isolated from various matrices with good precision and low limits of detection. This study has found that the sensitivity of the method can be greatly improved by the addition of salt to water samples, water to soil samples, or by heating. Headspace SPME can also be used to sample semi-volatile compounds, such as PAHs, from complex matrices.     

Detection of substituted benzenes in water at the pg/ml level using solid-phase microextraction and gas chromatography-ion trap mass spectrometry.

Solid-phase microextraction (SPME) is combined with gas chromatography-ion trap mass spectrometry (GC-IT-MS) for the analysis of benzene, toluene, ethyl benzene and xylene isomers (BTEX) in water. SPME is a recent technique for extracting organics from an aqueous matrix into a stationary phase immobilized on a fused-silica fiber. The analytes are thermally desorbed directly in the injector of a gas chromatograph. The wide linear dynamic range (five orders of magnitude) and pg sensitivity of the ion trap mass spectrometer in its full scan mode is an ideal detector for identifying and quantifying the analytes extracted with an SPME device. The combined method SPME-GC-IT-MS, using fibers coated with a 100-microns polydimethylsiloxane coating, showed a limit of quantitation (LOQ) of 50 pg/ml benzene in water. This corresponds to 5 pg of benzene absorbed onto the fiber. The limit of detection (LOD) was 15 pg/ml benzene. For o-xylene spiked at 50 pg/ml in water 50 pg were absorbed by the fiber indicating an LOQ and LOD 10 times better than for benzene. The detection limits obtained exceed the requirements of both the United States Environmental Protection Agency method 524.2 and the Ontario Municipal/Industrial Strategy for Abatement program, which range from 30 to 80 pg/ml and 500 to 1100 pg/ml, respectively. The linearity of the method extended over five orders of magnitude. Relative standard deviation ranged from 2.7 to 5.2% for 15 ng/ml BTEX in water and from 5.5 to 7.5% for 50 pg/ml BTEX in water. SPME-GC-IT-MS was used to evaluate the contamination level in laboratory, potable and wastewater sources.     

Real-Time Distinguishing of the Xylene Isomers Using Photoionization and Dissociation Mass Spectra Obtained by Femtosecond Laser Mass Spectrometry (FLMS)

Abstract

Distinguishing chemicals and improvement on analytical methods has a direct impact on modern chemical analysis. In this work, the dissociative ionization of xylene isomers was investigated using a femtosecond laser mass spectrometry (FLMS) method with a custom-built linear time-of-flight (TOF) instrument. Laser beams at 800?nm and 400?nm were used and intensity-dependent analysis of the obtained mass spectra was performed using principal component analysis (PCA) to distinguish the xylene isomers, which give identical mass spectra in appearance that cannot be distinguished using normal mass spectrometry methods. The results show that there is a statistically highly significant difference between the xylene isomers for two principal components (1 ? α?>?99.99%) and minimal information loss (<5%) took place during the PCA procedure. Also, the use of the k-medoid clustering method showed that the isomers may be distinguished in real-time for a wide range of ionization laser pulse powers with approximately 99% accuracy. The results suggest that real-time isomer analysis by the FLMS method is suitable for mass spectral identification applications. The FLMS method has been shown to be an important alternative to other mass spectrometric methods that use different ionization mechanisms.