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分光光度法测定水果中维生素C 总被引:2,自引:0,他引:2
在最佳实验条件下,硅钼黄能被维生素C定量地还原,在734.6nm处有最大吸收的硅钼蓝,维生素C质量浓度在0.001 000~0.020 00mg/mL范围内与硅钼蓝吸光度服从比尔定律,通过测定硅钼蓝的吸光度,测定维生素C的质量浓度,从而建立了硅钼蓝光度法测定维生素C的方法。探讨了反应温度、反应时间、放置时间、硅酸钠溶液用量、钼酸铵溶液用量、盐酸溶液用量、pH=10缓冲溶液用量等因素的影响,确定了硅钼蓝光度法测定维生素C的最佳条件。结果表明,线性回归方程为A=0.010 2+46.781c(mg/mL),线性相关系数(γ)=0.999 2,方法检测限为0.000 033mg/mL。该方法用于测定沙田柚、猕猴桃、柠檬中维生素C质量浓度,结果与文献报道的方法相符,加标回收率分别为97.6%~101.3%、97.6%~101.8%、97.3%~99.0%。 相似文献
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建立了硅钼蓝光度法测定硫普罗宁的新方法,详细探讨了硅钼蓝光度法测定硫普罗宁的各种影响因素。结果表明,在一定的反应条件下,体系中生成的硅钼黄可被硫普罗宁分子中的巯基(-SH)定量还原为硅钼蓝,通过测定硅钼蓝的吸光度,从而间接测定硫普罗宁的含量。显色体系最大吸收波长为686nm,硫普罗宁质量浓度在8.00~80.0μg/mL范围内与A呈良好的线性关系,线性回归方程为A=-0.0163+0.0104ρ(μg/mL),线性相关系数r=0.9995。方法用于测定硫普罗宁药片中硫普罗宁的含量,结果与标准方法相符。 相似文献
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在酸性介质中,硫离子可以定量地将硅钼黄还原为硅钼蓝,通过测定硅钼蓝的吸光度,可间接测定硫离子的含量,从而建立了硅钼蓝分光光度法测定水中硫的新方法。论文详细探讨了硅钼蓝分光光度法测定硫离子的各种影响因素。结果表明,显色体系的最大吸收波长为730nm,硫离子质量浓度在0.4000~8.000μg/mL范围内服从比尔定律,线性相关系数γ=0.9996。方法用于测定河水、山泉水、井水、温泉水中硫离子的含量,标准加入回收率分别为97.5%~105.0%、97.1%~101.0%、95.8%~96.7%、101.4%~102.1%。 相似文献
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在硫酸介质中,正硅酸与钼酸反应生成硅钼黄,硫酸亚铁还原为硅钼蓝,用分光光度法间接测定二氧化硅含量。测定波长采用680nm,二氧化硅质量浓度在0~1.0 mg/mL范围内符合比尔定律,线性回归方程A=0.8633C-0.0129,相关系数为0.9997。方法用于测定赤铁矿中高含量二氧化硅,相对标准偏差(n=6)不大于2.00%,加标回收率(n=6)在97.0%~99.7%之间。 相似文献
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研究了应用浮选萃取光度法的原理测定钛酸钡中痕量硅的方法。在pH为1.2时,硅与钼酸铵生成硅钼杂多酸(硅钼黄),用抗血酸将其还原为硅钼蓝,当通入空气时,生成的硅钼蓝吸附在气泡上,随气泡上升到有机相,最终浮选分离进入异戊醇。络合物最大吸收波长位于803 nm,硅含量在0~1.4 mg/L范围内符合比尔定律,摩尔吸光系数为3×104 L/(mol.cm),相关系数为0.996 7,加标回收率在96%~102.5%。该方法集分离与测定于一体,具有灵敏度高、选择性好、方便、快速的特点,可用于钛酸钡中硅的测定。 相似文献
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介绍了用钼蓝分光光度法测定氧化铝中二氧化硅的含量,在硝酸介质中硅与钼酸盐形成硅钼杂多酸,用抗坏血酸为还原剂,在810nm处测定,本方法测定结果准确,且重现性和稳定性均优于现行标准。 相似文献
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M. S. J. Simmonds W. M. Blaney F. Delle Monache M. Marquina Mac-Quhae G. B. Marini Bettolo 《Journal of chemical ecology》1985,11(12):1593-1599
Vismiones and ferruginins, representatives of a new class of lypophilic anthranoids from the genusVismia were found to inhibit feeding in larvae of species ofSpodoptera, Heliothis, and inLocusta migratoria. 相似文献
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Cheng-Le Zhao Shane Porzio Alan Smith Haiyan Ge H. T. Davis L. E. Scriven 《Journal of Coatings Technology and Research》2006,3(2):109-115
Despite its industrial importance, the subject of freeze-thaw (F/T) stability of latex coatings has not been studied extensively.
There is also a lack of fundamental understanding about the process and the mechanisms through which a coating becomes destabilized.
High pressure (2100 bar) freezing fixes the state of water-suspended particles of polymer binder and inorganic pigments without
the growth of ice crystals during freezing that produce artifacts in direct imaging scanning electron microscopy (SEM) of
fracture surfaces of frozen coatings. We show that by incorporating copolymerizable functional monomers, it is possible to
achieve F/T stability in polymer latexes and in low-VOC paints, as judged by the microstructures revealed by the cryogenic
SEM technique. Particle coalescence as well as pigment segregation in F/T unstable systems are visualized. In order to achieve
F/T stability in paints, latex particles must not flocculate and should provide protection to inorganic pigment and extender
particles. Because of the unique capabilities of the cryogenic SEM, we are able to separate the effects of freezing and thawing,
and study the influence of the rate of freezing and thawing on F/T stability. Destabilization can be caused by either freezing
or thawing. A slow freezing process is more detrimental to F/T stability than a fast freezing process; the latter actually
preserves suspension stability during freezing.
Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004 in Chicago,
IL. Tied for first place in The John A. Gordon Best Paper Competition. 相似文献
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Ethanol and (−)-α-Pinene: Attractant Kairomones for Bark and Ambrosia Beetles in the Southeastern US
In 2002–2004, we examined the flight responses of 49 species of native and exotic bark and ambrosia beetles (Coleoptera: Scolytidae
and Platypodidae) to traps baited with ethanol and/or (−)-α-pinene in the southeastern US. Eight field trials were conducted
in mature pine stands in Alabama, Florida, Georgia, North Carolina, and South Carolina. Funnel traps baited with ethanol lures
(release rate, about 0.6 g/day at 25–28°C) were attractive to ten species of ambrosia beetles (Ambrosiodmus tachygraphus, Anisandrus sayi, Dryoxylon onoharaensum, Monarthrum mali, Xyleborinus saxesenii, Xyleborus affinis, Xyleborus ferrugineus, Xylosandrus compactus, Xylosandrus crassiusculus, and Xylosandrus germanus) and two species of bark beetles (Cryptocarenus heveae and Hypothenemus sp.). Traps baited with (−)-α-pinene lures (release rate, 2–6 g/day at 25–28°C) were attractive to five bark beetle species
(Dendroctonus terebrans, Hylastes porculus, Hylastes salebrosus, Hylastes tenuis, and Ips grandicollis) and one platypodid ambrosia beetle species (Myoplatypus flavicornis). Ethanol enhanced responses of some species (Xyleborus pubescens, H. porculus, H. salebrosus, H. tenuis, and Pityophthorus cariniceps) to traps baited with (−)-α-pinene in some locations. (−)-α-Pinene interrupted the response of some ambrosia beetle species
to traps baited with ethanol, but only the response of D. onoharaensum was interrupted consistently at most locations. Of 23 species of ambrosia beetles captured in our field trials, nine were
exotic and accounted for 70–97% of total catches of ambrosia beetles. Our results provide support for the continued use of
separate traps baited with ethanol alone and ethanol with (−)-α-pinene to detect and monitor common bark and ambrosia beetles
from the southeastern region of the US. 相似文献
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It is well established that a wide range of drugs of abuse acutely boost the signaling of the sympathetic nervous system and the hypothalamic–pituitary–adrenal (HPA) axis, where norepinephrine and epinephrine are major output molecules. This stimulatory effect is accompanied by such symptoms as elevated heart rate and blood pressure, more rapid breathing, increased body temperature and sweating, and pupillary dilation, as well as the intoxicating or euphoric subjective properties of the drug. While many drugs of abuse are thought to achieve their intoxicating effects by modulating the monoaminergic neurotransmitter systems (i.e., serotonin, norepinephrine, dopamine) by binding to these receptors or otherwise affecting their synaptic signaling, this paper puts forth the hypothesis that many of these drugs are actually acutely converted to catecholamines (dopamine, norepinephrine, epinephrine) in vivo, in addition to transformation to their known metabolites. In this manner, a range of stimulants, opioids, and psychedelics (as well as alcohol) may partially achieve their intoxicating properties, as well as side effects, due to this putative transformation to catecholamines. If this hypothesis is correct, it would alter our understanding of the basic biosynthetic pathways for generating these important signaling molecules, while also modifying our view of the neural substrates underlying substance abuse and dependence, including psychological stress-induced relapse. Importantly, there is a direct way to test the overarching hypothesis: administer (either centrally or peripherally) stable isotope versions of these drugs to model organisms such as rodents (or even to humans) and then use liquid chromatography-mass spectrometry to determine if the labeled drug is converted to labeled catecholamines in brain, blood plasma, or urine samples. 相似文献
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Peter A. Edwards Grant Striemer Dean C. Webster 《Journal of Coatings Technology and Research》2005,2(7):517-527
Glycidyl carbamate chemistry combines the excellent properties of polyurethanes with the crosslinking chemistry of epoxy resins.
Glycidyl carbamate functional oligomers were synthesized by the reaction of polyfunctional isocyanate oligomers and glycidol.
The oligomers were formulated into coatings with several amine functional crosslinkers at varying stoichiometric ratios and
cured at different temperatures. Properties such as solvent resistance, hardness, and impact resistance were dependent on
the composition and cure conditions. Most coatings had an excellent combination of properties. Studies were carried out to
determine the kinetics of the curing reaction of the glycidyl carbamate functional oligomers with multifunctional and model
amines. Detailed kinetic analysis of the curing reactions was also undertaken. The results indicated that the glycidyl carbamate
functional group is more reactive than a glycidyl ether group.
Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, on October 27–29, 2004, in Chicago,
IL. 相似文献