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1.
为准确测定烟草浸膏中烟碱含量,以2-甲基喹啉为内标建立了测定烟草浸膏中烟碱的气相色谱-氢火焰离子化法(GC-FID),并测定了5个烟草浸膏样品.结果表明,方法的回收率为95.00%~98.58%,检出限为0.27 mg/g,定量限为0.89 mg/g.所测烟草浸膏中烟碱的质量分数在19.66~54.97 mg/g之间.方法简单、灵敏、准确,适用于烟草浸膏中烟碱的测定. 相似文献
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秦俊法 《广东微量元素科学》2011,18(4):1-10
从采样、洗涤、消化和测定4个方面论述了准确测定头发铅含量的条件和方法,提出了发铅检测各个流程的规范化建议.这些建议亦适用于头发其他元素的含量测定. 相似文献
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讨论了测定聚合氯化铁中OH/Fe物质的量比的几种方法,确定用过量碱沉淀法测定聚合氯化铁中的OH/Fe物质量比;同时研究了影响测定的各种因素,找出了最佳的测定条件.通过对合成试样和未知试样的测定,结果表明方法无系统误差存在,结果准确、可靠. 相似文献
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马景治 《分析测试技术与仪器》2020,26(1):61-66
采用X射线荧光光谱仪可以快速准确测定萤石中总钙的含量.但测定其中氟化钙含量时,一方面,由于样品中碳酸钙计入钙量,从而造成氟化钙测定结果准确性较差.另一方面,铜、锌等金属元素在熔融制样时对铂金坩埚腐蚀较大,因此需要进行酸处理除去碳酸钙及铜、锌等金属元素.然而,样品经过酸处理后,质量会发生变化,造成熔剂与样品的比例不一致,从而影响测定结果.对样品前处理条件、XRF分析中熔片和仪器工作条件等进行了优化,建立了熔融制样、X射线荧光光谱法(XRF)准确测定萤石中氟化钙含量的方法.方法干扰少,具有良好的准确度和精密度,操作简单,提高了分析效率. 相似文献
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焦立为 《理化检验(化学分册)》2007,43(10):886
挥发分作为评价石油焦质量的重要技术指标之一,其测定在石油焦分析中占有很重要的位置.由于挥发分是在无空气通入的情况下,将试样加热至(850±10)℃,并保持7 min,按照损失总质量与蒸发水分损失之间的差来确定挥发分.由于其技术条件不易控制而常常造成测定结果不准确.经过实践,总结出准确测定石油焦挥发分的技术条件. 相似文献
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Bolin Li Fang Guo Hao Hu Ping Liu Minjia Tan Jianyi Pan Linhui Zhai 《Journal of mass spectrometry : JMS》2020,55(1)
Column heating strategy is often applied in nano–high‐performance liquid chromatography–mass spectrometer (nanoHPLC‐MS) platform for enhancing the analytical efficiency of peptides or proteins. Nonetheless, the influence effects of column heating in peptides or proteins identification still lack of deep understanding. In this study, a systematic comparison of room temperature (RT) and column heating of nanoHPLC was done. Based on the data, under column heating condition, the backpressure of nanoHPLC can be decreased. Due to the increase of resolution, the peak widths of precursor ion were narrowed. As a result, in MS/MS data acquisition part, more time was spared for MS1 detecting and MS2 fragmenting, which eventually resulted in increased identification of peptides and proteins. Moreover, we also proposed the application scope of column heating by evaluating its influence on sample detection. On one hand, column heating significantly increased the identification of membrane proteins due to more efficient elution of highly hydrophobic peptides compared with RT. On the other hand, heating was not suitable for analyzing short or/and hydrophilic peptides with low retention time, which would be eluted out during sample loading process under high temperature and missed by mass spectrometric detection. In conclusion, our study provides a reference for rational application of column heating in proteomics research. 相似文献
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High-resolution thermogravimetric analysis (Hi-ResTM TG) in its variable heating rate mode was applied to commercially available diesel fuel additives under a nitrogen atmosphere.
A TGA 2950 from TA Instruments was used to run the experiments. For the selected diesel fuel additives, the use of variable
heating rate resulted in sharper transitions and clearer onset of degradation than in traditional constant heating rate experiments.
Moreover, the time required for experiments giving reasonable resolution was remarkably reduced compared to constant heating
rate experiments. The technique proved to be very useful in the study of multi-component systems, such as diesel fuel additives,
since it provides more detailed information regarding mass changes in the sample as a result of heat treatment when total
decomposition involves more than one stage i.e. mass changes stem from consecutive reactions.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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The influence of microwave heating on the stability of immobilized Candida antarctica lipase B was studied at 100 degrees in an organic medium. The microwave radiation was carried out before enzymatic reaction (storage conditions) or during the enzymatic catalysis (use conditions). In both cases, enzymatic stability was higher under microwave heating than under conventional thermal heating, in strictly identical operating conditions. Furthermore, the gain of enzymatic stability under microwave heating appears to be higher in a more polar solvent, which interacts strongly with the microwave field. Our results suggest that microwave radiation has an effect, not related to temperature, on the process of enzymatic inactivation. 相似文献
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[reaction: see text] Anodic intramolecular cyclization of alpha-(phenylthio)acetamides using a fluoride ion mediator was realized. Under ultrasonic irradiation, cyclization was accelerated markedly to give desired cyclized products in moderate to good yields. The local heating effect of ultrasonic irradiation seems to be more advantageous than usual heating. 相似文献
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微波辐射对TiO2制备及其光催化氧化乙醛性能的影响 总被引:5,自引:0,他引:5
采用微波辐射与常规加热法由TiO2溶胶制备出TiO2催化剂,采用高频低功率微波-光催化装置考察了微波对两种催化剂上CH3CHO光催化氧化转化率和产物分布的影响。结果表明,微波干燥制备的TiO2晶体比普通加热制备的TiO2晶体对乙醛有更高的光催化活性和更强的氧化能力,且它们对乙醛光催化氧化的途径不同,前者的初始中间体为甲醛和甲酸,后者的初始中间体却为乙酸。还发现,微波辐射对两种样品上乙醛的光催化转化率有不同的影响,对微波辐射法所制样品的影响比对常规加热法所制样品的影响显著。微波辐射通过场效应可加速光催化初始中间体的转化,但它不改变光催化反应的途径,反应途径取决于光催化剂的特性。 相似文献
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Stuart J. Williams 《Electrophoresis》2013,34(9-10):1400-1408
This work demonstrates the use of thin film heaters to enhance electrothermal pumping in microfluidic systems. Thin film heating electrothermal pumping is more efficient than Joule heating alone. Numerical simulations of an asymmetric electrode array are performed to demonstrate the advantages of incorporating thin film heaters. This specific simulation shows that thin film heater electrothermal pumping provides approximately two and one‐half times more volumetric flow than Joule heating alone for the same input power to both systems. In addition, external heating allows for electrothermal pumping to be applicable to low conductivity media. 相似文献
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TG/MS of Poly (Methyl Methacrylate), The Effect of Heating Rate on the Rate of Production of Evolved Gases 总被引:1,自引:1,他引:0
Thermogravimetric analysis coupled with quadrupole mass spectrometry was performed to study the effects of heating rate on
the rate of gasification of gases evolving from 0.5 mm particles size industrial-grade PMMA. The controlled mass loss measurements
and the evolved gases were conducted in pure nitrogen and various oxidative environments under heating rates of 2 to 5°C min-1. The results indicated major differences, in pure nitrogen, the rate of production of gases is steeper compared to those
associated with oxidative environment. Furthermore as the heating rate is lowered, it appears that the gases emanating from
the surface are more volatile in the sense that they burst more abruptly from the surface.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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Shinji Yamada Akinori Takasu Kazuhiko Kawamura 《Journal of polymer science. Part A, Polymer chemistry》2013,51(17):3732-3739
We examined the ring‐opening polymerization of ε‐caprolactone in toluene between 50 and 70 °C, and catalyzed by some Lewis and Brønsted acids to investigate the effects of microwave versus conventional heating on the kinetics and activation thermodynamics of the reaction. The polymerizations proceeded more rapidly when microwave heating, instead of conventional heating, was used to control the temperature. The number‐average molecular weight (Mn) of the polymer could be controlled even when microwave heating was used. To identify which thermodynamic activation constants were responsible for the accelerated polymerizations, we performed the reaction at different temperatures to obtain data for the Arrhenius and Eyring equations. Although the values for the activation energies and the activation enthalpies were larger when microwave heating rather than conventional heating was used, the frequency factors and the activation entropies (ΔS?) over compensated for the less favorable activation energies and enthalpies. The more favorable ΔG? found for the microwave‐assisted polymerizations mainly reflect the larger ΔS? values, and the rate accelerations appear to be a consequence of differently arranged intermediates and/or transition states. © 2013 Wiley Periodicals, Inc. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3732–3739 相似文献
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alpha-Crystallin, a major protein of the mammalian lens, plays a vital role in maintaining the structural stability and transparency of the lens. It performs this function through chaperone-like activity; it has recently been reported that heating alpha-crystallin enhances this ability. The present studies, using both time-resolved and steady-state fluorescence methods, were carried out to compare the conformational changes that result from heating with those that result from increasing protein concentration (up to 70 mg/mL). The relative fluorescence quantum yield from tryptophan (Trp) present in alpha-crystallin increases and then decreases with a concomitant shift of the emission maximum to longer wavelengths when either heating times or protein concentrations are increased. The time profile of fluorescence decay was resolved into three components with lifetimes of ca 0.5, 3 and 7 ns and emission maxima of ca 340, 342 and 350 nm, respectively. With longer heating time or increasing concentrations the contribution from the longer-lived component increases at the expense of the shorter-lived species. These data indicate that with heating or at higher concentrations the internal Trp residues move to the surface of the protein giving a more hydrophobic exterior and possibly explain the reported increased chaperone activity upon heating. As a result of the concentration studies, alpha-crystallin may be more efficient in its chaperone activity in vivo than has been determined by in vitro experiments. 相似文献
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Microwave (MW) heating was proven to efficiently solid-synthesize calcium carbide at 1750 °C, which was about 400 °C lower than electric heating. This study focused on the investigation of the diffusion behaviors of graphite and calcium oxide during the solid-state synthesis of calcium carbide by microwave heating and compared them with these heated by the conventional method. The phase compositions and morphologies of CaO and C pellets before and after heating were carefully characterized by inductively coupled plasma spectrograph (ICP), thermo gravimetric (TG) analyses, X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The experimental results showed that in both thermal fields, Ca and C inter-diffused at a lower temperature, but at a higher temperature, the formed calcium carbide crystals would have a negative effect on Ca diffusion to carbon. The significant enhancement of MW heating on carbon diffusion, thus on the more efficient synthesis of calcium carbide, manifested that MW heating would be a promising way for calcium carbide production, and that a sufficient enough carbon material, instead of CaO, was beneficial for calcium carbide formation in MW reactors. 相似文献