Limits in arson debris analysis by capillary column gas chromatography/mass spectrometry

Sample enrichment technology and instrumental sensitivity are no longer limiting factors in arson debris analysis. When pyrolyzed, petroleum based composite materials may produce artifacts. Urban air is another major source of interference since some of the components typically found in air, in particular alkylated aromatic hydrocarbons, are customarily used as indicators for the presence of gasoline. It is suggested to replace qualitative analysis with a quantitative approach, taking the sample matrix into consideration.     

High resolution gas chromatography/mass spectrometry analysis of the environmental pollutants methylnitronaphthalenes

We report the linear retention indices of the 14 methylnitro-naphthalenes on three high resolution capillary columns and their electron impact mass spectra. The analyses of the methylnitro-naphthalenes in an ambient air sample by gas chromatography/mass spectrometry with multiple ion detection utilizing 5% phenylmethylsilicone, 50% phenylmethylsilicone, and smectic columns are shown.     

Ultrasound-assisted extraction and on-line LC–GC–MS for determination of polycyclic aromatic hydrocarbons (PAH) in urban dust and diesel particulate matter

A method has been developed for determination of polycyclic aromatic hydrocarbons (PAH) in particulate matter from ambient air and diesel exhaust emissions. It is reproducible and accurate and, compared with similar methods for analysis of individual PAH components in complex matrices, it is relatively fast and simple. Single PAH components can be determined in samples of particulate matter from ambient air and diesel exhaust emissions with LOD of approximately 1 pg/sample. Further, sample throughput is high, because more than 20 samples can be extracted and prepared for analysis in one working (8-h) day. The particulate matter is subjected to ultrasound-assisted extraction, a technique that is shown to extract PAH from particulate material with efficiencies fully comparable with those of Soxhlet extraction. An aliphatic/PAH-enriched fraction is obtained by solid-phase extraction before isolation, separation, and identification/quantification of PAH by on-line liquid chromatography–gas chromatography–mass spectrometry. The method was validated by analysis of US National Institute of Standards and Technology (NIST) Standard Reference Materials (SRM) 1649a, Urban Dust, and 2975, Diesel Particulate Matter. Results from the method are in good agreement with the NIST-certified PAH concentrations and with NIST reference PAH concentrations.     

Performance characteristics of a new prototype for a portable GC using ambient air as carrier gas for on-site analysis

The performance characteristics of a portable GC instrument requiring no compressed gas supplies and using relatively lightweight transportable components for the analysis of volatile organic components in large-volume air samples are described. To avoid the need for compressed gas tanks, ambient air is used as the carrier gas, and a vacuum pump is used to pull the carrier gas and injected samples through the wall-coated capillary column and a photoionization detector (PID). At-column heating is used eliminating the need for a conventional oven. The fused silica column is wrapped with heater wire and sensor wire so that heating is provided directly at the column. A PID is used since it requires no external gas supplies and has high sensitivity for many compounds of interest in environmental air monitoring. In order to achieve detection limits in the ppb range, an online multibed preconcentrator containing beds of graphitized carbons and carbon molecular sieves is used. After sample collection, the flow direction through the preconcentrator is reversed, and the sample is thermally desorbed directly into the column. Decomposition of sensitive compounds during desorption is greater with air as the carrier gas than with hydrogen.     

Dual Adsorber-Capillary Column System for Gas Chromatographic Analysis of Air Samples

Abstract

An interface which allows thermal desorption and subsequent capillary gas chromatographic analysis of air samples is described. A small solid-sorbent trap is positioned between the sampling tube and capillary column. A sample thermally released from the sampling tube is transferred by a carrier gas at high flow rate to the trap and retained. From there it is again thermally released and transferred to the capillary column by carrier gas at a low flow rate, as required by capillary GC. The transfer and injection steps are effected by means of externally placed solenoid valves. The performance of the system depends on the desorption temperature and time allowed for transfer of the sample between the two adsorbers and the column. These parameters are programmable and can be changed to suit the requirements of a particular analysis. The system allows the analysis of sub-parts-per-billion concentrations of organic compounds in a comparatively simple and reproducible manner. Operation of the system does not require cryogenic cooling of either the trap or the GC oven. Chromatograms of a variety of air samples are presented and discussed.     

Comprehensive gas chromatography coupled to mass spectrometry for the separation of pesticides in a very complex matrix

The present research is focused on the development of a comprehensive two-dimensional gas chromatography–rapid scanning quadrupole mass spectrometric (GC x GC-qMS) methodology for the analysis of trace-amount pesticides contained in a complex real-world sample. Reliable peak assignment was carried out by using a recently developed, dedicated pesticide MS library (for comprehensive GC analysis), characterized by a twin-filter search procedure, the first based on a minimum degree of spectral similarity and the second on the interactive use of linear retention indices (LRI). The library was constructed by subjecting mixtures of commonly used pesticides to GC x GC-qMS analysis and then deriving their pure mass spectra and LRI values. In order to verify the effectiveness of the approach, a pesticide-contaminated red grapefruit extract was analysed. The certainty of peak assignment was attained by exploiting both the enhanced separation power of dual-oven GC x GC and the highly effective search procedure.     

Automation in the chemical analysis of suspect arson samples by GC/MS. A systematic approach

A method ist described that permits direct comparison of ion chromatograms between an isolate from a suspect fire debris sample and corresponding accelerant profiles. The system is highly automated and produces a diagnostic one page summary report for each sample. Side by side comparison of ion profiles is carried out between 4 common fuel types, e. g. gasoline, naphthenic type charcoal lighter fluid, mineral spirits, and kerosene, and the sample. Both qualitative and semiquantitative information is available. An on-line search can also be carried out in which mass spectra are compared between components in a suspect sample and standards that are contained in an accelerant library. The system is flexible and requires only minimal interaction with the analyst.     

全二维气相色谱在石油地质样品分析中的应用进展

对石油地质样品的化学组成进行全面准确的剖析,可以获得丰富的地球化学信息,为油气勘探工作提供科学依据。然而,该类样品除了组成复杂之外,还易受到各种物理（如蒸发、乳化、扩散、溶解和吸附）、化学（如光降解）和生物（如微生物降解）过程的影响。这些特点给样品的分析研究工作带来了极大的困难,传统的一维气相色谱/质谱技术很难对其进行理想的分离。全二维气相色谱（GC×GC）作为新发展起来的一种分离技术,在复杂样品分析方面具有独特的优势,虽然在石油地质样品分析中的应用相对较晚,但也日益受到关注。本文主要综述了近5年来GC×GC在石油地质方面国内外的研究进展以及存在的主要问题,并对今后的研究进行了展望。     

Analytical Study of a Resinous Material Used as Sealing in Ancient Pottery Found in an Archaeological Site by Thermally Assisted Hydrolysis Methylation–Gas Chromatography–Mass Spectrometry,Vibrational Spectroscopy and Light Microscopy

Abstract

A resin sample was found in the archaeological site of Lixus (Morocco), belonging to the second century BC. The resinous material was found inside an amphora containing iron remains used in the plug as sealing material to hermetically close the pottery. The resinous sample was studied by several analytical techniques, as thermally assisted hydrolysis and methylation–gas chromatography–mass spectrometry (THM–GC–MS), Fourier transformed infrared spectroscopy (FTIR), and light microscopy. The material was identified as a Pinaceae resin. Therefore, a modern pine resin was also analyzed to consider the influence of aging in the archaeological sample. The ancient material was found not too oxidized, owing to the conservation conditions inside the amphora, protected from air and moisture.     

Combination of dynamic time warping and multivariate analysis for the comparison of comprehensive two-dimensional gas chromatograms: application to plant extracts

Comprehensive two-dimensional gas chromatography (GC x GC) is now recognized as the preferred technique for the detailed analysis and characterization of complex mixtures of volatile compounds. However, for comparison purposes, taking into account all the information contained in the chromatogram is far from trivial. In this paper, it is shown that the combination of peak alignment by dynamic time warping and multivariate analysis facilitated the comparison of complex chromatograms of tobacco extracts. The comparison is shown to be efficient enough to provide a clear discrimination among three types of tobacco. A tentative interpretation of loadings is presented in order to give access to the compounds which differ from one sample to another. Once located, mass spectrometry was used to identify markers of tobacco type.     

毛细管色谱-质谱法测定环境大气中挥发性有机污染物

毛细管色谱-质谱法测定了环境大气中挥发性污染物。用液氧冷冻法和常温吸附法(TenaxGC)分别采集大气样品,然后用两种系统进行浓缩,并进入毛细管色谱-质谱体系,完成了有机污染物的定性定量分析。解决了一些色谱-质谱联用中的问题。并且还讨论了无分流进样问题,比较了两种采样方法。用此方法测定了某炼油厂环境大气中的污染物。     

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.     

Analysis of Semi-Volatile Aromatic Chlorinated Acids in Drinking Water by Liquid-Solid Extraction GC/MS

Abstract

An analytical procedure utilizing solid phase extraction with octadecylsilane bonded to silica (C₁₈) cartridges combined with gas chromatography/mass spectrometry (GC/MS) was developed to analyze semi-volatile chlorinated acids found in drinking water. A system has been designed which will enable the analysis of this class of compounds with minimum sample manipulation and detection limits in the low ng/L range. The overall accuracy and precision were comparable to other methods used for compliance purposes. Among the advantages of the developed methodology are its applicability for field sampling and at the same time, provides a simple and inexpensive mean for sample preservation.     

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.     

GC/MS中保留指数和保留温度回归分析应用于单萜烯结构确认

GC／MS定性分析中,由于同分异构体的质谱图相似,常常出现结构鉴定错误．同分异构体化合物的保留行为具有较大地差别,采用文献保留指数和保留温度测定值回归分析方法对2篇已发表论文进行了研究,发现了对单萜烯类同分异构体结构鉴定中存在的错误,并提出可能的正确结构．文献保留指数和保留温度测定值回归分析方法可以简化GC／MS色谱峰的定性分析过程,提高定性分析的准确性,在样品定性分析中具很强的使用价值．     

Investigating aroma diversity combining purge‐and‐trap,comprehensive two‐dimensional gas chromatography,and mass spectrometry

Headspace gas chromatography is frequently used for aroma profiling thanks to its ability to naturally exploit the volatility of aroma compounds, and also to provide chemical information on sample composition. Its main advantages rely on simplicity, no use of solvent, amenability to automation, and the cleanliness of the extract. In the present contribution, the most effective sampling (dynamic extraction), separation (multidimensional gas chromatography), and detection (mass spectrometry) techniques for untargeted analysis are exploited in combination, showing their potential in unraveling aroma profiles in fruit beers. To complete the overall analytical process, a neat workflow for data analysis is discussed and used for the successful characterization and identification of five different beer flavors (berries, cherry, banana, apple, and peach). From the technical viewpoint, the coupling of purge‐and‐trap, comprehensive two‐dimensional gas chromatography, and mass spectrometry makes the global methodology unique, and it is for the first time discussed. A (low‐)flow modulation approach allowed for the full transfer into the second dimension with mass‐spectrometry compatible flow (< 7 mL/min), avoiding the need of splitting before detection and making the overall method sensitive (1.2–5.2‐fold higher signal to noise ratio compared to unmodulated gas chromatography conditions) and selective.     

Multiresidue method using SPME for the determination of various pesticides with different volatility in confined atmospheres

An analytical method is described for assessing the vapour concentration of 11 pesticides (bioallethrin, chlorpyriphos methyl, folpet, malathion, procymidone, quintozene, chlorothalonil, fonofos, penconazole and trimethacarb) in confined atmospheres (e.g. a greenhouse after pesticide application). This study is a successful extension of a method previously developed by the authors for dichlorvos to much less volatile pesticides. Sampling was performed by using polydimethylsiloxane–solid phase micro-extraction (PDMS–SPME) fibres immersed in a 250-mL sampling flask through which air samples were dynamically pumped from the analysed atmosphere. After a 40-min sampling duration, samples were analysed by GC/MS.Calibration was performed from a vapour-saturated air sample. The linearity of the observed signal versus pesticide concentration in the vapour phase was proved from spiked liquid samples whose headspace concentrations were measured by using the proposed method. This procedure gave calibration curves with regression coefficients (R²) greater than 0.98, and the repeatability of these measurements was found with RSDs of 1.9–7.6%. As a field application test, this analysis procedure was used for the determination of gaseous procymidone concentrations as a function of time in the atmosphere of an experimental 8-m² and 20-m³ greenhouse. The pesticide was sprayed according to real cultivation conditions, and measurements were made for 80 h after application (8 measurements). The observed concentrations found ranged from 200 to 500 µg m^–3, thus indicating the level of contamination of the air breathed by people in such working conditions.Abbreviations GC/MS gas chromatography/mass spectrometry - SIM selective ion monitoring - FC43 perfluorotributylamine - RSD relative standard deviation - LOD limit of detection - LOQ limit of quantification     

Determination of benzene, toluene, ethylbenzene and xylenes in air by solid phase micro-extraction/gas chromatography/mass spectrometry

The aim of the study was to analyse BTEX compounds (benzene, toluene, ethylbenzene, xylenes) in air by solid phase micro-extraction/gas chromatography/mass spectrometry (SPME/GC/MS), and this article presents the features of the calibration method proposed. Examples of real-world air analysis are given. Standard gaseous mixtures of BTEX in air were generated by dynamic dilution. SPME sampling was carried out under non-equilibrium conditions using a Carboxen/PDMS fibre exposed for 30 min to standard gas mixtures or to ambient air. The behaviour of the analytical response was studied from 0 to 65 g/m³ by adding increasing amounts of BTEX to the air matrix. Detection limits range from 0.05 to 0.1 g/m³ for benzene, depending on the fibre. Inter-fibre relative standard deviations (reproducibility) are larger than 18%, although the repeatability for an individual fibre is better than 10%. Therefore, each fibre should be considered to be a particular sampling device, and characterised individually depending on the required accuracy. Sampling indoor and outdoor air by SPME appears to be a suitable short-delay diagnostic method for volatile organic compounds, taking advantage of short sampling time and simplicity.     

Analysis of turkish lignite tar by coupled LC/GC,GC/MS,and capillary SFC

This work describes the analysis of a pyrolysis product of a lignite sample obtained from the Turkish Goynuk reserve. The aliphatic, aromatic and polar compounds present in the tar are separated and identified by various chromatographic techniques: Capillary gas chromatography/mass spectrometry (GC/MS), on-line high performance microbore liquid chromatography/capillary gas chromatography (LC/GC) and capillary supercritical fluid chromatography (SFC). The suitability of each technique for this particular application is discussed, and semi-quantitative results are presented for the major components detected.     

Dynamic solid phase microextraction for sampling of airborne sarin with gas chromatography-mass spectrometry for rapid field detection and quantification

A portable dynamic air sampler and solid phase microextraction were used to simultaneously detect, identify, and quantify airborne sarin with immediate analysis of samples using a field portable gas chromatography-mass spectrometry system. A mathematical model was used with knowledge of the mass of sarin trapped, linear air velocity past the exposed sampling fiber, and sample duration allowing calculation of concentration estimates. For organizations with suitable field portable instrumentation, these methods are potentially useful for rapid onsite detection and quantification of high concern analytes, either through direct environmental sampling or through sampling of air collected in bags.