不用汞盐的比色法测定二氧化硫

大气中二氧化硫的测定,现普遍使用的是以四氯汞盐作吸收液的盐酸付玫瑰苯胺比色法。汞盐吸收液吸收效率高、稳定性好,但用汞量大,对操作人员的健康及环境污染均会带来一定的问题。近年来,在寻找无汞吸收液的工作方面取得了一定的进展。我们参考有关资料,用甲醛-邻苯二甲酸氢钾(KHP)缓冲液作吸收液(以下简称甲醛吸收液),对相应的分析方法作了一定的改进,取得了较好的效果。从而为革除汞吸收液提供了一条可行的途径。     

燃烧比色法测定有色金属中微量硫的改进——以甲醛吸收液代替汞盐吸收液

常用的燃烧副品红分光光度法测定有色金属中的微量硫时,采用汞盐做吸收液,既有害,显色反应又慢,不太方便。本文介绍改用甲醛邻苯二甲酸氢钾缓冲液作吸收液吸收SO_2,既消除了汞害,又提高了显色反应的速度,方法具有快速、灵敏度高等优点。适用于有色金属及其粉末产品中微量硫的测定。     

铜及铜合金中微量硫的测定

对于含硫量低于50ppm的试样,燃烧-碘量法和燃烧-硼酸盐法有一定的局限性,由于在滴定终点时指示剂颜色变化不明显,因而影响方法的准确度。为了提高燃烧法的灵敏度,曾提出将释出的SO_2吸收在四氯汞酸钠溶液中,加入品红和甲醛后生成紫色的品红磺酸衍生物,然后以分光光度法测定之。但该法操作繁琐、费时,不适于日常分析工作。为了发挥燃烧法定硫快速、简便的特点,我们采用碘离子选择电极测定铜及铜合金中硫,它与常规的燃烧-碘量法相比,具有     

氧弹分解-原子荧光法测定煤中汞的研究进展

介绍氧弹分解-原子荧光法测定煤中汞含量的研究进展。影响该方法主要因素为称样量、氧气浓度、吸收剂、还原剂、煤种以及灰分含量。分别综述了各个因素对该方法的影响,可为相关标准的制定提供参考。该方法能够简单、经济、快速地测定煤中汞的含量,但是目前学者们对于该方法的相关研究还存在分歧,需要进一步的研究验证;同时,还需要注意以下几个研究方向:吸收剂和还原剂的选择对汞回收率的影响;吸收剂在密闭氧弹中对汞的回收率及吸收时间的研究;氧弹废气中汞含量的测定;煤种和灰分含量对汞含量测定的影响。     

对氨基偶氮苯吸光光度法测定饮料中SO3^2^—

在食品工业中常用用SO_2、H_2SO_3、Na_2SO_3作防腐添加剂,SO_3~(2-)超标将对人体产生副作用。所以检验SO_3~(2-)含量是食品检验的重要指标。关于SO_3~(2-)测定常采用四氯汞钠吸收SO_2后进行测定,但此法步骤繁琐,使用试剂较多,误差较大,且四氯汞钠可引起环境污染。本文介绍对氨基偶氮苯光度法,其机理如下:     

废旧F732测汞仪部件与原子吸收光度计联用测定水中痕量汞

水中痕量汞的测定目前多采用冷原子吸收法。而借助原子吸收分光光度计的标尺扩展功能较一般测汞仪具有更好的灵敏度。本文利用废旧F732测汞仪的薄膜泵和石英管吸收池作为汞的原子化装置,使汞在普通原子吸收分光光度计上的测定变得简便、易行。用于水中痕量汞的测定,得到满意的效果。     

亚甲蓝褪色光度法测定二氧化硫

１引言 大气环境是人类赖以生存的必要条件。保护和改善大气环境质量,对于促进生产建设、发展科学技术、保障人民健康都有十分重要的意义。因此,大气质量监测就显得异常重要。在大气污染中二氧化硫含量的高低是衡量大气质量的重要指标之一。目前,监测大气二氧化硫的主要方法是四氯汞钾溶液吸收一盐酸副玫瑰苯胺比色法和甲醛缓冲溶液吸收－盐酸副玫瑰苯胺比色法。其它研究过的方法还有气体传感器法、气态分子吸收法等。我们利用二氧化硫的还原性,在较强酸性介质中,使亚甲基蓝还原为无色溶液,以此建立了直接测量大气二氧化硫的新方法,…     

石墨炉原子吸收法测定生物样品中硒和汞时添加钯的效果研究

在某些海豚的肝脏中积蓄着100ppm以上的硒和汞。当用石墨炉原子吸收法直接测定其中的硒和汞时,采用样品中添加钯的方法,以排除有机物的干扰,从而使汞和硒的测定灵敏度分别提高100倍以上。同时,本文还进一步探讨了在添加钯的情况下。汞对硒测定的干扰以及硒对汞测定灵敏度的增幅作用。     

金属化聚丙烯膜电容器中铅、镉及汞含量测定

探讨了用原子吸收光谱仪测定金属化聚丙烯膜电容器中铅、镉及汞含量的方法。结果表明,结合适宜的样品预处理,可用该法测定金属化聚丙烯膜电容器中铅、镉及汞含量,方法回收率为92.3%~106%,相对标准偏差小于2.5%。该法灵敏度高、干扰小。     

扩大冷原子吸收光谱法在分析中应用的初步探讨

冷原子吸收光谱法测定汞是利用常温下金属汞蒸气压大,以及它在空气中不易被氧化的特性。将试样化学消化处理后制成溶液,用还原剂(如SnCl_2或KBH_4等)将汞离子还原为金属汞,再把汞蒸气导入石英吸收管中,并测量汞的冷蒸气对汞灯的特定波长的光辐射的吸收信号。该法灵敏度很高,快速、准确,且设备简单。已被广泛用于生物、水质、岩石、土壤等各种样品中痕量汞的测定,成为测定汞的常规方法。     

蜂蜜中氯霉素残留量测定的不确定度评估

按照SN/T1864-2007《进出口动物源食品中氯霉素残留量的检测方法第2部分:液相色谱串联质谱法》对蜂蜜中氯霉素残留量进行分析。通过建立数学模型,对测量结果的各不确定度来源,如标准使用液、内标、回归方程、方法重复性等引入的不确定度分量及其灵敏系数进行分析和量化。当蜂蜜中氯霉素残留量为0.108μg/kg时,扩展不确定度为0.012μg/kg(k=2)。     

核磁共振INDOR法研究若干单糖分子的构型和构象

本文用核磁共振谱的INDOR,研究若干单糖在DMSO溶液中的构型和构象。在单糖分子中,除少数质子如差向异构氢(C₁—H)外,大多数质子处于相似的化学环境中,相邻者又彼此偶合,在常规核磁共振谱上产生的信号重迭交错,形成峰包,无法一一辨认以确定归属。从木糖、阿拉伯糖、甘露糖、鼠李糖等单糖在DMSO中的1NDOR谱,可间接测得C₂～C₄上质子的各组谱线,进而获得每一质子的化学位移及偶合常数。用Karplus方程定出相邻碳上质子的两面角及C—H键取向,因而确证这些分子在DMSO中的立体结构。     

THE PHOTOLYSIS OF TRYPTOPHAN IN THE PRESENCE OF OXYGEN

Abstract— Quantum yields for the destruction of tryptophan by a single 500 J flash in aqueous solution have been determined over the pH range 1–13 in both air-equilibrated and nitrogen-saturated conditions. When these quantum yields are compared with the quantum yields for radical formation and photoejection of electrons, it is found that there is good agreement only for the nitrogen-saturated case. In air-equilibrated solutions of tryptophan, there is a large disparity between the measured degradation quantum yields and those for photoejection of electrons and radical formation. Oxygen, therefore, is playing a major role in the photochemical decomposition and it is proposed that the major reaction which occurs, under normal atmospheric conditions, is the reaction of the lowest triplet excited state of tryptophan with oxygen.
Preliminary photolysis-product distributions against pH are discussed, and indicate that a total of nine major products are formed in the presence of oxygen.     

丙烯聚合络合催化剂形成过程的研究

以倍半物为还原剂还原TiCl_4,经异戊醚络合处理,然后在TiCl_4己烷溶液中35℃条件下热处理,制得对丙烯聚合具有高活性和高定向度的络合催化剂。研究了制备过程中各步反应产物的组成和结构特征,并讨论了TiCl_3低温晶型转变机理。     

THE ROLE OF HYDRATION IN THE PHOTOTRANSFORMATION OF PHYTOCHROME

Abstract— Changes in the visible absorption spectrum and in phototransformation of phytochrome have been found to be associated with dehydration and rehydration. These spectral properties explain the previously reported rapid appearance of phytochrome in imbibing seeds. No evidence was found for the orientation of the phytochrome chromophore in gelatin films or in preparations subjected to a shearing force.     

STEPS IN THE POPULATION OF THE EMITTER IN THE BACTERIAL LUCIFERASE REACTION

Abstract— The reaction of luciferase-bound flavin hydroperoxide with both I-¹H and 1–²H decanal has been examined at 2°C in both low (0.01 M ) and high (0.35 M ) phosphate buffer, pH 7, where the kinetics and deuterium isotope effects are quite different. Upon reaction in both buffers there are rapid (<2 ms) increases in absorption at both 380 and W nm, followed by decay over the subsequent seconds and minutes. The changes at 380 nm exhibit a primary isotope effect and are rapid compared to bioluminescence, indicating that the scission of the aldehyde C — H bond occurs prior to the step responsible for populating the electronically excited state. However, the final absorbance change at 600 nm decays in parallel to bioluminescence under the several different conditions studied, suggesting the involvement of a long-wavelength absorbing flavin species in the production of, the excited state. Evidence is also presented indicating that under certain conditions there may be two (sequential) steps, each of which exhibits a primary isotope effect involving the same H atom.     

合金中痕量元素标准物质研制进展

通过对国内外高温合金、铝合金痕量元素标准物质的比较,评述了我国合金中痕量元素标准物质在种类、量值水平及不确定度等方面的进展。     

THE ROLE OF SURFACE FORCES IN FOULING OF STAINLESS STEEL IN THE DAIRY INDUSTRY

The major cause of fouling of processing equipment in the Dairy Industry used for the pasteurization of milk and whey resides in particle formation in the bulk of the dairy fluid. As a result of processing at elevated temperatures, the heat sensitive whey proteins aggregate and calcium phosphate becomes insoluble and precipitates. Hence, the process of fouling can be understood as a subsequent deposition of these particles onto the heating surface.

On the basis of model calculations it is demonstrated that at neutral pH both the calcium phosphate particles, and to a limited extent also the whey proteins, are attracted by stainless steel. This is the result of the monopolar character of steel, which leads in an aqueous environment to an attractive Lewis acid/base interaction term with both components. In combination with the Lifshitz-van der Waals contribution both contributions to the overall interaction are sufficiently large to overcome the electrostatic repulsion at the given pH.

This result points to the specific role of stainless steel in the process of fouling and has far reaching consequences for the way the process of fouling can be controlled as the behaviour of the contaminants, e.g. their heat sensitivity, can not be altered.     

ON THE ROLE OF TYROSINE IN THE PHOTOCYCLE OF BACTERIORHODOPSIN

Abstract -The rate of formation of the M intermediate ( k _M) in the photocycles of bacteriorhodopsin (bR₅₇₀) and of nitrated bacteriorhodopsin (bR₅₃₂ⁿ), is measured over the range between pH 6.5 and 11.5. In the case of bR₅₇₀, k _M is markedly pH dependent, exhibiting a titration-like curve with pK ∽ 10.3. The pH dependency is completely eliminated by nitration. On the basis of previous work by Lemke and Oesterhelt (1981), the effect is attributed to the specific modification of the Tyr 26 residue. The data are rationalized by a mechanism in which deprotonation of Tyr 26 at the stage of the L intermediate constitutes a prerequisite for deprotonation of the retinal-lysine SchifT base. Both reactions are intimately associated with the photo-induced proton pump mechanism.