Application of water as a solvent in microwave-assisted extraction for analysis of PCBs and CBzs in fly ash

Polychlorinated biphenyls (PCBs) and chlorobenzenes (CBzs) are two classes of dioxin precursors formed in municipal solid waste incinerators (MSWIs); they produce negative health effects similar to those of dioxins. Reducing the analytical time required for determining the concentrations of these compounds in MSWIs is important for quickly evaluating their importance and assessing associated health risks. In the present study, water is used as a safe and environmentally friendly solvent in microwave-assisted extraction (MAE) for PCB and CBz analyses. MAE is compared with traditional Soxhlet extraction (SE) to determine the extraction efficiencies. The evaluation of extraction efficiencies shows that MAE has a high extraction efficiency compared with that of SE when water content is lower than 60%. Furthermore, the extraction time and organic solvent consumption are reduced with MAE compared with SE.     

Fluidized-bed extraction of polycyclic aromatic hydrocarbons from contaminated soil samples

Summary Due to the carcinogenity and ubiquity of polycyclic aromatic hydrocarbons in the environment they are of ongoing interest to analytical chemistry. In this study, a comparison of the classic Soxhlet extraction and, fluidized-bed extraction, has been conducted. The extraction of polycyclic aromatic hydrocarbons by this technique has been optimized considering as experimental variables the variation of the number of extraction cycles and the holding time after reaching the heating temperature by means of a surface response design. The significance of the operational parameters of the fluidized-bed extraction on the performance characteristics has been investigated. For the determination of the analytes a selective clean-up of the extracts followed by a fast gas chromatography method with mass spectrometric detection was used, resulting in low limits of detection (0.2 pg μL⁻¹). The accuracy of the complete analytical method was established by extraction and analysis of reference materials.     

Sediment Matrix Induced Response Enhancement in the Gas Chromatographic–Mass Spectrometric Quantification of Insecticides in Four Different Solvent Extracts from Ultrasonic and Soxhlet Extraction

The performance of ultrasonic and Soxhlet extraction using hexane, dichloromethane, ethylacetate/methyl-tert-butylether (1/3, v/v) and hexane/acetone (1/1, v/v) for the analysis of seventeen insecticides in sediments was evaluated. The contents of the extracts differed severely. The extracts obtained with ethylacetate/methyl-tert-butylether (1/3, v/v) and hexane/acetone (1/1, v/v) were dark yellow to green, whereas the extracts obtained with dichloromethane and hexane were light yellow and clear respectively. This is due to higher solubility of matrix compounds in ethylacetate/methyl-tert-butylether (1/3, v/v) and hexane/acetone (1/1, v/v). High loads of coextracted matrix compounds lead to matrix effects in the evaporation step of GC–MS measurements. This is known as matrix induced response enhancement effect. Matrix effects and recoveries were checked by analysis of spiked sediments. The suitable choice of extraction method in connection with an appropriate solvent separates the analytes from matrix compounds. Matrix effects are reduced and recoveries of spiked samples are improved.Revised: 6 January and 2 May 2005     

Evaluation of alternative solvents for improvement of oil extraction from rapeseeds

This present study was designed to evaluate the performances of five alternative solvents (alcohols: ethanol, isopropanol and terpenes: d-limonene, α-pinene, p-cymene) compared to n-hexane in rapeseed oil extraction. The extracted oils were quantitatively and qualitatively analyzed to compare the solvents’ performances in terms of kinetics, fatty acid compositions, lipid yields, and classes. Moreover, micronutrients in extracted oils were also respectively quantified by high-performance liquid chromatography (HPLC) and gas chromatography (GC). In addition, the interactions between alternative solvents and rapeseed oil have been theoretically studied with the Hansen solubility methodology to get a better comprehension of dissolving mechanisms. The results indicated that p-cymene could be the most promising solvent for n-hexane substitution with higher lipid yield and good selectivity, despite the micronutrient contents were relatively low.     

Comparison of hot Soxhlet and accelerated solvent extractions with microwave and supercritical fluid extractions for the determination of polycyclic aromatic hydrocarbons and nitrated derivatives strongly adsorbed on soot collected inside a diesel particulate filter

Several methods of extraction were optimized to extract polycyclic aromatic hydrocarbons (PAHs), their nitrated derivatives and heavy n-alkanes from a highly adsorptive particulate matter resulting from the combustion of diesel fuel in a diesel engine. This particular carbonaceous particulate matter, collected at high temperatures in cordierite diesel particulate filters (DPF), which are optimized for removing diesel particles from diesel engine exhaust emissions, appeared extremely refractory to extractions using the classical extracting conditions for these pollutants. In particular, the method of accelerated solvent extraction (ASE) is described in detail here. Optimization was performed through experimental design to understand the impact of each factor studied and the factors’ possible interactions on the recovery yields. The conventional extraction technique, i.e., Soxhlet extraction, was also carried out, but the lack of quantitative extractions led us to use a more effective approach: hot Soxhlet. It appeared that the extraction of the heaviest PAHs and nitroPAHs by either the optimized ASE or hot Soxhlet processes was far from complete. To enhance recovery yields, we tested original solvent mixtures of aromatic and heteroaromatic solvents. Thereafter, these two extraction techniques were compared to microwave-assisted extraction (MAE) and supercritical fluid extraction (SFE). In every case, the only solvent mixture that permitted quantitative extraction of the heaviest PAHs from the diesel soot was composed of pyridine and diethylamine, which has a strong electron-donor character. Conversely, the extraction of the nitrated PAHs was significantly improved by the use of an electron-acceptor solvent or by introducing a small amount of acetic acid into the pyridine. It was demonstrated that, for many desirable features, no single extraction technique stound out as the best: ASE, MAE or SFE could all challenge hot Soxhlet for favourable extractions. Consequently, the four optimized extraction techniques were performed to extract the naturally polluted diesel soot collected inside the DPF. Comparisons with the NIST standard reference material SRM 1650b showed that the soot collected from the DPF contained 50% fewer n-alkanes, and also markedly lower levels of PAHs (44 less concentrated) than SRM 1650b, and that the ratio of nitroPAHs to PAHs was increased. These results were attributed to the high temperatures reached inside the particulate filter during sampling runs and to the contribution of the catalytic DPF to aromatic and aliphatic hydrocarbons abatement.     

A New Method to Remove Neutral Template in the Synthesis of HMS

The synthesis of mesoporous molecular sieves is believed to be one of the most exciting discoveries in the field of material science1. The formation of mesoporous structure relies on the template effect of the surfactant micelles2-4. Generally three kinds of interactions are involved in this process, i.e. electrostatic charge matching, hydrogen bonding and coordinative interaction5. After template-directed synthesis procedure, the after-treatment process is needed to remove the surfactant temp…     

茶叶中咖啡因的提取实验装置的改进与探索

"茶叶中咖啡因的提取"是有机化学实验的一个经典实验,本文对该实验所用的原索氏提取器进行改进,得到内通气集热式索氏提取器并用于实验教学。通过对照实验,对改进索氏提取器和原索氏提取器的提取效果进行比较。结果表明,改进装置具有原装置的功能和特点,且提取时间更短、提取温度和提取率更高,可在高校推广使用。     

咖啡因提取的综合性实验教学

介绍了一个综合性化学实验。该实验以绿茶为原料,95%的乙醇为提取剂,通过索氏提取器提取、常压蒸馏及升华等实验操作,得到咖啡因产品。通过超高效合相色谱法（Ultra Performance Convergence Chromatography,UPC2）确定咖啡因的含量,熔点测定法及1H-NMR归属分析表征结构。本实验将经典的有机化学实验和先进的分析测试仪器相结合,提高了学生的实验综合能力,激发了学生的科研兴趣和探索精神。     

神木半焦粉末萃取物的组成特征

依次用石油醚、CS₂、CH₂Cl₂、丙酮和甲醇在索氏萃取器中萃取了神木半焦粉末,得到了五级萃取物(E_1-5)和最终的萃余物,总萃取率为1.76%。分别用气相色谱/质谱联用仪(GC/MS)、大气压固体探针/飞行时间质谱仪(ASAP/TOF-MS)和电喷雾电离/飞行时间质谱仪(ESI/TOF-MS)分析了各级萃取物。用GC/MS分析的结果表明,在E₁中C_15-24的直链烷烃和E₂中3与4环的芳烃比较丰富,在E_3-5中含杂原子有机化合物较丰富,特别是E₄和E₅中含氧有机化合物的含量最高。与用GC/MS分析的结果相比,用ASAP/TOF-MS和ESI/TOF-MS从E_3-5中检测出更多的含杂原子有机化合物。     

Isolation of flavonoids from aspen knotwood by pressurized hot water extraction and comparison with other extraction techniques

Pressurized hot water extraction (PHWE) conditions (time, temperature, pressure) were optimized for the extraction of naringenin and other major flavonoids (dihydrokaempferol, naringin) from knotwood of aspen. Extracts were analysed by GC-FID, GC-MS, HPLC-UV and HPLC-MS. The results were compared with those obtained by Soxhlet, ultrasonic extraction and reflux in methanol. Flavonoids were most efficiently extracted with PHWE at 150 °C and 220 bar with 35 min extraction time. Soxhlet with methanol gave slightly higher recoveries, but an extraction time of 48 h was required. Naringenin concentration was highest in knotwood (1.15% dry weight) and much lower in the sapwood. PHWE proved to be cheap, fast and effective for the isolation of biofunctional flavonoids from aspen knotwood, producing higher recoveries than 24 h Soxhlet extraction, sonication or 24 h reflux.