The composition and concentration of hydrocarbons in the range of C2 to C18 in downtown Los Angeles,CA

Ambient air samples were collected in the downtown Los Angeles (California) area and analyzed for non-methane hydrocarbons in the range of C2 to C18. Two daily samples were collected, using stainless steel canisters and Tenax-TA solid adsorbent cartridges, over four days in August 1991. The samples were analyzed using high resolution gas chromatographic separation and Fourier transform infrared/mass spectrometric detection (GC/IRD/MSD) or flame ionization detection (FID) of individual hydrocarbons. The comparison of hydrocarbon concentrations found in the Tenax and canister samples and the assessment of the contribution of semivolatile hydrocarbons (C10–C18 range) to the sum of non-methane hydrocarbons (C2–C10 or C2–C12), as measured by the canister method, is presented. This contribution ranges from ~7% to 15% (for C10–C18 range) and ~3% to 8% (for C12–C18 range). The semivolatile hydrocarbons also contribute ~16% to the total ozone forming potential of non-methane hydrocarbons.     

A high resolution GC-analysis method for determination of C2-C10 hydrocarbons in air samples

An analytical method for the determination of non-methane hydrocarbons (NMHC) in air was developed using simultaneously pressure and temperature programmed gas chromatography (GC) on a capillary column. The separation of C2-C10 hydrocarbons was performed in a single GC-run using a fused silica capillary column (FSCC) with a chemically bonded non-polar stationary phase (CP-Sil-5-CB). A combination of on-column cryofocusing and GC reinjection provided baseline separation of C2 hydrocarbons at subambient initial temperature (?40°C). The cryofocusing was performed on the column head immersed in liquid nitrogen. Quantitative retention of all C2-C10 hydrocarbons was achieved only when a temperature gradient is created along the cooled column section. The focused components are eluted from the column head without supplementary heating by removing the coolant. To eliminate matrix effects, the enrichment procedure was designed to remove CO₂ and H₂O. The detection limit was found to be 2.0 × 10^?12 g propane.     

Analysis of polycyclic aromatic hydrocarbons in solid sample material using a desorption device coupled to a GC/MS system

Summary Polycyclic aromatic hydrocarbons (PAH) today are ubiquitous detectable constituents of recent sediments. The compounds are adsorbed on particulate emissions and are thus transferred to the environment. To date the analysis of PAH in sediments, dust samples and plant material is based mainly on the application of solvent-extraction methods followed by liquid chromatography and/or gas chromatographic separation of the extracts.An alternative approach for the analysis of PAH in solid samples such as coal, sediments, dust samples and plant waxes is shown in this contribution. A commercially available device for the analysis of volatile compounds present in solid matter is connected on-line to a GC/MS system. The device enables the thermal desorption of hydrocarbons at a temperature of 320°C. Subsequently, the hydrocarbons trapped on the initial part of the capillary column are analyzed by GC/MS. The application of mass chromatography provides the possibility of detection and quantitation of PAH in complex mixtures even when they coelute with other compounds. The sample amount required varies between 1 and 10 mg depending on the hydrocarbon content.     

Determination of polycyclic aromatic hydrocarbons in aqueous samples by microwave assisted headspace solid-phase microextraction and gas chromatography/flame ionization detection

The novel pretreatment technique, microwave-assisted heating coupled to headspace solid-phase microextraction (MA-HS-SPME) has been studied for one-step in situ sample preparation for polycyclic aromatic hydrocarbons (PAHs) in aqueous samples before gas chromatography/flame ionization detection (GC/FID). The PAHs evaporated into headspace with the water by microwave irradiation, and absorbed directly on a SPME fiber in the headspace. After being desorbed from the SPME fiber in the GC injection port, PAHs were analyzed by GC/FID. Parameters affecting extraction efficiency, such as SPME fiber coating, adsorption temperature, microwave power and irradiation time, and desorption conditions were investigated.Experimental results indicated that extraction of 20 mL aqueous sample containing PAHs at optional pH, by microwave irradiation with effective power 145 W for 30 min (the same as the extraction time), and collection with a 65 μm PDMS/DVB fiber at 20 °C circular cooling water to control sampling temperature, resulted in the best extraction efficiency. Optimum desorption of PAHs from the SPME fiber in the GC hot injection port was achieved at 290 °C for 5 min. The method was developed using spiked water sample such as field water with a range of 0.1-200 μg/L PAHs. Detection limits varied from 0.03 to 1.0 μg/L for different PAHs based on S/N = 3 and the relative standard deviations for repeatability were <13%. A real sample was collected from the scrubber water of an incineration system. PAHs of two to three rings were measured with concentrations varied from 0.35 to 7.53 μg/L. Recovery was more than 88% and R.S.D. was less than 17%. The proposed method is a simple, rapid, and organic solvent-free procedure for determination of PAHs in wastewater.     

制备气相色谱在挥发性成分分离中的应用研究进展北大核心CSCD

分析型气相色谱仪对低沸点易挥发的有机化合物展现出优异的分离性能,通过在其色谱柱末端加装馏分收集装置,建立了现代制备气相色谱(Prep GC)技术,该技术可用于挥发性成分的快速分离富集。制备气相色谱仪是由分析型气相色谱仪改装而来,其进样系统、分离系统、检测系统、馏分收集系统也在不断地优化升级,以提高目标化合物的回收效率和纯度。Prep GC与现代波谱技术(如紫外可见吸收光谱、红外吸收光谱、拉曼光谱、质谱、X射线衍射、核磁共振波谱)耦合,可对分离富集得到的目标化合物的结构进行精准确证。近年来,与Prep GC在各种挥发性成分分离中的应用相关的报道逐渐增多,展现出良好的应用前景。然而,Prep GC在分离过程中也存在着无法制备热敏性化合物、分离成本高、易引入外源性污染等问题。该文根据近年来国内外研究学者的相关研究工作,对制备气相色谱仪的结构及其在精油单体化合物、昆虫信息素、食品和植物挥发性成分、地质生物标志物及持久性环境污染物的分离等领域的应用研究进展进行综述。最后,还对Prep GC在挥发性成分分离中的应用进行了总结与展望,旨在为拓展Prep GC应用领域提供参考。     

色谱法筛选C_9芳烃萃取精馏溶剂

将萃取精馏溶剂作为气相色谱固定液,利用气－液色谱法对Ｃ９芳烃所用溶剂进行了选择。共测试环丁砜、邻苯二甲酸二甲酯等７种溶剂。其中邻苯二甲酸二甲酯对Ｃ９芳烃异构体的分离效果较好。方法省时省力,消耗少,结果可靠。     

A cryogen-free refrigerating preconcentration device for the measurement of C2 to C4 hydrocarbons in ambient air

A cryogen-free refrigerating preconcentration device for the enrichment of trace amounts of highly volatile organic compounds in the atmosphere prior to analysis has been designed and evaluated. The device consists of a microtrap housed in an insulated box, which is cooled by a conventional refrigeration unit. Experimental parameters, including adsorbent mass, trapping temperature, and thermal desorption temperature, were optimized. The on-line coupling of the device to a GC allows sufficient enrichment and separation of C2 to C4 hydrocarbons in less than 40 min without a second cryotrap. The target compounds analysis showed good linearity (correlation coefficients >0.99) and repeatability (relative standard deviation <5%). Detection limits for the 10 volatile organic compounds ranged from 14 ppt to 52 ppt, under the conditions of a 500 mL sampling volume and -10 °C trapping temperature. Real air sample measurements were conducted at an urban site, and five VOCs including ethane, ethene, propane, propene and 1-butene were detected and quantified.     

Offline LC-GC x GC in combination with rapid-scanning quadrupole mass spectrometry

The present research is focused on the offline combination of normal-phase LC to double-oven GC x GC-quadrupole MS. Initially, a diesel sample was subjected to automated LC x GC in order to define the elution windows of four fractions, viz., saturated hydrocarbons, monocyclic aromatics, dicyclic aromatics, tri- + tetracyclic aromatics; each fraction was collected exploiting the LC system in a further analysis and subjected to large-volume-injection-GC x GC analysis using an apolar-polar column combination. The GC x GC operational conditions were tuned in relation to the specific separation requirements of each heart-cut. The main benefits of what can be defined as offline LC-GC x GC were: (i) the high first-dimension LC selectivity; (ii) the injection of high sample amounts in the GC x GC system, enabling the detection and quantification of a series of low-amount diesel constituents; (iii) improved GC x GC operational conditions for each heart-cut with respect to direct GC x GC.     

Multiplexed detection of nitrate and nitrite for capillary electrophoresis with an automated device for high injection efficiency

A simple automated nanoliter scale injection device which allows for reproducible 5 nL sample injections from samples with a volume of <1 microL is successfully used for conventional capillary electrophoresis (CE) and Hadamard transform (HT) CE detection. Two standard fused silica capillaries are assembled axially through the device to function as an injection and a separation capillary. Sample solution is supplied to the injection capillary using pressure controlled with a solenoid valve. Buffer solution flows gravimetrically by the junction of the injection and separation capillaries and is also gated with a solenoid valve. Plugs of sample are pushed into the space between the injection and separation capillaries for electrokinectic injection. To evaluate the performance of the injection device, several optimizations are performed including the influence of flow rates, the injected sample volume and the control of the buffer transverse flow on the overall sensitivity. The system was then applied to HT-CE-UV detection for the signal-to-noise ratio (S/N) improvement of the nitric oxide (NO) metabolites, nitrite and nitrate. In addition, signal averaging was performed to explore the possibility of greater sensitivity enhancements compared to single injections.     

气相色谱法测定大气中的CO、CO_2以及低级烃类物质

建立了运用气相色谱对大气中一氧化碳、二氧化碳以及3种低级烃类甲烷、乙烯和乙炔进行同时分析的方法。气相色谱分析系统由自动进样器、1个十通阀协同1个六通阀,以及1个十通阀协同1个四通阀组成,可以实现进样、分离和反吹功能。HP-PLOT Q开口毛细管柱用于5种气体的分离,柱后连接热导检测器;分离完成后,一氧化碳和二氧化碳通过甲烷转化炉中的镍催化作用转化为甲烷,用氢火焰离子化检测器进行检测。5种目标分析物在9 min内完全分离。一氧化碳、甲烷、二氧化碳、乙烯以及乙炔的线性范围分别为3.3~4 990.0、3.3~5 010.0、6.6~4 990.0、4.2~5 080.0、3.9~5 030.0μmol/mol,检出限为1.0~2.0μmol/mol,相关系数不低于0.997,相对标准偏差(RSD,n=5)不大于3.5%。该方法简单、准确,可操作性强。     

Analysis of polycyclic aromatic hydrocarbons (PAHs) in environmental samples: a critical review of gas chromatographic (GC) methods

Polycyclic aromatic hydrocarbons (PAHs) are frequently measured in the atmosphere for air quality assessment, in biological tissues for health-effects monitoring, in sediments and mollusks for environmental monitoring, and in foodstuffs for safety reasons. In contemporary analysis of these complex matrices, gas chromatography (GC), rather than liquid chromatography (LC), is often the preferred approach for separation, identification, and quantification of PAHs, largely because GC generally affords greater selectivity, resolution, and sensitivity than LC. This article reviews modern-day GC and state-of-the-art GC techniques used for the determination of PAHs in environmental samples. Standard test methods are discussed. GC separations of PAHs on a variety of capillary columns are examined, and the properties and uses of selected mass spectrometric (MS) techniques are presented. PAH literature on GC with MS techniques, including chemical ionization, ion-trap MS, time-of-flight MS (TOF-MS), and isotope-ratio mass spectrometry (IRMS), is reviewed. Enhancements to GC, for example large-volume injection, thermal desorption, fast GC, and coupling of GC to LC, are also discussed with regard to the determination of PAHs in an effort to demonstrate the vigor and robustness GC continues to achieve in the analytical sciences.     

Coupling of thermal desorption in modified closeable sampling columns with wide-bore capillary gas chromatography and mass spectrometric detection

In contrast to usability of Curie-point pyrolysis at 700°C directly attached to gas chromatography-mass spectrometry (GC-MS) for determination of organic wood preservatives in waste wood samples the investigation method reported here consists of thermal desorption at temperatures about 260°C in connection with GC-MS for peak identification or GC with flame ionization detection for quantitative analyses. So-called “modified closeable sampling columns” are used as batch-reactor in thermal desorption experiments. Desorbed vapours can be introduced on capillary columns without sample discrimination and without a disturbing lost of resolution. In this manner a lot of individual polycyclic aromatic hydrocarbons were determinated in waste wood samples, especially in railway sleepers.     

Coupled LC-GC-MS for on-line clean-up,separation, and identification of chlorinated polycyclic aromatic hydrocarbons at picogram levels in urban air

Coupled liquid chromatography – gas chromatography – mass spectrometry (LC-GC-MS) has been applied for on-line clean up, separation, and identification of chlorinated polycyclic aromatic hydrocarbons (CI-PAHs). A loop-type interface was used to couple the liquid chromatograph on-line with the GC-MS, and concurrent solvent evaporation was used for sample transfer. A back-flush technique was used in conjunction with a two-dimensional column system for isolation of CI-PAHs and polycyclic aromatic hydrocarbons (PAHs). This fraction was transferred on-line to the GC and separated on a capillary column. Selective and sensitive detection of CI-PAHs in the GC eluate was obtained by negative ion chemical ionization (NICI) mass spectrometry and selected ion monitoring (SIM). The combined on-line system for isolation, separation, and identification showed high precision and accuracy, and demonstrated a linear response from 1 to 1000 pg for chlorinated PAHs. The estimated detection limit was 250 fg for 1-chloropyrene and 1,6-dichloropyrene. The technique was demonstrated by analysis of urban air samples. The low detection limit made it possible to use the technique for analysis of personally carried monitoring equipment for measurement of exposure to CI-PAHs in the work environment.     

Remote,real-time,on-line monitoring of high-temperature samples by noninvasive open-path laser plasma spectrometry

A remote detection system based on optical emission spectrometry of laser-induced plasmas has been developed to record spectra in the visible region from samples placed at remote distances from the excitation source. Unlike from fiber-optic-based systems, light collection is performed remotely as well. Laboratory-scale experiments have shown the possibility of performing real-time analysis of samples placed remotely. The application in the noninvasive analysis of hot samples (at 1,200 degrees C) has been demonstrated as well, allowing the dynamic monitoring of selective elemental migration.     

Laser desorption fast gas chromatography–Mass spectrometry in supersonic molecular beams

A novel method for fast analysis is presented. It is based on laser desorption injection followed by fast gas chromatography-mass spectrometry (GC-MS) in supersonic molecular beams. The sample was placed in an open air or purged laser desorption compartment, held at atmospheric pressure and near room temperature conditions. Desorption was performed with a XeCl Excimer pulsed laser with pulse energy of typically 3 mJ on the surface. About 20 pulses at 50 Hz were applied for sample injection, resulting in about 0.4 s injection time and one or a few micrograms sample vapor or small particles. The laser desorbed sample was further thermally vaporized at a heated frit glass filter located at the fast GC inlet. Ultrafast GC separation and quantification was achieved with a 50-cm-long megabore column operated with a high carrier gas flow rate of up to 240 mL/min. The high carrier gas flow rate provided effective and efficient entrainment of the laser desorbed species in the sweeping gas. Following the fast GC separation, the sample was analyzed by mass spectrometry in supersonic molecular beams. Both electron ionization and hyperthermal surface ionization were employed for enhanced selectivity and sensitivity. Typical laser desorption analysis time was under 10 s. The laser desorption fast GC-MS was studied and demonstrated with the following sample/matrices combinations, all without sample preparation or extraction: (a) traces of dioctylphthalate plasticizer oil on stainless steel surface and the efficiency of its cleaning; (b) the detection of methylparathion and aldicarb pesticides on orange leaves; (c) water surface analysis for the presence of methylparathion pesticide; (d) caffeine analysis in regular and decaffeinated coffee powder; (e) paracetamol and codeine drug analysis in pain relieving drug tablets; (f) caffeine trace analysis in raw urine; (g) blood analysis for the presence of 1 ppm lidocaine drug. The features and advantages of the laser desorption fast GC-MS are demonstrated and discussed.     

Characterization of olive oil volatiles by multi-step direct thermal desorption-comprehensive gas chromatography-time-of-flight mass spectrometry using a programmed temperature vaporizing injector

The feasibility of a versatile system for multi-step direct thermal desorption (DTD) coupled to comprehensive gas chromatography (GC x GC) with time-of-flight mass spectrometric (TOF-MS) detection is studied. As an application the system is used for the characterization of fresh versus aged olive oil after treatment at 70, 175, 250 and 600 degrees C.     

用于昆虫外激素研究的微量顶空收集及热解吸气相色谱进样方法初探

描述了一个结合项空气流收集与无溶剂热解吸气相色谱进样的方法。用填充PorapskQ的微量注射器作为吸附管进行气流收集。将收集物不经溶剂洗脱直接进行热解吸进样。用人工合成的昆虫外激素化合物反-7-十二碳单烯乙酸酯（E-7-DA）及顺-5,反-7-十二碳二烯乙酸酯（Z-5,E-7-DDA）测定了方法的回收率,初步探索了运用于昆虫外激素分析的可行性,并讨论了提高回收率的途径。     

Achieving high peak capacity production for gas chromatography and comprehensive two-dimensional gas chromatography by minimizing off-column peak broadening

By taking into consideration band broadening theory and using those results to select experimental conditions, and also by reducing the injection pulse width, peak capacity production (i.e., peak capacity per separation time) is substantially improved for one dimensional (1D-GC) and comprehensive two dimensional (GC×GC) gas chromatography. A theoretical framework for determining the optimal linear gas velocity (the linear gas velocity producing the minimum H), from experimental parameters provides an in-depth understanding of the potential for GC separations in the absence of extra-column band broadening. The extra-column band broadening is referred to herein as off-column band broadening since it is additional band broadening not due to the on-column separation processes. The theory provides the basis to experimentally evaluate and improve temperature programmed 1D-GC separations, but in order to do so with a commercial 1D-GC instrument platform, off-column band broadening from injection and detection needed to be significantly reduced. Specifically for injection, a resistively heated transfer line is coupled to a high-speed diaphragm valve to provide a suitable injection pulse width (referred to herein as modified injection). Additionally, flame ionization detection (FID) was modified to provide a data collection rate of 5kHz. The use of long, relatively narrow open tubular capillary columns and a 40°C/min programming rate were explored for 1D-GC, specifically a 40m, 180μm i.d. capillary column operated at or above the optimal average linear gas velocity. Injection using standard auto-injection with a 1:400 split resulted in an average peak width of ～1.5s, hence a peak capacity production of 40peaks/min. In contrast, use of modified injection produced ～500ms peak widths for 1D-GC, i.e., a peak capacity production of 120peaks/min (a 3-fold improvement over standard auto-injection). Implementation of modified injection resulted in retention time, peak width, peak height, and peak area average RSD%'s of 0.006, 0.8, 3.4, and 4.0%, respectively. Modified injection onto the first column of a GC×GC coupled with another high-speed valve injection onto the second column produced an instrument with high peak capacity production (500-800peaks/min), ～5-fold to 8-fold higher than typically reported for GC×GC.     

Qualitative mass spectrometric analysis of the volatile fraction of creosote-treated railway wood sleepers by using comprehensive two-dimensional gas chromatography

The volatile composition of 20-year-old out-of-service creosote-treated railway wood sleepers was studied. The emitted volatile fraction was collected by means of dynamic purge-and-trap concentration at ambient temperature, and analyzed by comprehensive two-dimensional gas chromatography (GC x GC) hyphenated with mass spectrometric detection systems, using quadrupole (GC x GC/qMS) and time-of-flight (GC x GC/ToF-MS) mass analyzers and selective nitrogen-phosphorus detection (GC x GC-NPD). The analysis of mass spectrometry data and GC x GC retention time allowed the tentative identification of about 300 compounds based on spectrometric data and positioning of each compound in the GC x GC plot. Major important headspace components are polyaromatic hydrocarbons, phenols and benzene derivatives, hydrocarbons and heterocyclic compounds containing nitrogen, sulphur or oxygen atoms. Many of the reported compounds are listed as belonging to toxicological substance classes which have been related to harmful health effects. GC x GC provides greater speciation and evidence of composition heterogenicity of the sample than one-dimensional GC analysis, thus allowing to better demonstrate its potential toxicity. Data obtained by specific detection systems for N-heterocycles assisted mass data interpretation assignments. The enhanced separation power obtained after GC x GC compared to one-dimensional gas chromatography (1D-GC) together with spectral deconvolution and correlation with physical-chemical data, allowed the identification of complex isomer clusters, as demonstrated for alkylquinolines, and applied also to alkylphenols, alkylbenzenes and alkylnaphthalenes.     

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.