分光光度法与火焰原子吸收光谱法测定钢中硼的比较

提出了萃取-分光光度法和火焰原子吸收光谱法测定钢中硼的两种方法,比较了两者的线性范围、检出限、样品测定结果等.试验发现:分光光度法和火焰原子吸收光谱法在硼含量分别为0.11～3.2 mg·L-1和0.05～3.24 mg·L-1范围内时,吸光度与其质量浓度呈线性关系,检出限(3S/N)分别为0.033,0.036 mg·L-1.经检验,两种方法的测定结果之间无显著性差异.     

悬浮液进样-石墨炉原子吸收光谱法测定生物样品中微量铬

提出了固体悬浮液进样石墨炉原子吸收光谱法直接测定铬的方法,并对各分析条件进行了优化.采用1.2 g·L-1琼脂溶液为悬浮剂,将样品均匀悬浮于其中,由自动进样器直接将样品悬浮液注入石墨炉中,加入基体改进剂,石墨炉原子吸收光谱法测定生物样品中铬.在优化的试验条件下,方法的检出限(3σ)为0.5 pg·L-1.铬的质量浓度在50 μg·L-1以内呈线性关系,回归方程为A=0.2521 C 0.0311,样品加标回收率为98.6%～103.2%.     

微波消解样品-火焰原子吸收光谱法测定美白化妆品中铅和铜

乳液和水类美白化妆品经硝酸-过氧化氢混合液消解,粉类美白化妆品经硝酸-过氧化氢-氢氟酸混合液消解,用火焰原子吸收光谱法测定样品中铅和铜的含量。在优化的仪器工作条件下,铅和铜的质量浓度分别在9.0 mg·L-1和11.0 mg·L-1以内与其吸光度呈线性关系,检出限(3s)分别为21.8μg·L-1和16.2μg·L-1。方法用于美白化妆品中铅、铜的测定,测得回收率分别在98.0%~102.5%和96.7%~105.0%之间。     

ABS工程塑料中铅、铬(Ⅵ)、镉及汞含量测定

用浓硫酸与浓硝酸(1 5)的混合酸消解ABS工程塑料试样,消解过程中铅(Ⅱ)以PbSO4形式沉淀,用乙酸铵溶解PbSO4沉淀后在乙酸盐缓冲溶液中用火焰原子吸收光谱法(FAAS)测定铅,检出限为0.088 mg·L-1.溶液中镉(Ⅱ)也用FAAS法测定,其检出限为0.074 mg·L-1,溶液中汞采用氢化物发生,冷原子蒸气-原子吸收光谱法测定,其检出限为0.64 μg·L-1.六价铬采用二苯基羰酰二肼光度法测定,检出限为0.039 mg·L-1.对方法的精密度及回收率作了试验,测得相对标准偏差(n=7)均小于3.5%,回收率在91.8%～106.0%之间.     

改进的重铬酸盐法测定水和废水中化学需氧量

对重铬酸盐法测定水和废水中化学需氧量的国家标准方法作了改进。改进方法较原方法的取样量由20.00mL减少为10.00mL,氯离子掩蔽剂硫酸汞由固体改为溶液;改进方法受氯离子干扰的程度与国标方法相似,当氯离子质量浓度小于1 000mg·L-1时对测定结果无影响。改进方法的检出限为3 mg·L-1,对标准物质和标准溶液进行测定,测定结果的相对误差在0.96%~2.70%之间,标准偏差在0.80~5.6 mg·L-1之间,相对标准偏差(n=6)在0.80%~5.9%之间。方法应用于水样的测定,测定值与国标法测定值相符,测定值的标准偏差在0.94~20.5mg·L-1之间,相对标准偏差(n=6)在0.53%~11%之间。     

单扫描示波极谱法测定针剂中头孢他啶含量

提出了用单扫描示波极谱法测定药物中头孢他啶含量的方法.在0.10 mol·L-1硫酸底液中,头孢他啶在-0.96 V(vs.SCE)处有一灵敏的极谱还原峰,头孢他啶的质量浓度在8.0～2.0×103mg·L-1范围内与其峰电流呈线性关系,检出限(3S/b)为3.2 mg·L-1.用于头孢他啶针剂样品的分析,测得头孢他啶含量与高效液相色谱法所测得值一致.分析结果的相对标准偏差(n=6)在0.96 9,6～1.31%之间,回收率在98.7%～102.0%之间.     

离子色谱法测定水果中亚硝酸盐和硝酸盐

建立了离子色谱法测定水果中亚硝酸盐和硝酸盐的方法.试样溶液中亚硝酸盐和硝酸盐在YSA-8阴离子色谱柱分离,以4 mmol.L-1碳酸钠-3 mmol.L-1碳酸氢钠为流动相,电导检测.亚硝酸盐和硝酸盐的检出限分别为0.02 mg·L-1和0.11 mg·L-1,工作曲线的线性范围分别在0.2～20.0 mg·L-1和0.3～30.0 mg·L-1范围内.该方法已应用于水果中亚硝酸盐和硝酸盐的测定,测得回收率在93.4%～105.2%之间.     

石墨炉原子吸收光谱法测定药用辅料聚乳酸中残留锡

聚乳酸样用硝酸-硫酸消解后,石墨炉原子吸收光谱法测定聚乳酸样品中锡的残留量.用抗坏血酸作基体改进剂,方法检出限0.23 mg·L-1,工作曲线的线性范围为1～10 mg·L-1,相关系数为0.996 8,方法的平均回收率为97.1%,日内相对标准偏差为6.9%.方法满足中国药典2005年版的要求,可用于测定辅料聚乳酸中残留锡.     

火焰原子吸收光谱法间接测定白酒中甜蜜素

提出了一种火焰原子吸收光谱法间接测定白酒样品中甜蜜素的测定方法.采用乙醚将甜蜜素从酸化后的白酒样品中提取出,提取液经挥发去除乙醚后加浓硝酸置于100℃水浴中硝化,硝化产生的硫酸根与铬酸钡悬浮液反应生成硫酸钡,通过用火焰原子吸收光谱法测定反应中定量释出的铬酸根间接换算成甜密素含量.甜蜜素的质量浓度在0.35 g·L-1以内与吸光度呈线性关系,其线性回归方程为A=0.301 ρ<,甜>+0.018,检出限(3S/N)为0.02 g·L-1.在0.060,0.250,0.500 g·L-1的标准加入水平下进行了精密度试验,所得相对标准偏差(n=6)分别为8.93%,3.44%,3.63%.加标回收率在86.7%～105.0%之间.     

表面活性剂增敏火焰原子吸收光谱法测定铝合金中铜

以锌空心阴极灯作为光源,用火焰原子吸收光谱法测定了铝合金中铜量。试样溶解于盐酸及硝酸中,并在含有硝酸(1+1)溶液3.0mL的50mL酸性溶液中进行测定。在试样溶液中还加入5g.L-1乳化剂OP溶液1.5mL作为增敏剂,30g.L-1镧(Ⅲ)溶液4.0mL作为释放剂;后者的加入使硅、铝、镁、镍、锰、钙、钴及铁的允许共存量有显著提升。按此条件分析过程中不存在背景吸收干扰。测得吸光度与相应铜(Ⅱ)的质量浓度在6.0mg·L-1以内呈线性关系,其检出限(3s/k)为0.011 2 mg·L-1。应用此方法分析了一件铝合金试样,测得其铜量的平均值为1.656mg·g-1,测定值的相对标准偏差(n=6)为1.3%。同一试样,改用铜空心阴极灯进行分析,测得铜量的平均值为1.670mg·g-1,相对标准偏差(n=6)为0.92%。t-检验结果表明:用两种不同光源所测得的铜量的结果之间无显著性差异。     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.     

Synthesis of N-substituted carbazolones from α-iodo enaminones via Pd(0)-catalyzed intramolecular coupling under microwave irradiation

A variety of N-aryl and N-alkyl carbazolones were conveniently achieved in good to high yields via Pd₂(dba)₃-mediated intramolecular coupling of N-substituted α-iodo enaminones under microwave irradiation. The Pd(0)-catalyzed cyclization was found to proceed favorably with the more electron-deficient phenyl ring during the reactions involving unsymmetrical N,N-diaryl α-iodo enaminones. This unique property enables the construction of carbazolone skeleton containing nitro substituted benzenoid ring.     

Synthesis of substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles by intramolecular nitrilimine cycloaddition

Both substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles have been synthesized by the 3+2 intramolecular dipolar cycloaddition of nitrilimines to alkynes. This cyclization has been extended to more versatile 3-bromo derivatives by the use of alkynylbromides as dipolarophiles.     

Catalyst free,visible-light promoted photoaddition reactions between C60 and N-trimethylsilylmethyl-substituted tertiary amines for synthesis of aminomethyl-1,2-dihydrofullerenes

An efficient and benign method for the preparation of aminomethyl-substituted fullerenes has been developed. The process, involving catalyst free, visible-light irradiation of 10% EtOH-toluene solutions containing fullerene C₆₀ and N-trimethylsilylmethyl-substituted amines by using a 20 W compact fluorescent lamp, leads to formation of aminomethyl-substituted fullerene adducts in a highly efficient manner. The photoaddition reaction takes place via a pathway initiated by visible light absorption by C₆₀, followed by SET from the amine to the triplet excited state of C₆₀. Ethanol-promoted desilylation of the resulting a minimum radical then generates the corresponding α-amino radical which couples with the C₆₀ radical anion to form the anion precursor of the fullerene adducts. The new approach using visible-light takes place under mild conditions and it does not require the use of photocatalysts. Thus, the method developed in this effort could broadens the range of functionalized fullerene derivatives that can be readily prepared.     

Highly efficient and stereoselective cycloaddition of nitrones to indolyl- and pyrrolylacrylates

The reactions of various nitrones with indolyl- and pyrrolylacrylates proceeds regioselectively with high diastereoselectivity in the case of aldonitrones, and represents an effective method for obtaining new indolyl- and pyrrolyl-substituted isoxazolidine carboxylates stabilized by weak (CH?O) and moderate (NH?N) strength intramolecular hydrogen bonding. The resulting cycloadducts exhibit promising in vitro anti-influenza activities.     

Transition metal-free direct amination of benzoxazoles using formamides as nitrogen sources

A transition metal-free method for the direct amination of benzoxazoles using formamides as nitrogen sources is reported, which was mediated by an inexpensive and environmentally friendly tetrabutylammonium iodide/tert-butyl hydroperoxide system and gave the 2-aminobenzoxazole derivatives with moderate to good yields.     

l-Proline-catalyzed five-component domino reaction leading to multifunctionalized 1,2,3,4-tetrahydropyridines

Multifunctionalized 1,2,3,4-tetrahydropyridines are concisely synthesized in good yields via l-proline-catalyzed or l-proline/FeCl₃-cocatalyzed one-pot multicomponent reactions (MCRs). The MCRs involve a domino hydroamination/prins reaction/Mannich-type reaction/intramolecular dehydration-cyclization process. The molecular structure of 5baa, one of multifunctionalized 1,2,3,4-tetrahydropyridines, was confirmed by single-crystal X-ray diffraction.     

Studies of Photoionization of CF3 I by Femtosecond Time-resolved Mass Spectrometry

The multi-photon dissociative photoionization dynamics of CF3I has been studied with femtosecond two-color pump-probe time of flight mass spectra at a pump pulse of 265 nm and a probe pulse of 398 nm. The life constants of CF3I+ and its fragment ions CF3+ and I+ are obtained as (96±7), (198±130) and (167±6)fs, respectively. The multi-photon dynamics leading to these ions differ. CF3I+ corresponds to a (1+2′) transition with one-photon pump excitation to the A band of CF3I. CF3+ are mainly formed by a tow-photon probe excitation to the CF3+ with subsequent dissociation of parent ions. I+ are produced in (2+2′) combined with (1+1′+2′) process. The results provide information on the multi-photon pathways involved.