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71.
P. L. Wylie 《Chromatographia》1986,21(5):251-258
Summary A convenient procedure has been described for enhancing the sensitivity of equilibrium headspace gas chromatography. The technique
involves the cryogenic focusing of headspace vapors at the head of a 0.32 mm fusedsilica capillary column which has been coupled
to a packed column injection port. Cryofocusing is accomplished automatically by cooling the GC oven and results in enhanced
sensitivity with improved resolution. With this simple focusing technique no sample splitting is required which gives at least
a 10-fold increase in sensitivity. A Multiple Headspace Injection (MHI) technique has been described which allows several
rapid headspace injections to be made at the start of a single chromatographic run. Cryofocusing causes the injections to
be superimposed, thus increasing the sensitivity even further. These procedures have been demonstrated for flavor and aroma
analyses of toothpaste and soft drink samples.
Presented at the Symposium on Headspace GC, National American Chemical Society Meeting, Chicago, Ill., September 8–13, 1985 相似文献
72.
Loukatos P Kiaris M Ligas I Bourgos G Kanellaki M Komaitis M Koutinas AA 《Applied biochemistry and biotechnology》2000,89(1):1-13
The main objective of the present work was the removal of aluminum from wines produced by γ-alumina-supported yeast cells.
Reagents such as Na2CO3, NH4OH, albumin, and Ca(OH)2 were used. Calcium in the presence of albumin was effective, whereas other reagents were not so effective. Because of the
improved aroma and taste of distillates produced by γ-alumina-supported biocatalyst, volatile byproducts of distillates were
analyzed. They were also assessed by sensory tests. Methanol, acetaldehyde, ethyl acetate, propanol-1, isobutyl alcohol, and
amyl alcohols were determined in distillates. It was noted that the amounts of higher alcohols and amyl alcohols decreased
as the temperature of fermentation dropped, leading to a product of improved quality and reduced toxicity. 相似文献
73.
A system for automatic analysis of volatile compounds by purge-and-cold-trapping/capillary gas chromatography is described. It is suitable for analysis of volatile compounds in a wide variety of samples, such as water, food products and environmental samples. Possibilities and limitations of the system are evaluated in relation to several parameters. The efficiency of different types of cryogenic trap (open tubular, coated, packed) is also investigated; it depends on purge-flow rate, temperature of trapping, and total purge volume. Examples of the analysis of volatile compounds in foods and water are given. 相似文献
74.
Violeta D. Mitić Marija D. Ilić Vesna P. Stankov Jovanović Aleksandra S. Djordjevic Marija S. Marković Gordana S. Stojanović 《Natural product research》2020,34(18):2698-2701
AbstractThe chemical composition of the essential oil and the volatiles obtained by static headspace (HS) of Inula oculus-christi L. is presented. The GC-MS analysis of the hydrodistilled oil resulted in the identification of 90 components, representing 92.7% of the oil. The most abundant compounds were: caryophyllene oxide (9.8%), trans-longipinocarveol (9.2%), eucalyptol (7.3%) and intermedeol (6.2%). The major constituent of I. oculus-christi L. HS volatiles was eucalyptol (87.4%). The antioxidant activity was evaluated by four different methods: 2,2-diphenyl-1-picryl-hydrazylhydrate free radical assay (DPPH), 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) method, total reducing power (TRP), ferric reducing antioxidant power (FRAP), and cupric reducing antioxidant capacity (CUPRAC). Total phenolic content in (TPC) examined oil was 177.95?µg GAE/mg oil. Radical scavenging potential of the oil was promising RSC-DPPH was 57.4% and RSC-ABTS was 82.7%. 相似文献
75.
Several techniques are available for measuring organic volatiles in the atmosphere. For measurements at low and moderate pollution levels (between several μg m?3 and a fraction of a μg m?3), the existing methods can be adopted to a broad range of different compounds. Whole-air sampling in stainless-steel containers with metal bellows valves combined with subsequent gas chromatographic separation after preconcentration in the laboratory is probably the best procedure for low and medium molecular weight trace gases of moderate or low polarity and reasonable chemical stability (e.g., hydrocarbons and halocarbons). For organic compounds of lower volatility, adsorptive sampling on non-polar porous organic polymers (e.g., Tenax) and thermal desorption combined with cryotrapping and gas chromatographic separation of the sampled compounds is widely used. However, there are often substantial problems due to artefact formation or loss reactions. Owing to the generally larger sample volumes, these problems are even more pronounced for sorptive sampling techniques combined with sample recovery by solvent extraction. Unfortunately, the general understanding of the various processes of sample degradation due to chemical reactions of reactive components of the atmosphere with each other or with the sorbent is not yet sufficient to allow reasonable estimates of the extent of such interferences without elaborate test procedures. 相似文献
76.
The aim of the present study is to develop a method for following the changes in the chemical composition of volatile substances released by plants. Dynamic headspace enrichment, followed by on-line thermal desorption and cryotrapping was coupled with capillary gas chromatography. The technique was optimized by adjusting the sampling and desorption parameters and by designing a special condensing device to avoid the transfer of excessive amounts of water into the analytical column. Details are given for the characterization of volatiles compounds released by mosses. 相似文献
77.
Summary A mixed-phase capillary GC column has been designed for the separation of the compounds commonly present in the volatile fraction of cheeses. The design includes the calculation of the optimum phase concentration and the operating conditions. The evaluation of the resulting column indicates that its performance in the qualitative and quantitative analysis of cheese volatile compounds is better than those of other columns coated with a single stationary phase. 相似文献
78.
The aim of this study was to test the suitability and performance of various stationary phases and column dimensions for dynamic headspace gas chromatography of food aromas. The trials were performed using an aqueous test mixture containing thirty seven volatile flavor components of intense aroma, and a sample of ripe Swiss Emmental cheese. The best performance with both samples was obtained with a capillary column coated with a thick film of polydimethylsiloxane. This column resolved the greatest number of compounds in the cheese sample and resulted in the overlapping of one pair of peaks only from the test mixture. Because of its other advantages, i. e. high capacity owing to its film thickness, and insensitivity to the high moisture content of some samples or traces of oxygen in the carrier gas, the polydimethylsiloxane column appears suitable for the analysis of the volatile and highly polar compounds present in complex mixtures such as food aroma. 相似文献
79.
Ma X Zhu T Xu H Li G Zheng J Liu A Zhang J Du H 《Analytical and bioanalytical chemistry》2008,390(4):1133-1137
A chemical prototype sensor was constructed based on nanofiber-structured TiO2 and highly sensitive quartz resonators. The gas-sensing behavior of this new sensor to selected simulant warfare agents was
investigated at room temperature. Results showed rapid response and good reversibility of this sensor when used with high-purity
nitrogen. This provides a simple approach to preparation of materials needed as chemical sensors for selected organic volatiles
or warfare agents.
Figure Sensing behavior of TiO2 nanofiber sensor to chemical vapors 相似文献
80.