微量金测定中的某些问题

编辑同志: 在微量金的测定中,有两个问题值得商榷。1.试样的分解目前我国普遍使用王水溶矿。在快速分析中,也有人主张用盐酸+过氧化氢、盐酸+氯酸钾、盐酸+高锰酸钾等方法。但是,有人认为用王水分解试样,金的结果有偏低现象。我们以硅酸盐试样为对象,进行了几种溶矿方法的比较试验。结果见表1。     

碘化钾碘蓝分光光度法测定微量过氧化氢

基于在酸性介质中 ,过氧化氢与碘化钾、淀粉的显色反应 ,建立了碘化钾碘兰分光光度法测定微量过氧化氢方法。过氧化氢浓度在 0～ 2 5μg/2 5m L范围内有良好的线性关系 ,方法的相对标准偏差 1 .2 % ,回收率 97.2 %～1 0 1 .2 % ,检出限为 2 .0× 1 0 -3 mg/L。并应用于雨水、空气中微量过氧化氢的测定。     

高锰酸钾法、碘量法和铈量法测定过氧化氢的比较

过氧化氢是一种常用的化学试剂，可作为消毒剂、杀菌剂、脱氧剂、漂白剂和聚合反应的引发剂等。目前过氧化氢的分析方法有高效液相色谱法、紫外分光光度法、流动注射-分光光度法和化学滴定法、高锰酸钾法、碘量法和硫酸铈法等。本文分别对高锰酸钾法、碘量法和铈量法测定过氧化氢进行比较。     

萃取-催化氧化光度法测定H2O2的羟基自由基 (Ⅱ)

利用混合稀土与微量过氧化氢催化氧化二苯基碳酰肼，建立了萃取－催化氧化光度法测定过氧化氢的羟基自由基的新方法，该法具有仪器简单，体系稳定，操作方便等优点，非常适合于筛选羟基消除剂。     

靛红褪色光度法测定过氧化氢

过氧化氢是一种无公害的强氧化剂 ,可用作漂白剂、消毒剂、脱氧剂、液体燃料推进剂等 ,大气及雨水中的过氧化氢还与酸雨的形成有密切的关系 ,因此 ,深入研究微量过氧化氢的测定方法是十分必要的。微量过氧化氢的测定 ,可用化学发光分析法[1 ] 或催化极谱法[2 ] ,但褪色光度法测定过氧化氢未见报道。本文经试验发现 ,在 p H=3.5的乙酸 -乙酸钠缓冲溶液中 ,在 1 0 0°C加热的条件下 ,过氧化氢能与靛红发生褪色反应 ,其反应速度在一定范围内和过氧化氢的浓度成正比 ,据此 ,建立了褪色光度法测定痕量过氧化氢的新方法。方法的灵敏度高 ,选择性…     

碘量滴定法测定过氧化氢溶液浓度的改进

研究了用碘量滴定法测定过氧化氢浓度时，试剂的加入顺序和放置时间对测定结果的影响。结果表明，在用碘量滴定法测定过氧化氢浓度的过程中，酸化条件下，I^-与H2O2反应的最佳时间为5～10min。与高锰酸钾氧化法相比，碘量法测定效果较好一些。     

利用钛—硫氰酸盐—二安替比林甲烷三元络合物微量钛的萃取分光光度测定

目前,测定铬铁矿中微量钛的常用比色法有过氧化氢法、变色酸法、钛铁试剂法及二安替比林甲烷法。这些方法用于测定微量钛,灵敏度尚嫌偏低。为了提高灵敏度,有关文献中提出了用三元铬合物进行分光光度测定。这些方法有钛—DAPM—二氯化锡三元铬合物法、钛—硫氰酸盐—二苯胍法、钛—硫氰酸盐     

改进的高锰酸钾法滴定微量甲酸根的可行性研究

对常用高锰酸钾氧化还原法进行了改进,并与微量滴定法相结合,测定微量甲酸根含量.从精密度、准确度、线性范围及灵敏度4个方面分析了该方法的可行性,并将该方法分析结果与气相色谱法分析结果进行了比对.结果表明,该法对3种浓度的甲酸溶液测定结果的相对标准偏差为0.84%～1.8%(n=6).线性范围为100～1 100 mg/L,平均回收率为95.8%.     

离子色谱法测定高锰酸钾中以及高浓度硝酸根中的高氯酸根

地下水和地表水中的高氯酸根危害人体健康。由于环境水样中的高浓度硝酸根和高锰酸钾基体干扰高氯酸根的测定,本方法通过滴加一定量的过氧化氢以除去高锰酸根,然后对样品进行离心来消除干扰。运用Dionex IonPac AS11型阴离子分离柱,流动相为8mmol/LKOH溶液,大体积(200μL)进样,抑制性电导检测器来测定有高锰酸钾以及高浓度硝酸根干扰的水中痕量高氯酸根。本方法的线性范围0.5~20mg/L,检出限为5μg/L。     

微量铜的催化光度测定

动力学方法测定微量铜,有人研究了以过氧化氢或过硫酸盐为氧化剂的催化体系。在工作中我们发现酸性介质中由于铜的催化作用,空气中的氧可使邻苯二胺氧化生成黄色的产物,并研究了邻苯二胺和铜的反应条件及反应级数,拟定了测定微量铜的分析步骤,结果表明方法灵敏度和重现性均较满意,能测     

漂白粉中总钙量测定方法的改进

采用过氧化氢去除漂白粉中的有效氯,直接测定漂白粉中总钙量,探讨过氧化氢用量,反应时间,试剂加入顺序对实验结果的影响。结果表明,当过氧化氢用量为1.5～4.5 mL,反应时间为3 min时,试剂加入顺序为：过氧化氢―氨性缓冲溶液―Mg2＋-EDTA―铬黑T,体系对测定结果影响最小。用该方法测定了漂白粉中总钙量,其相对标准...     

Optimization of two methods for the analysis of hydrogen peroxide: high performance liquid chromatography with fluorescence detection and high performance liquid chromatography with electrochemical detection in direct current mode

Two complementary methods were optimized for the separation and detection of trace levels of hydrogen peroxide. The first method utilized reversed-phase high-performance liquid chromatography with fluorescence detection (HPLC-FD). With this approach, hydrogen peroxide was detected based upon its participation in the hemin-catalyzed oxidation of p-hydroxyphenylacetic acid to yield the fluorescent dimer. The second method utilized high performance liquid chromatography with electrochemical detection (HPLC-ED). With this approach, hydrogen peroxide was detected based upon its oxidation at a gold working electrode at an applied potential of 400 mV vs. hydrogen reference electrode (Pd/H(2)). Both methods were linear across the range of 15-300 μM, and the electrochemical method was linear across a wider range of 7.4-15,000 μM. The limit of detection for hydrogen peroxide was 6 μM by HPLC/FD, and 0.6 μM by HPLC/ED. A series of organic peroxides and inorganic ions were evaluated for their potential to interfere with the detection of hydrogen peroxide. Studies investigating the recovery of hydrogen peroxide with three different extraction protocols were also performed. Post-blast debris from the detonation of a mixture of concentrated hydrogen peroxide with nitromethane was analyzed on both systems. Hydrogen peroxide residues were successfully detected on this post-blast debris.     

Fluorometric determination of hydrogen peroxide using resorufin and peroxidase

A fluorometric method for the determination of hydrogen peroxide using resorufin as a substrate for peroxidase is described. Two procedures were developed for the determination of hydrogen peroxide. One involves the addition of hydrogen peroxide sample to a solution of peroxidase and resorufin in phosphate buffer, pH 6.4. Fluorescence measurements are performed before and after hydrogen peroxide addition. The within-run CVs for final concentrations of hydrogen peroxide of 200 and 40 nmol/liter were 1.7 and 7.6%, respectively, and the limit of quantitation was 9 nmol/liter. The second procedure, in which the initial reaction of hydrogen peroxide with resorufin is performed in citrate buffer at pH 4.5, and then the fluorescence is measured after the pH is adjusted to 9.2 with borate buffer, has a limit of quantitation of 4.4 nmol/liter with a within-run CV of 6.5% for a final hydrogen peroxide concentration of 20 nmol/liter. The method is linear at least up to 1 μmol/liter.     

Fluorimetric determination of hydrogen peroxide in water using acetaminophen

A fluorimetric procedure for the determination of hydrogen peroxide, based on the oxidation of acetaminophen with hydrogen peroxide in acidic medium, is described. The calibration graph was linear in the range 5.0 x 10(-8) - 2.4 x 10(-5) M hydrogen peroxide at an emission wavelength of 333 nm with excitation at 298 nm. The method has been applied to the determination of hydrogen peroxide in rain water, and the recoveries in milk samples were good.     

Hydrogen peroxide synthesis by direct photoreduction of 2-ethylanthraquinone in aerated solutions

A new synthesis method of hydrogen peroxide was investigated by the photoreduction of 2-ethylanthraquinone (AQ) in water-insoluble organic solvents. Through optimizing the photoreduction condition including solvent, atmosphere and irradiated time, the photolysis system of 1,3,5-trimethylbenzene/trioctyl phosphate (3:1) solvent mixture under oxygen atmosphere was found to give a high yield of hydrogen peroxide. Furthermore, the formation mechanism of hydrogen peroxide was proposed, i.e. photoreduction and subsequent oxidation of AQ. The photoreduction of 2-ethylanthraquinone undergoes the hydrogen abstraction from solvent to form the anthrahydroquinone, which is subsequently oxidized by oxygen to give hydrogen peroxide.     

Determination of hydrogen peroxide by iron(III) complex of thiacalix[4]arenetetrasulfonate on a modified ion-exchanger with peroxidase-like catalytic activity.

An iron(III) complex of thiacalix[4]arenetetrasulfonate on a modified anion-exchanger (Fe3+-TCAS(A-500)) has shown high peroxidase-like activity at pH 5 - 6 for the reaction of quinoid-dye formation between 3-methyl-2-benzothiazolinone hydrazone and N-(3-sulfopropyl)aniline in the presence of hydrogen peroxide. Utilizing the peroxidase-like activity of Fe3+-TCAS(A-500) for this reaction, a method using Fe3+-TCAS(A-500) was applied for the spectrophotometric determination of hydrogen peroxide. The calibration curve by the method using Fe3+-TCAS(A-500) was linear over the range from 1 to 10 microg of hydrogen peroxide in a 1 ml sample solution. The apparent molar absorptivity for hydrogen peroxide was 2.4 x 10(4) l mol(-1) cm(-1). which was about 80% of that by peroxidase under the same conditions. This determination method of hydrogen peroxide using Fe3+-TCAS(A-500) was applied for the determination of glucose in diluted normal and abnormal control serum I and II.     

Determination of hydrogen peroxide by xenon trioxide oxidation

Aqueous xenon trioxide solution has been used as the oxidizing agent in three precise methods of analysis for hydrogen peroxide. A catalytic method, which utilizes hydrogen peroxide to initiate the reaction between t-butanol and xenon trioxide, is described for determining amounts of hydrogen peroxide as low as 0.9 microg or 36 parts per milliard (ppM). A direct spectrophotometric titration was found to have a lower limit of about 50 microg, or 20 ppM. An indirect titrimetric method was also used to determine hydrogen peroxide in amounts as low as 50 microg with a relative standard deviation of 4% which decreased to 1 % for amounts over 200 microg.     

Simple and rapid determination of hydrogen peroxide using phosphine-based fluorescent reagents with sodium tungstate dihydrate.

A simple batch method for the fluorometric determination of hydrogen peroxide using phosphine-based fluorescent reagents has been developed. A rapid, mild and selective derivatization reaction was achieved by adding sodium tungstate dihydrate to the reaction mixture of hydrogen peroxide and a phosphine-based fluorescent reagent. When 4-diphenylphosphino-7-methylthio-2,1,3-benzoxadiazole was used as a reagent, the derivatization reaction was completed after 2 min at room temperature. The calibration curve was linear between 12.5 and 500 ng hydrogen peroxide in a 10 microL sample solution. This method is accurate and has potential for on-line applications.     

Peroxide-Ammonia Delignification of Pine Wood

Oxidative delignification of pine wood by hydrogen peroxide in aqueous ammonia was studied. A new method for producing cellulose and N-containing organic fertilizers was developed. It was demonstrated that a solution of hydrogen peroxide (3-9%) in aqueous ammonia delignified extensively wood to produce cellulose in yields up to 54.6% with a residual lignin content up to 1.1%. The process of pine-wood delignification by hydrogen peroxide in aqueous ammonia was described satisfactorily by a first-order kinetic equation.     

Potentiometric flow-injection determination of trace hydrogen peroxide based on its induced reaction in iron(III)-iron(II) potential buffer containing bromide and molybdenum(VI)

A rapid and highly sensitive potentiometric flow-injection method for the determination of trace hydrogen peroxide was developed by use of an Fe(III)-Fe(II) potential buffer solution containing bromide and Mo(VI). The analytical method was based on a linear relationship between a concentration of hydrogen peroxide and a largely transient potential change of an oxidation-reduction potential electrode due to bromine generated by the reaction of hydrogen peroxide with the potential buffer solution. The oxidation of bromide to bromine by hydrogen peroxide occurred very rapidly with the assistance of Mo(VI) when Fe(II) existed in the potential buffer solution. It was estimated by batchwise experiments that hydroxyl radical, OH., was generated by the reaction of hydrogen peroxide with Fe(II) as an intermediate, and subsequently oxidized bromide to bromine. In a flow system, analytical sensitivities to hydrogen peroxide obtained by the detection of the transient change of potential were enhanced about 75 fold compared with those obtained by using the potential change caused by the reaction of hydrogen peroxide with the potential buffer solution without bromide and Mo(VI). Sensitivities increased with decreasing concentration of the Fe(III)-Fe(II) buffer in the reagent solution. The detection limit (S/N = 3) of 4 x 10(-7) M (13.6 ppb) was achieved by using the 1 x 10(-4) M Fe(III)-Fe(II) buffer containing 0.4 M NaBr, 1.0 M H(2)SO(4) and 0.5% (NH(4))(6)Mo(7)O(24). Analytical throughput was approximately 40 h(-1) and the RSD (n = 6) was 0.6% for measurement of 4 x 10(-6) M hydrogen peroxide. The proposed method was applied to the determination of hydrogen peroxide in real rainwater samples, and was found to provide a good recovery for H(2)O(2) added to rainwater samples.