分析测试经验介绍(243~248)原子荧光法测定金矿中砷和铋的不确定度评估

通过建立数学模型,分析了原子荧光法测定金矿中砷和铋的测量不确定度的影响因素,计算各影响因素的不确定度分量,并计算金矿中砷和铋的合成标准不确定度和扩展不确定度.结果表明:测量不确定度主要由样品制备过程和标准曲线拟合构成.金矿中砷的含量为18.398μg/g,其扩展不确定度为0.555 3μg/g(k=2),结果符合测试规范要求.铋的含量为0.359 3μg/g,扩展不确定度为0.441 1μg/g(k=2),铋的不确定度偏大,不符合测试规范要求,应通过降低铋标准溶液的浓度和减少待测液的稀释倍数来降低标准曲线拟合产生的不确定度.     

The miracle role of lattice imperfections in benzene alkylation with methanol over mordenite

Mordenite (MOR) has demonstrated potential as a catalyst for alkylation due to high variability, intrinsic porosity, and outstanding stability. However, the contact probability of benzene and methanol has been limited by typical layered structures of MOR and there is no connection between layers. Here, we report the preparedness of H-MOR via a sequential post-treatment method based on a commercial MOR. H-MOR sample had appeared lattice imperfections inferred from characterization means. The samples were tested with benezene methylation reaction. Results show that the high conversion of benzene and the high selectivity of toluene were obtained from the miracle role of lattice imperfections in the H-MOR sample. Sequentially, based on the study of all catalyst structure and physical properties, a plausible reaction mechanism for the selectivity of the desired toluene was proposed.     

Speciation of Arsenic Compounds in the Urine of Rats Orally Exposed to Dimethylarsinic Acid Ion Chromatography with ICP–MS as an Element-Selective Detector

A combined ion chromatography (IC) with inductively coupled plasma mass spectrometry (ICP—MS) system as an element-selective detector has been used for the determination of arsenic compounds. Seven arsenic compounds were separated by cation-exchange chromatography. Subsequently, the separated arsenic compounds were directly introduced into the ICP—MS and were detected at m/z =75. Detection limits for the seven arsenic compounds ranged from 0.8 to 3.8 μg As/l. The IC–ICP–MS system was applied to the determination of arsenic compounds in the urine of dimethylarsinic acid (DMAA)-exposed rats. DMAA was the most abundant arsenic compound detected. Arsenous acid, monomethylarsonic acid and trimethylarsine oxide were also detected.     

Tolerance,bioaccumulation and biotransformation of arsenic in freshwater prawn (Macrobrachium rosenbergii)

Tolerance bioaccumulation and biotransformation of arsenic compounds by a freshwater prawn (Macrobrachium rosenbergii) were investigated. M. rosenbergii was exposed to 10, 20, 30 and 35 μg As cm⁻³ of disodium arsenate [abbreviated as As(V)], 25, 50, 100 and 120 μg As cm⁻³ of methylarsonic acid (MMAA), or 100,200, 300 and 350 μg As cm⁻³ of dimethylarsinic acid (DMAA). Tolerances (50% lethal concentration: LC₅₀) of the prawn against As(V), MMAA, and DMAA were 30, 100, and 300 μg As cm⁻³, respectively. The prawn accumulated arsenic compounds directly from aqueous phase and biotransformed them in part. Both methylation and demethylation of the arsenicals were observed in vivo. Highly methylated and less toxic arsenicals were less accumulated in M. rosenbergii.     

Arsenic biomethylation by the microorganism apiotrichum humicola in the presence of l-methionine-methyl-d3

The microorganism Apiotrichum humicola (previously known as Candida humicola) grown in the presence of either arsenate, arsenite, methylarsonic acid or dimethylarsinic acid, produces arsenic-containing metabolites in the growth medium. When L-methionine-methyl-d₃ is added to the cultures, the CD₃ label is incorporated intact into the metabolites to a considerable extent to form deuterated dimethylarsenic and trimethyl-arsenic species, indicating that S-adenosylmethionine, or some related sulphonium compound, is involved in the biological methylation. Conclusive evidence of CD₃ incorporation in the arsenicals found in the growth medium was provided by using a specially developed hydride generation-gas chromatography-mass spectrometry system (HG–GC–MS).     

Recognition of Dimethylarginine Analogues by Tandem Tudor Domain Protein Spindlin1

Epigenetic readout of the combinatorial posttranslational modification comprised of trimethyllysine and asymmetric dimethylarginine (H3K4me3R8me2a) takes place via biomolecular recognition of tandem Tudor-domain-containing protein Spindlin1. Through comparative thermodynamic data and molecular dynamics simulations, we sought to explore the binding scope of asymmetric dimethylarginine mimics by Spindlin1. Herein, we provide evidence that the biomolecular recognition of H3K4me2R8me2a is not significantly affected when R8me2a is replaced by dimethylarginine analogues, implying that the binding of K4me3 provides the major binding contribution. High-energy water molecules inside both aromatic cages of the ligand binding sites contribute to the reader–histone association upon displacement by histone peptide, with the K4me3 hydration site being lower in free energy due to a flip of Trp151.     

Polyphenolics with Strong Antioxidant Activity from Acacia nilotica Ameliorate Some Biochemical Signs of Arsenic-Induced Neurotoxicity and Oxidative Stress in Mice

Neurotoxicity is a serious health problem of patients chronically exposed to arsenic. There is no specific treatment of this problem. Oxidative stress has been implicated in the pathological process of neurotoxicity. Polyphenolics have proven antioxidant activity, thereby offering protection against oxidative stress. In this study, we have isolated the polyphenolics from Acacia nilotica and investigated its effect against arsenic-induced neurotoxicity and oxidative stress in mice. Acacia nilotica polyphenolics prepared from column chromatography of the crude methanol extract using diaion resin contained a phenolic content of 452.185 ± 7.879 mg gallic acid equivalent/gm of sample and flavonoid content of 200.075 ± 0.755 mg catechin equivalent/gm of sample. The polyphenolics exhibited potent antioxidant activity with respect to free radical scavenging ability, total antioxidant activity and inhibition of lipid peroxidation. Administration of arsenic in mice showed a reduction of acetylcholinesterase activity in the brain which was counteracted by Acacia nilotica polyphenolics. Similarly, elevation of lipid peroxidation and depletion of glutathione in the brain of mice was effectively restored to normal level by Acacia nilotica polyphenolics. Gallic acid methyl ester, catechin and catechin-7-gallate were identified in the polyphenolics as the major active compounds. These results suggest that Acacia nilotica polyphenolics due to its strong antioxidant potential might be effective in the management of arsenic induced neurotoxicity.     

Solid State S-Methylation of Thiols and O-Methylation of Phenols and Naphthols with Dimethyl Sulfate Under Microwave Irradiation

Abstract

Mild and efficient S-methylation of thiols and o-methylation of phenols and naphthols occurs with dimethyl sulfate (DMS) supported on basic alumina under microwave irradiation in solventless system.     

氢化物发生原子荧光光谱法测定污水中的砷

用HNO3-HClO4混合酸消解污水样,采用氢化物发生原子荧光光谱法测定污水中的砷含量。在最佳实验务件下,线性范围为0～40μg/L,检出限为0．4μg/L,测定结果的相对标准偏差小于4％,加标回收率为91．5％～100．9％。