金属材料分析方法的选择和施行第六讲金属材料中稀土元素的测定(续)

2Ce3 BiO3- 6H Ce4 Bi3 3H2OFe2 Ce4 Fe3 Ce3 试样溶液中加入硫酸铵是为了防止铋(Ⅲ)的水解。镁合金中单独测定铈的光度测定法,较为成熟且合理的方法尚不多见。但基于铈具有三价和四价之间的价态变化的特征,仍有可能建立一种不需要预先分离的直接光度测定法。例如3,3′-二甲基-4,4′-二氨基联苯(3,3-′dimethyl-4,4-′benzidine),又称邻联甲苯胺(o-tolidine)曾用于钢铁中铈的测定。在镁合金中以铈作为合金元素的有MB8及ZM3,ZM4等几种牌号。前一种为镁锰系变形镁合金,其主要合金组分除0.15%~0.35%(质量分数下同)铈外,有1.3%~2.27%锰,0.3%左右锌及0.2%左右铝;后两种为镁锌锆系铸造镁合金,其中铈的含量较高(2.5%~4.0%),其余合金元素为(0.2%~3.0%)锌及(0.5%左右)锆,余量为镁。根据上述情况,建立用邻联甲苯胺作为试剂的镁合金中铈的光度测定法可从以下几点考虑:(1)邻甲苯胺与铈(Ⅳ)反应的基本原理:在酸性溶液中四价铈能将邻甲苯胺氧化而生成有颜色的化合物,其颜色可能是蓝色、绿色或黄色,这与溶液的介质...     

铬(Ⅲ)离子催化铈(Ⅳ)离子氧化四氢糠醇的反应动力学及机理

在酸性介质中用氧化还原滴定法研究了铈(Ⅳ)离子在铬(Ⅲ)离子催化作用下,于25～40℃区间氧化四氢糠醇的反应动力学.结果表明反应对铈(Ⅳ)和四氢糠醇均为一级.准一级速率常数kobs随催化剂[Cr(Ⅲ)]增加而增大,亦随[H+]增加而增大,而随[HSO-4]增加而减小.在氮气保护下,反应不能引发丙烯酰胺聚合,说明在反应中没有自由基产生.提出了催化剂、底物和氧化剂间生成双核加合物的反应机理.通过kobs与HSO-4的依赖关系,并结合Ce(Ⅳ)在溶液中的平衡,找到了本反应体系的动力学活性物种是Ce(SO4)2.还计算出一些速率常数及相应的活化参数.     

双硫腙褪色光度法测定痕量铈

研究了Ce(Ⅳ)在H2SO4介质中和溴化十六烷基吡啶存在下催化H2O2氧化双硫腙的褪色反应及其动力学条件,测定了反应级数和表观活化能,建立了测定痕量铈的新方法。双硫腙的最大吸收波长为450nm,该方法的检出限为1 9×10-9g/mLCe(Ⅳ),线性范围为0～150ng/mLCe(Ⅳ),方法可用于人发中痕量铈的测定。     

金橙褪色光度法测定痕量铈(Ⅳ)

基于在硫酸介质中,铈(Ⅳ)催化H2O2氧化金橙使其褪色的反应,建立了测定痕量铈(Ⅳ)的新方法。该法的线性范围为0~250μg/L,检出限为5.8×10-9g/mL。用本法对人发中的铈(Ⅳ)含量进行了测定,分析结果满意。     

关于钒的滴定法中铬、铈的干扰问题

滴定法测定钒常采用在室温条件下,用高锰酸钾溶液氧化至高价后,用硫酸亚铁铵标准溶液滴定,指示剂则多数采用邻苯氨基苯甲酸。在此方法中主要的干扰元素为铬和铈。铬是钢铁中常用的合金元素,在冷溶液中用高锰酸钾溶液氧化钒时可能有少量铬(Ⅲ)被氧化至高价,可加亚砷酸钠溶液使铬(Ⅵ)选择性地被还原,从而避免其干扰。氧化还原测定也是测定铈的主要方法之一。四价铈是强氧化剂,Ce~(4+)/Ce~(3+)电对的氧化还原电位与溶液介质和酸的浓度有关,在1mol·L~(-1)的HCl、HNO_3、HClO_4和0.5mol·L~(-1)H_2SO_4溶液介质中分别为1.28V、1.61V、1.70V和1.44V。而且在磷酸介质中由于生成铈与磷酸根的络合物,使其氧化还原电位降低,因此三价铈更容易被氧化。在磷酸介质中用硝酸铵或高锰酸钾可使铈定量氧化。因此,在钒的滴定法测定中,如果有铈     

邻苯二酚衍生物与稀土元素配位反应的研究(V)——3,4-二羟基苯甲酸与铈(Ⅲ)的配位与转型反应

研究了稀土元素铈(Ⅲ)离子与3,4-二羟基苯甲酸(H3L)在水溶液体系中生成羧基配位化合物的条件,表征其组成为Ce(H2L)2(OH)·3H2O,并研究了该配合物在一定条件下,铈离子由羧基配位反应变为由两八邻酚羟基配位的配合物[Ce(HL)n]的转型反应及氧化成铈(Ⅳ)配合物的反应.     

二安替比林—（3,4）—二甲氧基苯基甲烷与铈显色反应的研究及应用

二安替比林芳香族甲烷衍生物被高价金属离子氧化而显深色,因此能用作这类离子的显色剂.我们曾合成过一系列的二安替比林芳香族甲烷衍生物,并广泛用于钒,铬,铈的测定.在此基础上我们研究了二安替比林-(3,4)-二甲氧基苯基甲烷(DADMPM)与Ce(Ⅳ)的显色反应条件及应用,用于镁合金中痕量铈的测定,体系灵敏度高,稳定性好,结果满意.1 试验部分1.1 主要仪器与试剂722型分光光度计铈标准溶液:用优级纯硫酸铈按常规方法配成含Ce(Ⅳ)100μg·ml~(-1)贮备液,标定,使用时稀释成5.0μg·ml~(-1)的标准工作液.Mn(Ⅱ)溶液:用MnSO_4·H_2O配成6.0mg·ml~(-1)的水溶液     

用催化容量法测定矿石中微量锇和钌

本文探讨了用催化容量法测定矿石中的微量锇和钌。利用在硫酸介质中微量锇或钌对四价铈和三价砷的催化反应,经过一定时间后,可加入一定量的亚铁,把催化反应过程中剩余的四价铈还原,使催化反应停止,然后用四价铈反滴定过量的亚铁,求出催化反应过程中剩余四价铈的量(以V表示)。实验结果指出,在10毫升2当量的硫酸溶液中,四价铈和三价砷的开始浓度分别为0.02和0.15当量,硫酸汞为0.2％,反应温度为25°.0C时,微量锇和钉的催化反应均为一级反应。当催化反应的时间固定为10分钟,并以1-logV对锇钉浓度作标准曲线,指出,锇的量在0—0.040微克,钌在0—0.0125微克,线性关系均良好。如样品中锇、钌的含量较大或较小时,可用缩短或延长催化时间的办法来绘制校准曲线,其线性关系仍然很好。     

2-乙基己基膦酸单2-乙基己基酯从硫酸溶液中萃取铈(Ⅳ)的机理

研究了2-乙基己基膦酸单2-乙基己基酯的正己烷溶液在硫酸介质中萃取铈(Ⅳ)和硫酸的平衡规律。通过IR,NMR 测定和科率法研究,提出了在不同硫酸浓度下铈(Ⅳ)和硫酸的萃取机理。研究了不同溶剂和温度对萃取平衡的影响,计算了浓度平衡常数K、△H、△Z和△S。     

含氟硫酸介质中伯胺N1923对Ce(Ⅳ)的萃取

铈(Ce)在轻稀土矿物中常与诸如F等多种其它元素伴生,针对矿物处理过程中得到的同时含有Ce(Ⅳ)和F^-等多组分复杂体系硫酸浸出液,从铈氟综合回收并丰富理论依据的角度出发,对伯胺N1923在含氟硫酸介质中Ce(Ⅳ)的萃取及反萃过程进行了研究。考察了酸度、萃取剂浓度、盐析剂浓度及温度对萃取过程的影响,采用斜率法初步讨论了反应机理。研究表明,预先质子化处理后的伯胺N1923在硫酸介质中可同时萃取Ce(Ⅳ)和F^-,H₂SO₄浓度对Ce(Ⅳ)和F^-的萃取过程无显著影响。Ce(Ⅳ)的萃取率随水相中F^-浓度的增加而增大,萃取过程符合加合机理,其萃合物可表示为CeF(SO₄)_1.5(RNH₃·HSO₄)_1.5。通过考察不同温度下N1923对Ce(Ⅳ)的萃取分配比并计算相应的反应平衡常数及热力学参数,表明萃取过程为自发进行的、熵焓双驱动的放热反应。在含氟体系中,体积...     

Generation and detection of levuglandins and isolevuglandins in vitro and in vivo

Levuglandins (LGs) and isolevuglandins (isoLGs), formed by rearrangement of endoperoxide intermediates generated through the cyclooxygenase and free radical induced oxidation of polyunsaturated fatty acids (PUFAs), are extraordinarily reactive, forming covalent adducts incorporating protein lysyl ε-amino groups. Because they accumulate, these adducts provide a dosimeter of oxidative injury. This review provides an updated and comprehensive overview of the generation of LG/isoLG in vitro and in vivo and the detection methods for the adducts of LG/isoLG and biological molecules in vivo.     

Enthalpies of solution of purine and adenine in water and in dimethylsulfoxide

Journal of Solution Chemistry - Enthalpies of solution of purine and adenine in water and in demethylsulfoxide were measured calorimetrically in the temperature range 25–40°C. ΔH s...     

Determination of diazepam and nordazepam in milk and plasma in the presence of oxazepam and temazepam

For studies on the excretion of drugs into milk a sensitive high-performance liquid chromatographic assay was developed to quantitate diazepam and nordazepam in the milk and plasma of humans and rabbits in the presence of their major metabolites, oxazepam and temazepam. Flurazepam was used as an internal standard. The assay involves extractions with diethyl ether and an additional acid clean-up step. Chromatographic separation was achieved by a LiChrospher 60 RP-select B (5 microns) column and KH2PO4- acetonitrile (69:31, v/v) adjusted to pH 2.80 as a mobile phase. The same extraction and chromatographic conditions were suited to both types of samples, milk and plasma. The limits of determination using ultraviolet detection at 241 nm was for diazepam 20 ng/ml and for nordazepam 15 ng/ml. The absolute recoveries of diazepam, nordazepam and flurazepam in human milk were 84, 86 and 92% and in human plasma 97, 89 and 94%, respectively. The within- and between-day accuracy and precision for diazepam and nordazepam in milk and plasma at all concentrations tested (20-1500 ng/ml) were better than 8%. The high fat content which occurs in rabbit milk presented no limitation for the extraction of lipophilic diazepam: the method was successfully used to monitor milk and plasma concentrations of diazepam and nordazepam in lactating New Zealand White rabbits during 26-h infusions of diazepam (1.4 mg/h).     

Coassembly of Nanorods and Nanospheres in Suspensions and in Stratified Films

The entropically driven coassembly of nanorods (cellulose nanocrystals, CNCs) and nanospheres (dye‐labeled spherical latex nanoparticles, NPs) was studied in aqueous suspensions and in solid films. In mixed CNC‐latex suspensions, phase separation into an isotropic latex‐NP‐rich and a chiral nematic CNC‐rich phase took place; the latter contained a significant amount of latex NPs. Drying the mixed suspension resulted in CNC‐latex films with planar disordered layers of latex NPs, which alternated with chiral nematic CNC‐rich regions. In addition, fluorescent latex NPs were embedded in the chiral nematic domains. The stratified morphology of the films, together with a random distribution of latex NPs in the anisotropic phase, led to the films having close‐to‐uniform fluorescence, birefringence, and circular dichroism properties.     

Comparison and correlation of in vitro, in vivo and in silico evaluations of alpha, beta and gamma cyclodextrin complexes of curcumin

In the present study investigated the effect of curcumin (CUR) alpha (α), beta (β) and gamma (γ) cyclodextrin (CD) complexes on its solubility and bioavailability. CUR the active principle of turmeric is a natural antioxidant agent with potent anti-inflammatory activity along with chemotherapeutic and chemopreventive properties. Poor solubility and poor oral bioavailability are the main reasons which preclude CUR use in therapy. Extent of complexation was β-CD complex (82 %) > γ-CD (71 %) > α-CD (65 %). Pulverization method resulted in significant enhancement of CUR (0.002 mg/ml) solubility with CUR α-CD complex (0.364 mg/ml) > CUR β-CD complex (0.186 mg/ml) > CUR γ-CD complex (0.068 mg/ml). Gibbs-free energy and in silico molecular docking studies favour formation of α-CD complex > β-CD complex > γ-CD complex. With reference to CUR, relative bioavailability of CUR α-CD, CUR β-CD and CUR γ-CD complexes were 460, 365 and 99 % respectively. CUR–CD complexes exhibited increased bioavailability with an increase in t_½, tmax, Cmax, AUC, Ka, and MRT; and a decrease in Ke, clearance and Vd values. AUC increase was CUR α-CD complex > CUR β-CD complex > CUR γ-CD complex. Significant difference (p < 0.05) was observed between CUR α-CD complex and CUR γ-CD complex by one-way ANOVA and Dunnett’s post hoc test for multiple comparison analysis. Correlation observed between in vitro, in vivo and in silico methods indicates potential of in silico and in vitro methods in CD selection.     

Homo- and hetero-complexes of exchangeable apolipoproteins in solution and in lipid-bound form

The self-association state of human plasma apolipoprotein E (apoE) in solution and in complexes with dimyristoylphosphatidylcholine (DMPC) varying in stoichiometry was studied in sub-micromolar concentration range by gel filtration, fluorescence anisotropy, fluorescence quenching and energy transfer measurements with apolipoprotein labeled with lysine-specific fluorescent dyes. Together, these results confirm the equilibrium scheme for various apoE structures in solution: oligomer (in aged preparations) <==> 'closed' tetramer <==> 'open' tetramer ('molten globule' state) <==> native or partially denatured monomer <==> fully denatured monomer. Within DMPC:apoE discoidal complex (125:1) the apolipoprotein association state seems to be intermediate between that in solution and in larger vesicular complex (1000:1); for both complexes, the degree of exposure of fluorescein chromophores into water phase decreased. Hetero-associates of apoA-I and apoC-III-1 in solution and in the complexes with DMPC appear to behave similarly to apoE. When extrapolated to native HDL particles, 'molten globule' state seems to be a structure responsible for the interaction of exchangeable apolipoproteins with phospholipid. For a first time, the location of various apolipoprotein molecules on disc periphery was confirmed. The lysine residue(s) seems to locate closely to reacting residue(s) within apolipoprotein molecules in associates, however, with different package constraints for discoidal versus vesicular complexes with phospholipid.     

Electrochemical Fluorination of Benzamide and Acetanilide in Anhydrous HF and in Acetonitrile

Electrochemical fluorination of benzamide in anhydrous hydrogen fluoride does not involve the amide group but occurs exclusively at the aromatic ring, yielding isomeric fluoro- and difluorobenzamides and 3,3,6,6-tetrafluoro-1,4-cyclohexadienecarboxamide. Electrochemical fluorination of benzamide in acetonitrile as solvent gives the same products, as well as benzonitrile and its fluorinated derivatives and products of hydrolysis and fluorination of acetonitrile. Electrochemical fluorination of acetanilide in anhydrous HF leads to complete tarring of the reaction mixture, while its fluorination in acetonitrile results in selective formation of m-fluoroacetanilide.