不同前处理制样方法对钢中氧、氮测定结果的影响

讨论了不同物理和化学制样方法对钢中氧、氮测定结果的影响。试验结果表明,物理制样采用锉刀打磨样品表面后剪切,再用乙醚清洗除去油污;化学制样先用20%盐酸溶液溶解样品表面氧化层,再用滴加了4滴30%过氧化氢的10%草酸溶液浸泡,取出后依次用水、无水乙醇浸洗,风干。用以上两种方法制样,钢标准样品中氧、氮含量测定值与标示值一致。在测定钢中氮含量时,可用乙醚清洗后直接测定,以缩短检测周期和减轻劳动强度。该研究结果可用于指导钢样品中氧、氮含量测定时样品的处理。     

硝酸铋共沉淀—火焰原子吸收法测定蒸馏酒中痕量铅

蒸馏酒中铅的测定方法,常用消化样品-双硫腙比色法或稀释样品-火焰原子吸收光度法。前者操作复杂,重现性差,且用剧毒药品氰化钾。后者灵敏度不高,不能测定含铅量低的酒样。本文报道了用硝酸铋作共沉淀剂分离富集、火焰原子吸收光度法测定蒸馏酒中痕量铅的方法。该方法操作简便,灵敏度高(95％置信度的检出限为0.005mg·L~(-1)),线性范围宽,基体没有干扰。相对标准偏差为2.2％～4.5％。回收率为100.2％～103.2％。对样品进行测定,结果与双硫腙比色法一致。     

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.     

测定酒和水中氰化物的间接光度法

建立了测定微量氰化物的间接光度法,其氰化物含量在0～3.0μg范围内符合比尔定律。此法用于酒和水中微量氰化物的测定,结果与国家标准方法相吻合,加标回收率为95％～102％。此法简便快速,选择性及重现性也令人满意。     

过铬酸的结构式和反应机理及其在分析化学中的应用

一、引言在定性分析中,当重铬酸盐或铬酸盐在强酸性溶液中(H_2SO_4,HCl或HNO_3)与过氧化氢作用生成蓝色的过铬酸,能被乙醚或其他有机溶剂萃取。过铬酸在水溶液中是不稳定的,易分解成三价绿色的铬离子和氧气。这个反应是用作铬的特效检验,分离和比色测定。由于过铬酸的结构式至今尚未完全肯定下来,     

碘-淀粉吸光光度法间接测定砷

目前，光度法测定砷的报道较多。利用铬(Ⅵ)氧化砷(Ⅲ)，剩余的铬(Ⅵ)与溴邻苯三酚红形成有色络合物，借此可间接测定微量砷(Ⅲ)。但反应需在50～70℃水浴中进行，整个反应时间需110min。本文报道了用定量溴酸钾与砷(Ⅲ)反应，剩余的溴酸钾与碘化钾反应生成I3^-，利用I3^-与淀粉生成蓝色络合物，可以间接测定微量砷(Ⅲ)，方法简便快速，基本无干扰。     

火焰原子吸收光谱法测定蜂胶铬软胶囊中铬

目的：建立蜂胶铬软胶囊质量控制的方法。方法采用浓硝酸-过氧化氢混合液微波消解样品,火焰原子吸收光谱法测定蜂胶铬软胶囊中铬含量。结果铬元素在0.4～2.5 mg· L-1范围内线性关系良好,样品铬测定值为49.92μg/粒,相对标准偏差为3.29％。茶叶标准物质（ GSB-7）中铬元素的测定值与认定值相吻合。结论实验表明,方法简单、准确、可行,可作为蜂胶铬软胶囊中铬的检测方法。     

矿石中微量铬的萃取测定

二苯碳酰二肼与铬生成红紫色络合物,已广泛应用于各种矿物、岩石、钢铁及合金中微量铬的测定,但铁、钒干扰较大,虽能以碱熔后分离与放置后比色,但给方法带来某些局限。铬的萃取分离研究较早的是用甲基异丁酮在低于10℃下进行,但萃取操作不便。高分子胺应用于萃取分离铬,对消除某些干扰离子取得较好效果。本文在0.1-1M硫酸介质中,以高分子胺N235萃取铬(Ⅵ),有机相以二苯碳酰二肼在乙醇均相溶液中直接显色。矿石经过氧化钠碱熔后水浸,以锇盐或甲醛催化破坏过氧化氢,然后酸化后萃取光度测定,应用在几种不同类型矿石中铬的测定,结果良好。     

氧化还原滴定法测定铝铬中间合金中铬

铝铬中间合金中铬含量较高(质量分数在2.0%～3.0%之间),采用二苯基羰酰二肼光度法测定铬[1],由于试液的吸取量太少易产生较大误差,无法保证结果准确度.本法采用氢氧化钠-过氧化氢溶解试样,硝酸酸化,在硫酸-磷酸介质中用过硫酸铵作氧化剂,将三价铬氧化成六价铬,用硫酸亚铁铵标准溶液滴定六价铬,测定铝铬中间合金及铝合金中高含量的铬.     

脉冲悬浮体进样火焰原子吸收光谱法直接测定土壤中铬

以阴离子表面活性剂SDS为增敏试剂,脉冲悬体进样火焰原子吸收光谱法直接测定土壤中格,结果表明,SDS在土壤悬浮体中对铬的吸收信号表现出明显的增敏作用,铬的绝对灵敏度为7．90ng(进样体积为500ul),直接测定土壤中铬的检出限达4．3ng,加标回收率99．4％,相对标准偏差3％（n=3),方法可直接测定NBS标准物质蕃茄叶中铬。     

石墨炉原子吸收法检测胎盘镉水平

建立了硝酸消化、石墨炉原子吸收法（GFAAS）测定胎盘中镉含量的方法。取0．3g胎盘于110℃烤箱烘烤1h,在80℃水浴下HNO3、H202顺序消化1h,消化后定容至2mL;D2灯校正背景,样本基体匹配、标准曲线法测定。结果表明,此法相对标准偏差〈10％,回收率为89．4％～91．2％,此检测方法稳定,简便可行,胎盘取材方便,对新生儿无损伤,对新生儿镉负荷的检测评估具有一定的意义。     

Differential selectivity in electrochemical oxidation of ascorbic acid and hydrogen peroxide at the surface of functionalized ormosil-modified electrodes

Functionalized ormosil-modified electrodes have been developed for electroanalytical applications. The functionalized ormosil-modified electrodes are made by encapsulating potassium ferricyanide/potassium ferrocyanide within ormosil film derived from an optimum composition of 3-aminopropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane and phenyltrimethoxy silane in acidic medium in absence of Nafion/crown ether (system 1), in the presence of Nafion (system 2) and in the presence of dibenzo-18-crown-6 (system 3). Another modified electrode (system 4) is also developed using the reaction product of potassium ferricyanide, 3-aminopropyltrimethoxysilane and either tetrahydrofuran (THF) or cyclohexanone followed by ormosil formation in the presence of 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane and phenyltrimethoxy silane in acidic medium. The electrochemical oxidation of hydrogen peroxide and ascorbic acid conducted at the surface of these four types of functionalized electrodes shows very interesting observations on the selective sensing of ascorbic acid and peroxide. The results based on cyclic voltammetry justify the relative performances on the kinetics of hydrogen peroxide oxidation and reduction. System 3 shows relatively much better oxidation kinetics of hydrogen peroxide as compared to other three systems with relatively weak reduction kinetics whereas system 4 shows relatively faster reduction kinetics of hydrogen peroxide as compared to other three systems. Similarly system 4 shows excellent response to ascorbic acid whereas system 3 shows insensitivity to ascorbic acid under similar experimental conditions. Typical response curve for the analysis of hydrogen peroxide and ascorbic acid using system 3 and system 4 respectively are reported. The results show that system 3 is the best for probing hydrogen peroxide with lowest detection limit of 0.5 μM without any interference from ascorbic acid as commonly encountered using many conventional and chemically modified electrodes.     

Speciation of hexavalent chromium in waters by liquid-liquid extraction and GFAAS determination

Diperoxo chromium oxide is produced by reaction of hydrogen peroxide on chromium(VI). Diperoxo chromium creates a complex with ethyl acetate, while chromium(III) remains in an unchanged form in the aqueous phase. By this means chromium(VI) can be extracted into ethyl acetate from the aqueous phase. The optimal conditions of Cr(III)-Cr(VI) separation, as well as the chromium content of the ethyl acetate phase were determined with graphite furnace atomic absorption spectrometry. In the second extraction of Cr(VI) from ethyl acetate back into water phase an additional preconcentration of chromium(VI) can be carried out. The detection limit (3σ) of the developed method found to be 200 ng dm^− 3 for the first extraction and 50 ng dm^− 3 after using the twofold extraction. In consequence of the matrix free ethyl acetate phase after the first extraction, with this separation a really extensive preconcentration of chromium(VI) can be realized.     

Determination of chromium in ores, rocks and related materials, iron, steel and non-ferrous alloys by atomic-absorption spectrophotometry after separation by tribenzylamine-chloroform extraction

A method for determining trace and moderate amounts of chromium in ores, concentrates, rocks, soils and clays is described. After fusion of the sample with sodium peroxide, the melt is dissolved in dilute sulphuric acid. The chromium(III) produced by the hydrogen peroxide formed is co-precipitated with hydrous ferric oxide. The precipitate is dissolved in 0.7M sulphuric acid and chromium oxidized to chromium(VI) with ceric ammonium sulphate. The chromium(VI) is extracted as an ion-association complex into chloroform containing tribenzylamine and stripped with ammoniacal hydrogen peroxide. This solution is acidified with perchloric acid and chromium determined by atomic-absorption spectrophotometry in an air-acetylene flame, at 357.9 nm. Barium and strontium do not interfere. The procedure is also applicable to iron and steel, and nickel-copper, aluminium and zirconium alloys. Up to 5 mg of manganese and 10 mg each of molybdenum and vanadium will not interfere. In the absence of vanadium, up to 10 mg of tungsten will not interfere. In the presence of 1 mg of vanadium, up to 1 mg of tungsten will not interfere.     

Determination of lead in vinegar by ICP-MS and GFAAS: evaluation of different sample preparation procedures

Lead concentrations of 59 different types of vinegars (15-307 μg l⁻¹ in balsamic vinegars and 36-50 μg l⁻¹ in wine vinegars) were determined using both inductively coupled plasma mass spectrometry (ICP-MS) and graphite furnace atomic absorption spectrometry (GFAAS). Although the precision of direct analyses, following simple aqueous dilutions, with either instrumental method was poor; that precision, following nitric acid and/or hydrogen peroxide digestions, markedly improved with either instrument and the values obtained with the two instruments were in good agreement. The efficacy of different digestions, including (1) nitric acid using a heating block, with or without addition of hydrogen peroxide and (2) mixtures of nitric acid and hydrogen peroxide using ultraviolet (UV) photolysis, were then assessed. The latter procedure was found to be much faster and more efficient, but it was limited by the relatively high levels of contaminant lead in hydrogen peroxide. Consequently, it is recommended that lead concentrations in vinegar be measured following a nitric acid digestion and UV photolysis to oxidize all organic matter before ICP-MS or GFAAS analysis; and it is further recommend that the thermal settings for the latter analyses be adjusted to account for the apparent presence of relatively volatile organolead compounds in vinegar digests.     

偶氮二甲酸二异丙酯的合成

以氯甲酸异丙酯、水合肼为主要原料,制备肼-1,2-二甲酸二异丙酯,然后用双氧水氧化制得偶氮二甲酸二异丙酯(DIAD)。 研究确定了最佳的反应条件:在0 ℃以下乙醚溶剂中,水合肼和氯甲酸异丙酯反应2 h,制备肼-1,2-二甲酸二异丙酯;n(肼-1,2-二甲酸二异丙酯)∶n(双氧水)=1:1.1,在-5~5 ℃下反应2 h,双氧水氧化得到偶氮二甲酸二异丙酯,总收率为90.7%,采用红外光谱、核磁共振等技术手段验证了中间体及目标产物结构。     

二氧化硒催化过氧化氢氧化萘丙醛制萘丙酸的研究

萘丙酸((±)-2-(6-甲氧基-2-萘基)-丙酸)的右旋体有解热镇痛特效,国内生产中由萘丙醛氧化成酸系采用多伦试剂,耗费大量硝酸银。我们采用过氧化氢作氧化剂,结果表明,制得的产品纯度高,而且成本低。     

Speciation of Cr(III) and Cr(VI) by Means of Melamine-Urea-Formaldehyde Resin and FAAS

 A method is described for the quantitative preconcentration and separation of trace chromium in water by adsorption on melamine-urea-formaldehyde resin. Cr(VI) is enriched from aqueous solutions on the resin. After elution the Cr(VI) is determined by FAAS. The capacity of the resin is maximal at ∼ pH 2. Total chromium can be determined by the method after oxidation of Cr(III) to Cr(VI) by hydrogen peroxide. The relative standard deviations (10 replicate analyses) for 10 mg/L levels of Cr(VI), Cr(III) and total chromium were 1.5, 3.5 and 2.8% respectively. The procedure has been applied to the determination and speciation of chromium in lake water, tap water and chromium-plating baths.     

Determination of pKa value, kinetic studies of decomposition and oxygen transfer for chromium(VI) peroxide

The determination of pK_a value for the unstable chromium(VI) peroxide, CrO(O₂)₂(H₂O) in aqueous solution is presented. The pK_a value is found to be (1.55 ± 0.03). The kinetic decomposition of chromium(VI) peroxide is dependent on the concentration of hydrogen peroxide in the pH range between 2.5 and 4.0. We have proposed the possible explanation for the formation of triperoxo chromium complex of hydrogen peroxide which is dependent on decomposition. Activation of coordinate peroxide in chromium(VI) peroxide observed in the kinetic studies is by reduction of thiolato-cobalt(III) complex. The rate constant (M⁻¹ s⁻¹, 15 °C) for the oxygen atom transfer reaction from CrO(O₂)₂(OH)⁻ to (en)₂Co(SCH₂CH₂NH₂)²⁺ is found to be (25.0 ± 1.3).     

丙烯环氧化反应中TS-1催化剂失活研究

采用丙烯气相进料,在预混段中先与双氧水的甲醇溶液混合后进入固定床反应器,考察了进料液中pH值、丙二醇单甲醚、乙硫醇以及铁锈等对丙烯环氧化连续反应中TS-1分子筛催化剂性能的影响。结果表明,进料液体pH值对催化剂的催化性能有影响,适宜的进料液体pH值在7左右;副产物丙二醇单甲醚含量的增加不会对催化剂性能产生影响;乙硫醇量的增加使环氧丙烷选择性下降,但不会引起催化剂的失活;而进料液体中铁锈的引入会导致催化剂中部分孔堵塞,使催化剂部分失活。当进料液中的pH值用0.1mol/L的氨水调节为7左右,在反应温度55℃,反应压力0.7MPa,TS-1催化剂具有较好的稳定性,经130h的连续试验考察,双氧水的转化率和环氧丙烷的选择性约为90%。