吹扫捕集-气相色谱法测定水中苯系物

利用HP-Innowax毛细管色谱柱,对对二甲苯和间二甲苯进行了分离研究,并建立吹扫捕集-气相色谱法测定水中6种常见苯系物的方法。当水样进样体积为25mL时,方法检出限为0．08～0．30μg/L,用该方法对实际水样中的6种苯系物进行测定,回收率为69．0％～111.9％,测定结果的相对标准偏差均小于4％。     

空气中苯系物的GC-MS/SIM定量分析方法研究

用活性炭采样管富集车间空气中的苯系物，以二硫化碳为解吸剂，经毛细管柱GC—MS选择离子法测定样品中苯系物，峰面积定量。     

吹扫捕集/气相色谱－同位素比值质谱联用测定水体中痕量苯系物单体碳同位素

建立了吹扫捕集（P&T）/气相色谱－同位素比值质谱（GC/C－IRMS）联用测定水体中痕量苯系物单体碳同位素的方法。优化了吹扫时间、吹扫温度和干吹时间,确定最优吹扫捕集效率,并通过测试不同质量浓度的苯系物水溶液,计算水体中痕量苯系物的检出限。结果表明,在35 ℃下吹扫捕集13 min,干吹时间3 min条件下,水样中苯、甲苯、乙苯、间/对二甲苯、邻二甲苯、苯乙烯、异丙苯的吹扫捕集效率分别为95.0%、90.2%、71.3%、59.1%、69.4%、50.8%和70.1%,7种苯系物单体碳同位素的标准偏差（STD）为0.06‰ ~ 0.29‰。7种苯系物的质量浓度在0.50 ~ 20.00 μg/L范围内与峰面积的线性关系良好,相关系数（r2）为0.998 6 ~ 0.999 5,在各浓度下7种苯系物单体碳同位素值的标准偏差为0.090‰ ~ 0.48‰,进样量及进样方式的差异不会导致碳同位素分馏。水样中苯、甲苯、间/对二甲苯、邻二甲苯和苯乙烯的检出限为1.00 μg/L,乙苯和异丙苯为0.50 μg/L。该方法可以极大提高水体中苯系物单体碳同位素的检出限,结果准确可靠,满足水体中痕量苯系物单体碳同位素分析的需求。     

捕集阱顶空-气相色谱法测定水中低浓度苯系物

建立了捕集阱顶空-气相色谱检测水中低浓度苯系物的方法。在捕集阱顶空平衡温度70℃,10 min平衡时间,色谱温度70℃(2 min),10℃/min升温至学20℃,保持2 min,载气流量2.5 mL/min的条件下,6种苯系物分离效果良好,在0.16~40μg/L范围内,苯系物浓度与色谱峰面积呈良好的线性关系,相关系数为0.9994~0.9999;使用捕集阱极大地提高了苯系物分析的灵敏度,方法检出限分别为:苯0.025 ng/L、甲苯0.025 ng/L、乙苯0.023 ng/L、对,间二甲苯0.025 ng/L、邻二甲苯0.027 ng/L、异丙苯0.022 ng/L;本法测定苯系物RSD≤5.1%,加标回收率为79.1%~104.9%。本方法应用于自来水中低浓度苯系物的分析,效果良好。     

空气中苯系物测定有关问题的探讨

对HJ 584–2010《环境空气苯系物的测定活性炭吸附/二硫化碳解吸–气相色谱法》和HJ 583–2010《环境空气苯系物的测定固体吸附/热脱附–气相色谱法》进行解析,结合监测工作实际情况,从采样、分析各个关键环节总结归纳了方法要点,提出了实际应用中的注意事项。为环保监测系统进行空气中苯系物测定方法的选择及正确应用提供借鉴。     

电厂废气中饱和水蒸气对活性炭变压吸附捕集CO2的影响

由于热电厂废气中含有高湿饱和水蒸气,选用疏水材料活性炭为吸附剂,利用真空变压吸附技术研究了活性炭分离电厂废气中水蒸气和二氧化碳的可行性和优越性,研究了水对CO₂捕集的影响。实验分析表明,水在活性炭上的“S”型等温吸附曲线有利于真空条件下被解吸。同时,圆锥模型描述了水蒸气在吸附床内的浓度分布。结果表明,即使水蒸气可以被活性炭吸附,但它的存在不影响CO₂的捕集。每个循环操作可在相对较短的解吸时间和较高的解吸压力下完成。实验中单床三步变压吸附工艺可以使CO₂回收率高达80%,CO₂纯度达43%。     

吹扫捕集/气相色谱－质谱联用法同时测定食品接触材料及制品中9种苯系物的迁移量

为评估食品接触材料及制品中苯系物的迁移风险,建立了同时测定食品接触材料及制品中9种苯系物在4%乙酸、10%乙醇和橄榄油中迁移量的吹扫捕集/气相色谱－质谱联用法（P&T/GC－MS）。采用HP－INNOWax毛细管色谱柱对迁移实验后的9种苯系物进行分离,选择离子监测（SIM）模式进行检测。结果表明,9种苯系物的分离效果良好,在0.50 ~ 5.0 μg/kg或0.50 ~ 5.0 μg/L范围内线性关系良好,相关系数（r2）均不小于0.995,方法检出限为0.15 μg/kg,方法定量下限为0.50 μg/kg,加标回收率为78.5% ~ 107%,相对标准偏差（n = 6）为1.1% ~ 9.2%。该方法具有较高的准确度和较好的重现性,可用于食品接触材料及其制品中9种苯系物迁移量的测定。     

吹扫捕集气相色谱法测定水中苯系物

采用吹扫捕集-气相色谱法测定生活饮用水中苯系物(笨、甲苯、乙苯、邻、间、对二甲苯、异丙苯、苯乙烯),并对吹扫捕集的条件进行优化,缩短了分析周期,提高了方法的灵敏度和准确度.方法的最低检出浓度为0.9～1.7μg/L,相对标准偏差为0.63%～1.36%(n=7),平均加标回收率为97.4%～101.3%.本方法适合于地表水和生活饮用水中苯系物的测定.     

气相色谱法测定密闭空间空气中7种苯系物

建立气相色谱法测定密闭空间空气中异丙苯等7种苯系物的方法。采用活性炭富集采样,二硫化碳解吸样品,DB-624毛细管柱分离,实现了对异丙苯、正丙苯、特丁苯、正丁苯、仲丁基苯、1,3,5-三甲苯、1,2,4-三甲苯等7种苯系物完全分离并准确测定,特别是可以将难分离的1,3,5-三甲苯和仲丁基苯完全分离。建立的7种苯系物工作曲线线性良好,相关系数r^2≥0.997,加标回收率在83.2%~111.0%之间,测定结果的相对标准偏差不大于6.3%(n=6),方法检出限为0.02~0.06 mg/m^3。该方法选择性好,测量范围宽,方法检出限低,可用于密闭空间空气中异丙苯等7种苯系物的测定。     

闭路循环动态针捕集/气相色谱-质谱法测定卷烟烟丝挥发性成分

建立了闭路循环动态针捕集/气相色谱-质谱测定卷烟烟丝中挥发性化学成分的方法,优化了采集模式、捕集与解吸条件,考察了动态针捕集(NT)的解吸率,并与固相微萃取方法进行了对比。结果表明,填充Carboxen1000的捕集针,在样品加热温度为80℃,以3 m L/min流速浸入式闭路循环捕集30 min,并在250℃下解吸5 min为最佳条件;在卷烟烟丝中共检出有机酸、酯、醛、醇类等45种化合物,其中相对标准偏差(RSD)小于5%的有27种,占化合物数量的60%。NT捕集方式的灵敏度、重复性均优于固相微萃取,更适用于卷烟烟丝中挥发性成分分析。     

沥青基球状活性炭气相吸脱附行为研究

本文利用热重法研究了一系列沥青基球状活性炭对蒸汽及正已烷蒸汽的动态吸脱附曲线。结果表明,PSAC对苯蒸汽的吸附及再生性能优良。随吸附温度的降低、比表面积的增大、总孔容及微孔容的增大,PSAC对苯蒸汽的吸附容量增大。PSAC对正已烷的吸附速度大于对苯蒸汽的吸附速度,但其对正已烷的平衡吸附容量小于对苯蒸汽的平衡吸附容量。     

Quantifizierung organischer Substanzen in Aktivkohleextrakten mit Hilfe der Gas-Chromatographie/Massenspektrometrie

Summary Use of activated carbon plays a significant role in water technology and analytical chemistry. Therefore determination of substances adsorbed on activated carbon is of special interest. As an example, granulated activated carbon (GAC) from a water treatment plant was serially extracted with different organic solvents. Quantitative determination of some selected compounds in the combined extracts was done by gas chromatography/mass spectrometry. The method of internal standard addition and calibration by response factors was used. The determined compounds (all of substituted benzene type) were extracted from the GAC in the concentration range from 0.2 mg/100 g (m-dichlorobenzene) to 5 mg/100 g (nitrobenzene). Relative standard deviation for double determination of five independent samples from the GAC filter was less than ±20%Spike experiments were performed to determine recovery efficiences. As expected, substance specific differences appeared and the recoveries were between 36% (m-dichlorobenzene) and 80% (nitrobenzene). A significant limitation for quantitative determination results from lack of available substances for calibration.     

Improvement of activated carbon for air sampling

In order to improve the charcoal tube method, activated carbon was treated with benzyl chloride (5 and 20%) in methylene chloride and heated (300 degrees C). The carbons were evaluated with regards to water uptake, adsorption of toluene and carbon tetrachloride, desorption characteristics for polar compounds and storage stability of ketones. Carbons treated with benzyl chloride picked up less moisture, showed higher desorption efficiencies for polar compounds and lower catalytic activity compared with untreated carbons and those heat-treated with helium at 800 degrees C. The best results were obtained with 20% benzyl chloride.     

Desulfurization of liquid fuels by adsorption on carbon-based sorbents and ultrasound-assisted sorbent regeneration

Several carbon-based adsorbents, CuCl/AC, PdCl2/AC, and Pd/AC (where AC denotes activated carbon), were studied for desulfurization of a model jet fuel by selective adsorption of thiophenic molecules. Comparisons with gamma-Al2O3 support and desulfurization of a commercial jet fuel were also studied. The results showed that the selective sulfur adsorption capacity of PdCl2 was higher than that of CuCl and Pd(0), in agreement with molecular orbital results. It was also found that the activated carbon is the best support for pi-complexation sorbents to remove sulfur-containing compounds, i.e., benzothiophene and methylbenzothiophene. Among all the adsorbents studied, PdCl2/AC had the highest capacity for desulfurization. A significant synergistic effect was observed between the carbon substrate and the supported pi-complexation sorbent, and this effect was explained by a geometric effect. The saturated sorbent was regenerated by desorption assisted by ultrasound with a solvent of 30 wt % benzene and 70 wt % n-octane. The results showed that the amount of sulfur desorbed was higher with ultrasound, 65 wt % desorption vs 45 wt % without ultrasound in a static system at 50 degrees C.     

Determination of volatile organic hydrocarbons in water samples by solid-phase dynamic extraction

In the present study a headspace solid-phase dynamic extraction method coupled to gas chromatography–mass spectrometry (HS-SPDE-GC/MS) for the trace determination of volatile halogenated hydrocarbons and benzene from groundwater samples was developed and evaluated. As target compounds, benzene as well as 11 chlorinated and brominated hydrocarbons (vinyl chloride, dichloromethane, cis-1,2-dichloroethylene, trans-1,2-dichloroethylene, carbon tetrachloride, chloroform, trichloroethylene, tetrachloroethylene, bromoform) of environmental and toxicological concern were included in this study. The analytes were extracted using a SPDE needle device, coated with a poly(dimethylsiloxane) with 10% embedded activated carbon phase (50-μm film thickness and 56-mm film length) and were analyzed by GC/MS in full-scan mode. Parameters that affect the extraction yield such as extraction and desorption temperature, salting-out, extraction and desorption flow rate, extraction volume and desorption volume, the number of extraction cycles, and the pre-desorption time have been evaluated and optimized. The linearity of the HS-SPDE-GC/MS method was established over several orders of magnitude. Method detection limits (MDLs) for the compounds investigated ranged between 12 ng/L for cis-dichloroethylene and trans-dichloroethylene and 870 ng/L for vinyl chloride. The method was thoroughly validated, and the precision at two concentration levels (0.1 mg/L and a concentration 5 times above the MDL) was between 3.1 and 16% for the analytes investigated. SPDE provides high sensitivity, short sample preparation and extraction times and a high sample throughput because of full automation. Finally, the applicability to real environmental samples is shown exemplarily for various groundwater samples from a former waste-oil recycling facility. Groundwater from the site showed a complex contamination with chlorinated volatile organic compounds and aromatic hydrocarbons. Figure SPDE Principle     

Porous structure of activated carbons and tert-butylbenzene breakthrough dynamics

The structural and adsorptive characteristics of six activated carbons were studied by means of nitrogen and benzene adsorption and water desorption. Tert-butylbenzene (TBB) breakthrough dynamics was analyzed by using several integral equations solved with a regularization/singular-value decomposition procedure. TBB interaction with texturally different activated carbons with the presence of preadsorbed or adsorbed water under dynamic conditions was illustrated by the breakthrough plots handled with several models. The influence of the type of activated carbons, their pore size distributions, water vapor, and TBB flow rate on the breakthrough times (tb) and the dynamic capacity of the carbon beds has been explored with better results for a carbon sample possessing a maximal contribution of mesopores at half-width x>1.5 nm among the carbons studied (which also appears on benzene adsorption) and a major contribution of microporocity as VDS/Vp approximately 0.88 and SK/SBET approximately 0.15. Another adsorbent, which is characterized by a similar total porosity but a larger micropore volume, a smaller contribution of mesopores (SK/SBET approximately 0.08), greater total and miroporous specific surface areas, and greater intensity of the pore size distribution at x<1.5 nm, shows the second result in dynamic TBB retention.     

The active and passive sampling of benzene, toluene, ethyl benzene and xylenes compounds using the inside needle capillary adsorption trap device

A new and simple method of solventless extraction of volatile organic compounds (VOCs) from air is presented. The sampling device has an adsorbing carbon coating on the interior surface of a hollow needle, and is called the inside needle capillary adsorption trap (INCAT). This paper describes a study of the reproducibility in the preparation and sampling of the INCAT device. In addition, this paper examines the effects of sample volume in active sampling and exposure time in passive sampling on the analyte adsorption. Analysis was achieved by sampling the air from an environmental chamber doped with benzene, toluene, ethyl benzene and xylenes (BTEX) compounds. Initial rates of adsorption were found to vary among the different compounds, but ranged from 0.0099 to 0.016 nmol h(-1) for passive sampling and from 2.2 to 10 nmol h(-1) for active sampling. Analysis was done by thermal desorption of the adsorbed compounds directly into a gas chromatograph injection port. Quantification of the analysis was done by comparison to actively sampled activated carbon solid phase extraction (SPE) measurements.     

Rapid determination of trace nitrophenolic organics in water by combining solid-phase extraction with surface-assisted laser desorption/ionization time-of-flight mass spectrometry

A rapid technique for the screening of trace compounds in water by combining solid-phase extraction (SPE) with activated carbon surface-assisted laser desorption/ionization (SALDI) time-of-flight mass spectrometry is demonstrated. Activated carbon is used both as the sorbent in SPE and as the solid in the SALDI matrix system. This eliminates the need for an SPE elution process. After the analytes have been adsorbed on the surfaces of the activated carbon during SPE extraction, the activated carbon is directly mixed with the SALDI liquid and mass spectrometric analysis is performed. Trace phenolic compounds in water were used to demonstrate the effectiveness of the method. The detection limit for these compounds is in the ppb to ppt range.     

Comparative study of solvent extraction and thermal desorption methods for determining a wide range of volatile organic compounds in ambient air

This paper compares two analytical methods for determining levels of 90 volatile organic compounds (VOCs) commonly found in industrial and urban atmospheres. Both methods are based on two official methods for determining benzene levels and involve collecting samples by active adsorptive enrichment on solid sorbents. The first method involves solvent extraction and uses activated charcoal as a sorbent. After sampling, the sorbent is extracted with 1 mL of carbon disulfide and then 1 μL of the extract is analysed in a GC-MS. The second method involves thermal desorption (TD) and uses Tenax TA and Carbograph 1TD as sorbents, which allows the whole sample to be analysed. In general, the thermal desorption method showed the best repetitivity and recovery and the lowest limit of detection and quantification for all target compounds. Because of its lower sensitivity, the solvent extraction method needs the preconcentration of large sample volumes of air (720 L vs. 2.64 L for the thermal desorption method) to yield similar limits of detection.The performance of both methods in real samples was tested in a location near to a petrochemical complex. The results of the 24-h samples for the solvent extraction method were compared with the average of 12 2-h samples for the TD method. In some cases, both methods found differences in the VOC concentrations, especially in those compounds whose concentrations fluctuate significantly during the day.