Design and application of Hadamard-injectors coupled with gas and supercritical fluid sample collection systems in Hadamard transform-gas chromatography/mass spectrometry

A novel Hadamard transform-gas chromatography/mass spectrometry (HT-GC/MS) system equipped with on-line sample collection systems is described. A Hadamard-injector was successfully designed and then coupled with an on-line adsorption/desorption system for detecting volatile organic compounds (VOCs) and a supercritical fluid extraction (SFE) system, respectively, by HT-GC/MS. Six VOCs and three pesticides were used as model compounds. In the former case, an activated-charcoal trap was used to trap VOCs from the indoor air. After 10 L of indoor air had passed through the trap, the condensed components were heated and simultaneously injected into the GC column through the Hadamard-injector, based on Hadamard codes. In a second experiment, a sample of rice was spiked with three types of pesticides and the sample then extracted using a commercially available supercritical fluid extractor. After extraction, the extracted components were transferred to a holding tank and simultaneously injected into the GC column also using the Hadamard-injector. The findings show that, in both cases, the combination of on-line sample collection methods and the use of the Hadamard transform resulted in improved sensitivity and detection. Compared to the single injection used in most GC/MS systems, the signal-to-noise (S/N) ratios were substantially improved after inverse Hadamard transformation of the encoded chromatogram.     

The Determination Of Sub Part-Per-Billion Levels Of Volatile Organic Compounds In Air By Pre-Concentration From Small Sample Volumes

Abstract

Trace level Volatile Organic Compounds (VOCs) in ambient air are normally determined according to EPA Method TO-14. This method describes the analysis in ambient air of 41 VOCs, ranging in boiling point from -29 to 215°C. It covers a concentration range from 0.2 to 20 parts per billion, volume/volume (ppb), and specifies sample enrichment of a 400 mL air sample on glass beads at -160°C. While this sample volume provides sub-ppb levels of VOC detection for target analytes when using a quadrupole mass spectrometer detector in SIM mode or when using GC detectors, the identification of non-target analytes may only be done in full scan mode for higher concentrations. Also with this sample volume a Nafion dryer is needed for water removal thereby lowering the recovery of polar VOCs.

Because of the very high sensitivity of the ion trap MS, relatively small air volumes (60 mL) are adequate to obtain the required or lower detection levels. An integrated air analysis system based on a GC-ion-trap MS has been investigated and is described. This system has a built-in cryogenic trap and necessary valving, internal standard gas sampling loop, and is controlled from the GC-MS workstation. The linearity, precision, and method detection levels obtainable with this system when using small volumes are reported. In addition, examples of the quantitative and qualitative analysis of ambient air samples are shown.     

大气环境中挥发性有机化合物的测定

 参考美国环保局大气中挥发性有机化合物 (VOCs)的标准分析方法TO14A和TO15 ,采用预浓缩器与气相色谱联用 ,以质谱或氢火焰离子化检测器检测 ,建立了 5 6种VOCs(主要是臭氧前体物 )的快速分析方法。该方法在同一台仪器上采用单柱、单检测器 ,准确测定了高浓度CO2 下的VOCs。方法检出限为 0 1μg·m-3 ,相对标准偏差(RSD)为 2 5 7%～ 9 82 %。用该法分析了实际大气样品中的VOCs,结果令人满意。     

Application of a Self-developed Proton Transfer Reaction-Mass Spectrometer to On-line Monitoring Trace Volatile Organic Compounds in Ambient Air

Real-time and on-line monitoring volatile organic compounds(VOCs) are valuable for real-time evalua- ting air quality and monitoring the key source of pollution. A self-developed proton transfer reaction-mass spectrometer(PTR-MS) was constructed and applied to on-line monitoring trace VOCs in ambient air in Hefei, China. With the help of a self-developed catalytic converter, the background signal of the instrument was detected and the stability of the instrument was evaluated. The relative standard deviation of signal at m/z 21 was only 0.74% and the detection limit of PTR-MS was 97 part per trillion(97×10^-12, volume ratio). As a case of the air monitoring in Hefei, the ambient air at Dongpu reservoir spot was on-line monitored for 13 d with our self-developed PTR-MS. Meanwhile, a solid-phase micro-extraction(SPME) technique coupled to gas chromatography-mass spectrometry/mass spectrometry (GC-MS/MS) was also used for the off-line detection of the air. The results show that our self-developed PTR-MS can be used for the on-line and long-term monitoring of VOCs in air at part per trillion level, and the change trend of VOCs concentration monitored with PTR-MS was consistent with that detected with the conventional SPME-GC-MS. This self-developed PTR-MS can fully satisfy the requirements of air quality monitoring and real-time monitoring of the key pollution sources.     

S_2OF_(10)气体标准样品制备方法和测定方法研究

提出了一系列的安全、方便、可靠、在线和可连续操作的热解吸／色谱分析柱制备Ｓ２ＯＦ１０纯品、指数稀释法配制Ｓ２ＯＦ１０标准样品、应用定量校正系数测定样品中痕量Ｓ２ＯＦ１０的方法和技术。分别采用气相色谱、红外光谱、气相色谱／质谱等方法对色谱制备的Ｓ２ＯＦ１０纯品进行了纯度分析和测定。配制Ｓ２ＯＦ１０标准气体的体积分数范围为８．０×１０－７～２．６×１０－４。气相色谱测定Ｓ２ＯＦ１０的定量校正系数为０．１９７,测定方法的相对误差范围为１．８％～２０％。     

Construction and validation of an automated spray-and-trap gas chromatograph for the determination of volatile organic compounds in aqueous samples

An automated spray-and-trap (ST) chromatographic system was constructed for fast and efficient extraction of volatile organic compounds (VOCs) in aqueous samples with the capability to be deployed in the field for unattended continuous monitoring of surface or ground water. This system was built upon a commercial gas chromatograph with full automation capability using self-developed hardware and software. For sample analysis, fine droplets of the aqueous solution were generated in the extraction chamber by pressure expansion of a clean air stream through a spray nozzle. A portion of the VOCs distributed into the gas phase was retained by a multi-sorbent micro-trap kept at ambient temperature. Flash heating of the sorbent trap desorbed the enriched VOCs onto the gas chromatography (GC) with flame ionization detection (FID) for hydrocarbons or electron-capture detection (ECD) for halocarbons. In order to validate the performance of the ST method. it was compared with a more conventional method, i.e., a purge-and-trap (PT), by analyzing a serious of standard solutions containing benzene, toluene, ethylene. and o-, m-xylenes. Using a purge-and-trap method as a reference for complete extraction, the ST method showed less sensitivity. Extraction recoveries are in consistent with Henry's law constants. To test response time the ST-GC-ECD was periodically switched between tap and underground waters. Negligible carry-over of halogenated species and reproducibility better than 2% relative standard deviation (R.S.D.) can be achieved regardless of large concentration difference between the two sources, thus demonstrating applicability of the ST system for on-site monitoring.     

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。     

电子制冷预浓缩-双柱气相色谱-质谱/氢火焰检测器法测定空气中104种挥发性有机物

基于吸附剂辅助电子制冷预浓缩技术，建立了多维切割双柱气相色谱-质谱/氢火焰离子化检测器（GC-MS/FID）同时测定环境空气中104种挥发性有机物（VOCs）的方法。将采集于苏玛罐中的环境空气样品在配有吸附剂的电子制冷预浓缩系统中富集、脱附、除水、除CO₂和浓缩，然后通过GC-MS/FID的多维切割单元将C₂~C₃组分和C₄~C₁₂组分分别引入PLOT柱和InterCap-624柱进行分离。C₂~C₃组分用FID检测，以保留时间定性、外标法定量；C₄~C₁₂组分采用电子轰击离子源质谱检测，以保留时间和特征离子定性、内标法定量。考察了冷阱吸附剂种类、辅助压力控制单元压力设置、双柱切换时间切割点等参数对分析结果的影响，优化了GC-MS/FID条件，并评估了在此优化条件下的方法性能。104种VOCs在0.0446~0.892 μmol/m³范围内线性关系良好，相关系数（r）为0.9984~0.9999，对0.0446 μmol/m³和0.223 μmol/m³水平的混合标准气体重复6次进样，平均回收率为86.4%~116.1%，相对标准偏差为0.9%~11.3%；方法的检出限为0.145~1.90 μg/m³，定量限为0.435~5.70 μg/m³。该法稳定性好，灵敏度高，操作简便，可用于环境空气中104种VOCs的测定。     

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.     

Analytical methods for detection of nonoccupational exposure to pesticides

An analytical protocol is developed to analyze for 33 compounds in ambient air around the household, drinking water, and from dermal contact while applying pesticides. Soxhlet extraction is used on both the polyurethane foam plugs, which were used as air sample trapping media, and the gloves reflecting dermal contact. The extraction procedure of U.S. Environmental Protection Agency (EPA) Method 608 is used for water samples. A stringent gas chromatography/electron capture detection (GC/ECD) and gas chromatography/mass spectroscopy/multiple ion detection (GC/MS/MID) analytical approach parallel to the procedures of the current EPA contract laboratory program is used for analysis.     

Optimisation of pre-treatment and ionisation for GC/MS analysis for the determination of chlorinated PAHs in atmospheric particulate samples

Chlorinated polycyclic aromatic hydrocarbons (ClPAHs) have been discovered to represent ubiquitous environmental pollutants in the last decade. In the present study, sample pre-treatment and ionisation conditions associated with the gas chromatography/mass spectrometry (GC/MS) analysis of ClPAHs were evaluated. The optimal pre-treatment of ambient air particulate samples was achieved using fractionation over silica gel with 10% dichloromethane in n-hexane as the eluent. The optimised condition of GC/MS with electron impact ionisation permitted analysis of all target ClPAHs. Not all target ClPAHs were detected using GC/MS with negative chemical ionisation, although this technique exhibited greater sensitivity for several of the compounds compared to electron impact ionisation. The analytical method was applied to the survey of ClPAHs in atmospheric particulate matter obtained close to an industrial site and in a standard sample of tunnel dust. Fourteen and eighteen species of ClPAHs were detected in the industrial air samples and tunnel dust, respectively, confirming the capability of the method. The compositions of ClPAHs were significantly different between air samples and tunnel dust. It suggests that alternative emission sources rather than vehicle exhaust could play a significant role in the air.     

Development and evaluation of a calibration gas generator for the analysis of volatile organic compounds in air based on the injection method

The development and operational evaluation of a calibration gas generator for the analysis of volatile or ganic compounds (VOC) in air is described. Details of the construction, as well as of the evaluation of the apparatus are presented here. The performance of the test gas generator is validated both by on-line GC analysis of the calibration gas produced and by off-line analysis of adsorptive samples taken from the generated calibration gas. Both, active and passive sampling have been used, and the results demonstrate the excellent accuracy and precision of the generated test gas atmosphere: For the 11 investigated organic compounds (aromatic and halogenated compounds), the found values were in most cases within 5% of the target value with a reproducibility of better than 3% RSD (as determined by the analysis of the sampled adsorbent tubes). Custom made adsorbent tubes were used for active and passive sampling and in both cases were analysed by thermal-desorption GC. Particularly the combination of passive sampling and thermodesorption-GC analysis offers significant advantages over the commonly used active sampling on activated charcoal, followed by CS2 desorption in terms of avoidance of hazardous solvents, potential for automation and improved detection limits. Both sampling techniques are capable for monitoring VOCs at concentrations and under conditions relevant for workplace monitoring.     

Novel sample preparation technique with needle-type micro-extraction device for volatile organic compounds in indoor air samples

A novel needle-type sample preparation device was developed for the effective preconcentration of volatile organic compounds (VOCs) in indoor air before gas chromatography–mass spectrometry (GC–MS) analysis. To develop a device for extracting a wide range of VOCs typically found in indoor air, several types of particulate sorbents were tested as the extraction medium in the needle-type extraction device. To determine the content of these VOCs, air samples were collected for 30 min with the packed sorbent(s) in the extraction needle, and the extracted VOCs were thermally desorbed in a GC injection port by the direct insertion of the needle. A double-bed sorbent consisting of a needle packed with divinylbenzene and activated carbon particles exhibited excellent extraction and desorption performance and adequate extraction capacity for all the investigated VOCs. The results also clearly demonstrated that the proposed sample preparation method is a more rapid, simpler extraction/desorption technique than traditional sample preparation methods.     

Analytical bias among different gas chromatographic approaches using standard BTX gases and exhaust samples

In this study, the analytical compatibility of the gas chromatographic (GC) approach was evaluated through a cross‐calibration exercise. To this end, three aromatic volatile organic compounds (VOCs: benzene, toluene, and p‐xylene (BTX)) were simultaneously analyzed with four individual instrumental setups (type I = GC with MS plus solid phase microextraction (SPME) method, II = GC with flame ionization detection (FID) plus SPME, III = fast GC‐FID plus SPME, and IV = GC‐FID plus air server/thermal desorption (AS/TD) method). A comparison of basic quality assurance (QA) data revealed considerable differences in DL values among the methods with moderate variabilities in the intercompound sensitivity. In light of the differences in detection properties, the analytical bias involved for each methodological approach was assessed by the relative relationship between analytes and basic operating conditions. The results suggest that the analysis of environmental samples at ultra‐low concentration levels (at or below ppb level) can be subject to diverse sources of bias. Although detection properties of target compounds seem to be affected by the combined effects of various factors, changes in the sample concentration levels were seen to be the most consistent under the experimental setups analyzed in this study.     

Isolation of essential oils from tobacco by gas co-distillation/solvent extraction

Summary The essential oils have been isolated from tobacco leaves using a simple gas co-distillation apparatus. The method involves co-distillation with water under the continuous stream of an inert gas with subsequent single solvent extraction of the distillate. The extract is analysed on GC and GC/MS in splitless injection mode without further concentration. The method was evaluated for reproducibility using n-octadecane as an internal standard. The distillation-extraction procedure was reporducible with an average deviation of ±3% for the major constituents. The present method was applied to the analyses of the essential oils of other agricultural products.Dedicated to Dr. L. S. Ettre on the occasion of his 60th birthday.     

A new approach to determine method detection limits for compound-specific isotope analysis of volatile organic compounds

Compound-specific isotope analysis (CSIA) has been established as a useful tool in the field of environmental science, in particular in the assessment of contaminated sites. What limits the use of gas chromatography/isotope ratio mass spectrometry (GC/IRMS) is the low sensitivity of the method compared with GC/MS analysis; however, the development of suitable extraction and enrichment techniques for important groundwater contaminants will extend the fields of application for GC/IRMS. So far, purge and trap (P&T) is the most effective, known preconcentration technique for on-line CSIA with the lowest reported method detection limits (MDLs in the low microg/L range). With the goal of improving the sensitivity of a fully automated GC/IRMS analysis method, a commercially available P&T system was modified. The method was evaluated for ten monoaromatic compounds (benzene, toluene, para-xylene, ethylbenzene, propylbenzene, isopropylbenzene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, fluorobenzene) and ten halogenated volatile organic compounds (VOCs) (dichloromethane, cis-1,2-dichloroethene, trans-1,2-dichloroethene, carbon tetrachloride, chloroform, 1,2-dichloroethane, trichloroethene, tetrachlorethene, 1,2-dibromoethane, bromoform). The influence of method parameters, including purge gas flow rates and purge times, on delta13C values of target compounds was evaluated. The P&T method showed good reproducibility, high linearity and small isotopic fractionation. MDLs were determined by consecutive calculation of the delta13C mean values. The last concentration for which the delta13C value was within this iterative interval and for which the standard deviation was lower than +/-0.5 per thousand for triplicate measurements was defined as the MDL. MDLs for monoaromatic compounds between 0.07 and 0.35 microg/L are the lowest values reported so far for continuous-flow isotope ratio measurements using an automated system. MDLs for halogenated hydrocarbons were between 0.76 and 27 microg/L. The environmental applicability of the P&T-GC/IRMS method in the low-microg/L range was demonstrated in a case study on groundwater samples from a former military air field contaminated with VOCs.     

Evaluation of an in-injection port thermal desorption-gas chromatography/mass spectrometry method for analysis of non-polar organic compounds in ambient aerosol samples

Thermal desorption coupled with gas chromatography/mass spectrometry (TD-GC/MS) is an alternative to solvent extraction (SE)-based GC/MS (SE-GC/MS) for the analysis of non-polar organic compounds in filter or impactor-collected aerosols. TD-GC/MS has no sample pretreatment and requires a small filter aliquot for detecting individual organic compounds. The performance of an in-injection port TD-GC/MS is evaluated for polycyclic aromatic hydrocarbons (PAHs), n-alkanes, iso-/anteiso-alkanes, hopanes, steranes, branched alkanes, cyclohexanes, alkenes, and phthalates in standards and ambient air samples. Replicate analysis for 132 organic compounds showed relative standard deviations <10%, with the majority <5%. Accuracy for 15 PAHs, determined with NIST standard reference material (SRM) 1649a urban dust, was within +/-5% of the certified values. TD-GC/MS and SE-GC/MS method comparisons for 14 Hong Kong ambient samples agreed within 11% for 106 non-polar compounds. For 19 Tong Liang, China samples, agreement was within 13% for 23 PAHs.     

Determination of ppt levels of atmospheric volatile organic compounds in Yakushima, a remote south-west island of Japan

An analytical method was utilized to detect ppt levels of VOCs in air. The method was based on the US-EPA method TO-14, consisting of canister sampling, three module enrichment and GC/MS analysis. Target compounds included chlorofluorocarbons (four kinds), benzene and its derivatives (14), halogenated hydrocarbons (20), and others (three). The minimum detection limits of the method for the target compounds ranged from 0.016 to 0.040 ppb (0.06–0.23 μg/m³). The recoveries of the target compounds ranged from 77 to 113% and relative coefficients of variation (n=4) were 3.0–9.0%. The sampled air was stable for at least 14 days after pressurizing with humidified nitrogen gas at 200 kPa (absolute pressure). The method was applied to analyze the VOCs in the air of Yakushima, a remote island of south-west Japan where no distinct local pollution source is considered.     

On-line immunoaffinity column-liquid chromatography-tandem mass spectrometry method for trace analysis of diuron in wastewater treatment plant effluent sample

An on-line immunoaffinity column with liquid chromatography/tandem mass spectrometry (IAC-LC-MS/MS) method for the determination of diuron in water matrices was described. This method used a sol-gel immunoaffinity column (20 mm x 4 mm I.D.) for on-line sample cleanup and enrichment, a monolithic analytical column (100 mm x 4.6 mm I.D.) for separation, and a triple quadrupole mass spectrometer for quantitation. The major challenges for the on-line set-up were discussed. The optimized on-line protocol was emphasized by the fact that low limit of quantitation (LOQ) of 1.0 ng/L was achieved with only 2.5-mL sample. In addition, a satisfactory accuracy ( approximately 90% of recovery) and precision (<6% of relative standard deviation) at 50 ng/L concentration were also obtained. Due to the ability of the sol-gel immunoaffinity column to eliminate matrix effect, the on-line IAC-LC-MS/MS analysis method can reliably determine diuron in wastewater treatment plant effluent sample.     

Simultaneous quantification of polar and non-polar volatile organic compounds in water samples by direct aqueous injection-gas chromatography/mass spectrometry

A direct aqueous injection-gas chromatography/mass spectrometry (DAI-GC/MS) method for trace analysis of 24 volatile organic compounds (VOCs) in water samples is presented. The method allows for the simultaneous quantification of benzene, toluene, ethyl benzene, and xylenes (BTEX), methyl tert-butyl ether (MTBE), tert-butyl alcohol (TBA), as well as a variety of chlorinated methanes, ethanes, propane, enthenes and benzenes. Applying a liquid film polyethylene glycol or a porous layer open tubular (PLOT) divinylbenzene GC capillary column to separate the water from the VOCs, volumes of 1-10 microL aqueous sample are directly injected into the GC. No enrichment or pretreatment steps are required and sample volumes as low as 100 microL are sufficient for accurate quantification. Method detection limits determined in natural groundwater samples were between 0.07 and 2.8 microg/L and instrument detection limits of <5 pg were achieved for 21 out of the 24 evaluated VOCs. DAI-GC/MS offers both good accuracy and precision (relative standard deviations 相似文献