氢化物原子荧光光谱法测定虾中砷和汞

建立了氢化物原子荧光法同时测定虾中砷和汞的方法.研究了样品前处理及实验条件对测定砷、汞的原子荧光强度的影响,并探讨了共存离子对测定砷、汞的干扰和消除的方法.本方法具有操作简便、快速、灵敏度高等优点,砷和汞的检出限分别为0.026 μg/L和0.020 μg/L;相对标准偏差分别为1.7%～9.4%和1.2%～9.4%;回收率为98%～106%.     

氢化物发生-原子荧光光谱法同时测定食品添加剂碳酸钙中的砷和汞

应用氢化物发生-原子荧光光谱法同时测定食品添加剂碳酸钙中的砷和汞,并对样品中的主要成份及共存元素可能对检验结果的影响和实验条件进行了研究.结果表明,加入硫脲-抗坏血酸溶液后,碳酸钙中主要成份钙及可能存在的共存元素铁、铅、镉、铜、锑、硒、锡、铬、锌等不干扰砷和汞的测定.方法检出限为砷0.0124 μg/L,汞0.0009μg/L,回收率为砷101.8%～102.2%,汞102.5%～106.0%.精密度为砷0.37%,汞0.95%.建立的氢化物发生-原子荧光光谱法同时测定食品添加剂碳酸钙中砷和汞的分析方法能满足日常检验的要求.     

氢化物发生-原子荧光光度法测定鱼体内的砷和汞

采用硝酸-高氯酸湿式消解法消解样品,利用AFS-230E原子荧光光度计测定了赣州市赣江交汇处鱼体内砷和汞的含量,选择了最佳实验条件.结果表明,所得砷和汞的检出限分别为0.020、0.008 μg/L,测定砷、汞标准溶液各6次,所得砷、汞标准溶液的平均值分别为0.099、0.103 μg/mL,相对标准偏差RSD分别为2...     

微波消解样品-蒸气发生-原子荧光光谱法测定石脑油中砷和汞

提出了微波消解样品-蒸气发生-原子荧光光谱法测定石脑油中砷和汞的方法.采用微波消解法处理样品,优化了微波消解条件和仪器工作条件,解决了消解液中过剩酸对测定的干扰.砷、汞的检出限分别为0.11,0.045 μg·L-1;线性范围分别在1.0～100.0,0.5～50.0 μg·L-1之间,砷和汞的相对标准偏差均小于4%,回收率分别在95.2%～97.2%,92.9%～95.2%之间.     

氢化物发生-双道原子荧光光谱法同时测定锰渣中砷和汞

取一定量锰渣样,经王水和硫酸消解后,在盐酸-硫脲-抗坏血酸混合介质中,采用原子荧光光谱法同时测定砷和汞.优化条件下,砷检出限为0.0135 μg/L,相对标准偏差(RSD)为1.9％,加标回收率为98.8％～105％;汞检出限为0.0091 μg/L,RSD为2.8％,加标回收率为91.7％～96.0％.所建立的方法,...     

电感耦合等离子体质谱法测定精油中砷、钡、铋、镉、铬、铅、锑、汞含量

研究了采用微波消解-电感耦合等离子体质谱仪测定精油中重金属元素砷、钡、铋、镉、铬、铅、锑、汞含量的方法,确定了实验的最佳条件.方法检出限在0.3～3 μg/kg之间,回收率为84.9%～101.5%,RSD在0.9%～4.7%之间.     

中成药中微量砷的溶出伏安法分析

研究了利用阳极电位溶出法测定中成药-牛黄解毒丸中的微量砷的可行性. 实验采用金膜电极作工作电极的三电极系统, 在浓度为4.8 mol/L HCl和1.1 mol/L HNO3的混合底液中, 砷在峰电位(Ep)为 0.16 V (vs. SCE)左右有一灵敏的一阶导数峰, 在选定的实验条件下, 该峰峰高(Hp)与砷的质量浓度在0.5～5 μg/L之间有较好的线性关系, 相关系数r=0.9954, 检出限为0.17 μg/L, 精密度平均值为2.8%, 回收率在96.78%～103.3%之间, 常见干扰离子Pb2 、 Zn2 、 Cd2 、 Cu2 、 Hg2 对砷的测量无影响. 在线性范围内对牛黄解毒丸样品中的砷量进行了测定.     

离子色谱-氢化物发生原子荧光光谱联用技术在砷形态分析中的应用

建立了离子色谱-氢化物发生原子荧光光谱联用分离4种常见有毒砷化合物的方法. 二者通过内径0.25 mm的PEEK管直接相连. 实验对影响分离度和测定灵敏度的参数进行了优化. 在优化条件下, 质量浓度均为50 μg/L的4种砷化合物混合标准溶液平行7次进样, 得到DMA、 As(Ⅲ)、 MMA和As(Ⅴ)的色谱峰面积的相对标准偏差(RSD)为2.8～3.0%. 250 μL进样的线性范围为5～1000 μg/L, 检出限为0.8～1.2 μg/L (三倍基线噪音峰高). 用建立的方法测定了砷处理后的水稻木质部伤流液中的砷量, 4种砷化合物的加标回收率为89%～105%. 该装置接口简单, 方法分离度好, 灵敏度高, 可用于实际样品中痕量砷化合物的形态分析.     

光诱导蒸气发生-高效液相色谱-电感耦合等离子体质谱联用测定汞形态

以紫外光诱导化学蒸气(UV-CVG)发生为接口,建立了高效液相色谱与电感耦合等离子体质谱联用测定无机汞、甲基汞的分析方法.对色谱条件、紫外光化学反应还原剂甲酸浓度、紫外光化学反应管长度等系统操作条件进行了优化.在优化的系统条件下,4 μg/L无机汞和甲基汞的色谱峰高的相对标准偏差(RSD,n=11)分别为0.72％和0.66％;无机汞和甲基汞的线性范围为0.1～10μg/L,100 μL进样检出限分别为0.011和0.0093 μg/L.用DORM-2角鲨鱼肉参考物质验证了方法的准确性,测试结果与推荐值吻合;对沼泽湿地水样中无机汞和甲基汞的加标回收率分别在99％～106％和94％～110％范围内.     

碱熔-氢化物发生原子荧光光谱法连续测定锑精矿中的砷、铋、硒、锡

建立了氢化物发生原子荧光光谱法测定锑精矿中砷、铋、硒、锡的方法.研究了基体及共存元素的干扰情况,实验表明,在酒石酸、硫脲-抗坏血酸存在下,适当的增加酸度可以有效地消除干扰.采用Na2O2熔解样品,用HCl酸化,无需分离基体,实现了锑精矿中砷、铋、硒、锡的连续测定,其回收率为90.6%～103.8%,检出限分别为0.35、0.20、0.65和0.35 μg/L.应用该方法分析了锑精矿样品,结果令人满意.     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.     

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008.     

Sulfur-directed metal-free and regiospecific methyl C(sp3)–H imidation of thioanisoles

Regiospecific and direct imidation of the methyl C(sp³)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products.     

Selective syntheses of 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones via temperature-dependent Rh(II)-carbenoid-mediated 2H-azirine-ring expansion

The Rh(II)-catalyzed reaction of 2-carbonyl-substituted 2H-azirines with ethyl 2-cyano-2-diazoacetate or 2-diazo-3,3,3-trifluoropropionate provides an easy access to 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones. These compounds can be selectively prepared from the same starting material using temperature as the only varied parameter. The 2-azabuta-1,3-diene intermediate, a common precursor for both heterocyclic products, isomerizes into 2H-1,3-oxazine under kinetic control, while 1H-pyrrol-3(2H)-one is the sole product of the reaction at elevated temperatures. According to DFT-calculations a one-atom oxazine ring contraction involving ring-opening to a 2-azabuta-1,3-diene intermediate, followed by a 1,5- and 1,2-prototropic shift leads to the consecutive formation of imidoylketene and azomethine ylide, which then further undergo cyclization to the pyrrole derivative.     

Copper catalyzed/mediated synthetic methodology for ebselen and related isoselenazolones

Scope of the copper catalyzed/mediated selenium-nitrogen coupling reaction has been studied for the synthesis of isoselenazolones. It is noticed that the 2-chloro, 2-bromo-, and 2-iodo-aryl amides substrates can be exploited in the selenium-nitrogen coupling reaction by employing 25-100 mol % of CuI/1,10-phenanthroline (L) and potassium carbonate as a base in DMF. Furthermore, electron rich 2-chloro-arylamides also underwent selenium-nitrogen coupling reaction to give biologically important selenium-nitrogen heterocycles. Also, copper-catalyzed selenium-nitrogen coupling reaction has been meticulously applied for the synthesis of diaryl diselenides having methoxy, amine, and amide functionality from respective aryl iodides in the presence of stoichiometric amount of succinimide as an external Se-N coupling partner.