活性炭复合滤嘴吸附性能的热脱附研究

采用热脱附与气相色谱-质谱联用技术对活性炭滤嘴中活性炭和乙酸纤维脱附的组分进行了定性分析,并用峰面积归一化法测定了所含挥发性成分的质量分数,活性炭脱附组分共鉴定出芳香族化合物、醛酮类、烟碱、酸类、酯类等62种挥发性化合物.结果表明方法具有较好的重现性;为评价活性炭滤嘴的吸附性能提供了一种参考方法.     

Effect of the rare earth in the perovskite-type mixed oxides AMnO3 (A=Y, La, Pr, Sm, Dy) as catalysts in methanol oxidation

The effect of the rare earth in the perovskite-type mixed oxides AMnO₃ (A=Y, La, Pr, Sm, Dy) on catalytic properties in methanol oxidation was investigated in this work. The perovskites were prepared by reactive grinding in order to enhance the specific surface area in comparison with other classical synthesis procedures. These catalysts were characterized by N₂ adsorption, X-ray diffraction, H₂ temperature-programmed reduction (TPR-H₂), O₂-, CH₃OH- and CO₂-temperature-programmed desorption (TPD). The activity of the five catalysts under study in the methanol oxidation reaction was evaluated. The behaviour of the α-O₂ from the surface of the perovskite was strongly related to the nature of the A-site cation and particularly to its electronegativity but also to its density. Concerning the β-O₂ from the bulk, the rare earth only induces an indirect effect notably due to structural modifications. As suggested in a previous study, the activity in methanol oxidation was directly linked with the surface oxygen density. Under an excess of α-oxygen, the reaction intermediate was found to be a monodentate carbonate that decomposes into CO₂. The stability of monodentate carbonates was also found to be related to the electronegativity of the rare earth during both CH₃OH- and CO₂-temperature-programmed desorption. However, as soon as a lack of α-oxygen was observed in the structure, the dominant reaction intermediate was a bidentate carbonate that induces a consumption of anion vacancies in spite of the production of CO₂. Nevertheless, the accumulation of these carbonates leads to a decrease in the oxidation rate since their desorption requires high temperatures.     

The influence of a small amount of active sites on the adsorption kinetics of nitrogen on ruthenium

Recently, Dahl et al. [S. Dahl, A. Logadottir, R.C. Egeberg, J.H. Larsen, I. Chorkendorff, E. Törnqvist, J.K. Nørskov, Phys. Rev. Lett. 83 (1999) 1814; S. Dahl, E. Törnqvist, I. Chorkendorff, J. Catal. 192 (2000) 381] have proposed very interesting hypothesis that the rate of dissociation and adsorption of nitrogen on Ru(0 0 0 1) facet is totally dominated by the presence of a small amount of step sites on Ru(0 0 0 1) terraces. Following this idea, a kinetic model, based on applying the Statistical Rate Theory approach, was developed in order to explain if such mechanism is able to explain the observed features of the system N₂/Ru(0 0 0 1). As a result, it was stated that the activation barrier for adsorption on the active (step) sites is equal to 36 kJ/mol; in turn, the adsorption energy of nitrogen atoms on the active sites is 43 kJ/mol. It implies that the rate of adsorption via the active sites is much faster than direct adsorption on the three-fold hollow sites; moreover, the occupation of the active sites is always close to zero at the investigated temperatures, so they are not blocked and may act as an indirect channel for adsorption. Thus, the rate of nitrogen adsorption on Ru(0 0 0 1) surface is governed by the rate of diffusion of nitrogen atoms from the active sites into the three-fold hollow sites. The analysis of thermodesorption spectra revealed an important role of repulsive interactions between the N atoms adsorbed on the hollow sites, the associated interaction parameter between nearest neighbors was estimated to be 5 kJ/mol. The presence of small amount of gold on Ru(0 0 0 1), apart of blocking the active sites, seems to remove the repulsion between nitrogen atoms.     

Direct analysis of fatty acid profile from milk by thermochemolysis-gas chromatography-mass spectrometry

The fatty acid composition of milk is of considerable interest due to their nutritional and functional properties. Although rapid milk fat separation and transesterification procedures have been developed, the overall procedure remains time consuming, specially, for the analysis of a large number of samples. In this work, a fast and simple method for direct profiling of fatty acids from milk using thermochemolysis has been developed. This method has the capability of directly analyse fatty acids from one drop of milk without fat extraction or cleanup. Our approach for thermochemolysis is based on thermal desorption integrated with a cold trap inlet. The optimized method does not present isomerisation/degradation of polyunsaturated fatty acid and shows milk fatty acid profiles comparable to the conventional method based on fat extraction and alkaline transesterification. Overall, this method has demonstrated significant potential for high throughput analysis of fatty acids in milk.     

Analysis of hydrocarbons in coal and rock samples by on-line combination of thermodesorption,gas chromatography and mass spectrometry

Summary GC-MS analysis of hydrocarbons, thermally mobilized from rock and coal samples (“thermodesorption”) at 320°C, provides valuable and readily available information of organic geochemical significance. Two oil shale and three coal samples of different rank have been selected for this study. The molecular patterns of compound classes of various saturated and aromatic hydrocarbons are recorded here by employing mass chromatography of selected ions. The method described is of particular importance for the detection of those volatile constituents in coals and sedimentary rocks, which are usually not recovered during elaborate workup procedures (i.e. solvent extraction, liquid chromatography) due to evaporation losses.     

Quantification of organic acids in particulate matter by coupling of thermally assisted hydrolysis and methylation with thermodesorption-gas chromatography–mass spectrometry

A quantitative method for the determination of organic acids in atmospheric particles is developed. The method couples a derivatisation step (thermally assisted hydrolysis and methylation) and a Curie point pyrolyser as a thermal desorption technique and gas chromatography–mass spectrometry (CPP-GC–MS). Among the reagents tested (tetramethylammonium hydroxide (TMAH), tetramethylammonium acetate (TMAAc) and phenyltrimethylammonium hydroxide (TMPAH)), the best performance was found using TMAAc as a derivatisation reagent for the reaction time of 4 s at 510 °C as heating temperature. Calibration was performed for a series of fatty acids (FA), dicarboxylic acids (DCA) and terpenoic acids (TA) under these conditions. Coefficients of determination (R²) were between 0.94 and 0.98. Limits of detection (LOD) were in the nanogram-range between 0.1 and 3.6 ng. The method is applied on atmospheric particle samples to obtain the quantification reproducibility and quantification limits. Reproducibility was determined in terms of relative standard deviations (RSD) for ambient aerosol samples collected by a high-volume-sampler (HVS, RSD = 6–45%, n = 10) and a Berner impactor (BI, RSD = 5–34%, n = 10). Based on 24 h sampling time the developed method enables quantification of all three classes of acids for both sampling techniques. Calibration data and presented volume concentrations are compared with literature data. A comparison with an off-line methylation-GC–MS using BF₃ as a derivatisation reagent and capillary electrophoresis coupled mass spectrometry (CE-MS) showed a good agreement. Minimal sample preparation is the main advantage of the developed method. Depending on the sensitivity requirements the present method can be a fast and simple alternative to GC–MS techniques with conventional sample preparation steps for semi-volatile organic acids.     

公交车场挥发性有机物暴露水平的GC-MS测定

空气中的挥发性有机物(volatileorganiccompounds,VOCs)日益受到大家的关注,这不仅因为它们具有强烈的环境效应,而且在较高浓度下可直接危害人体健康。研究表明机动车尾气已成为广州市区VOCs的主要来源,街区VOCs的暴露水平高于北美和欧洲的一些国家。目前很多研究报道了广州公共场所,如街道、商场等地的VOCs暴露水平,公交车场内的VOCs在广州还少有报道,本研究选择了广州某室内公交车场研究其VOCs的暴露水平。     

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.