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排序方式: 共有361条查询结果,搜索用时 203 毫秒
311.
Antonio Valverde Ana Aguilera Mariano Rodriguez Maria Brotons 《Journal of environmental science and health. Part. B》2013,48(3):204-213
Supercritical fluid extraction (SFE) was evaluated to be applied for residue analysis of 22 gas chromatography/electron capture detector-nitrogen phosphorus detector (GC/ECD-NPD) amenable pesticides in rice, wild rice and wheat. Samples were extracted with supercritical carbon dioxide at 200 atm pressure and 50°C temperature, using methanol as a static modifier. Mean recoveries obtained with the proposed SFE method at two spiking levels with four replicates per level are compared with those obtained with an ethyl acetate-based solvent extraction/gel permeation chromatography (GPC) clean up method. Both methods gave consistent high recoveries for almost all the pesticides from all the commodities with overall mean recoveries higher than 70% with relative standard deviations lower than 20%. Remarkable exceptions were captafol and dimethoate, for which low and/or non-reproducible recoveries were obtained with the SFE method. Residue levels determined with both methods in nine different incurred samples of wheat, containing some of the studied pesticides, were very similar, but, in all cases, slightly higher levels were determined with the SFE method. 相似文献
312.
《Journal of environmental science and health. Part. B》2013,48(4):653-664
Abstract Crude enzyme from a soil fungus, Aspergillus flavus, was isolated from a field soil following repeated applications of metolachlor [2-Chloro-N-(methoxy-1-methylethyl)-2′-ethyl-6′-methyl acetanilide]. Metolachlor hydrolysis by the crude enzyme extract was determined by enzyme assay. The tests were performed in phosphate buffer, pH 7.5, and the reaction was carried out at two herbicide concentrations (20 and 100 μg mL?1) and two crude extract volumes (0.2 and 0.5 mL of the homogenized crude extract mixture). The rate of metolachlor degradation was found faster in samples containing higher volume of crude extract, (T 1/2, 5.7 h) for both concentrations of the herbicide. The activities of enzymes responsible for dechlorination coupled with hydroxylation, N-dealkylation, and breaking of amide linkage were found responsible in the degradation. 相似文献
313.
Bruno Spinosa DeMartinis Fernando Mauro Lanças 《Journal of environmental science and health. Part. B》2013,48(5):539-547
Abstract Supercritical fluid extraction (SFE) is a rapid and convenient method for the isolation of organic compounds from environmental samples. This paper describes a supercritical carbon dioxide (CO2) extraction system that uses a newly designed extraction cell to recover organic compounds from an aqueous matrix. Analysis of the extracts by gas chromatography‐electron capture detector (GC‐ECD) indicated that the herbicide trifluralin (2,6‐dinitro‐N,N‐dipropyl‐4‐trifluoromethylaniline) could be quantitatively extracted by using the SFE system proposed with small amounts of sample. The percentage of recovery obtained with the SFE system described was twice as high as the result obtained using a conventional solid‐phase extraction technique. Extraction by SFE was completed in a short period of time using a simple and low‐cost home‐made system that did not require the use of organic solvents. 相似文献
314.
Carla L. Barberis Cecilia S. Carranza Stella M. Chiacchiera Carina E. Magnoli 《Journal of environmental science and health. Part. B》2013,48(12):1070-1079
The effect of six glyphosate concentrations on growth rate and aflatoxin B1 (AFB1) production by Aspergillus section Flavi strains under different water activity (aW) on maize-based medium was investigated. In general, the lag phase decreased as glyphosate concentration increased and all the strains showed the same behavior at the different conditions tested. The glyphosate increased significantly the growth of all Aspergillus section Flavi strains in different percentages with respect to control depending on pesticide concentration. At 5.0 and 10 mM this fact was more evident; however significant differences between both concentrations were not observed in most strains. Aflatoxin B1 production did not show noticeable differences among different pesticide concentrations assayed at all aW in both strains. This study has shown that these Aspergillus flavus and A. parasiticus strains are able to grow effectively and produce aflatoxins in high nutrient status media over a range of glyphosate concentrations under different water activity conditions. 相似文献
315.
Baig MN Leeke GA Hammond PJ Santos RC 《Environmental pollution (Barking, Essex : 1987)》2011,159(7):1802-1809
Extractions of volatile organic compounds (VOC’s) in contaminated soil from petroleum site were performed with supercritical carbon dioxide at different temperatures, pressures, extraction times, solvent flow rates, soil moisture contents and soil acidity. Three soil systems were investigated in order to compare the best parameters for extraction. A central composite rotatable design has been used to evaluate the influence of operation conditions on the extraction efficiency to generate model equations representing the types of soil. The results indicate that at least 70-80% of the initial amount of VOC’s can be removed at moderate temperatures even at very high moisture content. Supercritical extraction is best suited to silt type soils which have a low adsorption capacity. VOC’s recoveries from the artificial contaminated soil samples were higher in comparison with real contaminated soils. At moderate temperatures, the extraction efficiency for real soils is low because pollutants bind strongly to the soil. 相似文献
316.
以Ti(OC4H9)4为原料,溶胶-凝胶法制备纳米TiO2 薄膜,用原子力显微镜(AFM)观察了纳米TiO2薄膜的形貌,X-射线衍射(XRD)考察相同条件下粉体的相结构.研究水中橡椀栲胶的光催化降解行为.结果表明,橡椀栲胶的降解可用Langmuir-Hinshelwood方程来描述,即浓度较高时,栲胶降解液的光催化降解符合零级动力学方程;浓度较低时,栲胶降解液的光催化降解符合一级动力学方程.外加H2O2对橡椀栲胶的光催化降解有极大的促进作用,但这种促进作用会因为光生电子效率的影响而有一个极限值.在远离橡椀栲胶溶液等电点的起始pH值条件下光催化降解效果较好,且在碱性条件下的降解速率高于酸性条件下的降解速率. 相似文献
317.
采用二氯甲烷液液萃取-氮吹浓缩-丙酮定容去除干扰物,用气相色谱检测水中的阿特拉津,根据保留时间定性,外标法定量.本方法适用于水中阿特拉津的残留量分析,最低检测浓度为4.51×10-2 μg∕L. 相似文献
318.
Stroud JL Rhodes AH Semple KT Simek Z Hofman J 《Environmental pollution (Barking, Essex : 1987)》2008,156(3):664-670
The aim of this paper was to measure the changing desorbable fraction and bioaccessibility of phenanthrene in two different soils with increasing soil-phenanthrene contact time using supercritical fluid extractions (SFE). Both soils were spiked with 100 mg kg−1 phenanthrene and aged for 28 d. Desorption profiles were measured every 7 d using selective SFE conditions and the results were compared to 14C-phenanthrene mineralisation assays. Selective SFE showed significant differences in the rates and extents of desorption in the two soils, likely to be due to different organic matter composition. Post-extraction fitting of data yielded consistent SFE extraction times within ageing soils for bioaccessibility prediction. 相似文献
319.
320.
钻井废液的超临界水氧化处理及动力学分析 总被引:2,自引:0,他引:2
在反应温度为500~600℃、压力为25~30 MPa、停留时间为30~600 s的条件下,在连续式反应器中研究了钻井废液的超临界水氧化反应.结果表明:钻井废液的COD去除率可达90.00%以上;在600℃、停留时间为600 s时,钻井废液氧化后,剩余收集液的COD<120 mg/L,满足《污水综合排放标准》(GB 8978-1996)中的二级标准.用幂函数方程描述了氧化剂过量时钻井废液超临界水氧化的反应动力学规律,反应速率常数与温度的关系符合Arrhenius公式,随停留时间的增加、温度的升高,有机物的去除率显著增加;反应速率常数随压力升高而增加,但反应速率常数的增幅随压力的升高而减小,反应活化体积不是常数.在25 MPa时,反应活化能和频率因子分别为(17 745.430 40±1 114.983 42)kJ/mol和1.152 3×10-4s-1模型计算值与实验值的误差在±15%以内. 相似文献