Stability of compressed gas mixtures containing low level volatile organic compounds in aluminum cylinders

Compressed gas mixtures containing up to twenty-six volatile organic compounds (VOCs) in a balance of nitrogen have been prepared and analyzed at the National Institute of Standards and Technology (NIST). The mixtures are contained in aluminum cylinders and the hydrocarbons included are aromatic or aliphatic, both saturated and unsaturated and some containing a halogen, oxygen or nitrogen atom. The individual compounds are present at concentrations ranging from 0.1–3000 nmol/mol and the relative standard uncertainty in the concentration of each is between ±2–5%. The stability of the mixtures over various time intervals is discussed.     

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   

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.     

An extended saturated liquid density equation

The recently developed saturated liquid density correlation of Iglesias-Silva and Hall for halogenated paraffins is extended to other classes of compounds involving paraffins, cycloparaffins, olefins, diolefins, cyclic-olefins, aromatics, alcohols, ethers, liquefied inorganic gases, and others. The two adjustable parameters of the correlation are optimized and reported for 126 compounds. The average error for 5377 experimental data points was 0.27%. The correlation is extended to multicomponent mixtures. A set of mixing rules is proposed. The correlation with this set of mixing rules is used to predict the saturated liquid density of 86 multicomponent systems consisting of LNG, heavy hydrocarbons, CO₂, H₂S, alcohols and halogenated paraffins. The average of error for 1378 experimental data points was 1.03% with 0 bias with respect to experimental data. These values compare well with the values from well-known correlations. For polar compounds or multicomponent systems containing polar compounds, the computation of saturated liquid density by this correlation shows superiority with respect to the other correlations.     

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.     

Dry ice-originated supercritical and liquid carbon dioxide extraction of organic pollutants from environmental samples

Packed in a high-pressure vessel and under calculated conditions, dry ice can be used as a source of carbon dioxide for supercritical CO₂ extraction or liquid CO₂ of organic compounds from environmental samples. Coupled with a fluid modifier such as toluene, dry ice-originated supercritical CO₂ (Sc CO₂) achieves quantitative extraction of many volatile organic compounds (VOCs) and semivolatile organic compounds (SOCs) including polycyclic aromatic hydrocarbons (PAHs), n-alkanes, and polychlorinated biphenyls (PCBs) from solid matrices. Compared to contemporary manual or automated supercritical fluid extraction (SFE) technologies, this novel technique simplifies SFE to a minimum requirement by eliminating the need of a high-pressure pump and any electrical peripherals associated with it. This technique is highly suitable to analytical areas where sample preservation is essential but difficult in the sampling field, or where sample collection, sample preparation, and analysis are to be done in the field.     

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。     

Determination of Tetrachloroethylene and Other Volatile Halogenated Organic Compounds in Oil Wastes by Headspace SPME GC–MS

Oil wastes and slops are complex mixtures of hydrocarbons, which may contain a variety of contaminants including tetrachloroethylene (perchloroethylene, PCE) and other volatile halogenated organic compounds (VHOCs). The analytical determination of PCE at trace levels in petroleum-derived matrices is difficult to carry out in the presence of large amounts of hydrocarbon matrix components. In the following study, we demonstrate that headspace solid-phase microextraction (HS-SPME) combined with GC–MS analysis can be applied for the rapid measurement of PCE concentration in oil samples. The HS-SPME method was developed using liquid paraffin as matrix matching reference material for external and internal calibration and optimisation of experimental parameters. The limit of quantitation was 0.05 mg kg⁻¹, and linearity was established up to 25 mg kg⁻¹. The HS-SPME method was extended to several VHOCs, including trichloroethylene (TCE) in different matrices and was applied to the quantitative analysis of PCE and TCE in real samples.     

Analysis of complex industrial samples by gas chromatography; a report on selected past activities

Summary A review of past activities concerning selected industrial analytical problems is given. This includes the following question: preparation of pure gas mixtures to be used for calibration, catalytic conversion of ester and pyridin samples to carbon dioxide and a one-point calibration method using peak heights, both for quantitative analysis, analysis of gas mixtures containing fluorine and inorganic fluorine compounds and the determination of the oxygen and fluorine content of the sample, separation and identification of hydrocarbons in shale oil and petroleum fraction samples, and analysis of wine.     

Development of a screening method to determine the pattern of fermentation metabolites in faecal samples using on-line purge-and-trap gas chromatographic–mass spectrometric analysis

An on-line screening method to analyse volatile organic compounds (VOCs) in faecal samples was developed. VOCs were isolated from a standard solution or faecal samples using a purge-and-trap system and identified and quantified by GC–MS. The experimental conditions were optimised and the performance of the system was evaluated. Linear calibration curves were obtained with correlation coefficients of at least 0.992. RSDs within and between days were less than 10%. The method was successfully applied to the analysis of faecal samples, yielding 135 different volatile organic compounds identified in 11 faecal samples. Of those, 22 VOCs were found in all volunteers, whereas 34 VOCs were person-specific.     

Performance and characteristics of a trace gas analyzer for the determination of volatile organic compounds in air

An instrument has been developed and tested for the continuous measurement of volatile organic compounds (VOC) in air. The system consists of a gas chromatograph equipped with a dedicated sampling device that allows the sample to be transferred to a cooled microtrap via sampling loops (10, 100, 250 ml) or via a direct pump transfer to the trap. The microtrap is placed in the chromatographic oven just below a modified split-splitless injector, allowing direct liquid injection for calibration of the system; the injector is in communication with the sampling valve equipped with the loop and the sampling pump. The system allows 24-hour sampling and analysis of a large number of VOC (up to 25 individual hydrocarbons ranging from C2 C9) and also polar volatile organic compounds PVOC. Thanks to the particular trap geometry, a minimum consumption of liquid nitrogen (between 150 300 ml) is needed for each analytical run and no water managing system is normally required for humid air samples.     

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.     

Study of the relative response factors of various gas chromatograph-flame ionisation detector systems for measurement of C2-C9 hydrocarbons in air

The assumption of an instrument response that is linear with carbon number is frequently used to quantify atmospheric non-methane hydrocarbons (NMHCs) when using gas chromatography (GC) and detection by flame ionisation detector (FID). In order to assess the validity of this widely used method the results of intercomparison measurements by 14 laboratories across Europe were evaluated. The intercomparison measurements were made on synthetic, gravimetrically-prepared, gas mixtures containing 30 hydrocarbons (C2-C9) in the low ppbv range, using various different GC-FID systems. The response per carbon atom of GC-FID systems to individual NMHCs, relative to that of butane, were found to differ by more than 25% across different systems. The differences were mostly caused by analytical errors within particular GC-FID systems and to a more minor degree by systematic deviations related to the molecular structure. (Correction factors due to the molecular structure would lessen the differences, e.g. by about 5% for olefin compounds.) The differences were larger than 10% even after elimination of obvious outliers. Thus, calibration of GC-FID systems with multicomponent NMHC mixtures is found to be essential whenever the accuracy of NMHC measurements is required to be better than about 10%. If calibration by multicomponent gas mixtures is not possible and effective carbon atom response factors are used to quantify the individual NMHC compounds then the particular analytical system should be carefully characterised and its responses to individual compounds be verified.     

Atmosphärenchemie biogener Kohlenwasserstoffe

Large quantities of volatile organic compounds (VOCs) are released by terestrial vegetation into the atmosphere. As a result of chemical reactions of these biogenic VOCs the concentrations of several climatically relevant trace species are significantly affected. There is substantial evidence that biogenic hydrocarbons influence, for example, the regional distribution of tropospheric ozone and the formation of organic aerosols. The article attempts to elucidate the current state of knowledge about this particular part of the carbon cycle between biosphere and atmosphere. Furthermore, still open questions about the influence of natural VOCS on chemical and physical processes in the troposphere are discussed.     

Rapid removal of selected volatile organic compounds from gaseous mixtures using a new dispersive vapor extraction technique: A feasibility study

A new dispersive vapor extraction (DVE) technique for rapid removal of selected volatile organic compounds (VOCs) from gaseous mixtures was investigated. In this technique, less than 1.0 mL of a volatile solvent was vaporized for 8 min in a 250-mL flask containing a gaseous mixture. The flask was then cooled under running tap water for 2-3 min to induce condensation of the vapor and co-extraction of the VOCs from the headspace. The technique was tested over a concentration range of 4-23 ppb, and resulted in extraction efficiencies ranging from 80 to 97% for the VOCs tested. Because of its simplicity and the relatively short sampling time, DVE could potentially lead to high sample throughput and rapid air analysis.     

Microanalysis of Volatile Organic Compounds (VOCs) in Water Samples – Methods and Instruments

Volatile organic compounds (VOCs), due to their toxicity and persistence in the environment, are particularly important pollutants. Some of these compounds are mutagens, teratogens or carcinogens, while others are responsible for the degradation of organoleptic parameters such as taste and odour of water. This review focuses on a number of key procedural steps in the analysis of volatile organic compounds (VOCs) in water samples. A wide spectrum of techniques for the isolation and preconcentration of the aforementioned pollutants for trace organic analysis by gas chromatography are presented and discussed. The advantages and disadvantages of these techniques are discussed and novel developments are also taken into consideration.     

A high-temperature sensor analyzer: Determination of difficult volatile organic impurities in solvents

It was shown that an automated analyzer with solid-electrolyte sensor cells can be used to determine difficult volatile organic impurities (technical oils, gasoline, and kerosene) in organic solvents (alcohols, acetone, and turpentine) by their two-stage oxidation with atmospheric oxygen at 100 °C (evaporation of a light fraction) and at a temperature of 900 °C and higher (burning impurities). Optimum conditions are found for the rapid determination of trace amounts of MS-20 oil in washing solvents (ethanol, benzene): time of determination, 5 min/sample; aliquot portion, 10 μL; linearity range of the calibration graph, from 20 to 100 mg/L of organic impurity; detection limit, 2.5 mg/L; RSD ≥ 8%. The results of determining the concentrations of gasolines of different grades and other organic mixtures for identifying substance grades are discussed. The novelty and advantages of the developed method consist in the rapid and quantitative determination of the octane number and other parameters of hydrocarbon fuels without preliminary sample preparation and also in the possibility of analyzing liquid samples of any other origin without resorting to the chemical methods of analysis. The ecological safety of the method is also important.     

Perdeuterated n-alkanes for improved data processing in thermal desorption gas chromatography/mass spectrometry I. Retention indices for identification

The identification of organic compounds by GC/MS is useful in various areas such as fuel, indoor and outdoor air and flavour and fragrance applications. Multi-compound mixtures often contain isomeric compounds which have similar mass spectra and sometimes cannot be unambiguously identified by library search alone. Retention indices can help with confirmation of identification if they are reproducible. Using perdeuterated n-alkanes as a reference series for calculation of retention indices in GC/MS has a clear benefit because of the distinctive ion trace of m/z 34. Thermal desorption is useful for analysis of volatile organic compounds (VOCs) in air after sampling on appropriate sorbent cartridges. Comparison of indices between three systems, consisting of a thermal desorption unit, a gas chromatograph and a mass spectrometer, showed good agreement for compounds with well-defined peaks, whereas retention times varied.     

Evaluation of septa quality for automatic SPME-GC-MS trace analysis

The vials used for the preparation of breath samples for automated solid-phase microextraction-gas chromatography-mass spectrometry analysis are crimped with septa. These septa often emit specific volatile organic compounds (VOCs) confounding the measurement results of breath samples. In the current paper, 14 different brands of magnetic caps with silicone-polytetrafluoroethylene (PTFE), butyl-PTFE, or butyl rubber septa were tested. The total emission of septa over a 4 h period was also evaluated. The tested septa emitted 39 different compounds, which are mainly hydrocarbons, alcohols, and ketones. Acetone and toluene are the most abundant out-gassing products. The concentration of acetone was in the range from 55 to 694 ppb for butyl-PTFE septum (brand 14) and butyl rubber (brand 10), respectively. The measured toluene amount was 69-1323 ppb for the septum brand 14 and brand 8 (silicone-PTFE), respectively. Generally, the butyl rubber septa released higher amounts of contaminants in comparison to the silicone ones.