A novel quantitation method for phthalates in air using a combined thermal desorption/gas chromatography/mass spectrometry application

In this study, a novel quantitation method was developed to facilitate the simple and effective sampling and analysis of phthalates in air based on a sorbent tube-thermal desorption-gas chromatography-mass spectrometry system combination. The performance of the thermal desorption-based analysis was assessed using three different sorbent combinations [1]: quartz wool (QW) [2], glass wool (GW), and [3] quartz wool plus Tenax TA (QWTN) in terms of relative recovery in reference to a direct injection method. There was no significant difference in the average recovery rate for seven target phthalates based on sorbent tube type (QW, 70.2 ± 4.28; GW, 73.2 ± 8.8; and QWTN, 72.5 ± 5.02%). However, the recovery rate of phthalates in each sorbent tube type was distingusihed by physicochemical properties of the target compound (e.g., molecular weight and boiling point). The recovery rate of the QW tube was high for dimethyl phthalate and diethyl phthalate compared to other sorbent tubes, while that of the GW tube exhibited greater values for dibutyl phthalate, benzyl butyl phthalate, di(2-ethylhexyl) adipate, di(2-ethylhexyl) phthalate, and di-n-octyl phthalate. The simple sorbent tube-thermal desorption approach is feasible for the quantitation of seven phthalates present at 0.45–24.5 ng m⁻³ levels in actual air samples (20 L).     

Gas chromatographic approach for the determination of carbonyl compounds in ambient air

In this study, an effort was made to apply gas chromatography (GC) with a flame ionization detector (FID) to the determination of gaseous carbonyls (without derivatization) at sub ppb level. A GC system interfaced with a multi-function thermal desorber system (TD) was hence tested for the collection and analysis of gaseous carbonyls. During this study, the calibration properties of five carbonyl compounds - acetaldehyde, propionaldehyde, butyraldehyde, isovaleraldehyde, and valeraldehyde - were evaluated by varying the operation conditions of the TD system (i.e., sample transfer approaches and sorbent types of cold trap). The results were generally discernible between compounds (light and heavy carbonyls) and/or between selected concentration levels. Most interestingly, the GC detection properties of the lighter aldehydes (acetaldehyde and propionaldehyde) varied significantly, as they were sensitively affected by the types of cold trap combination. However, the heavier aldehydes - butyraldehyde, isovaleraldehyde, and valeraldehyde - maintained highly constant trends for GC calibration. According to this study, a GC-based quantification of aldehydes can be completed by an optimized setup of TD system.     

Determination of volatile organic compounds in urban and industrial air from Tarragona by thermal desorption and gas chromatography-mass spectrometry

This study describes the optimisation of an analytical method to determine 54 volatile organic compounds (VOCs) in air samples by active collection on multisorbent tubes, followed by thermal desorption and gas chromatography-mass spectrometry. Two multisorbent beds, Carbograph 1/Carboxen 1000 and Tenax/Carbograph 1TD, were tested. The latter gave better results, mainly in terms of the peaks that appeared in blank chromatograms. Temperatures, times and flow desorption were optimised. Recoveries were higher than 98.9%, except methylene dichloride, for which the recovery was 74.9%. The method's detection limits were between 0.01 and 1.25 μg m⁻³ for a volume sample of 1200 ml, and the repeatability on analysis of 100 ng of VOCs, expressed as relative standard deviation for n = 3, was lower than 4% for all compounds. Urban and industrial air samples from the Tarragona region were analysed. Benzene, toluene, ethylbenzene and xylenes (BTEX) were found to be the most abundant VOCs in urban air. Total VOCs in urban samples ranged between 18 and 307 μg m⁻³. Methylene chloride, 1,4-dichlorobenzene, chloroform and styrene were the most abundant VOCs in industrial samples, and total VOCs ranged between 19 and 85 μg m⁻³.     

Optimised chromatographic method for the measurement of selected polychlorinated biphenyls in ambient air

The focus of this study was to optimise selected polychlorinated biphenyl analysis in air by gas chromatography. Sample preparation was improved by using an automatic solid/liquid extraction system and columns with 1.5 g of Florisil for cleaning extracts. Better precision on clean-up results was obtained from Florisil cartridges, when compared to those obtained with silica gel. Analytical procedure was checked by participating in an inter-comparison exercise. Finally, we have considered usefulness of evaluating uncertainties associated to our method because of the large handling samples and the extremely low concentrations of PCBs in ambient air.     

Comparative study of solvent extraction and thermal desorption methods for determining a wide range of volatile organic compounds in ambient air

This paper compares two analytical methods for determining levels of 90 volatile organic compounds (VOCs) commonly found in industrial and urban atmospheres. Both methods are based on two official methods for determining benzene levels and involve collecting samples by active adsorptive enrichment on solid sorbents. The first method involves solvent extraction and uses activated charcoal as a sorbent. After sampling, the sorbent is extracted with 1 mL of carbon disulfide and then 1 μL of the extract is analysed in a GC-MS. The second method involves thermal desorption (TD) and uses Tenax TA and Carbograph 1TD as sorbents, which allows the whole sample to be analysed. In general, the thermal desorption method showed the best repetitivity and recovery and the lowest limit of detection and quantification for all target compounds. Because of its lower sensitivity, the solvent extraction method needs the preconcentration of large sample volumes of air (720 L vs. 2.64 L for the thermal desorption method) to yield similar limits of detection.The performance of both methods in real samples was tested in a location near to a petrochemical complex. The results of the 24-h samples for the solvent extraction method were compared with the average of 12 2-h samples for the TD method. In some cases, both methods found differences in the VOC concentrations, especially in those compounds whose concentrations fluctuate significantly during the day.     

New method for determination of trihalomethanes in exhaled breath: Applications to swimming pool and bath environments

A method for the estimation of the human intake of trihalomethanes (THMs), namely chloroform, bromodichloromethane, dibromochloromethane and bromoform, during showering and bathing is reported. The method is based on the determination of these compounds in exhaled breath that is collected by solid adsorption on Tenax using a device specifically designed for this purpose. Instrumental measurements were performed by automatic thermal desorption coupled to gas chromatography with electron capture detection. THMs in exhaled breath samples were determined during showering and swimming pool attendance. The levels of these compounds in indoor air and water were also determined as reference for interpretation of the exhaled breath results. The THM concentrations in exhaled breath of the volunteers measured before the exposure experiments showed a close correspondence with the THMs levels in indoor air where the sampler was located. Limits of detection in exhaled breath were dependent on THM analytes and experimental sites. They ranged between 170 and 710 ng m⁻³ in the swimming pool studies and between 97 and 460 ng m⁻³ in the showering studies. Application of this method to THMs determination during showering and swimming pool activities revealed statistically significant increases in THMs concentrations when comparing exhaled breath before and after exposure.     

In-tube silylation in combination with thermal desorption gas chromatography-mass spectrometry for the determination of hydroxy polycyclic aromatic hydrocarbons in water

For the determination of hydroxy polycyclic aromatic hydrocarbons (OH-PAHs), a simple and sensitive method based on the silylation of OH-PAHs using N,O-bis(trimethylsilyl)trifluoro acetamide (BSTFA) in combination with thermal desorption gas chromatography-mass spectrometry (TD-GC-MS) is described. This method was performed by way of direct silylation in a TD unit (in-tube silylation) coupled to a GC inlet. Both a good detection limit (4.1-1200 pg L⁻¹, S/N = 3) and higher precision (relative standard deviation < 4% on average) were achieved for 21 OH-PAHs studied using the full scan mode (m/z = 40-550). These good results were due to the highly efficient derivatization of the OH-PAHs, which was attributed to not only the moisture-free environment and programmable heating in the TD tube for the in-tube silylation, but also to the constant vapor generation of BSTFA using a capillary introduction method. Although recoveries of 21 OH-PAHs from the spiked 3% NaCl solution ranged between 9 and 304%, those of 11 OH-PAHs fell between 70 and 130% (R.S.D. < 11%). Thus, the present method was applied to a seawater sample collected from an industrial port, and nine OH-PAHs including 1- and 2-OH-fluorenone and 1,8- and 2,6-OH-anthraquinone were determined at concentrations of 0.49-5.8 ng L⁻¹. Along with these OH-PAHs, significant amounts of several long chain fatty acids (C₁₂, C₁₆, C₁₈, C₂₀ and C₂₂) and bisphenol A were also identified in the seawater sample using reference data in a library of mass spectra (match factor: >80%).     

Sorbent-based sampling methods for volatile and semi-volatile organic compounds in air. Part 2. Sorbent selection and other aspects of optimizing air monitoring methods

Sorbent tubes/traps are widely used in combination with gas chromatographic (GC) analytical methods to monitor the vapour-phase fraction of organic compounds in air. Applications range from atmospheric research and ambient air monitoring (indoor and outdoor) to occupational hygiene (personal exposure assessment) and measuring chemical emission levels. Part 1 of this paper reviewed the main sorbent-based air sampling strategies including active (pumped) tube monitoring, diffusive (passive) sampling onto sorbent tubes/cartridges plus sorbent trapping/focusing of whole air samples that are either collected in containers (such as canisters or bags) or monitored online. Options for subsequent extraction and transfer to GC(MS) analysis were also summarised and the trend to thermal desorption (TD)-based methods and away from solvent extraction was explained. As a result of this trend, demand for TD-compatible sorbents (alternatives to traditional charcoal) is growing. Part 2 of this paper therefore continues with a summary of TD-compatible sorbents, their respective advantages and limitations and considerations for sorbent selection. Other analytical considerations for optimizing sorbent-based air monitoring methods are also discussed together with recent technical developments and sampling accessories which have extended the application range of sorbent trapping technology generally.     

Rapid and sensitive determination of morphine in street opium samples by thermal desorption gas chromatography using a microfurnace pyrolyzer

Thermal desorption of the alkaloids in opium samples at 300 degrees C using a vertical microfurnace pyrolyzer was followed by their on-line gas chromatographic (GC) analysis on a large-bore glass capillary column. This method permitted rapid and sensitive determination of the content of the main alkaloid, morphine, in the small (ca. 100 microg) opium samples with a relative standard deviation within 4% for 5 runs. The observed morphine contents of about 12 to 15 w/w% in the given opium samples were in fairly good agreement with those estimated by a conventional GC-MS method.     

Two-dimensional gas chromatography for determination of volatile compounds in ambient air

A two-dimensional gas chromatograph is described for the analysis of volatile compounds. The chromatographic system consists of two separate chromatographs linked together with an interface containing an intermediate trap. The trap is cooled with nitrogen (?150°C) and a cryogradient is created inside the trap enclosure. The sample is reinjected during controlled (chromatographic) conditions, using thermostated air. The sample components are eluted from the trap as narrow symmetrical peaks; the shape and width of the peaks eluted do not noticeably affect the subsequent chromatography. The enrichment of n-butane in the trap is quantitative in the range 10^?10 – 10^?5 g.     

Programmed temperature vaporizer based method for the sensitive determination of trihalomethanes and benzene,toluene, ethylbenzene and xylenes in soils

A methodology based on the coupling of a headspace autosampler with a GC and a MS detector operating in SIM mode has been developed for the determination of volatile organic compounds (THMs and BTEX) in soils. The GC device used is equipped with a programmable temperature vaporizer (PTV) packed with Tenax-TA^® to introduce the samples (the injection mode used was solvent vent), and a modular accelerated column heater (MACH™) to control column temperature. The proposed measurement procedure reduces the sample pretreatment step to a minimum. Combined use of solvent vent injection mode and mass spectrometry detection allows a highly sensitive method to be proposed, with limits of detection of the order of ng/kg for all the target compounds. Furthermore, the capillary column used allows rapid separations of compounds in less than 4.60 min, affording a very short total analysis cycle time of 9 min.     

Gas-phase cleanup method for analysis of trace atmospheric semivolatile organic compounds by thermal desorption from diffusion denuders

A novel gas-phase cleanup method was developed for use with a thermal desorption method for analysis of trace semivolatile organic compounds (SOCs) in the atmosphere using diffusion denuder samplers to separate gas-phase from particle-associated fractions. The cleanup selectively removed hydrogen-bonding chemicals from samples, including much of the background matrix of oxidized organic compounds that is present in ambient air samples. Abraham solvation parameters were found to be useful predictors of recovery of compounds through the cleanup method; most compounds with A + B < 0.3 and L ≤ 12.3 were fully recovered through the cleanup method. Addition of the cleanup method successfully produced baseline resolution in air samples and improved method precision. The utility of the method was demonstrated in an investigation of the built environment as a continuing source of semivolatile persistent, bioaccumulative, and toxic chemicals (PBTs) to the atmosphere.     

热脱附-气相色谱-三重四极杆串联质谱法测定环境空气中的挥发性有机物

采用热脱附(TD)结合气相色谱-三重四极杆串联质谱(GC-MS/MS)建立了环境空气中23种挥发性有机物(VOCs)同时检测的分析方法。空气样品通过主动采样的方式富集到装有Tenax-TA填料的热脱附管中,热解吸后在选择反应监测(SRM)模式下用GC-MS/MS进行检测,内标法定量。结果表明,23种VOCs在0.01~1 ng和1~100 ng低、高两个范围内线性关系良好,相关系数(r²)均大于0.99,方法定量限为0.00008~1 μ g/m³。加标水平为2、10和50 ng时,23种VOCs的平均回收率为77%~124%。除了最低加标水平的氯苯,相对标准偏差(RSD, n=6)均小于20%。对市内3个采样点的环境空气进行测定,其中苯、甲苯、乙苯、二甲苯、苯乙烯、1,2,4-三甲基苯和六氯丁二烯均有检出。实验证明,该TD和GC-MS/MS相结合的检测方法具有准确、可靠、灵敏度高等优点,适用于环境空气中VOCs的同时测定。     

Sorbent-based sampling methods for volatile and semi-volatile organic compounds in air: Part 1: Sorbent-based air monitoring options

Sorbent tubes/traps are widely used in combination with gas chromatographic (GC) analytical methods to monitor the vapour-phase fraction of organic compounds in air. Target compounds range in volatility from acetylene and freons to phthalates and PCBs and include apolar, polar and reactive species. Airborne vapour concentrations will vary depending on the nature of the location, nearby pollution sources, weather conditions, etc. Levels can range from low percent concentrations in stack and vent emissions to low part per trillion (ppt) levels in ultra-clean outdoor locations. Hundreds, even thousands of different compounds may be present in any given atmosphere. GC is commonly used in combination with mass spectrometry (MS) detection especially for environmental monitoring or for screening uncharacterised workplace atmospheres. Given the complexity and variability of organic vapours in air, no one sampling approach suits every monitoring scenario. A variety of different sampling strategies and sorbent media have been developed to address specific applications. Key sorbent-based examples include: active (pumped) sampling onto tubes packed with one or more sorbents held at ambient temperature; diffusive (passive) sampling onto sorbent tubes/cartridges; on-line sampling of air/gas streams into cooled sorbent traps; and transfer of air samples from containers (canisters, Tedlar^® bags, etc.) into cooled sorbent focusing traps. Whichever sampling approach is selected, subsequent analysis almost always involves either solvent extraction or thermal desorption (TD) prior to GC(/MS) analysis. The overall performance of the air monitoring method will depend heavily on appropriate selection of key sampling and analytical parameters. This comprehensive review of air monitoring using sorbent tubes/traps is divided into 2 parts. (1) Sorbent-based air sampling option. (2) Sorbent selection and other aspects of optimizing sorbent-based air monitoring methods. The paper presents current state-of-the-art and recent developments in relevant areas such as sorbent research, sampler design, enhanced approaches to analytical quality assurance and on-tube derivatisation.     

Development of a novel solid-phase extraction element for thermal desorption gas chromatography analysis

A novel solid-phase extraction element is developed for sorptive enrichment of dilute analytes from liquid samples with high extraction efficiencies due to its larger amounts of polydimethylsiloxane (PDMS) absorbent than the conventional syringe type of solid-phase microextraction (SPME). The extraction element is made of titanium (Ti) open tubular tube (30 mm x 1.2 mm i.d. x 1.6 mm o.d.) coated with a chemically bonded layer of PDMS (500 microm in thickness). The extraction element combined with thermal desorption-gas chromatography-mass spectrometry using a pyrolysis-gas chromatography-mass spectrometry system was used to extract and analyze a typical herbicide, bethrodine in water samples over a concentration range from 2.5 to 2.5 x 10(4) ng/l. Thus obtained calibration curve showed good linearity for the tested whole concentration range with regression coefficient of 0.992. Detection limit of 0.5 ng/l level was achieved and the reproducibility of the measurements for bethrodine at 10 ng/l level was found to be fairly good with relative standard deviation below 7.5%.     

Development of a new pyrolyzer for thermal desorption and/or pyrolysis gas chromatography of polymeric materials

A new vertical microfurnace-type pyrolyzer for thermal desorption and/or pyrolysis-gas chromatography has been developed. The pyrolyzer consists of two independent temperature-controlled ovens. Initially, in the desorption process, a sample cup containing the polymeric sample of interest is inserted into an oven at 300°C; the sample is then re-positioned at the upper part of the pyrolyzer where the temperature is maintained at room temperature. The resulting vaporized components such as residual solvents and additives give a desorption chromatogram. The relative peak intensities of desorbed plasticizers in acrylonitrile butadiene-rubber gave a relative standard deviation (RSD) of less than 2%. Subsequently, pyrolysis of the remaining polymer is conducted by dropping the sample cup into the second, pyrolyzing, oven at 55°C; at this stage the pyrogram is recorded. The resulting two chromatograms of desorbed components and pyrolysis products make it easier to characterize the polymer formulation than the complicated pyrogram obtained by an ordinary, single-step pyrolysis.     

On-site determination of polynuclear aromatic hydrocarbons in seawater by stir bar sorptive extraction (SBSE) and thermal desorption GC-MS

The identification and quantification of semi-volatile contaminants dissolved in water is currently done in laboratory after a sampling step. This procedure is not satisfactory first because risks of samples contamination and analytes losses remain, in particular when these are present in ultra-trace concentrations, and secondly because procedures are time-consuming. The coupling of the stir bar sorptive extraction (SBSE), a new device of extraction technique, and a new generation of gas chromatography mass spectrometry (GC-MS), the field apparatus EM 640 S from Bruker, could be an answer to the challenge of on-site analysis. This analytical system was used to analyze 24 PAHs, among them 15 EPA priority pollutants. It was shown that this coupling led to encouraging results with LODs around the sub-ppt level for most of the compounds and R.S.D. included between 1 and 48%. The existence of competition phenomena between the various analytes inside the absorbent phase was demonstrated with the release (up to 80%) of light compounds. This result shows the necessity to work on the kinetic domain rather than on the thermodynamic equilibrium that is influenced by nature and concentration of other compounds. The matrix effects were also studied through the comparative analysis of ultrapure water, artificial and natural seawaters spiked with PAHs and the influence of ionic strength and particulate organic matter was investigated.     

Stability of workroom air volatile organic compounds on solid adsorbents for thermal desorption gas chromatography

The storage stability of the occupationally frequently occurring compounds, methylethylketone, methylisobutylketone, benzene, toluene, tetrachloroethylene, n-butylacetate, -pinene, β-pinene, limonene and n-decane, has been investigated on the adsorbents Tenax TA, Chromosorb 106 and Carbotrap using thermally desorbable tube type samplers, commonly utilized in ambient and workroom atmospheric measurements. Fifty and 500 ng of each compound were loaded on the various adsorbents tubes, stored at both ambient (20 °C) and refrigerated (4 °C) temperatures and analysed by means of thermal gas chromatography with mass spectrometric detection on days 0, 7, 14 and 28 after exposure. A 90% storage recovery was chosen as acceptance criteria for storage stability, and statistical testing by Student's t-test, analysis of variance and Bonferroni post hoc tests were employed to investigate the effect of the categorical variables storage time, storage temperature and analyte loading on the different adsorbents. Chromosorb 106 showed the overall best behaviour with recoveries of 90% or better for all analytes during the 28-day test period. Tenax TA and Carbotrap yielded lower recoveries and were more influenced by variations in storage time, storage temperature and analyte loading. Refrigerated temperatures were best avoided for storage on Tenax TA, but may increase the recovery of some compounds on Carbotrap (e.g. n-butylacetate). The blank build-up on the adsorbents was also investigated, and Carbotrap and Tenax TA showed no signs of artefact development over time. Chromosorb 106, however, contained inherently more artefacts that build up over time, which in spite of the excellent storage capability, may limit its use in field studies where long storage times are normal.