微分电位溶出法连续测定饮料中的铜铅镉锌

建立了微分电位溶出法连续测定饮料中痕量铜、铅、镉、锌的新方法。在HAc- Na Ac( p H4 .5)～ 3.5× 1 0 -2 mol·L-1KCl～ 2 .6× 1 0 -5 mol· L-1Hg2 +介质中测定锌 ,然后调节底液为 0 .0 1 mol·L-1HCl,连续测定铜、铅、镉。铜、铅、镉、锌 ,检出限分别为 4 ,0 .1 ,2 ,4 μg· L-1,线性测定范围 Zn2 +:0～ 30 0 μg·L-1,Cu2 +、Pb2 +、Cd2 +:0～ 2 2 0μg· L-1,回收率为 83.4 %～ 1 0 3.3% ,RSD<3.4 % ( n=7)。该法较好解决了金属互化物的影响 ,样品不需消化便可直接测定。     

双波长吸光光度法同时测定多巴和酪氨酸的研究

研究了双波长吸光光度法同时测定多巴和酪氨酸。在 pH 1 2 .0 0的硼砂 氢氧化钠缓冲介质中 ,多巴和酪氨酸的含量分别在 0～ 2 0 .0 μg·ml-1和 0～ 1 9.0 μg·ml-1范围内呈良好线性关系 ,方法检出限和摩尔吸光系数 :多巴为 0 .2 3 μg·ml-1和 1 .2 0× 1 0 4L·mol-1·cm-1,酪氨酸为 0 .2 7μg·ml-1和 1 .48× 1 0 4L·mol-1·cm-1,方法的灵敏度和和选择性均较好 ,应用于尿液中多巴和酪氨酸的测定。     

双硫腙修饰玻碳电极阳极溶出伏安法测定痕量镉和铅

报道了双硫腙修饰玻碳电极同时测定痕量镉和铅的电分析方法。镉和铅离子通过与电极表面的双硫腙发生螯合作用而富集在电极表面 ,同时在 -1 .2 0V(vs.SCE)还原成零价镉和铅 ,当电极电势从 -1 .2 0V向 -0 .3 0V扫描时 ,被还原的镉和铅从电极表面溶出 ,分别于 -0 .78V和 -0 .4 8V左右形成灵敏的阳极溶出峰。优化了支持电解质及pH值、双硫腙用量、富集电位及时间等实验参数。利用该修饰电极测定镉、铅的线性范围分别为 1 .0×1 0 - 8～ 2 .5× 1 0 - 6 mol L和 5 .0× 1 0 - 9～ 2 .5× 1 0 - 6 mol L。检测限分别为 5 .0× 1 0 - 9mol L和7.0× 1 0 - 1 0 mol L。该法用于实际水样中镉和铅的测定 ,平均回收率分别为 99.3 0 %和 99.5 4 %。     

微分电位溶出伏安法同时测定甘草中痕量铅和镉

建立了在NH4OAc HOAc介质中,用微分电位溶出伏安法测定中药甘草中痕量铅和镉的方法,利用该法对中药甘草煎煮前后及其煎液中铅和镉的含量进行测定。试验表明,镉和铅分别在-0.66V(vs.SCE)和-0.47V(vs.SCE)电位处形成两个灵敏的二次微分溶出峰;铅在0～0.8mg·L-1,镉在0～0.4mg·L-1范围,峰电流与浓度呈良好的线性关系;铅和镉检出限分别为0.15和0.1μg·L-1,相对标准偏差≤1.39%;铅和镉加标回收率在94%～103%之间。结果表明,该甘草样品中铅和镉含量均低于国家安全标准,甘草煎煮液中铅的浸出率较高,镉的浸出率则较低,方法也适用于其它类似中药。     

锑电极电位溶出法测定锌、镉、铅

提出了采用锑电极作为工作电极同时测定痕量重金属锌、镉、铅的电位溶出法。探讨了同时测定锌、镉、铅的最佳条件。在pH=5.0的HAc-NaAc缓冲溶液中,Zn2+、Cd2+、Pb2+分别在-1.07、-0.70、-0.52 V得到灵敏的电位溶出峰。沉积时间为60 s时,锌、镉、铅的质量浓度分别在0~16.0、0~1.6、0~0.08 μg/mL范围内,与各自微分电位溶出峰高呈线性关系,检出限分别为4.0、0.3、0.03 μg/L。测定了水样中痕量锌、镉、铅的含量,结果令人满意。     

单扫描示波极谱法连测铅锌

铅和锌极谱测定方法很多 ,有在碱性介质中测定 ,也有在强酸性介质中测定。铅和锌连测有时也有报道[1,2 ] ,但测定范围局限于微量及半微量分析。本法特点是在同一份溶液中连测铅和锌 ,测定范围扩至常量 ,干扰少 ,重现性好。铅的回收率为 95%～1 0 0 % ,锌的回收率为 97%～ 99% ,适合于铜矿及铅锌矿中铅和锌的分析。1　试验部分1 .1　主要试剂与仪器铅 [3]和锌 [4 ]标准溶液 :均为 2 mg·ml-1抗坏血酸溶液 :1 0 0 g· L-1硫氰酸钾溶液 :50 g·L-1HOAc- Na OAc缓冲溶液 [5] :p H4.5明胶溶液 :2 .5g· L-1试剂均为分析纯JP3- 1型示波仪 ,三…     

微波消解-AAS法测定果蔬罐头中镉铅铜锌

采用微波制样技术,用石墨炉和火焰原子吸收法测定果蔬罐头中的镉铅铜锌的四种微量元素.镉、铅、铜、锌的线性范围分别为0～8μg·L~(-1)、0～100μg·L~(-1)、0～4mg·L~(-1)、0～5mg·L~(-1),检出限分别为0.19μg·L~(-1)、2.80μg·L~(-1)、20μg·L~(-1)、60μg·L~(-1),相对标准偏差均小于5%,方法简便、快速,结果准确可靠.     

示波极谱法测定皮蛋中微量铅

在 pH 5 .2～ 5 .8的六次甲基四胺 HCl底液中 ,Pb2 +与邻菲啉 (phen)共存体系于- 0 .4 9V(vs .SCE)处产生一灵敏的极谱吸附波 ;铅浓度在 0 .0 15～ 0 .8μg·ml- 1范围内与峰电流呈良好线性关系 ,检出限可达 0 .0 0 8μg·ml- 1,线性回归方程为Iy=6 .80 + 12 4 .0 0Cx,相关系数为0 9973。用该方法测定了皮蛋中微量铅 ,试样加标回收率为 96 %～ 10 4 % ,相对标准偏差小于2 5 % ,结果与原子吸收吸光光度法一致。该方法准确、简便、选择性好。     

次甲基蓝-溴酸钾体系动力学光度法测定甲醛

在硫酸介质中 ,基于甲醛对溴酸钾氧化次甲基蓝 (MB)显著的促进作用 ,建立了测定甲醛的动力学光度法。线性范围为 0 .4 8～ 5 .6 0 μg·ml- 1,检出限为 0 .2 2 μg·ml- 1。对浓度水平为 1.6 μg·ml- 1甲醛的 10次平行测定的RSD为 0 .4 86 %。方法用于检测酚醛树脂以及动物标本室内空气中甲醛含量 ,结果满意     

钴（Ⅲ）—亚硝基R盐体系极谱波研究及锌电解液中钴的快速测定

提出了一个测定微量钴 (Ⅱ )的极谱吸附波新体系。在pH 9.5的柠檬酸铵底液中 ,钴(Ⅲ ) NRS络合物在 - 0 .5 7V(vs .SCE)有一良好的吸附波 ,二阶导数波峰电流与钴浓度在 0 .0 1～1.2 μg·ml- 1范围内呈线性关系 ,检出限为 5ng·ml- 1。研究了极谱波性质和形成机理 ,应用于锌电解液中微量钴的分析 ,简便快速 ,结果准确     

从物质本原到干水:水的概念的发展史

在古代哲学中,水被视为一种物质本原。17世纪化学学科形成后,水被定义成一种化学元素。18世纪的化学革命中,水被发现是氢氧化合物。19世纪原子分子论的创立,使水的概念得到微观表征。至20世纪,重水的发现和干水的发明使水的概念有了新的发展。总之,水的概念的发展史,反映了化学思想的发展和科学技术的进步,对化学研究和化学教育均有重要的启示。     

多金属氧酸盐催化的水氧化研究进展

氢气以其清洁无污染、燃烧值高等优点成为未来最具潜力的可再生能源之一,而清洁生产氢气的最佳选择之一即为裂解水. 利用太阳能模拟光合作用实现水的全分解产生氢气和氧气是目前最为理想的能源转化方式,并且已经引起了众多研究者的关注. 水分解的半反应之一--水氧化反应由于其过程复杂,一直是制约水分解的瓶颈. 所以寻找高效、稳定的水氧化催化剂便成为了突破该瓶颈的关键. 多金属氧酸盐是一类以前过渡金属氧簇为基本单元形成的多金属氧簇化合物. 由于多金属氧酸盐在物理、化学性质方面具有无法比拟的特性,使得其在催化、药物、纳米科技和材料科学等方面已被广泛地应用. 多金属氧酸盐的全无机配体可很好地抵御水氧化反应的强氧化性环境,故将其作为水氧化催化剂越来越引起研究者们的注意,并且已有多种多金属氧酸盐被设计为水氧化催化剂. 本文详细介绍了各种不同过渡金属取代的多金属氧酸盐水氧化催化剂的研究进展.     

A model study on the mechanism and kinetics for the dissociation of water anion

Quantum chemical computations using both density functional theory (B3LYP functional) and wavefunction (MP2 and CCSD(T)) methods, with the 6-311++G(3df,2p) and aug-cc-pVnZ (n = D,T,Q) basis sets, in conjunction with a polarizable continuum model (PCM) method for treating structures in solution, were carried out to look again at a series of small negatively charged water species [(H₂O)_n]^•–. For each size n of [(H₂O)_n]^•– in aqueous solution with n = 2, 3, and 4, two distinct structural motifs can be identified: a classical water radical anion formed by hydrogen bonds and a molecular pincer in which the excess electron is directly interacting with H atoms. In aqueous solution, both motifs have comparable energy content and likely coexist and compete for the ground state. Some water anion isomers can dissociate when interaction with a water molecule, [(H₂O)_n]^•– + H₂O → H^•(H₂O)_m + OH^–(H₂O)_n–m, through successive hydrogen transfers with moderate energy barriers. This reaction can also be regarded as a water-splitting process in which the H transfers involved take place mainly within a water trimer, whereas other water molecules tend to stabilize transition structures through microsolvation rather than direct participation. Calculated absolute rate constants for the reversed reaction H^•(H₂O)₂ + OH^–(H₂O)₂ → [(H₂O)₄]^•־ + H₂O with both H and D isotopes agree well with the experimentally evaluated counterpart and lend a kinetic support for the involvement of a tetramer unit.     

电解离子水及其生成器

本文介绍了电解离子水的制备原理和应用。原水经电解后，阳极室生成酸性离子水，阴极室生成碱性离子水。酸性离子水具有杀菌消毒作用，碱性离子水具有保健作用。同时，简要介绍了离子水生成器的研究进展。     

Determination of differences in free and bound water contents of beef muscle by DSC under various freezing conditions

The differences in bound water content of beef semimembranous muscle samples obtained from previously chilled (24 h at +4°C) middle-aged beef carcasses were determined by the use of DSC. Initially, samples obtained from fresh, unprocessed meat were frozen at –40, –50 or –65°C to determine their melting peaks for freezable water (free water) content with the use of DSC. The samples were then subjected to an environment with an ambient temperature of –30, –35, –40 or –45°C, with no air circulation, or with an air circulation speed of 2 m s^–1, until a thermal core temperature of –18°C was attained; this was followed by thawing the samples until a thermal core temperature of 0°C was reached. This process was followed by subjecting the samples to the ambient temperatures mentioned above, to accomplish complete freezing and thawing of the samples, with DSC, and thereby determination of the freezable water contents, which were then used to determine the peaks of melting. The calculated peak areas were divided by the latent heat of melting for pure water, to determine the freezable water contents of the samples. The percentage freezable water content of each sample was determined by dividing its freezable water content by its total water content; and the bound water content of each sample was determined by subtracting the percentage free water content from the total. In view of the fact that the free water content of a sample is completely in the frozen phase at temperatures of –40°C and below, the calculations of free and bound water contents of the samples were based on the averages of values obtained at three different temperatures.     

Determination of freezable water content of beef semimembranous muscle DSC study

The freezable water contents of samples obtained from previously chilled semimembranous muscle of middle-aged beef carcasses after a 24 h cooling period a room at in 5±1C were determined by differential scanning calorimetry (DSC) at –5, –10, –15, –20, –30, –40, –50 and –65C. This was accomplished by freezing the samples at the above-mentioned temperatures, followed by thawing to 35C, and measuring the melting peaks of freezable water. The areas of these peaks were determined by using the peak integration method programs through a computer linked to the DSC, and they were then used to determine the latent heat of melting (H _m) in kJ kg^–1 at each freezing temperature. The resultant latent heat of melting per sample was divided by the latent heat for pure water to determine the amount of freezable water present in these samples. This amount of freezable water was divided by the total water content of the meat sample to determine the percentage of freezable water in the sample. The percentage of freezable water was subtracted from 100 to determine the percentage of bound water present in the sample.     

Analysis of Fischer-Tropsch by-product waters by gas chromatography

This paper describes a quantitative technique for the determination of organic constituents in Fischer-Tropsch by-product waters. Temperature-programmed gas chromatography on derivatized bonded polar capillary columns provides the required separation that permits reliable quantitation of individual compounds. A preliminary combined gas chromatographic–mass spectrometric survey to identify the components present in Fischer-Tropsch by-product waters is presented. The elution order of 58 identified components is tabulated. Components identified in a typical Fischer-Tropsch by-product water include C₁–C₉ linear and branched alcohols, C₃? C₈ ketones, C₂? C₆ carboxylic acids, and C₂? C₄ linear aldehydes.     

Interaction of water with the regenerated cellulose membrane studied by DSC

One to three endothermal peaks atributted to melting of bulk and interfacial water were observed by DSC in the regenerated cellulose — water system. The profiles of thermal effects depend on water content, time of conditioning, film pretreatment and the conditions applied during the preceding freezing-thawing cycles. The occurrence might be deduced of melting-crystallisation processes. A large amount of non-freezable strongly bounded water was also detected. Although cellulose absorbs water quickly after immersion, the structural changes consisting on ordering of polymer fraction occur during further conditioning due to increase in strength of water binding. Using the membranes in the separation module at 90°C causes weakening of these bonds. Differences between interaction of particular cellulose films with water can be detected during the first, the second and the third heating. This revised version was published online in July 2006 with corrections to the Cover Date.     

Water sorption and permeation in chitosan films: Relation between gas permeability and relative humidity

The water sorption of chitosan has been studied at 20 °C. Water transport is governed by a Fickian process for relative humidities lower than 0.4, and in that range of partial pressures, the diffusion coefficient is concentration‐dependent. At a higher activity, anomalous diffusion is observed. The sorption isotherm is well described by the Guggenheim‐Anderson‐de Boer (GAB) model, and the clustering phenomenon observed at high relative pressures can be studied with the parameters of this model. The water permeability coefficient greatly increases with the relative pressure, and the water plasticization effect leads to a loss of the gas barrier properties under wet conditions. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 3114–3127, 2001