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)

第三次沉淀是草酸沉淀，经过前两次分离，干扰稀土（Ⅲ）最终以草酸盐沉淀的共存元素已经除去。这次沉淀是以草酸盐的形式得到稀土的沉淀并最终得到符合化学计量要求的稀土氧化物。应予说明，试样如含有钇及钪，在整个分离过程中均与稀土元素在一起，故最终也包括在总稀土的含量之中。     

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）

2．1．2 沉淀草酸稀土时草酸的加入量及溶液的酸度条件与稀土的氢氧化物和氟化物相比,草酸稀土沉淀的溶解度相对较大,因此,溶液体积不宜太大和稀土离子的量不宜太少是进行草酸稀土沉淀时的两项基本要求。为使草酸稀土的沉淀尽可能地完全,一般要求     

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）

2金属材料中稀土元素的测定2.1重量测定法重量测定法常应用于稀土元素含量较高的合金的分析。可用稀土-硅-镁中间合金作为例子说明稀土总量的重量测定法在这种合金的分析中的应用。稀土硅镁之间合金的主成分是硅、稀土、铁和镁,同时还含少量或微量的钙、锰、钛、铝、磷等元素。此外,由于稀土矿源不同,可能会含有某些特殊元素。例如包头稀土矿还给合金带入一定量的钍。表1中列举了几种稀土-硅-镁合金标准物质的组份,供参考。根据这一合金的组成,在最终进行稀土元素的沉淀、灼烧及称量之前必须先使稀土与共存的干扰测定的元素分离,然后选择一…     

三价稀土碳酸盐的制备及热分解产物在冰晶石-氧化铝熔体中的溶解度

不同价态的稀土氧化物,在熔盐中的溶解度差异很大。用碳酸盐沉淀工艺可方便地使稀土碳酸盐中的稀土呈三价状态。在1000℃的冰晶石熔体中,Ce_2O_3的溶解度为13.6Wt％,约为CeO_2溶解度的10倍。由碳酸盐工艺制得的三价轻稀土氧化物因其结构疏松,活性大,溶解速度较快,在冰晶石熔体中的溶解度为14.9Wt％。同样条件下,经灼烧而得的其他轻稀土氧化物(RE_xO_y),在熔体中溶解很慢,且其中的CeO_2在渣中被富集。     

灼烧时间对稀土氧化物粒度、比表面积和形貌的影响(Ⅲ)

将在一定沉淀条件下制备的稀土草酸盐在850℃下灼烧1－24h，得到Nd2O3,Eu2O3和Y2O3样品。利用Coulter地数法，比表面积分析仪和扫描电镜研究了灼烧时间对稀土氧化物的粒度，比表面积和形貌的影响。结果表明，长时间灼烧虽有利于改善颗粒的粒度分布，但会导致颗粒的比表面积急剧减小，且在产品中生成大的团聚体。     

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)

(8)钨酸沉淀重量法测定钨的一项缺点是所得到的钨酸虽经多次洗涤仍然吸附带人一定量的其他共存元素，如硅、铁、钛、铬、钼、钒、铌、钽等，因而随后灼烧所得的三氧化钨是不纯的，其中夹杂了上述元素的氧化物。因此，在最终取得钨的测定结果之前要用各种方法将夹杂在三氧化钨中的其他元素的氧化物一一测定，将所测得的结果换算成氧化物的质量从不纯三氧化钨的质量中减去。几种主要的国内外标准方法中所用的测定这些夹杂元素的方法可大致归纳如下。     

稀土处理钢用中间包覆盖剂岩相分析

分析了现场覆盖剂和实验室自配覆盖剂岩相结构，探讨了稀土氧化物在覆盖剂中的赋存状态。结果表明：在本实验条件下的覆盖剂，原渣矿物组成主要是黄长石，另有少量镁橄榄石和含铁的硅酸盐；稀土氧化物在覆盖剂中主要以稀土硅酸盐形式存在；当稀土氧化物含量增加到一定数量时，覆盖剂开始出现固态未溶的稀土氧化物，说明其在覆盖剂中有一定的溶解度；稀土氧化物在覆盖剂中可以部分代替CaO，形成稀土硅酸盐，其形成物种类随覆盖剂碱度降低有增加的趋势。     

灼烧温度对单一稀土氧化物粒度、比表面积和形貌的影响（Ⅰ）

分别以稀土元素Y,Pr,Nd,Sm,Eu,Tb,Dy,Er和Lu的草酸盐为前体原料,固定的灼烧时间为3h,在800－1500℃范围内不同灼烧温度下制备了系列单一稀土氧化物,利用Coulter计数法,比表面积分析仪和扫描电镜研究了灼烧温度对稀土氧化物的粒度,比表面积和形貌的影响,结果表明,各稀土氧化物的中位粒径和团聚程度随灼烧温度升高而增大,而比表面积则逐渐减小。     

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)

(2)草酸盐沉淀重量法测定铝合金中稀土总量(详见GB/T 6987.32-2001). 此方法适用于含稀土总量ω(RE)≥1.5%～10%的铝合金.     

电解氧化分解稀土沉淀废水中草酸的研究

为有效去除稀土草酸沉淀废水中残留的草酸,采用电解氧化探索氧化分解废水中草酸的可行性。考察不同阳极、反应温度、反应时间、废水初始酸度等因素对氧化效果的影响。草酸的氧化速度随反应温度、电流和反应时间的增加而升高,随初始酸度的增加反而降低,确定了优化工艺条件。[C_2O_4~(2-)]=1.84 g·L~(-1),[H~+]=0.90 mol·L~(-1)的Eu草酸沉淀废水,在反应温度30℃,电流1.5 A,反应时间5 h,草酸的氧化率可达99%,废水中残留的草酸质量浓度仅为0.01 g·L~(-1),处理后的废水可直接返回稀土萃取分离,实现了工艺流程的闭路循环。     

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.     

Fluorimetric quantification of clodronate and alendronate in aqueous samples and in serum

The bisphosphonates clodronate and alendronate are drugs in the therapy of osteoporosis or Paget's disease. They are highly hydrophilic and therefore of low oral bioavailability. Determination methods for bisphosphonates are often laborious and expensive equipment is needed. The presented quantification method based on kinetic measurement of the fluorescence decrease of an Al³⁺-morin complex can be used to determine the bisphosphonate content in aqueous and plasma samples. The intra- and inter-assay accuracies were found to be within 98.8% and 102.3% of the target samples for clodronate and within 97.2% and 105.0% of the target samples for alendronate. The LOQ was defined as 15.6 ng/ml for clodronate and 62.5 ng/ml for alendronate. In serum samples, intra- and inter-assay accuracy was found to be within 99.0% and 101.6% of the target samples for clodronate and within 97.8% and 102.6% of the target samples for alendronate. In serum samples, the LOQ was defined as 1.55 mg/ml for clodronate and 0.39 mg/ml for alendronate. Though less sensitive in serum, the presented method could support research on the development of drug delivery systems in vitro and in vivo for the investigated and other structurally related bisphosphonates.     

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.