光化学反应在流动注射分析中的应用研究：Ⅳ.亚甲基蓝光化学反应体…

基于抗坏血酸光化学还原亚甲基蓝光化学反应，建立了流动注射光化学反应测定抗坏血酸的新方法，方法线性范围为０．１２－５．６０μｇ／ｍｌ，进样频率为５６－６０次／ｈ。应用于维生素Ｃ片剂中抗坏血酸的测定，结果满意。     

光化学反应在流动注射分析中的应用研究V.硝酸根-鲁米诺光化学反应体系化学发光法测定痕量硝酸根

基于紫外光照射下硝酸根能够转化生成过氧化亚硝酸酯及过氧化亚硝酸酯氧化鲁米诺而产生化学发光,建立了流动注射光化学反应测定痕量硝酸根的新方法。测定硝酸根的线性范围是5×10(-8)～1×10(-4)mol/L,进样频率为60～80次/h.     

光化学反应在流动注射分析中的应用研究 Ⅲ.甲基橙光化学反应体系测定亚硝酸根、硝酸根和铁(Ⅲ)

基于NO_2~-、NO_3~-和Fe(Ⅲ)对甲基橙光化学褪色反应的催化作用,利用自制流通式光化学反应器,建立了流动注射光化学反应同时测定NO_2~-和NO_3~-以及测定Fe(Ⅲ)的新方法。测定NO_2~-和NO_3~-的线性范围都是0.1～3.2mg/L,每小时可测30～40个样品,测定Fe(Ⅲ)的线性范围为0.06～1.2mg/L,进样频率为60～80次/h。应用于蔬菜中NO_2~-、NO_3~-的测定和茶叶中铁的测定,结果满意。     

光化学反应中照射光强的测定

化学光强计是利用某些光化学反应中反应物的消耗(或产物的生成)和吸收的光量子具有定量关系,来测定照射光强的一种比较精确的方法,它是测定光化学反应量子收率的重要手段。在各种化学测定光强的方法中,二苯酮/二苯甲醇是一种常用的方法,它用于测定335—360nm波长的光强,因此可以在亮室操作,使用方便,但不及草酸高铁钾测量的范围广泛。 Moore等人对二苯酮和二苯甲醇的光化学反应进行了研究。在光照下二苯酮吸收335—360nm相应     

乙烯雌酚光化学反应的低温燐光分析

乙烯雌酚 (Diethylstilbestrol)是合成的类雌激素 ,光极弱。在 0 .1mol/LNaOH中经UV光照 2 0min后反式异构化为顺式 ,产生极强的光 (λex/λem=32 0 /4 5 0nm ,τ =0 .89s) ,不同浓度激素 (0 .1mg/L～1g/L)UV光照后与光强度呈线性关系 ,检出限为 1μg/L。光化学反应后产物在室温放置 2星期不变。乙烯雌酚在酸中经UV光照 1h后光 (λex/λem=310 /4 6 0nm ,τ =1.0 6s)也增加 ,为碱中光照后的 1/15 ,乙烯雌酚量 (40～ 1mg/L)与光强度呈线性相关 ,检出限为 0 .15mg/L。将在HCl中光化学反应产物 ,加碱碱化后光明显增强 (4倍 ) ,在碱中UV光照后加酸酸化 ,则光下降 7倍 ,是酚羟基离子化与否的结果。本法用光化学反应不仅产生强的光 ,且提高分析的专一性。对市售乙烯雌酚片分析 ,含 0 .995± 0 .0 4 7mg/片 ,与标示值 (1mg/片 )相符。也可用于生物组织中乙烯雌酚的分析测定。     

光化学反应的从头算研究

光化学反应是最基本也是最重要的物理化学过程之一,在诸多领域有着广泛的应用。由于计算方法的限制以及光化学反应过程的错综复杂性,光化学反应机理的从头算研究是极具挑战性的国际前沿课题之一。本文综述了近20年来羰基化合物光化学反应机理从头算研究的一些进展,总结了羰基化合物电子激发态的特性和光化学反应过程的规律性,为深入研究光化学反应提供一些有用的信息。     

柱后光化学反应荧光检测高效液相色谱法测定茶叶中的五种菊酯类农药残留

建立了柱后光化学反应荧光检测高效液相色谱法测定茶叶中菊酯类农药残留的方法。采用Hypersil ODS色谱柱，以乙腈／水为流动相、梯度洗脱进行分离。用自制的光化学反应器作为荧光衍生装置，优化了柱后光化学反应的实验条件，并用于茶叶样品中菊酯类农药残留的测定。方法的检出限为0．012～0．048μg／g(干重)；线性范围0．040～8．0μg／g，相对标准偏差3．4％～6．4％(0．1mg／L，n=8)。     

受限介质中光化学反应的研究

提高化学反应的选择性始终是化学家关注的热点. 本工作以光Fries重排反应、Norrish/Yang光环化反应、9-取代蒽衍生物的光二聚反应以及不对称光化学反应为例, 结合近年来在受限介质中光化学反应研究的最新进展, 总结了利用受限介质控制化学反应选择性的一般规律.     

光化学反应在流动注射分析中的应用研究：Ⅲ.甲基橙光化学反应…

基于ＮＯ２＾－，ＮＯ３＾－和Ｆｅ（Ⅲ）对甲基橙光化学褪色反应的催化作用，利用自制流通式光化学反应应器，建立了流动注射光化学反应同时测定ＮＯ２＾－和ＮＯ３＾－以及测定Ｆｅ（Ⅲ）的新方法。测定ＮＯ２＾－和ＮＯ３＾－的线性范围都是０．１－３．２ｍｇ／Ｌ，每小时可测３０－４０个样品。测定Ｆｅ（Ⅲ）的线性范围为０．０６－１．２ｍｇ／Ｌ，进样频率为６０－８０次／ｈ。应用于蔬菜中ＮＯ２＾－，ＮＯ３＾－的测定和茶     

芳砜在微环境中的光化学反应

本文研究了十二烷基磺酸钠-正戊醇-水三组分体系相图, 并用小角度X衍射仪确定了相图中液晶区域为层状。在不同微环境(W/O型微乳液、液晶、O/W型微乳液)中, 研究了对甲基苄基苄基砜(ASO2B)的光化学反应影响。结果发现微环境对反应产物分布(笼效应)有很大影响。外加磁场明显降低笼效应。证实了芳砜的光化学反应经历自由基中间体, 并且反应的激发态为三重态。     

Kinetic spectrofluorimetric determination of trace ascorbic acid based on its inhibition on the oxidation of pyronine Y by nitrite

A highly sensitive spectrofluorimetric method is proposed for the determination of trace amount of ascorbic acid using a new indication. The method is based on the inhibition of ascorbic acid on the oxidation of pyronine Y (PRY) by nitrite. The detection limit for ascorbic acid is 0.012 microg ml(-1), the linear range of the determination is 0.02-0.36 microg ml(-1). Analytical parameters, such as reagent concentration, pH, reaction temperature and time, were optimized. The relative standard deviations of eleven replication determinations of 0.12 and 0.24 microg ml(-1) ascorbic acid were 1.4 and 0.72%, respectively. This method has been used to determine ascorbic acid in pharmaceuticals, vegetables, fruits and soft drink with satisfactory results.     

Kinetic determination of ascorbic acid by the BZ oscillating chemical system

A new analytical method for the determination of ascorbic acid by the perturbation caused by different amounts of ascorbic acid on the BZ oscillating chemical system involving the Ce(IV)-catalyzed reaction between potassium bromate and malonic acid in a acidic medium is proposed. The method relies on the linear relationship between the change in the oscillation amplitude of the chemical system and the concentration of ascorbic acid, which is in this work exposed for the first time. The calibration curve is linearly proportional to the concentration of ascorbic acid over the range 3.5x10(-6)-4.7x10(-4) M, with the regression coefficient is 0.9975. Two different methodologies were used to address the determination. Some aspects of the potential mechanism of action of ascorbic acid on the BZ oscillating chemical system are discussed in detail.     

Kinetic spectrophotometric determination of ascorbic acid by reduction of toluidine blue

A simple kinetic method is described for the determination of ascorbic acid. The procedure is based on the reduction of toluidine blue with ascorbic acid. The rate of reaction is followed by measuring the decrease in absorbance of toluidine blue (lambda(max) = 600 nm) as a result of its decolorization upon reduction by ascorbic acid. Ascorbic acid in the range of 3-35 microg/ml was determined using slope and fixed time methods of analysis, while the variable time method allowed the determination of 5-50 microg/ml of ascorbic acid. The percent relative standard deviation of the method varied from 0.78 to 1.32% depending on the kinetic method used. The high sensitivity of the method also allows determination of low levels of ascorbic acid in some fruits and vegetables such as dew melon, water melon, parsley and coriander.     

Indirect Flow-Injection Analysis of Ascorbic Acid by Photochemical Reduction of Methylene Blue

Abstract

Ascorbic acid was determined indirectly by spectrophotometry at 666 nm based on the photochemical reduction of methylene blue using flow-injection analysis. The carrier stream was 12.7 μgml^?1 methylene blue in phthalate-HCl buffer solution at pH 3.2. The reactor was irradiated with a 500-Watt halogen lamp to facilitate the development of the photochemical reaction. The system allows determination of ascorbic acid in the range 0.18–6.12 μgml^?1 with relative standard deviations of 2.09 and 0.31% for 1.97 and 4.92 μgml^?1 samples, respectively, and a sampling frequency of 50–55 h^?1. The proposed method was applied successfully to the determination of ascorbic acid in vitamin C tablets.     

Kinetic-spectrophotometric determination of ascorbic acid by inhibition of the hydrochloric acid-bromate reaction

A new analytical method was developed for the determination of ascorbic acid in fruit juice and pharmaceuticals. The method is based on its inhibition effect on the reaction between hydrochloric acid and bromate. The decolourisation of Methyl Orange by the reaction products was used to monitor the reaction spectrophotometrically at 510 nm. The linearity range of the calibration graph depends on bromate concentration. The variable affecting the rate of the reaction was investigated. The method is simple, rapid, relatively sensitive and precise. The limit of detection is 7.6 x 10(-6) M and calibration rang is 8 x 10(-6)-1.2 x 10(-3) M ascorbic acid. The relative standard deviation of seven replication determinations of 8 x 10(-6) and 2 x 10(-5) M ascorbic acid was 2.8 and 1.7%, respectively. The influence of potential interfering substance was studied. The method was successfully applied for the determination of ascorbic acid in pharmaceuticals.     

Spectrophotometric determination of ascorbic acid in pharmaceutical preparations and fruit juices

Conditions were established for the determination of ascorbic acid using phsophovanadotungstic acid as reagent. The method was applied to the determination of ascorbic acid in pure form, pharmaceutical preparations and fruit juices. The method is sensitive (2-24 micrograms ml-1 of ascorbic acid) and rapid and tolerates the presence of common ingredients usually found in fruit juices. The results obtained with the proposed method showed good agreement with those given by the standard method.     

Fluorimetric determination of total ascorbic acid by a stopped-flow mixing technique

A simple, rapid and automatic fluorimetric method for the determination of total ascorbic acid is described. The method makes use of the stopped-flow mixing technique in order to achieve the rapid oxidation of ascorbic acid by dissolved oxygen to dehydroascorbic acid, which then reacts with o-phenylenediamine to form a fluorescent quinoxaline. The initial rate and fluorescence signal of this system are directly proportional to the ascorbic acid concentration. The calibration graph was linear over the range 0.1-30 microg ml(-1) (kinetic method) and 0.25-34 microg ml(-1) (equilibrium method). The precision (% RSD) was close to 0.5%. The method has been used for the determination of ascorbic acid in pharmaceutical formulations, fruit juices, soft drinks and blood serum.     

Spectrophotometric determination of ascorbic acid with potassium hexacyanoferrate(III)

A new, simple and rapid method of determination of ascorbic acid in amounts of 45-360 mug is described. The ascorbic acid is determined spectrophotometrically at 420 nm from the decrease in absorbance it causes in 1 x 10(-3)M hexacyanoferrate(III) in McIlvaine buffer at pH 5.2. The proposed method is suitable for the determination of ascorbic acid in pharmaceutical preparations and probably natural products.     

Kinetic method for determination of ascorbic acid on flow injection system by using its catalytic effect on the complexation reaction of an ultra sensitive colorimetric reagent of porphyrin with Cu(II)

A kinetic method performed on a flow injection system is described for the determination of ascorbic acid by using its catalytic effect on the complexation reaction of Cu(II) with 5,10,15,20-tetrakis(4-N-trimethyl-aminophenyl)porphyrin. The characteristic spectrum of porphyrin (Soret band), which shows intense absorption around 400 nm (epsilon>2.0 x 10(5) cm(-1)M(-1)), was used first time for determining ascorbic acid. By incorporating the complexation reaction into a flow injection system, ascorbic acid could be determined either over a broad dynamic range of 0.1-1000 microg/ml or at a trace level below 5 ng/ml. Good repeatability was also achieved by testing a working standard of 0.1 microg/ml with 10 injections at a throughput of 35 h(-1), obtaining a relative standard deviation of 0.11%. Substances like amino acids, vitamins, sugars, organic acids and metal ions, showed no or little interference even present at high concentrations. The method was validated in the determination of ascorbic acid contents of some commercially available soft drinks by comparison with the official 2,6-dichloroindophenol method with reasonable agreement.     

Determination of ascorbic acid in elemental diet by high-performance liquid chromatography with electrochemical detection.

Determination of ascorbic acid in a multi-component elemental diet was performed by high-performance liquid chromatography with electrochemical detection. This method is suitable for the routine determination of ascorbic acid in elemental diet because it is simple, rapid, sensitive, highly selective and reproducible. The calibration graph of ascorbic acid was linear in the range 0-1.0 micrograms. The recovery of ascorbic acid was over 95% by the standard addition method. There was good agreement between the concentrations of ascorbic acid stated and found.