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61.
Thanner H. Krempl P. W. Selic R. Wallnöfer W. Worsch P. M. 《Journal of Thermal Analysis and Calorimetry》2003,71(1):53-59
Quartz-homeotypic gallium (ortho-) phosphate, GaPO4, is of special interest for resonator applications asking for temperature compensated cuts with higher electro-mechanical coupling than quartz and operational temperatures up to 970°C. The crystal microbalance technique, well known for quartz (QCM) which can be used only at moderate temperatures, can now be extended to much higher temperatures using GaPO4 crystals, benefiting from all three advantages mentioned above. Two different experiments were done to demonstrate the advantages of a crystal microbalance based on GaPO4. First, the GaPO4 resonator was used for film thickness determination and compared with a commercial QCM. This experiment demonstrated that the measuring range can be extended by using GaPO4 resonators instead of quartz. The second experiment demonstrates the possibility for thermogravimetric analysis up to 720°C by using a new concept for resonator mounting.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
62.
重氮树脂与十二烷基硫酸钠相互作用研究罗杨磊曹维孝(北京大学化学与分子工程学院北京100871)关键词重氮树脂,十二烷基硫酸钠,负性PS版随着化学与生命科学领域的发展,大分子与小分子在溶液的相互作用越来越受到关注.表面活性剂因其具有自组装能力,... 相似文献
63.
64.
离子选择电极—流动注射分析法动力学测定葡萄糖存在下的果糖 总被引:3,自引:0,他引:3
本文将离子电极与流动注射分析相结合,利用30℃下,在强碱性介质中,果糖和葡萄糖与2,4-二硝基酚钠反应速度明显差异,动力学测定了葡萄糖存在下果糖的含量。自制了2,4-二硝基酚电极作为动力学电位测定用的工作电极。本法测定果糖的范围为0.02~1.00mol/L,其RSD为4.0%~4.9%,RE为1.0~5.0%;当C葡/C果≤3倍时,葡萄糖的干扰不超过5%;本法也曾成功地用于果葡萄浆测定,其RSD 相似文献
65.
高效离子排斥色谱法测定饮料中的糖精钠 总被引:3,自引:0,他引:3
提出了一种用高效离子排斥色谱法测定饮料中糖精钠的新方法。以IonPac ICE-AS 6柱为分离柱,0.10 mmol/LH2SO4+甲醇(9+1)为淋洗液,202nm波长下紫外检测。在1-100mg/L范围内,糖精钠的含量与峰面积呈 良好线性关系。检出限为0.60ng,灵敏度优于以往采用离子交换色谱-电导检测法的结果。在实验条件下,饮料 中常见有机酸以及其它人工合成甜味剂等均不产生干扰。方法用于饮料中糖精钠的测定,加标回收率为98%~ 105%。此外还比较了电导检测、紫外检测和经化学抑制系统后紫外检测等三种检测方式对测定灵敏度的影响。 相似文献
66.
Precise conductance measurements are reported on dilute aqueous solutions of the sodium and potassium salts of orthophosphoric
acid at 25 ∘C. Conductance measurements on solutions of electrolytes such as these phosphate salts that exist in solution as complicated
mixtures of ions have previously proved difficult to interpret. To overcome this, a mathematical method has been developed
to calculate the concentrations of all the species in the aqueous system M3PO4/M2HPO4/M2HPO4/H3PO4 (M = Na or K) over a continuous range of stoichiometries. The Lee–Wheaton conductance equation has been used to interpret
the conductance of these multicomponent solutions in terms of the limiting ionic conductances and concentrations of all the
ions in the solution. The limiting molar conductances of the ions H2PO4
− and HPO4
2− and the ion-pair formation constants of these ions with sodium and potassium ions were determine
This work has enabled the accurate determination of solution parameters for the important hydrogenphosphate ions in water
and provides an excellent example of the use of an advanced conductance theory in the analysis of the conductance of multicomponent
electrolyte systems. 相似文献
67.
Controlled potential coulometric (CPC) studies were carried out for developing a method to determine gallium at milligram levels, in the mixed supporting electrolyte medium (4 M NaClO4 + 0.5 M NaSCN), employing stirring mercury as a working electrode. Investigations for optimization of working electrode potentials, quantity of charge, level of background current and electrolysis time for achieving quantitative reduction of Ga(III) to Ga and its oxidation back to Ga(III), were undertaken. Effect of gallium content and interference of zinc in of gallium determination were also studied. The developed methodology was employed for the determination of gallium in pure Ga as well as in synthetic U + Ga mixture solutions. Accuracy and precision values of better than 0.5% were obtained at 1-2 mg levels. 相似文献
68.
69.
Frey PA 《Chemical record (New York, N.Y.)》2001,1(4):277-289
Research on the mechanism of action of coenzyme B12, adenosylcobalamin, as a graduate student introduced the author to the field of organic free radicals in enzymology. Twenty years later, related work on S-adenosylmethionine (SAM) as a "poor man's coenzyme B12" was initiated in a detailed analysis of the mechanism of action of lysine 2,3-aminomutase (LAM). The interconversion of L-lysine and L-beta-lysine is catalyzed by LAM, which requires SAM, pyridoxal-5'-phosphate (PLP), and a [4Fe-4S] cluster as coenzymes. The mechanism of this reaction has been delineated as a radical isomerization, in which radical formation is initiated by the [4Fe-4S]-dependent cleavage of the SAM into methionine and the 5'-deoxyadenosyl radical. The mechanism of this process is discussed, together with the role of this radical in hydrogen abstraction from lysine to initiate the substrate radical isomerization. The chemistry underlying the functions of SAM, PLP, and [4Fe-4S] in the action of LAM is novel in all respects, except for the formation of a lysine-PLP aldimine at the active site. Of the four free radicals in the mechanism, three have been characterized by EPR spectroscopy. In the suicide inactivation of adenosylcobalamin-dependent dioldehydrase (DDH) by glycolaldehyde, the formation of cob(II)alamin and 5'-deoxyadenosine is accompanied by the conversion of glycolaldehyde to cis-ethanesemidione radical at the active site. The cis-ethanesemidione radical has been characterized by EPR spectroscopy. Its exceptional stability at the active site is the basis for the inactivation of DDH by glycolaldehyde. 相似文献
70.