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采用气相色谱-质谱联用法研究了微波条件对食品接触材料中双酚A在水、乙酸(3%,体积分数)、乙醇(10%,体积分数)、橄榄油4种食品模拟物中迁移行为的影响。在微波加热下,食品快速升温并能将热量传递给外部包装,从而加速包装材料中双酚A向食品的迁移。研究了不同微波温度、时间和功率下双酚A在4种食品模拟物中的迁移规律,结果表明:微波对双酚A迁移有显著影响,迁移量随着微波温度、时间和功率的增加而增加。在相同加热温度和时间条件下,微波加热方式中双酚A在4种食品模拟物种的迁移量均高于水浴加热。 相似文献
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1.用称重、化学分析、X射线相分析等方法研究六硼化镧于800及1000°在空气中的氧化作用。2.在试验中采用酸洗除氧化膜方法求得真实氧化量、结果表明以原试样单位表面积计的氧化量(μ)随温度、时间的增加而增加。3.生成物之一氧化硼在试验条件下将部分挥发。由于氧化硼挥发速度的差(己廾)导致800°与1000°时生成的氧化膜之组成有所不同,而试样在各温度下不同的重量变化系氧化增重和氧化硼挥发而减重两因素加合的结果。 相似文献
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用热重红外光谱联用技术研究混煤热解特性 总被引:16,自引:4,他引:16
用热重分析仪和傅里叶红外光谱仪,对混煤在惰性气氛中的慢速热解特性进行了动态分析,考察了煤种、掺混比例以及加热速率对热解的影响。结果表明,混煤的热解与单煤的热解有相似之处,热解组分的析出随温度的变化规律一致,但其组分析出量并不是单煤热解析出量的简单叠加。由于掺混煤种间的相互作用,混煤热解气体在析出时间和析出量上均发生了变化。通过对红外吸收光谱的分析,发现混煤热解气体析出规律受掺混煤种的影响很大,高活性煤种的存在会降低混煤热解的初析温度,增加热解气体的析出量,其掺混比例越高,影响也越明显。 相似文献
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微波在柴油机滤烟器催化再生中的应用:Ⅰ.滤烟器在氮气中的微波加热温 … 总被引:1,自引:1,他引:0
利用柴油机台架装置及微波加热装置考察了柴油机催化滤烟器的微波加热温升效应。结果表明,过滤体上捕集的烟碳量对催化滤烟器在氮气中的微波加热温升至关重要,烟碳量的微小增加,可引起滤烟体温度的显著升高。另外,当微波加热过程中隔离氧气时,滤烟体上出现了明显的金属氧化物催化剂被碳还原的现象。 相似文献
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用XPS研究了Fe-Al和Co-Al合金,并与金属铁粉和钴粉作了比较。结果表明在真空中加热时Fe-Al合金表面的铁的氧化物被部分地还原成金属铁,与此同时表面的金属铝部分地氧化成氧化铝。该现象可用下述氧化—还原反应来解释: Fe_2O_3+2Al→2Fe+Al_2O_3对于Co-Al合金在真空中加热时也观察到类似的氧化—还原反应。实验结果还表明在真空中加热时Fe-Al合金和Co-Al合金表面都发生铝偏析,其偏析程度随加热时间增加而增加。 相似文献
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银负载量及反应气预处理对银催化剂上氢气中CO选择氧化反应的影响 总被引:2,自引:0,他引:2
考察了银负载量及反应气预处理对银催化剂上CO选择氧化反应的影响.结果表明,O2转化率、CO的转化率及选择性都随着银负载量的增加而升高,CO氧化的选择性随着温度的降低而升高,低温下的选择性可达70%~80%.CO-TPR谱显示,产物CO2脱附量及脱附温度的次序与CO选择氧化活性有一致的对应关系.当反应气处理温度为300℃时,催化剂上CO氧化活性最高;随着反应气处理温度的继续升高,CO氧化活性及选择性反而降低.金属银的粒子尺寸随着银负载量的增加而增大;高温下反应气处理后,金属银粒子的尺寸明显减小.催化剂上CO氧化活性及选择性与银粒子的大小及催化剂的表面结构有关. 相似文献
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《Analytical letters》2012,45(6):519-527
Abstract Reaction heats measured in a microcalorimeter between varying amounts of human serum and 700 IU of lipase (EC 3.1.1.3) and those between serum and 8 U of cholesterol oxidase (EC 1.1.3.6) were significantly linear with the contents of triglycerides (r=1.00) and cholesterol (r=0.99), respectively. However, when sera from 13 human volunteers were subject to comparative study between the micro-calorimetric and spectrophotometric methods, the correlation became less appreciable (r=0.70 and r=0.71) presumably due to the individual variations in free glycerol and cholesterol ester-constituents that were deliberately omitted in the microcalorimetric method but were routinely included in the standard (multi-enzymatic) spectro-photometric clinical method. The contribution of interfering substances, if any, is not totally ruled out. 相似文献
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J. Kaloustian Paulette Lechene De La Porte T. El-Moselhy H. Lafont H. Portugal 《Journal of Thermal Analysis and Calorimetry》2005,82(2):331-338
Summary Cholesterol constitutes the major component of most gallstones. It was identified and determined in gallstones by thermal
analysis technique (DSC and TG-DTA), mainly by the use of the melting temperature (Tonset=145°C and Tmax=149°C) and by DTG peak decomposition (Tmax=364°C). Cholesterol anhydrous (ChA), which showed endothermic polymorphic peak, Tmax=40°C, without mass loss, was differentiated from cholesterol monohydrate (ChH), which showed a broad endothermic peak, Tmax=59°C, attributed to loss of water of crystallization (theoretical 4.45%). Morphological studies of gallstones were performed
by optical microscopy and scanning electron microscopy (SEM). The stones consisted of a pigmented core with a variably-sized
irregular central cavity, surrounded by a radially arranged deposits of plate-like ChH. The outer part of the stones showed
ChA crystal arborescences. X-ray microanalysis gave a typical spectrum rich in C and O, and in some instances the presence
of P, which was attributed to the presence of phospholipids. CaCO3 was easily characterized by TG with the use of DTG decomposition peak at 674°C. 相似文献
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The nanocomposite electrode comprising of polypyrrole (PPY) and carboxy functionalized multiwalled carbon nanotubes (MWCNT) has been electrochemically fabricated onto indium–tin–oxide (ITO) electrode using p‐toluene sulfonic acid (PTS). Cholesterol oxidase (ChOx) and cholesterol esterase (ChEt) have been immobilized onto this PPY– MWCNT/ITO nanocomposite electrode using N‐ethyl‐N‐(3‐dimethylaminopropyl) carbodiimide and N‐hydroxy succinimide chemistry for estimation of esterified cholesterol. The ChEt–ChOx/PPY–MWCNT/PTS/ITO bioelectrode has been characterized using Fourier transform infrared spectroscopy, electrochemical techniques, and scanning electron microscope. This ChEt–ChOx/PPY–MWCNT/PTS/ITO nanobioelectrode has a response time of about 9 s, linearity of 4 × 10?4 to 6.5 × 10?3 M/l of cholesterol oleate concentration, Km of 0.02 mM, and thermal stability of upto 45°C. This electrode exhibits improved biosensing characteristics compared with other total cholesterol electrodes reported in literature till date and can be used to estimate cholesterol in blood serum samples. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Kinetic studies of cholesterol oxidation catalyzed by soluble cholesterol oxidase fromBrevibacterium were conducted. The optimum temperature and pH were found to be 40–45°C and 7.0, respectively. A plot of initial reaction
rate versus cholesterol concentration is sigmoidal in shape. Analysis of the data suggests that the reaction follows a concerted
model and not a stepwise model. 相似文献
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Roque Bru Jose M. López-Nicolás Estrella Núñez-Delicado Dolores Nortes-Ruipérez Alvaro Sánchez-Ferrer Francisco Garciá-Carmona 《Applied biochemistry and biotechnology》1996,61(1-2):189-198
The capability of cyclodextrins to enhance greatly the solubility in water of poorly water-soluble substances makes them an
ideal alter native for investigating the expression of enzyme activity with such substrates in aqueous solution. This capability
is demonstrated by using soybean lipoxygenase with linoleic acid/β-cyclodextrin and di ethylstilbestrol/γ-cyclodextrin, and
cholesterol oxidase with choles terol/methyl-β-cyclodextrin. 相似文献
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Huseyin Bekir Yildiz Dilek Odaci Demirkol Serkan Sayin Mustafa Yilmaz Ozcan Koysuren Musa Kamaci 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(10):1075-1084
Accumulation of cholesterol in human blood can cause several health problems such as heart disease, coronary artery disease, arteriosclerosis, hypertension, cerebral thrombosis, etc. Therefore, simple and fast cholesterol determination in blood is clinically important. In this study, two types of amperometric cholesterol biosensors were designed by physically entrapping cholesterol oxidase in conducting polymers; thiophene capped poly(ethyleneoxide)/polypyrrole (PEO-co-PPy) and 3-methylthienyl methacrylate-co-p-vinyl benzyloxy poly(ethyleneoxide)/polypyrrole (CP-co-PPy). PEO-co-PPy and CP-co-PPy were synthesized electrochemically and cholesterol oxidase was immobilized by entrapment during electropolymerization. The amperometric responses of the enzyme electrodes were measured by monitoring oxidation current of H2O2 at +0.7 V in the absence of a mediator. Kinetic parameters, such as Km and Imax, operational and storage stabilities, effects of pH and temperature were determined for both entrapment supports. Km values were found as 1.47 and 5.16 mM for PEO-co-PPy and CP-co-PPy enzyme electrodes, respectively. By using these Km values, it can be observed that ChOx immobilized in PEO-co-PPy shows higher affinity towards the substrate. 相似文献
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《Green Chemistry Letters and Reviews》2013,6(2):173-177
One-pot silica promoted selective aromatization of ring-A of cholesterol using N-bromosuccinimide (NBS) has been performed. The structure of the compound has been characterized by spectral analysis (UV, FT-IR, NMR, and Mass). 相似文献