原子荧光法测定茶叶中的硒含量

采用原子荧光法测定茶叶中的硒含量,对样品消解温度及仪器条件进行了优化。还原剂为1.0%硼氢化钾–0.5%氢氧化钾溶液,载流液为3%盐酸溶液。在优化条件下,硒的质量浓度在0~20 ng/mL范围内与荧光强度呈良好的线性关系,相关系数r=0.999,检出限为0.8 ng/mL。该法的加标回收率为88.08%~101.39%,测定结果的相对标准偏差为2.03%~4.84%(n=6)。该方法实际操作性强,准确度高,适用于日常检验工作中对批量茶叶中硒含量的测定。     

硫氰酸铵比浊法测定微量硒

在2.4 mol/L HCl介质中, Se(Ⅳ)与过量的硫氰酸铵反应析出单质硒, 并形成稳定的悬浊液, 据此建立了比浊法测定硒的新方法. 实验了酸度、还原剂用量、温度和时间的影响, 确定了最佳测定条件. 选择测定波长为320 nm, 线性范围为0～0.25 μg/mL, 检出限为0.0294 μg/mL. 方法用于测定硒强化营养盐和健康平衡盐中硒含量, 结果与荧光法一致, 相对标准偏差小于1.6% (n=5), 平均回收率为100.0%～101.4%.     

高压罐消解-氢化物发生原子荧光法测定食品中的硒

利用高压罐消解-氢化物发生原子荧光法测定食品中的硒.在4mol/LHCl介质中利用AFS-2201双道原子荧光光度计对国家一级标准物质奶粉进行测定.测定硒元素曲线的浓度在0～100.0 ng/mL之间呈良好的线性关系,相关系数为0.9998,其检出限为0.47 μg/L.实验结果表明本方法可用于食品中硒含量的测定和监控.     

石墨炉原子吸收法测定食品添加剂甲壳素中的镉和铅

采用程序控制温度,一次完成甲壳素样品的炭化和灰化,通过氢氟酸-硝酸消除灰分中硅的干扰,用石墨炉原子吸收法直接测定其中的镉和铅.镉的浓度在0～50 ng/mL范围内与吸光度呈良好的线性关系,相关系数r= 0.9990;铅的浓度在0～300 ng/mL范围内与吸光度呈良好的线性关系,相关系数r=0.9990 .镉的回收率为90.6%～102.0%,测定结果的相对标准偏差为4.37%(n=8);铅的回收率为91.3%～102.1%,测定结果的相对标准偏差为8.67%(n=8).     

衍生气相色谱法快速测定食品包装材料中甲醛

本文建立了测定食品包装材料中甲醛的衍生气相色谱法.方法的检出限达到0.01 ng/mL.本法在0～0.8 μg/mL范围内有较好的线性关系,相关系数R=0.9999,平均回收率为99.8%～100.2%.     

光化学-荧光分析法研究(Ⅷ)——波长扫描-反应速差分析法

提出了波长扫描-光化学反应速差荧光分析同时测定双组分的方法,以核黄素的光分解反应和甲萘醌的光还原反应为例考察了方法的可行性.结果表明,核黄素、甲萘醌浓度分别在(0～1.20)μg/mL和(0～2.70)μg/mL范围内呈良好的线性关系(γ为0.999和0.998).检出限分别为0.22ng/mL和2.6ng/mL(n=11).平均回收率分别为101%、99%.     

用四氨基铝酞菁共振光散射技术测定纳克级核酸

痕量核酸对四氨基铝酞菁的共振散射光产生增强作用,且增强程度与核酸浓度之间有良好的线性关系.据此建立了测定核酸的高灵敏共振散射光增强分析方法.在pH=6.0、最大散射波长400nm处,测定小牛胸腺DNA(CTDNA)、鲑鱼精子DNA(SMDNA)和酵母RNA(YeastRNA)的线性范围分别是0～250ng/mL,0～200ng/mL和0～400ng/mL,检测限分别为1.4ng/mL,1.4ng/mL和2.7ng/mL.该法简单,灵敏度高,用于实际样品中核酸含量的测定,所得结果与紫外吸收法一致.     

高效液相色谱-荧光检测法测定环境水中的苯胺和苯酚

建立了用高效液相色谱荧光检测法同时测定环境水中苯胺和苯酚的分析方法。色谱柱为EclipseXDB C8(4.6mmi.d.×150mm,5μm),流动相为甲醇 磷酸盐缓冲液(0.1mol/L磷酸二氢钾 0 1mol/L磷酸氢二钠,pH6.87)V(甲醇)∶V(磷酸盐缓冲液)=50∶50,流速1 0mL/min,柱温25℃,检测波长0minλex/λem=230/340nm(测定苯胺),3.5minλex/λem=215/300nm(测定苯酚)。测定苯胺的线性范围0.2～120ng,r=0.9999,检出限0.01ng;测定苯酚的线性范围0.4～500ng,r=0.9998,检出限0.02ng,回收率98.1%～101.2%。该方法已用于对环境水中苯胺和苯酚的测定。     

石墨炉原子吸收法测定美白化妆品中铅和镉

本文采用石墨炉原子吸收法测定了美白化妆品中铅、镉含量.铅、镉测定的线性范围分别为0～176 ng/mL、0～88 ng/mL,相关系数r均为0.9998,回收率分别为98.2%～101.1%和98.9%～101.8%,相对标准偏差分别为1.73%和1.46%.     

光化学荧光分析法研究(Ⅵ)——混合色素的光化学速差动力学荧光分析法测定

以光化学荧光衍生化法测定苋菜红(AM)和直接耐晒嫩黄5GL(DY)2种偶氮色素,研究了同时测定这2种色素混合物的光化学速差动力学荧光分析的原理和方法。AM和DY的浓度分别在0～220ng/mL和0～120ng/mL范围内呈良好的线性关系,相关系数皆为0.999,检出限为0.64ng/mLAM和0.045ng/mLDY。相对标准偏差分别为1.6%(n=8)和1.8%(n=7)。该法用于人工合成混合样品的测定效果良好。     

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%.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

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.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.     

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.     

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.     

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.