NaF-SnCl_2光度法测定磷的方法中,钼磷黄还原为钼磷蓝的反应式应如何表述?

答 :关于钼磷杂多酸还原为钼磷蓝的反应式一般表示为 :(ＮＨ4 ) 3 Ｈ4 [ＰＭｏ2 Ｏ7) 6]+2ＳｎＣｌ2 +4ＨＣｌ　　　　　　 (ＮＨ4 ) 3 Ｈ4 [Ｐ(Ｍｏ2 Ｏ5)·5 (Ｍｏ2 Ｏ7) ]+2ＳｎＣｌ4 +2Ｈ2 Ｏ但有报道认为在有ＮａＦ存在下 ,反应中不可能有ＳｎＣｌ4 或ＳｎＣｌ2 - 6的形式的化合状态 ,因为ＳｎＦ2 - 6的积累稳定常数的对数值ｌｇβ6等于 2 5 ,远高于ＳｎＣｌ2 - 6的积累稳定常数的对数值 (ｌｇβ6=14)。此外 ,一般认为磷钼蓝分子中只有 2个Ｍｏ(Ⅵ )被还原为Ｍｏ(Ⅴ )。但用光度滴定法研究钼磷蓝的结果表明在 12个Ｍｏ(Ⅵ )中有 4个Ｍ…     

新型离子液体作为溶剂萃取光度法测定环境水中超痕量钼

离子液体是一种绿色溶剂,可替代易挥发的有机溶剂用于液/液萃取。在阳离子表面活性剂CTMAB存在下,Mo(Ⅵ)与9-(2-羟基-5-偶氮对甲苯)苯基荧光酮(MBASF)反应形成稳定的络合物,其最大吸收波长位于522 nm。在显色后的体系中加入离子液体-1-丁基-3-三甲基硅咪唑六氟磷酸盐([C4tmsim][PF6]),Mo-MBASF络合物被高效萃取进入离子液体相。由于离子液体在萃取前后均为透明液体,可直接用于光度法测定钼。在1000 mL水样中,0~4μg Mo(Ⅵ)符合比尔定律,络合物的表观摩尔吸光系数达1.2×107L.mol-1.cm-1。绝大多数离子可大量存在,方法具有高的灵敏度和选择性,已应用于环境水样中超痕量钼的测定。     

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 .7　对硫氰酸盐萃取光度法的讨论(1)　方法的优缺点在 2 .3及 2 .5节的讨论中都提到了在水溶液中显色时 ,硫氰酸钼 (Ⅴ )络离子存在着灵敏度不够高、稳定性较差等问题。对水溶液中显色条件的研究主要是解决这些问题 ,而其中解决稳定性是一个核心问题。2 .6节选录的 4则方法 ,由于采用了萃取方法 ,使上述缺点得到一定的克服 ,由于钼 (Ⅴ )与硫氰酸盐所形成的橙红色络合物是一种离子型络合物 ,有很大的离解度 ,[ＭｏＯ(ＮＣＳ) 5]2 - 络阴离子的不稳定常数达 8× 10 - 2 。因此为了使反应中能保持尽可能多的钼 (Ⅴ )离子以 [ＭｏＯ(ＮＣＳ) …     

硫化态Mo/γ-Al2O3催化剂活性位的低温CO-FTIR方法表征及噻吩HDS活性

ＭｏＳ2 是钼基加氢精制催化剂 [Ｃｏ(Ｎｉ)Ｍｏ/γ Ａｌ2 Ｏ3]活性相的主要组份 ,其形态与结构对Ｃｏ(Ｎｉ)Ｍｏ/γ Ａｌ2 Ｏ3的加氢脱硫 (ＨＤＳ)、加氢脱氮 (ＨＤＮ)活性的影响至关重要[1 ,2 ] .目前 ,人们通常使用的ＴＰＲ方法虽可测定过渡金属硫化物的表面活性位 ,并可有效地区分位于催化剂活性相 (ＭｏＳ2 ｓｌａｂ)周边的硫物种 ,但对不同价态的钼尚无法鉴别[3] .本文制备了硫化态Ｍｏ/γ Ａｌ2 Ｏ3催化剂 ,以ＣＯ为探针分子 ,利用ＦＴＩＲ技术在液氮温度 (77Ｋ)下考察了催化剂的表面活性位 (钼物种 )及催化噻吩ＨＤＳ的活性 .1　实…     

读者园地

问 :保证 12 磷钼杂多酸的迅速、定量形成 ,应满足哪些条件 ?浙江读者———徐进　　答 :金属材料中磷的光度测定法 ,以形成磷钼杂多酸为基础的方法占有主导地位。测定中 ,生成磷钼杂多酸的反应可表达如下 :　　ＨＰＯ2 -4+ＭｏＯ2 -4Ｈ+ＯＨ-过渡状态的无色磷钼杂多酸Ｈ+ ,ＭｏＯ2 - 4ＯＨ-　 [Ｐ(Ｍｏ3 Ｏ10 ) 4 ]3 -由上述反应可知 ,要保证磷钼杂多酸的迅速定量形成 ,应满足以下基本要求 :(1)必须使试样中的磷全部转化成正磷酸(Ｈ3ＰＯ4 )形式。(2 )在一定的酸度条件下 ,保证有足够过量的钼酸盐存在 ,当有一定量的正磷酸溶液中加入钼酸…     

钼烷氧基配合物的合成及β-H消去反应

许多过渡金属的烷氧基配合物具有对酮和醛的催化加氢以及对醇的催化脱氢的均相催化作用[1,2 ].过渡金属烷氧基配合物同过渡金属烷基配合物一样可以发生 β Ｈ消去反应 ,生成氢基配合物和醛或酮[3].对于重过渡系单核烷氧基配合物的合成和性质已有很多报道[4],而对钼的单核烷氧基配合物的研究比较少 .有关一系列二茂钼烷氧基配合物的合成已有报道[5].本文合成了几种二茂钼烷氧基衍生物 ,并对其 β Ｈ消去反应进行了研究 .Ｃｐ2 ＭｏＯＨＭｏＣｐ2ＯＨ2 (ＯＴｓ- ) 2ＲＯＨ2ＰＭｅ3Ｃｐ2 ＭｏＯＲＰＭｅ3 ＯＴｓ- Δ Ｃｐ2 ＭｏＨＰＭｅ3 ＯＴ…     

读者园地

问 :1.形成杂多酸后与原钼酸相比其还原性有何差异 ?2 .用磷钼蓝光度法测定磷时 ,常用的还原剂有哪些 ?浙江读者———张伟答 1.可以查得钼酸盐中的Ｍｏ(Ⅵ )的标准电极电位Ｅ°Ｍｏ(Ⅳ ) /Ｍｏ(Ⅴ ) 为 0 .4Ｖ (ｖｓ .ＮＨＥ ,0 .5ｍｏｌ·Ｌ- 1Ｈ2 ＳＯ4 介质 ) ,但硅钼杂多酸中的Ｍｏ(Ⅳ )的标准电极电位在相同条件下提高到 +0 .5 9Ｖ ,磷钼杂多酸中的Ｍｏ(Ⅳ )的标准电位值则提高到 +0 .63Ｖ。由此可见 ,在杂多酸分子中的Ｍｏ(Ⅳ )与钼酸盐中的Ｍｏ(Ⅳ )相比 ,更易于被还原剂还原 ,生成呈蓝色的“杂多蓝”。答 2 .还原 12 磷钼杂多酸的…     

2-羟基-3-甲氧基苯基荧光酮光度法测定合金钢中的微量钼

研究钼 (Ⅵ )与 2 羟基 3 甲氧基苯基荧光酮 (HMPF)的显色反应。在磷酸介质中 ,在阳离子表面活性剂CTMAB作用下 ,钼 (Ⅵ )与HMPF形成红色配合物 ,其最大吸收波长为 5 2 5nm ,表观摩尔吸光系数为 1.34× 10 5L/ (mol·cm) ,钼的浓度在 0～ 15 μg/(2 5mL)范围内服从比耳定律。可不经分离测定合金钢中的钼。用该法测定合金钢标准样品中的钼 ,测定结果与标准值相吻合 ,RSD为 0 .85 %～ 1.5 2 %。     

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…     

钒（V）—2—（2—噻唑偶氮）—5—二甲氨基苯甲酸显色反应的研究

钒是具有重要用途的元素 ,其测定受到重视。二安替比林甲烷类[1]及杂环偶氮苯酚类显色剂[2 ,3]测定钒灵敏度和选择性较高 ,变色酸偶氮类显色剂[4 6 ]的应用也曾有报道 ,而杂环偶氮苯甲酸类显色剂研究较少[7,8]。本文研究了钒 (Ⅴ )与 2 (2 噻唑偶氮 ) 5 二甲氨基苯甲酸 (ＴＡＭＢ)的显色反应 ,结果表明 ,在 ｐＨ 3 .5 3 .8甲酸 ＮａＯＨ缓冲介质中 ,钒(Ⅴ )与ＴＡＭＢ反应生成一种稳定的可溶于水的蓝色配合物。1　试验部分1.1　仪器与试剂72 1型分光光度计ｐＨＳ 2型酸度计钒 (Ⅴ )标准溶液 :用偏钒酸铵 (ＮＨ4 ＶＯ3)水溶后配成含钒 1…     

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.     

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.     

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.