Determination of dimethylselenide and dimethyldiselenide by gas chromatography-photoionization detection

A simple method for the determination of volatile selenium compounds employing a gas chromatograph equipped with a photoionization detector is described. The method involves the direct injection of dimethylselenide (DMS) or dimethyldiselenide (DMDS) into the gas chromatograph; no derivatization of the sample was required. The photoionization detector was capable of detecting 60 pg (0.55 pmol) of DMS and 150pg (0.80pmol) DMDS. Sensitivity was 10-50 times greater with DMS and 4-20 times greater with DMDS when the photoionization detector was employed than when the flame ionization detector was employed.     

On-site monitoring of biogenic emissions from Eucalyptus dunnii leaves using membrane extraction with sorbent interface combined with a portable gas chromatograph system

Membrane extraction with sorbent interface, combined with a portable gas chromatograph system (MESI-Portable GC) for continuous on-line monitoring of biogenic volatile organic compounds (BVOCs) emissions (from leaves of Eucalytus dunnii in a greenhouse), is presented herein. A sampling chamber was designed to facilitate the extraction and identification of the BVOCs emitted by the Eucalytus dunnii leaves. Preliminary experiments, including; enrichment times, microtrap temperatures, stripping gas flow rates, and desorption temperatures were investigated to optimize experimental parameters. The main components of BVOCs released by the Eucalytus dunnii leaves were identified by comparing the retention times of peaks with those of authentic standard solutions. They were then confirmed with solid phase microextraction coupled with gas chromatography and mass spectrometry (SPME-GC-MS). BVOC emission profiles of [small alpha]-pinene, eucalyptol, and [gamma]-terpinene emitted by intact and damaged Eucalytus dunnii leaves were obtained. The findings suggest that the MESI-Portable GC system is a simple and useful tool for field monitoring changes in plant emissions as a function of time.     

Gas chromatographic determination of benzene, toluene, ethylbenzene and xylenes using flame ionization detector in water samples with direct aqueous injection up to 250 microl

A simple method of solventless extraction of volatile organic compounds (benzene, toluene, ethylbenzene and xylenes) from aqueous samples was developed. This method allows direct injection of large volume of water sample into a gas chromatograph using the sorption capacity of the sorbent Chromosorb P NAW applied directly in the injection port of gas chromatograph. The system prevent water penetration into a column, keep it adsorbed on its surface until the analytes are stripped into a column, and the residual water is purging using split flow. The limit of detection ranging from 0.6 for benzene to 1.1 microg l(-1) for o-xylene and limit of quantification ranging 2.0-3.6 microg l(-1) are lower that those reached by gas chromatography with flame ionization detection and direct aqueous injection before.     

Membrane in tandem with a helical sorbent trap as continuous sampling technique of the polyvinyl chloride thermo-oxidative degradation products for their on-line gas chromatographic monitoring

A flat membrane in tandem with a helical sorbent trap has been used for continuous sampling of the volatile organic products generated in the thermal degradation process of the polyvinyl chloride (PVC) in air, followed by on-line gas chromatographic separation and mass spectrometric identification. The membrane and trap tandem makes automatic collection, concentration, and injection of PVC volatile and semivolatile degradation products, and it is simple in terms of instrumentation and operation. The poly(dimethylsiloxane) (PDMS) membrane used in this study shows a low permeation for oxygenated derivatives and a high permeation for volatile aromatic and non-aromatic hydrocarbon, and chlorinated hydrocarbons. Consequently, the final chromatogram is significantly simplified. By heating the trap at fixed intervals of time, consecutive gas chromatograms are obtained in the monitoring process. The sensitivity of the method depends on the parameters that affect the time of trapping, and the permeation through the membrane.     

Polymer analysis using pyrolysis-GC-FTIR-MS and GC-AED

Volatile pyrolysates of a methyl methacrylate-butadiene-styrene copolymer (MBS) have been analyzed using a capillary gas chromatograph equipped with a Fourier transform infrared detector in tandem with a mass selective detector, and a gas chromatograph-atomic emission detector system. Among the volatile compounds observed were monomers used for synthesis of the polymer. Numerous oligomers of higher boiling point were also found; identification of these could be used to give structural information about the parent polymer. Combining information from these techniques was found to be extremely useful for the analysis of polymer pyrolysis products. In characterizing each compound it was found particularly helpful to juxtapose feature-specific chromatograms (e.g., single ion monitoring from the mass-selective detector and the selected wavelength chromatography from the infrared detector).     

莪术药材的闪蒸气相色谱测定及其模式识别分析研究

建立了莪术药材的闪蒸-气相色谱法(FE-GC),采用FE-GC测定了3个产地的9个莪术样品.0.4mg的粉末样品, 在200℃下闪蒸,经色谱分离,基于闪蒸色谱图上分离鉴定到的35个共有峰的相对强度,结合化学模式识别即主成分分析和系统聚类分析法对莪术样品进行了鉴别分析.3个产地的莪术样品可以很好地得到区别.本法快速、简便、准确, 不失为药材质量控制的良好方法.     

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.     

Solid sorbent collection and gas chromatographic determination of bis(2-chloroethyl)sulfide in air at trace concentrations

This article describes a method for the quantitative determination of the toxic military agent bis(2-chloroethyl)-sulfide (or sulfur mustard) in air or other similar gases at parts-per-trillion levels. The method entails the adsorptive trapping of mustard vapor on a bed of Tenax-GC, followed by the transfer of trapped mustard to a smaller sorbent bed and the thermal desorption of the mustard into a gas chromatograph equipped with a flame photometric detector. Interference from an oxidizing gas (probably NO2) in the air is circumvented by sampling through a filter impregnated with triethanolamine (TEA) which selectively attenuates the NO2 while transmitting the mustard. The method is found to possess adequate accuracy and precision for most purposes, and the detection limit is observed to depend on the magnitude of the sample or sorbent background response rather than on instrument noise, adsorptive sampling capacity, or other fundamental limitations of the hardware.     

Concentration of volatile organic compounds from solvents by sustained chromatographic evaporation

A system for quantitative concentration of volatile organic trace compounds present in organic solvents is described. Evaporation of the solvent is carried out inside a glass capillary tube by the action of a carrier gas, and large volumes can be reduced by a repeated sample injection and a cyclic flow reversal. Best recovery is obtained when a barrier of pure solvent is maintained ahead of the sample during concentration. Four rotary valves are employed for sample and solvent injection and direction of the gas flow. In principle, indefinite sample volumes can be handled, the limit being set by system contaminants. The process was evaluated both off-line and on-line to a gas chromatograph. Concentration of compounds like methylcyclopentane, hexane, and cyclohexane present in pentane in the low nanogram range and subsequent on-line transfer to a gas chromatograph could be performed with a quantitative recovery. The technique was applied to analysis of trace volatiles in drinking water. Detection limits were estimated to be approximately 0.02 ng/L for normal hydrocarbons (FID detection) when concentration of a pentane extract from a one litre water sample was carried out.     

The combined use of thermal desorption and selected ion flow tube mass spectrometry for the quantification of xylene and toluene in air

Thermal desorption (TD) is commonly employed for volatile chemical analysis, it being the method of choice for occupational health and safety monitoring. TD allows for offline capture of volatiles onto a solid sorbent followed by desorption and analysis at a later time. Although TD is routinely used in conjunction with gas chromatography (TD-GC), the assay throughput is low and requires the use of gas standards for quantification. Another technique increasingly employed for volatile chemical analysis, selected ion flow tube mass spectrometry (SIFT-MS), is capable of real-time absolute (i.e. without calibration standards) quantification of volatile chemicals present at single digit parts per billion or higher concentrations. SIFT-MS is, however, normally used for online direct analysis of gas samples rather than offline collection and analysis. The goal of this study was to determine whether a combination of TD and SIFT-MS could be used to quantify volatile compounds, specifically xylene and toluene, more rapidly than TD-GC and without the need for calibration standards. SIFT-MS was able to quantify xylene and toluene levels within 45 s of desorption. Due to the robustness of the SIFT-MS analysis in the presence of water vapour and other major components of air, the purging of tubes usually required to remove these constituents during the TD cycle was not required, therefore reducing the TD cycle time. Comparing the quantity of xylene and toluene applied to the TD tube with the absolute levels quantified by SIFT-MS subsequent to desorption suggested a recovery of over 95% of the applied compound. We conclude that the combination of TD and SIFT-MS allows more rapid and accurate quantification of xylene and toluene (compared with TD-GC) to be achieved without the need for calibration standards, features which may be advantageous in applications requiring rapid analysis and high throughput.     

Dispersive Liquid–Liquid Extraction Based on Freezing of the Organic Drop, Followed by GC for the Determination of Methyl Methacrylate in Wastewater

Crude oil reservoirs typically contain more water than oil, which is emulsified with the oil. During oil production, the emulsion is broken with demulsifiers. Most recently, based on methyl methacrylate, after which, the water, containing the methyl methacrylate, is discharged into surface waters. Significant health hazards have been associated with methyl methacrylate, and a limit of 30 ppm in ground waters has been established. This paper describes the preconcentration of methyl methacrylate from the separated water, using dispersive liquid–liquid microextraction, followed by freezing of the organic drop in an ice bath which facilitated separation of the phases (by centrifugation). In the optimized method, 15.0 μL of 2-dodecanol was rapidly injected into 5 mL water samples, followed by stirring, freezing, and decantation, then direct injection into the gas chromatograph equipped with a flame ionization detector. The method was optimized for: choice of extraction solvent, volume of extraction solvent, pH, ionic strength, temperature and extraction time.     

Coupling device for desorption of drugs from solid-phase extraction-pipette tips and on-line gas chromatographic analysis.

Solid-phase extraction-pipette tips were used for micro solid-phase extraction of lidocaine and diazepam. Off-line desorption was done after in-vial collection for reference purposes, whereas with on-line desorption the eluate was directly introduced in the gas chromatograph. With both methods the total eluate (100 microl) was introduced into the GC system, which was equipped with a programmed-temperature vaporiser (PTV) for large volume injection. For on-line desorption a laboratory-made coupling device was developed to connect the pipette tips with the injector of the PTV. The coupling device was applied successfully since no leakage occurred at the connection of the coupling device and the pipette tip. No significant differences in recovery of lidocaine and diazepam and in presence of impurities were observed between chromatograms obtained with either off-line or on-line desorption. Preliminary experiments with standard solutions showed recoveries of about 75% for a concentration level of 1 microg/ml. The system seems particularly suitable for high-throughput analysis.     

Direct determination of tri-<Emphasis Type="Italic">n</Emphasis>-butyl phosphate by HPLC and GC methods

The high performance liquid chromatography and gas chromatography methods were investigated for their applicability in determining micro-level concentrations of tri-n-butyl phosphate (TBP). A high performance liquid chromatograph (HPLC) equipped with refractive index detector was used in determining TBP up to 2 ppm concentration level in the aqueous nitric acid solutions. The gas chromatography incorporated with Thermionic Detector (NPD) and Flame Photometric Detector (FPD) were examined for their potential in analyzing TBP in organic phase up to sub-ppm level. The results indicated that HPLC-RI technique is well suited for direct analysis of aqueous phase. For organic phase analysis, gas chromatographic methods with the TID and FPD were suitable but performance of detectors deteriorated often due to fouling.     

Injection by Programmed Temperature Vaporization Injection (PTV) of Gaseous Samples for Gas Chromatography – Atomic Emission Spectrometry (GC-AED)

Programmed temperature vaporization injection (PTV) coupled to gas chromatography and atomic emission detector (AED) has been studied for large volume injection of gaseous samples. As examples of the effectiveness of the technique, the results of the analysis of a series of headspace samples of foods such as garlic and onion, and of landfill gases are presented. The volumes of gaseous samples reconcentrated varied from a few milliliters up to liters depending on analyte dilution, through focusing onto a sorbent trap, then rapid liberation into the GC-AED system by programmed thermal desorption. Despite the high carrier gas flow rates associated with direct PTV-GC, AED performance and sensitivity were unaffected. The detailed elemental information obtained from the PTV-GC-AED analyses was confirmed using a PTV coupled to a gas chromatograph with ion trap detector mass spectrometer as detector (PTV-GC-ITD/MS).     

Automated high-speed analysis of selected organic compounds in urban air by on-line isotopic dilution cryofocusing gas chromatography/mass spectrometry

An automated environmental air monitor has been developed to measure selected organic compounds in urban air. The instrument is based on a cryofocusing-thermal desorption gas chromatographic mass spectrometry technique where the mass spectrometer is a slightly modified residual gas analyzer (RGA). The RGA was chosen as a detector because the whole system must be robust for long periods, with 24-h continuous air monitoring. RCA are extremely simple and seemed the most reliable mass spectrometers for this purpose. Moreover, because they have no physically limited ion source, contamination is considerably reduced, so maintenance intervals are longer. The gas chromatograph is equipped with a computer-controlled six-way sampling valve, with a 100-mL sampling loop and thermal desorption cold trap injector. Environmental air is enriched with an isotopically labeled internal standard in the sampling line. This internal standard is added with a validated, custom-made, permeation tube device. The “on-line” internal standard provides for high quality quantitative data because all variations in instrument sensitivity in cryofocusing or in thermal desorption efficiency are taken into account. High repetition rates (down to 5 min for a full analytical cycle) are obtained with the use of an isothermal gas chromatography program, microbore capillary column, and environmental air sampling during the gas chromatography run.     

Determination of phosphine and other fumigants in air samples by thermal desorption and 2D heart-cutting gas chromatography with synchronous SIM/Scan mass spectrometry and flame photometric detection

Fumigants and volatile industrial chemicals are particularly hazardous to health when a freight container is fumigated or the contaminated material is introduced into its enclosed environment. Phosphine is now increasingly used as a fumigant, after bromomethane--the former fumigant of choice--has been banned by the Montreal Protocol. We have enhanced our previously established thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) method by integrating a second gas chromatographic dimension and a flame photometric detector to allow the simultaneous detection of phosphine and volatile organic compounds (VOCs), providing a novel application. A thermal desorption system is coupled to a two dimensional gas chromatograph using both mass spectrometric and flame photometric detection (TD-2D-GC-MS/FPD). Additionally, the collection of mass spectrometric SIM and Scan data has been synchronised, so only a single analysis is now sufficient for qualitative scanning of the whole sample and for sensitive quantification. Though detection limits for the herewith described method are slightly higher than in the previous method, they are in the low μL m(-3) range, which is not only below the respective occupational exposure and intervention limits but also allows the detection of residual contamination after ventilation. The method was developed for the separation and identification of 44 volatile substances. For 12 of these compounds (bromomethane, iodomethane, dichloromethane, 1,2-dichlorethane, benzene, tetrachloromethane, 1,2-dichloropropane, toluene, trichloronitromethane, ethyl benzene, phosphine, carbon disulfide) the method was validated as we chose the target compounds due to their relevance in freight container handling.     

SPME Analysis of Potential Attractants for Palm Weevils

Abstract

Solid-phase microextraction was applied for the analysis of a mixture of potential attractants for palm weevils, constituted by seven organic compounds. Various fibers, coated with different sorbent phases, were used in this study and the best results were obtained with the polydimethylsiloxane (PDMS)/divinylbenzene (DVB) and the Carboxen/PDMS fibers. A waiting time of 5 min before sampling was adequate for sample homogenisation and a sampling time of 30 min was used to obtain good extraction efficiencies. A complete desorption of the analytes into the injection port of the gas chromatograph was achieved with an injection time of 1 min. The detection limit of the method ranged from 0.29 to 156 ng/ml for the different components of the mixture, with a lower detection limit for the compounds with higher affinity for the fiber coating. This method was used in the analysis of volatiles released from a diffuser filled with the attractant mixture.     

On-site environmental analysis by membrane extraction with a sorbent interface combined with a portable gas chromatograph system

A novel device, membrane extraction with a sorbent interface (MESI) coupled with a portable gas chromatograph (GC) system, has been developed. The main components of this system include a membrane module, a microtrap, and a control unit for the heater and cooler. The membrane module, as an on-line sample-introduction device for this system, can be manipulated in different configurations, allowing for the selective permeation of analytes across the membrane into the carrier/stripping gas. The analytes are trapped and concentrated onto a microtrap, which serves as an injector for gas chromatography separation. A concentration pulse of the trapped analytes is generated through direct electrical heating of the microtrap. The characteristics of this system have been explored, and its applicability and effectiveness have been demonstrated in field monitoring applications including the analysis of toluene in wastewater, Volatile organic compounds (VOCs) in laboratory air, and chloroform in swimming-pool water. This system is very promising, as it is a simple, fast, and portable tool for on-site process environmental monitoring.     

Sample preparation for gas chromatographic determination of halogenated volatile organic compounds in environmental and biological samples

In this review, the wide spectrum of the techniques of isolation and/or preconcentration and final determination of halogenated volatile organic compounds (HVOCs) in water, air, soil, sediment and biological fluids are presented and discussed. The techniques discussed are solvent microextraction, solid phase extraction, gas extraction (static and dynamic techniques), membrane processes and passive sampling. Also, direct techniques, such as direct aqueous injection into gas chromatography (GC) column and membrane inlet mass spectrometry, are presented. Main attention is paid to the practical application of these techniques during all HVOCs determination.     

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.