微波消解-石墨炉原子吸收光谱法测定纸质食品包装材料中的痕量镉

建立了微波消解–石墨炉原子吸收光谱法测定纸质食品包装材料中痕量镉的检验方法。样品经微波消解后,以硝酸镍为基体改进剂,试验确定了石墨炉原子吸收法测定镉的最佳仪器条件。镉的质量浓度在0～10μg/L与吸收峰面积呈良好的线性关系,线性相关系数r=0.9997,检出限为0.025μg/L。将该法用于纸质食品包装材料中痕量镉的测定,并进行加标回收试验,回收率为96.0%～105.5%,相对标准偏差不大于4.4%(n=10)。     

湿法消解–石墨炉原子吸收标准加入法测定土壤中的镉

土壤样品经过硝酸–氢氟酸于130℃加热回流处理后,采用石墨炉原子吸收标准加入法测定半消解样品中镉的含量。以5%氯化铵或0.1%硝酸钯作为化学改进剂,灰化温度为500℃、原子化温度为2 000℃。当标准系列吸光度在0.18以内时,镉标准溶液的质量浓度在0~3.0μg/L内与吸光度呈良好的线性,相关系数r=0.998 6,方法的检出限为0.02 mg/kg,实际样品测定结果的相对标准偏差为3.93%~5.30%(n=5)。用该法与国标方法对土壤标准样品进行测定,两种方法测定结果一致。该法快速、简便,适用于土壤中镉含量的快速检测。     

氢化物发生-原子荧光法测定纯铜中镉

用717阴离子交换树脂填充柱选择性吸附CdCl42-阴离子,以实现其与大量铜基体的分离。在标准溶液中匹配适当基体浓度并采用氢化物发生-原子荧光法,实现了铜/镉质量比为2000~50000的纯铜中痕量镉的测定。在基体铜的浓度为50mg/L的样品消化液中,镉的检出限为0.2μg/L;精密度为3.0%(n=7,3.0μg/L),镉浓度在1.0~25.0μg/L范围内呈良好线性关系。本法适用于纯铜中痕量镉的测定。     

微波消解–石墨炉原子吸收光谱法测定空气中碲

建立微波消解–石墨炉原子吸收光谱法测定空气中的碲。采用微孔滤膜收集样品,以硝酸–双氧水混合体系微波消解滤膜,氯化钯为基体改进剂,在优化的仪器工作条件下测定。碲的质量浓度在0~15μg/L范围内与吸光度线性关系良好,相关系数为0.999 5,方法检出限为0.14μg/L。样品加标回收率在95.6%~104.0%之间,测定结果的相对标准偏差为1.15~1.37%(n=7)。该方法操作简单、灵敏度高,适用于空气中微量碲的测定。     

氢化物发生-原子荧光光谱法测定牡蛎中的镉

利用HNO3–HClO4混合酸消解样品,采用氢化物发生–原子荧光光谱法测定牡蛎中镉的含量。在优化的仪器工作条件下,镉的质量浓度在0.20～1.50μg/L范围内与荧光强度呈良好的线性关系,线性相关系数为0.9992,检出限为0.10μg/L,测定结果的相对标准偏差为4.48%(n=12),加标回收率为94.3%～106.1%。测定了标准物质贻贝GB 08571中镉的含量,测定结果与标准值一致。该方法可满足牡蛎中微量镉的分析测定。     

顺序注射氢化物发生-原子荧光光谱法同时测定环境水样中砷和镉

目的考察了光电倍增管负高压、砷和镉灯电流、原子化器高度、载气流量、屏蔽气流量、增敏剂等因素对测定结果的影响。方法建立一种顺序注射氢化物发生-原子荧光光谱法同时测定水样中砷和镉含量的方法。结果载流HCl的浓度为0.60 mol/L,KBH4质量浓度为20g/L,增敏剂硫脲和钴离子的质量浓度分别为80 g/L和70 g/L时,同时测定砷和镉的效果最佳。在最佳实验条件下,砷和镉的检出限分别为0.009 3μg/L和0.12μg/L,加标回收率为92.3%～103.9%,相对标准偏差小于3.5%,被测水样中共存离子对砷和镉的测定没有干扰。结论该法操作方便、快速,用于环境水样中砷和镉的同时测定,具有很好的可行性和实用性。     

石墨炉原子吸收光谱法测定食盐中镉的含量北大核心CSCD

提出了石墨炉原子吸收光谱法测定食盐中镉含量的方法。称取食盐样品0.5 g,用1%(体积分数,下同)硝酸溶液溶解并定容至50 mL,摇匀,配制成待测样品溶液。以1%硝酸溶液为溶剂,配制成含10 g·L^(-1)磷酸二氢铵和10 g·L^(-1)抗坏血酸的基体改进剂。测定时,采用自动进样器吸取1.0μL基体改进剂至20μL待测样品溶液中。优化后的石墨炉升温条件:干燥温度为120℃,灰化温度为350℃,原子化温度为700℃,净化温度为2 700℃。结果显示:镉的质量浓度在0.1~2.0μg·L^(-1)内与其对应的吸光度呈线性关系,检出限(3s/k)为0.001 mg·kg^(-1);对含不同质量分数镉的氯化钠加标溶液进行测定,测定值的相对标准偏差(n=6)均小于4.0%;对不同类型的食盐样品进行加标回收试验,镉回收率为92.0%~101%。     

石墨炉原子吸收分光光度法测定大气颗粒物中的镉

将大气颗粒物样品采集在有机滤膜上(或滤筒中)，用硝酸、高氯酸消解，以石墨炉原子吸收分光光度法测定其中镉的含量。在0．00～8．00μg/L范围内对镉的质量浓度与吸光度数据进行回归，得线性方程为A：0．016 0．041X，相关系数r=0．9991，回收率为90％～94％，测定结果的相对标准偏差为2．1％～7．5％，检出限为0．366μg/L，该方法适用于大气和固定污染源排气中镉的测定。     

氢化物发生–原子荧光法测定地下水中的镉

建立用氢化物发生–原子荧光法测定地下水中镉的方法。探讨了还原剂硼氢化钾用量及地下水中共存元素干扰对镉测定结果的影响,优化了仪器工作条件。优化的实验条件:介质为2%的盐酸溶液;还原剂为2%的硼氢化钾溶液;载气为氩气,流量为510 mL/min;主阴极灯电流为60 mA。镉的质量浓度在0~10μg/L范围内与荧光强度的峰面积呈良好的线性关系,线性相关系数为0.999 2,检出限为0.03μg/L。测定结果的相对标准偏差为1.24%~6.07%(n=7),加标回收率为90.1%~103.0%。该方法具有较高的灵敏度、精密度和准确度,可用于地下水中镉的测定。     

超级微波消解-石墨炉原子吸收光谱法测定不同类型土壤中的镉

采用超级微波消解仪对样品进行前处理,对比不同消解体系的消解效果,选择合适的消解体系,采用石墨炉原子吸收光谱法测定镉浓度,同时优化基体改进剂、灰化温度等工作参数,确定最佳的分析条件。探讨并建立超级微波消解-石墨炉原子吸收光谱法测定不同类型土壤镉含量的方法。在最优条件下,标准曲线在0～1.0μg/L浓度范围内线性关系良好,相关系数r=0.999,检出限浓度为0.04μg/L,定量限浓度为0.12μg/L,方法准确度为94.5%～110%,相对标准偏差RSD为0.60%～5.4%,方法应用于不同类型土壤标准物质镉的测定,测得结果均在标准值范围内。方法简便快捷、准确高效、用酸量低、节约环保,便于在基层推广,适用于批量处理不同类型镉污染土壤样品。     

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.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.