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。     

Determination of oxygenated volatile organic compounds in ambient air using canister collection-gas chromatography/mass spectrometry.

This research attempts to establish a method to measure 11 kinds of oxygenated volatile organic compound (OVOC) in ambient air by using the canister collection-gas chromatography/mass spectrometry (GC/MS) method. Since several compounds such as acetone exhibited high blank concentrations due to their laboratory use, stringent quality control was conducted for the VOC-free added water and the VOC-free nitrogen gas. In order to prevent the decline of recovery rates due to lack of sufficient relative humidity, it is necessary to add VOC-free water when pressurizing and diluting the air samples. Thus, all the target compounds in ambient air were obtained from the canisters at high recovery rates without significant contamination. Furthermore, the canister collection-GC/MS method makes it possible to apply simultaneous air monitoring of OVOCs as well as volatile hazardous air pollutants without additional sampling.     

热脱附-气相色谱-质谱法测定环境空气中67种挥发性有机物

采用热脱附-气相色谱-质谱法,建立了同时分析环境空气中67种挥发性有机物的分析方法。对比了5种不同填充材料不锈钢吸附管对78种挥发性有机物的吸附能力。填充材料为Tenax TA和Carbograph 1TD的混合填料吸附管对分析物的捕集效果最好,在30 mL/min高纯He气持续吹脱45 min的情况下,未发生穿透（即穿透率小于10%）的化合物达67种,分析物的种类包括芳香烃、脂肪烃、卤代烃和含氧挥发性有机物等。优化了使用该吸附管测定67种目标物时的热脱附条件。在5~100 ng范围内,目标化合物的色谱响应值与其量间具有良好的线性关系,其相关系数（r）均在1.0000~0.9977之间。方法检出限为0.3~2.4 ng,以采样体积1 L计算,检出限为0.3~2.4 μg/m³。加标量为20 ng时,7次重复实验目标化合物回收率均在81.6%~114.9%之间,目标化合物的相对标准偏差为1.2%~10.1%。采用该方法对某车厢内空气进行了检测,检出了包括酯类、卤代烷烃、卤代烯烃以及芳香族化合物在内的19种目标化合物,其范围为1.1~84.1 μg/m³。该方法准确、可靠、灵敏度高,实现了对环境空气中67种目标污染物的准确定量。     

Full-range analysis of ambient volatile organic compounds by a new trapping method and gas chromatography/mass spectrometry

This study investigated the feasibility of analyzing a full range of ambient volatile organic compounds (VOCs) from C(3) to C(12) using gas chromatograph mass spectrometry (GC/MS) coupled with thermal desorption. Two columns were used: a PLOT column separated compounds lighter than C(6) and a DB-1 column separated C(6)-C(12) compounds. An innovative heart-cut technique based on the Deans switch was configured to combine the two column outflows at the ends of the columns before entering the MS. To prevent the resolved peaks from re-converging after combining, two techniques were attempted (hold-up vs. back-flush) to achieve the intended "delayed" elution of heavier components. Thus, the resulting chromatogram covering the full range of VOCs is a combination of two separate elutions, with the heavier section following the lighter section. With the hold-up method, band-broadening inevitably occurred for the delayed C(6)-C(7) DB-1 compounds while the light compounds eluted from the PLOT column. This broadening problem resulted in peak tailing that was largely alleviated by adding a re-focusing stage while the DB-1 compounds were back-flushed, and this modified technique is referred to as the back-flush method. With this modification, the separation of the C(6)-C(7) compounds improved dramatically, as revealed by the decrease in peak asymmetry (As) and increase in resolution. Linearity and precision for these peaks also improved, yielding R(2) and RSD values better than 0.9990 and 2.8%, respectively.     

Construction of an automated gas chromatography/mass spectrometry system for the analysis of ambient volatile organic compounds with on-line internal standard calibration

An automated sampling and enrichment apparatus coupled with a gas chromatography/mass spectrometry (GC/MS) technique was constructed for the analysis of ambient volatile organic compounds (VOCs). A sorbent trap was built within the system to perform on-line enrichment and thermal desorption of VOCs onto GC/MS. In order to improve analytical precision, calibration accuracy, and to safe-guard the long-term stability of this system, a mechanism to allow on-line internal standard (I.S.) addition to the air sample stream was configured within the sampling and enrichment apparatus. A sub-ppm (v/v) level standard gas mixture containing 1,4-fluorobenzene, chloropentafluorobenzene, 1-bromo-4-fluorobenzene was prepared from their pure forms. A minute amount of this I.S. gas was volumetrically mixed into the sample stream at the time of on-line enrichment of the air sample to compensate for measurement uncertainties. To assess the performance of this VOC GC/MS system, a gas mixture containing numerous VOCs at sub-ppb (v/v) level served as the ambient air sample. Various internal standard methods based on total ion count (TIC) and selective ion monitoring (SIM) modes were attempted to assess the improvement in analytical precision and accuracy. Precision was improved from 7-8% RSD without I.S. to 2-3% with I.S. for the 14 target VOCs. Uncertainties in the calibration curves were also improved with the adoption of I.S. by reducing the relative standard deviation of the slope (Sm%) by an average a factor of 4, and intercept (Sb%) by a factor of 2 for the 14 target VOCs.     

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.     

便携式气相色谱-质谱仪测定空气中挥发性有机污染物的准确性

便携式气相色谱-质谱仪(便携式GC-MS)能同时对多组分复杂有机物进行定性定量分析,在环境监测尤其是事故现场应急监测中发挥越来越重要的作用。本文比较了便携式GC-MS与EPATO-14A方法分析测定环境空气中低浓度挥发性有机物(VOCs)的性能,并探讨了利用定量环(loop环)模式测定高浓度VOCs的准确度。结果表明,采用内标标准曲线定量,HAPSITE便携式GC-MS测定空气中VOCs的检出限与EPATO-14A方法相当,准确度和精密度略低,但均符合环境监测分析的要求。利用loop环可对大部分10-6级的高浓度VOCs样品进行较为准确的测定,在突发性环境污染事故中可以得到基本准确的结果。     

Determination of volatile organic compounds in ambient air. Comparison of methods

Two analytical methods for the determination of benzene vapour in ambient air are compared in this paper. The methods differ from each other in the sampling technique, type of sorbent, method of extraction and method of detection. The investigation of the methods using various techniques for sample analysing showed a significant influence of the way in which the analysis is carried out, on the final result of the analysis. Calculation of the standard deviations, relative standard deviations and confidence intervals allowed for assessment of the precision and repeatability of the methods. Of the two examined methods, that using an automated system of contaminant sampling and thermodesorption was more precise. This method has been applied to measurements of concentrations of benzene, toluene and xylenes in ambient air.     

Analysis of volatile organic compounds in polymers by dynamic headspace and gas chromatography/mass spectrometry

An experimental method for the analysis of volatile organic compounds in polymers is described. The technique involves dynamic headspace sampling, collection, and concentration of the volatiles in a cold trap, followed by capillary column gas chromatography/mass spectometry. Flow switching is carried out by the Deans switching technique. Four technical polymers used as pharmaceutical packaging materials have been analyzed in order to demonstrate the method.     

Determination of complex mixtures of volatile organic compounds in ambient air: an overview

This article reviews developments in the sampling and analysis of volatile organic compounds (VOCs) in ambient air since the 1970s, particularly in the field of environmental monitoring. Global monitoring of biogenic and anthropogenic VOC emissions is briefly described. Approaches used for environmental monitoring of VOCs and industrial hygiene VOC exposure assessments are compared. The historical development of the sampling and analytical methods used is discussed, and the relative advantages and disadvantages of sorbent and canister methods are identified. Overall, there is considerable variability in the reliability of VOC estimates and inventories. In general, canister methods provide superior precision and accuracy and are particulary useful for the analysis of complex mixtures of VOCs. Details of canister methods are reviewed in a companion paper. C. C. Austin is an Invited Scientist of the National Research Council of Canada.     

Determination of complex mixtures of volatile organic compounds in ambient air: canister methodology

Canister methodology is applicable to 150 polar and nonpolar VOCs found in ambient air from parts-per-billion by volume (ppbv) to parts-per-million (ppmv) levels, and has been validated at parts-per-trillion (pptv) levels for a subset of these analytes. This article is a detailed review of techniques related to the collection of volatile organic compounds (VOCs) in evacuated Summa and fused-silica-lined canisters, and their analysis by gas chromatography/mass spectrometry (GC/MS). Emphasis is placed on canister cleaning, VOC stability in canisters, sample dilution, water management, and VOC cryogenic and sorbent preconcentration methods. A wide range of VOC preconcentration and water management methods are identified from the literature, and their relative merits and disadvantages are discussed. Examples of difficulties that commonly arise when processing canister samples are illustrated, and solutions to these problems are provided.     

Detection of volatile organic sulfur compounds in water by headspace gas chromatography and membrane inlet mass spectrometry

Two gas chromatographic methods, GC-FID (flame ionization detection) and GC-ELCD (electrolytic conductivity detector) are compared in tlie analysis of volatile organic sulfur compounds (VOSCs) in water samples with a membrane inlet mass spectrometry (MIMS) technique. Carbon disulfide, ethanethiol, dimethyl sulfide, ethyl-methyl sulfide, thiophene, and dimethyl disulfide were used as test compounds. Linear dynamic ranges were found to be two decades with the GC-ELCD method and four decades with the GC-FID and MIMS methods. Detection limits were at low (μg/1 levels with the two gas chromatographic methods and clearly below μg/1 level with the MIMS method. Analysis of one sample takes 40 min with the gas chromatographic methods and five minutes with the MIMS method. The selectivity was good, especially with the GC-ELCD and the MIMS method. In addition, quantitative results obtained with spiked water samples by the three methods are compared.     

Direct analysis of volatile organic compounds in foods by headspace extraction atmospheric pressure chemical ionisation mass spectrometry

Rationale

The rapid screening of volatile organic compounds (VOCs) by direct analysis has potential applications in the areas of food and flavour science. Currently, the technique of choice for VOC analysis is gas chromatography/mass spectrometry (GC/MS). However, the long chromatographic run times and elaborate sample preparation associated with this technique have led a movement towards direct analysis techniques, such as selected ion flow tube mass spectrometry (SIFT‐MS), proton transfer reaction mass spectrometry (PTR‐MS) and electronic noses. The work presented here describes the design and construction of a Venturi jet‐pump‐based modification for a compact mass spectrometer which enables the direct introduction of volatiles for qualitative and quantitative analysis.

Methods

Volatile organic compounds were extracted from the headspace of heated vials into the atmospheric pressure chemical ionization source of a quadrupole mass spectrometer using a Venturi pump. Samples were analysed directly with no prior sample preparation. Principal component analysis (PCA) was used to differentiate between different classes of samples.

Results

The interface is shown to be able to routinely detect problem analytes such as fatty acids and biogenic amines without the requirement of a derivatisation step, and is shown to be able to discriminate between four different varieties of cheese with good intra and inter‐day reproducibility using an unsupervised PCA model. Quantitative analysis is demonstrated using indole standards with limits of detection and quantification of 0.395 μg/mL and 1.316 μg/mL, respectively.

Conclusions

The described methodology can routinely detect highly reactive analytes such as volatile fatty acids and diamines without the need for a derivatisation step or lengthy chromatographic separations. The capability of the system was demonstrated by discriminating between different varieties of cheese and monitoring the spoilage of meats.     

Fullerenes-extracted soot: a new adsorbent for collecting volatile organic compounds in ambient air

Fullerenes-extracted soot (FES) is the by-product of fullerenes production. Retention characteristics at different temperatures for 17 volatile organic compounds (VOCs) on FES are measured. The adsorption and desorption efficiencies for VOCs on FES adsorbent tubes range from 40.8 to 117%, most of them being 100+/-20%. The values are compared with Tenax GR, an adsorbent commonly used in environmental analysis. FES can be used as an adsorbent of low cost to collect VOCs in environmental samples.     

Characterization of the volatile organic compounds of Italian 'Fossa' cheese by solid-phase microextraction gas chromatography/mass spectrometry

Fossa cheese is an Italian hard cheese, ripened for up to 3 months in underground pits dug into tuffaceous rock. During this period, the cheese develops a unique flavour and intense and somewhat piquant aroma. Solid-phase microextraction gas chromatography/mass spectrometry (SPME-GC/MS) was utilized to characterize the volatile organic compounds (VOCs) of Fossa cheese. A total of 75 VOCs were separated and identified; in particular, the major class of compounds found in the cheeses ripened in the pits were the esters of fatty acids. Discriminant analysis of volatile profiles allowed us to distinguish between cheeses in different stages of seasoning (60-day-old cheese and cheese ripened an additional 90 days in and out of the pits).     

Novel multi-sorbent for sampling and determination of trace volatile organic sulfur compounds in ambient air

Novel adsorbent APSG-MW (average particle size 215?µm and specific surface 98 m²?g^?1) bonding multi-walled carbon nanotubes (MWCNTs) on silica gel are obtained. Then the sampling tubes filled with Tenax TA and APSG-MW are prepared and the adsorptive capacity of Tenax TA/APSG-MW for volatile organic sulfur compounds (VOSCs) is studied. The data show that the adsorption and desorption recoveries of multi-sorbent for VOSCs are satisfactory (>85%), and the breakthrough values are large (>16?L?g^?1) enough to absorb VOSCs in ambient air. The sampling precision of the sorbent tubes meets TO-17 criteria. The sampling tubes are successfully used to concentrate and analyze a sample of landfill air, and the major S compounds are identified.     

Application of femtosecond laser mass spectrometry to the analysis of volatile organic compounds

Femtosecond (fs) lasers have high intensity and ultrashort pulse duration. Tunneling ionization occurs for molecules subject to such intense laser fields. We have studied the mass spectra of a variety of molecules irradiated by intense fs laser pulses. These molecules include some typical volatile organic compounds contained in human breath and in the atmosphere. The results demonstrate that all of these molecules can be ionized by intense fs laser pulses. Dominant parent ion and some characteristic ionic fragments are observed for each molecule. The degree of fragmentation can be controlled by adjusting the laser intensity. Moreover, saturation ionization can occur for each molecule by increasing the laser intensity. These features indicate that fs laser mass spectrometry can be a sensitive tool to identify and quantify volatile organic compounds in human breath.     

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.     

顶空气相色谱-质谱法测定玩具中的10种挥发性有机物

建立了检测玩具中10种挥发性有机物(VOC)残留量的顶空气相色谱-质谱(HS-GC-MS)方法。样品经140 ℃、45 min静态顶空后,通过DB-624色谱柱分离和质谱检测,外标法定量。该方法对于不同VOC的定量限(LOQ)均在0.66 mg/kg以下,线性范围为0.001～2.0 μg,平均回收率在79%～106%之间,相对标准偏差(RSD)在0.4%～5.6%之间。该方法具有准确灵敏、简单快速等特点,将其应用于实际玩具样品的检测取得了良好效果。