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排序方式: 共有307条查询结果,搜索用时 109 毫秒
81.
82.
Kei Toda Haruka KuwaharaHidetaka Kajiwara Kazutoshi HirotaShin-Ichi Ohira 《Analytica chimica acta》2014
The highly odorous compound methanethiol, CH3SH, is commonly produced in biodegradation of biomass and industrial processes, and is classed as 2000 times more odorous than NH3. However, there is no simple analytical method for detecting low parts-per-billion in volume ratio (ppbv) levels of CH3SH. In this study, a micro gas analysis system (μGAS) was developed for continuous or near real time measurement of CH3SH at ppbv levels. In addition to a commercial fluorescence detector, a miniature high sensitivity fluorescence detector was developed using a novel micro-photomultiplier tube device. CH3SH was collected by absorption into an alkaline solution in a honeycomb-patterned microchannel scrubber and then mixed with the fluorescent reagent, 4-(N,N-dimethylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (DBD-F). Gaseous CH3SH was measured without serious interference from other sulfur compounds or amines. The limits of detection were 0.2 ppbv with the commercial detector and 0.3 ppbv with the miniature detector. CH3SH produced from a pulping process was monitored with the μGAS system and the data agreed well with those obtained by collection with a silica gel tube followed by thermal desorption–gas chromatography–mass spectrometry. The portable system with the miniature fluorescence detector was used to monitor CH3SH levels in near-real time in a stockyard and it was shown that the major odor component, CH3SH, presented and its concentration varied dynamically with time. 相似文献
83.
Siam benzoin is a natural resin that contains up to 65% of coniferyl benzoate. Treatment of this material with an esterase
followed by an alcohol dehydrogenase in a one-pot procedure gave 1.5 g/L coniferaldehyde in 36% molar yield. Several lipases
and esterases were tested, but only pig liver esterase gave significant results. Various alcohol oxidases and alcohol dehydrogenases
were screened for their ability to oxidize coniferyl alcohol to coniferaldehyde. Horse liver alcohol dehydrogenase coupled
with a cofactor regeneration system was the most efficient of the enzymes tested. 相似文献
84.
Co—Mo/Al2O3型重整预加氢催化剂的研制 总被引:3,自引:0,他引:3
考察了不同方法制备的Co-Mo/Al2O3型重整预加氢催化剂对石油加氢脱硫活性的影响,选出了一种工业生产步骤简单,金属含量容易控制,并且不腐蚀设备的碱必等量共浸法制备的DS-948催化剂。该催化剂在温度350℃,压力3.0MPa,液体空速6.0h^-1,体积氢油比70的条件下,满足了双金属重整催化剂对精制石油脑油杂质含量的要求。 相似文献
85.
86.
三层前向人工神经网络全局最优逼近 总被引:6,自引:0,他引:6
提出了求解不等式约束非线性优化问题的群体复合形进化算法 ,提出的算法能充分利用目标函数值的信息、优化搜索过程具有较强的方向性和目标性 ,收敛速度较快 ,且是全局优化算法 ;将群体复合形进化算法应用于三层前向人工神经网络逼近 ,提出了三层前向人工神经网络全局最优逼近算法 ;将三层前向人工神经网络全局最优逼近算法应用于实例 ,表明了提出的全局最优逼近算法的有效性 . 相似文献
87.
催化动力学光度法测定锅炉给水中异抗坏血酸钠 总被引:1,自引:0,他引:1
基于催化动力学过程,研究了新型锅炉给水除氧剂异抗坏血酸钠的分光光度法测定。试验表明,这一方法操作简便,快速、准确提高,可测至5μg.L^-1异抗坏血酸钠。 相似文献
88.
高效液相色谱法测定猪皮下脂肪、背最长肌和血清中粪臭素和吲哚含量 总被引:2,自引:0,他引:2
建立了高效液相色谱法测定猪皮下脂肪、背最长肌和血清中的粪臭素和吲哚含量的方法。脂肪样品的去脂预处理采用固相萃取 ,脂肪用甲醇提取后 ,提取液通过sep pakC18小柱 ,脂肪和脂肪酸被保留在C18小柱上。色谱条件 :流动相为乙腈∶水 =4 0∶6 0 ;EclipseXDBC8、5 μm、4 .6× 15 0mm不锈钢柱 ,柱温 30℃ ;荧光检测波长 :EX 2 70nm ,EM 35 0nm ;皮下脂肪、背最长肌和血清中粪臭素和吲哚测定方法平均回收率 (n =6 )分别为98.1%和 97.0 % ,96 .4 %和 94 .1% ,10 2 .12 %和 98.9%。 相似文献
89.
Mahesar SA Sherazi ST Abro K Kandhro A Bhanger MI van de Voort FR Sedman J 《Talanta》2008,75(5):1240-1244
A rapid method has been developed to extract and quantitatively measure the total oil content in poultry feeds using a domestic microwave oven. The optimized extraction procedure involves the replicate (6×) extraction of 5 g of ground feed with 12 ml of hexane for 20 s in a 900 W oven. Each replicate involves the collection of the resulting miscella and its replacement with fresh solvent for re-extraction. The collected extracts were centrifuged and transferred to a vial. The solvent was evaporated to a constant weight and the residual lipid weighed. In comparison to conventional Soxhlet extraction method, lipid contents obtained using the optimized microwave procedure was not significantly different. However, FTIR analysis indicated that the microwave procedure was superior in minimizing the formation of free fatty acids (FFA) relative to the Soxhlet procedure if the temperature of the sample was kept within the range of 45–50 °C. This simple, sequential extraction procedure is rapid, highly efficient and provides a simple mean of quantitating the lipid content of poultry feed in less than 40 min without the need for specialized microwave oven. 相似文献
90.
GC×GC-ECD: a promising method for the determination of dioxins and dioxin-like PCBs in food and feed
Haglund P Korytár P Danielsson C Diaz J Wiberg K Leonards P Brinkman UA de Boer J 《Analytical and bioanalytical chemistry》2008,390(7):1815-1827
There is a need for cost-efficient alternatives to gas chromatography (GC)–high-resolution mass spectrometry (HRMS) for the
analysis of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (PCBs) in food and feed. Comprehensive two-dimensional
GC–micro electron capture detection (GC×GC-μECD) was tested and all relevant (according to the World Health Organisation,
WHO) PCDD/Fs and PCBs could be separated when using a DB-XLB/LC-50 column combination. Validation tests by two laboratories
showed that detectability, repeatability, reproducibility and accuracy of GC×GC-μECD are all statistically consistent with
GC-HRMS results. A limit of detection of 0.5 pg WHO PCDD/F tetrachlorodibenzo-p-dioxin equivalency concentration per gram of fish oil was established. The reproducibility was less than 10%, which is below
the recommended EU value for reference methods (less than 15%). Injections of vegetable oil extracts spiked with PCBs, polychlorinated
naphthalenes and diphenyl ethers at concentrations of 200 ng/g showed no significant impact on the dioxin results, confirming
in that way the robustness of the method. The use of GC×GC-μECD as a routine method for food and feed analysis is therefore
recommended. However, the data evaluation of low dioxin concentrations is still laborious owing to the need for manual integration.
This makes the overall analysis costs higher than those of GC-HRMS. Further developments of software are needed (and expected)
to reduce the data evaluation time. Combination of the current method with pressurised liquid extraction with in-cell cleanup
will result in further reduction of analysis costs.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献