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31.
32.
A technique has been developed for performing headspace GC-MS analysis of volatile components of food, in which the carrier gas flow is reversed during sampling in order to overcome problems caused by the diffusion of substances not retained by the cold trap. Chromatographic profiles of volatile compounds from cheeses, obtained at room temperature, provide confirmation of the validity of the reversed flow technique, and the versatility of the system is evidenced by its successful application to both solid and liquid matrixes: the absence of any discrimination against the various components reveals its efficacy for compounds with a wide range of volatility. Addition of internal standards to the sample enables the use of the technique for quantitative analysis. 相似文献
33.
Air sampling of aromatic hydrocarbons in the presence of ozone by solid-phase microextraction 总被引:3,自引:0,他引:3
Effects of ozone on air sampling of standard gas mixtures of aromatic hydrocarbons were tested using solid-phase microextraction (SPME). Standard concentrations of ozone ranging from 10 ppb (v/v) to 6400 ppm (v/v) were generated using an in-house built ozone generator based on corona discharge. Effects of temperature, discharge voltage, and oxygen flow on the ozone generation were tested. The working dc voltage had the greatest effect on generated ozone concentration and was proportional to the ozone concentration. Generation temperature and oxygen flow rate were inversely proportional to ozone concentrations. Produced ozone was mixed with standard benzene, toluene, ethylbenzene, and xylenes (BTEX) gas at less than 100 ppb (v/v). Air samples were collected with poly(dimethylsiloxane) (PDMS) 100 microm SPME fibers and analyzed by gas chromatography (GC)-flame ionization detection (FID) and GC-MS. Significant reductions of BTEX concentrations were observed. In addition, some products of BTEX-ozone-oxygen reactions were identified. SPME worked well as a rapid sampler for BTEX and BTEX-ozone-oxygen reaction products. No significant deterioration of the PDMS coating and no significant reduction of absorption capacity were observed after repeated exposure to ozone. 相似文献
34.
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36.
《Analytical letters》2012,45(2):223-234
Abstract A new method is described that facilitates determining the efficiency of air sampling traps to adsorb and thermally desorb volatile organic compounds. A known volume of a liquid standard of volatile organic compounds is vaporized into an air stream, a fraction of which is collected on an air sampling trap. This trap is subsequently thermally desorbed and analyzed using a GC/FID. The efficiency of the trap to adsorb and thermally desorb each compound tested is calculated. 相似文献
37.
《Analytical letters》2012,45(13):2048-2059
A simple and rapid discrimination of four lung cancer related volatile organic compounds (VOCs) was achieved with a novel colorimetric sensor array. Based on the cross-responsive mechanism, the sensor system exhibited high sensitivity to selected lung cancer biomarkers, including p-xylene, styrene, isoprene, and hexanal with concentrations varying from 50 ppb to 500 ppb. By extracting color information, it provided good selectivity and fine discrimination of selected gases via pattern recognition with Fisher linear discriminant (FLD). Additionally, with the employment of the Takagi-Sogeno Fuzzy Neural Network (TSFNN), different concentrations of selected VOCs were discriminated. It also suggested that the colorimetric sensor array proposed could not only distinguish different lung cancer related VOCs but also discriminate specific VOCs of different concentrations with an average rate of classification up to 95%. Our preliminary study demonstrated that the cross-responsive sensor array had infinite potential for further clinical and commercial use for early diagnosis of lung cancer. 相似文献
38.
《Analytical letters》2012,45(5):721-729
The extraction and determination of volatile compounds in mice urine were performed using headspace solid-phase microextraction and gas chromatography-mass spectrometry. In order to optimize the extraction conditions, experimental design was applied. A sample volume of 108 µl, a temperature of 148.6°C, and a time of 94 minutes were found to be the optimal conditions. Samples of male and female mouse urine were analyzed to determine volatile compound profiles. A total of 36 organic compounds including ketones, aldehydes, and terpenes were detected. The results revealed that compounds such as 2-isopropyl-4,5-dihydrothiazole, which is considered a male sexual pheromone, were only detected in male urine samples, whereas others like benzaldehyde were especially abundant in female mouse urine. A comparison of female samples corresponding to different stages of the estrous cycle was also performed. 相似文献
39.
Sample pretreatment before chromatographic analysis is the most time consuming and error prone part of analytical procedures, yet it is a key factor in the final success of the analysis. A quantitative and fast liquid phase microextraction technique termed as gas purge microsyringe extraction (GP-MSE) has been developed for simultaneous direct gas chromatography-mass spectrometry (GC-MS) analysis of volatile and semivolatile chemicals without cleanup process. Use of a gas flowing system, temperature control and a conventional microsyringe greatly increased the surface area of the liquid phase micro solvent, and led to quantitative recoveries of both volatile and semivolatile chemicals within short extraction time of only 2 min. Recoveries of polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs) and alkylphenols (APs) determined were 85-107%, and reproducibility was between 2.8% and 8.5%. In particular, the technique shows high sensitivity for semivolatile chemicals which is difficult to achieve in other sample pretreatment techniques such as headspace-liquid phase microextraction. The variables affecting extraction efficiency such as gas flow rate, extraction time, extracting solvent type, temperature of sample and extracting solvent were investigated. Finally, the technique was evaluated to determine PAHs, APs and OCPs from plant and soil samples. The experimental results demonstrated that the technique is economic, sensitive to both volatile and semivolatile chemicals, is fast, simple to operate, and allows quantitative extraction. On-site monitoring of volatile and semivolatile chemicals is now possible using this technique due to the simplification and speed of sample treatment. 相似文献
40.
P. Konieczka M. Prokopowicz B. Zygmunt J. F. Biernat J. Namieśnik 《Chromatographia》2000,51(1):S249-S260
A new approach to the preparation of standard gaseous mixtures based on thermal decomposition of surface compounds, has been
reviewed. The method is used to prepare standard mixtures containing volatile analytes such as thiols, isothiocyanates, carbon
monoxide, carbon dioxide, ammonia, amines, ethylene and methyl chloride. The method enables the preparation of the standard
immediately before a calibration step. It is specially useful for the generation of standard mixtures containing volatile,
malodorous, unstable and toxic compounds.
Presented at Balaton Symposium on High Performance Separation Methods, Siófok, Hungary, September 1–3, 1999 相似文献