金属材料分析方法的选择和施行 第三讲 钢铁中钼的测定(续)

2 .4　抗坏血酸还原 硫氰酸盐直接光度法用氯化亚锡作还原剂的硫氰酸钼(Ⅴ )光度法的缺点已如上述。如采用还原能力低于氯化亚锡的抗坏血酸作还原剂 ,则钼 (Ⅵ )只能被还原为五价 ,从而使显色反应的灵敏度、色泽的稳定性均有改善 ,分析结果的重现性也较好。特别是在分析含钨钢时 ,钨(Ⅵ )的干扰也相对较小。迄今为止 ,用抗坏血酸作还原剂钼的硫氰酸盐光度法虽然已获较广泛的应用 ,但尚未纳入标准方法。(1 )方法 1　钢铁中钼的快速测定———抗坏血酸还原、硫氰酸盐光度法[摘自《材料化学分析方法》一书的增补修改稿 ,上海材料研究所 ,1 981 …     

金属材料分析方法的选择和施行第五讲金属材料中钨的测定(续)

2　钨测定方法的选择及施行2.1　钨的重量测定法测定合金钢、钨铁等金属材料中大量钨,包括国内外标准在内的分析方法主要采用重量法,如 GB/T 223.43-1994,GB/T 7731.1987,ГОСТ12349-83及ATSM E30 77 等。在 ASTM的一些合金钢的新标准方法(如E352,E353,E354)中均未列入钨的测定方法。可以认为,测定高含量钨目前尚没有可以代替钨酸沉淀重量法的新方法。钨的钨酸沉淀重量测定法乃基于将试样中的钨(Ⅵ)以难溶的钨酸状态析出。由于酸的介质(盐酸或硝酸)和温度条件的不同,钨酸的沉淀状态有黄色钨酸(H2WO4)和白色胶状的含水钨酸(H2WO…     

金属材料分析方法的选择和施行第三讲钢铁中钼的测定(续)

2 .9　对 2 .8节所选录的三测方法的讨论2 .9.1　 2 氨基苯硫酚萃取光度法(1)显色剂与钼 (Ⅵ )的反应2 氨基苯硫酚为含硫给予体的显色剂 ,与钼(Ⅵ )形成绿色络合物 ,不溶于水 ,可用氯仿萃取。已经证实钼 (Ⅵ )与 2 氨基苯硫酚 (简写作ＨＬ)络合物的摩尔比为 1比 3,经用元素分析及红外光谱测定证明络合物分子中存在Ｏ -Ｈ及ＭＯ =Ｏ结构 ,支持了络反应系由ＭｏＯ(ＯＨ ) 3+ 离子与显色剂ＨＬ反应 ,生成不带电荷的ＭｏＯ (ＯＨ )Ｌ3络合物的实验事实。方法 1中采用的反应时水相的酸度条件为 ｐＨ=2 ,而实验所测得的定量萃取的水相中的适宜…     

金属材料分析方法的选择和施行第三讲钢铁中钼的测定(续)

2 .5　对抗坏血酸还原 硫氰酸盐直接光度法的讨论(1)　抗坏血酸与钼 (Ⅵ )的还原反应据报道抗坏血酸在微酸性条件下的标准氧化还原电位值Ｅ°为 + 0 .32 6Ｖ(ｖｓ.ＳＣＥ)。其还原能力低于氯化亚锡 ,只能将钼 (Ⅵ )还原至五价状态。因此 ,使钼 (Ⅴ )与硫氰酸盐所形成的络合物在稳定性和灵敏度方面均有所改善。抗坏血酸与钼 (Ⅵ )的还原反应可用下式表示 :(2 )　显色反应的酸度条件在单纯钼 (Ⅵ )、硫氰酸盐与抗坏血酸反应体系的情况下 ,当溶液的硫酸浓度 [ｃ(1/ 2Ｈ2 ＳＯ4 ) ]大于2 .5ｍｏｌ·Ｌ- 1到 7.0ｍｏｌ·Ｌ- 1,显色反应可立即完…     

铬(Ⅵ)-二溴茜素紫-OP体系显色反应的研究及其在金属材料分析中的应用

本文研究了在HCl与H_3pO_4的混合酸介质中,乳化剂OP存在下,铬(Ⅵ)与2.7-二溴茜素紫(DBV)的显色反应。配合物组成Cr(Ⅵ):DBV=1:3,表观摩尔吸光系数为2.74×10~4L·mol~(-1).cm~(-1)(λmax=416nm)。反应的选择性高,常见金属离子均不干扰铬(Ⅵ)的测定,拟定了用二溴茜素紫分光光度法测定金属材料中铬的方法。     

金属材料分析方法的选择和施行：第五讲 金属材料中钨的测定（续）

(5)方法的精密度(见表9)表9方法的精密度Tab.9 Precision of the method钨含量水平范围w(W)%Level ofW-concentration重复性限rRepeatability再现性限RReproducibity0.0035~0.100lgr=-1.4937+0.7575 lgmR=0.0001620+0.1609m2.2.6对测定钨量硫氰酸盐-盐酸氯丙嗪-三氯甲烷萃取光度法的讨论(1)2.2.5节所引述的方法最早发表于“理化检验-化学分册”1985,21(3):130~133。之后,经过大量的试验验证,于1989年接纳为国家标准方法。在4~6 mol·L-1盐酸介质中(方法中反应的实际盐酸浓度为4.5 mol·L-1),钨(Ⅵ)被氯化亚锡溶液还原为钨(Ⅴ)后与硫氰…     

D201×4树脂吸附铬(Ⅵ)的研究

铬 (Ⅵ )的化合物都是有毒的 ,它对农作物、微生物和其它生物有很大的危害作用 ,对人体会引起严重毒害 ,已成为公认的致癌物质。国家规定的Ⅱ类排放标准是铬含量必须小于 0 .0 5毫克 /升[1 ] 。目前处理含铬 (Ⅵ )废水的方法有两大类 :一类是把铬 (Ⅵ )还原为铬 (Ⅲ ) ,然后再使铬 (Ⅲ )转化为沉淀除去。另一类是直接处理铬 (Ⅵ )。第一类方法步骤繁琐 ,第二类方法中离子交换法优势明显 ,不仅治理了含铬 (Ⅵ )的废水 ,同时又回收了铬 (Ⅵ ) ,特别适合治理大量的含铬 (Ⅵ )废水 ;也是高分子配位化学发展的一个重要趋势[2 ,3] 。Ｄ2 0 1× 4树…     

金属材料分析方法的选择和施行 第三讲 钢铁中钼的测定(续)

(2 )对α 安息香肟重量法测钼的解说α 安息香肟早在 1932年已被应用作为钼 (Ⅵ )的沉淀剂并建立了钢铁中钼的重量测定方法。之后该方法先后被美国ＡＳＴＭ和日本ＪＩＳ接受为标准方法。我国也于 1989年公布为国家标准方法。该方法的主要优点为干扰相对较少 ,易于掌握 ,结果的准确度较好。现结合国家标准 (ＧＢ 2 2 3.2 8- 1989)方法作解说。可以将整个方法解析为 5个步骤 :①试样的溶样 ;②共存组分的干扰及其预处理 ;③钼 (Ⅵ )的沉淀 ;④α 安息香肟钼沉淀的灼烧及称重 ;⑤结果的计算。(1)试样的溶解 :这一步骤的目的是要将试样中的钼完…     

负载8－羟基喹啉的活性炭吸附富集吸光光度法测定水中痕量铜

拟定了用负载8-羟基喹啉的活性炭对水中痕量铂(Ⅵ)进行预富集的方法，探讨了活性炭吸附钼(Ⅵ)及有机试剂的作用机理。在试验条件下，100mg活性炭负载8-羟基喹啉后可提高对钼(Ⅵ)的吸附效果，同时除去干扰离子，用吸光光度法测定水中痕量钼(Ⅵ)，结果满意。     

金属材料分析方法的选择和施行：第五讲 金属材料中钨的测定（续）

(2)显色反应要求的酸度钨(Ⅴ)与硫氰酸盐的显色反应宜在较强的盐酸介质中进行。在按方法的溶样条件下,所进行的盐酸对显色反应的影响的试验结果表明,盐酸浓度低于c(HCl)=3 mol·L-1,显色反应速度缓慢,且钼(Ⅴ)的干扰严重,钨(Ⅴ)显色反应的灵敏度也稍低;盐酸浓度大于4.5 mol·L-1,经10 min显色反应可完成,而盐酸浓度达6.0 mol·L-1,经8~10 min显色即完成且灵敏度也比其他较低酸度时略高。按所引方法操作时显色溶液中盐酸浓度约为5 mol·L-1。过高的盐酸浓度(大于6.5 mol·L-1)容易使硫氰酸盐分解,对显色反应不利。(3)钨(Ⅵ)的还原剂与硫氰…     

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...     

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.     

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).     

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.     

Structure of dimethoxyamine in the crystalline and gaseous phases and in solution

Conclusions It has been established by the methods of x-ray diffraction analysis and electron diffraction analysis and measurements of the dipole moments and the birefringence that in the crystalline and gaseous phases, as well as in solution, N,N-dimethoxyamine has a gauche-gauche conformation, which is stipulated by a stabilizing nO-N-O* orbital interaction. The geometric parameters of the molecule have been determined.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2235–2242, October, 1986.     

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.