Effects of Standing Time during Pretreatment on the Nitrite Concentration Detected by Spectrophotometric Method

Food safety problems caused by excessive nitrite addition have been frequently reported and the detection of nitrite in food is particularly important. The standing time during the pretreatment of primary sample has a great influence on the concentration of nitrite tested by spectrophotometric method. In this context, three kinds of food samples are prepared, including canned mustard, canned fish and home-made pickled water. A series of standing times are placed during the sample pretreatments and the corresponding nitrite contents in these samples are detected by spectrophotometric method based on N-ethylenediamine dihydrochloride. This study aims to find out a reasonable standing time during the pretreatment of food sample, providing influence factor for precise detection of nitrite.

Catalytic spectrophotometric determination of trace selenium in microemulsion after separation and enrichment by SDG

A new catalytic spectrophotometric method was developed for the determination of trace amount of Se（Ⅳ） in microemulsion medium. The method is based on the catalytic effect of traces of Se（Ⅳ） on the oxidation of 2＇,4＇-dichlorophenylfluomne （p-CPF） by potassium bromate with HNO3 as an activator in the presence of nonionic microemulsion medium. Under optimum conditions, the calibration graph is linear in the range of 0.4-15 μg·L^-1 of Se（Ⅳ） at 480 nm. The detection limit achieved is 9.86 × 10^-10μg·L^-1. Samples were dissolved and the obtained trace Se（Ⅳ） was separated and enriched by sulphydryl dextrane gel （SDG）. The method has been applied for determination of trace selenium with satisfactory results.

Solid-phase extraction of trace Au(Ⅲ) with SDG and determination by the catalytic spectrophotometric method

The new catalytic kinetic spectrophotometric method for Au（III） determination was developed and validated. It was based on the catalytic effect of gold on the oxidation of sudan red III by ammonium peroxodisulfate （（NH4）2S2O8） with nitrilo triacetic acid as an activator in microemulsion and H2SO4 medium. Under optimum conditions, there was the linearity of the calibration curve in the concentration range from 0 to 20 μg/L Au（Ⅲ） at 520 nm. The relative standard deviation was 3.0% with a correlation coefficient of 0.9986. The detection limit achieved was 9.75 × 10^-5 μg/mL. A new method using a column packed with sulfhydryl dextrose gel （SDG） as a solid-phase extractant has been developed for the preconcentration and separation of Au（Ⅲ） ions. The method has been applied to the determination of trace gold with satisfactory results.

Reaction mechanism of methyl nitrite dissociation during co catalytic coupling to dimethyl oxalate:A density functional theory study

Dissociation of methyl nitrite is the first step during CO catalytic coupling to dimethyl oxalate followed by hydrogenation to ethyl glycol in a typical coal to liquid process. In this work, the first-principle calculations based on density functional theory were performed to explore the reaction mechanism for the non-catalytic dissociation of methyl nitrite in the gas phase and the catalytic dissociation of methyl nitrite on Pd(111) surface since palladium supported on alpha-alumina is the most effective catalyst for the coupling. For the non-catalytic case, the calculated results show that the CH_3O–NO bond will break with a bond energy of 1.91 eV, and the produced CH_3O radicals easily decompose to formaldehyde, while the further dissociation of formaldehyde in the gas phase is difficult due to the strong C–H bond. On the other hand, the catalytic dissociation of methyl nitrite on Pd(111) to the adsorbed CH_3O and NO takes place with a small energy barrier of 0.03 eV. The calculated activation energies along the proposed reaction pathways indicate that(i) at low coverage, a successive dehydrogenation of the adsorbed CH_3O to CO and H is favored while(ii) at high coverage, hydrogenation of CH_3O to methanol and carbonylation of CH_3O to methyl formate are more preferred. On the basis of the proposed reaction mechanism,two meaningful ways are proposed to suppress the dissociation of methyl nitrate during the CO catalytic coupling to dimethyl oxalate.

Catalytic Spectrophotometric Determination of Ultratrace Amounts of Silver with Solubilizing Effect of Nonionic Surfactant

The synthesis and analytical properties of 4,4'-bis(antipyrinyl-4-diazoamino)biphenyl (BAPDAB) were described for the first time. A catalytic kinetic method for thedetermination of silver was proposed. In the presence of Triton X-100 as a solubilizing agent and2,2'-dipyridyl as an activator, silver has a very strong catalytic effect on oxidative decolorationof BAPDAB by persulfate in acetic acid medium. The reaction was followed spectrophotometrically bymeasuring the decrease of absorbance of BAPDAB at 478 nm and 50 ℃. The calibration graphs are ofgood linearity in the range of 8.0 * 10^(-10)-1.0 * 10^(-6) mol/L by a fixed time method. The limitof detection is down to 5.0 * 10^(-10) mol/L. The catalytic reaction is pseudo-first-order withrespect to silver, which in real samples was determined with satisfactory results.

Studies on the roles of vanadyl sulfate and sodium nitrite in catalytic oxidation of benzyl alcohol with molecular oxygen

An efficient catalytic system consisting of vanadyl sulfate/sodium nitrite was disclosed previously for the oxidation of benzylic alcohols into aldehydes with molecular oxygen.However,the roles of catalyst components were not investigated.In this paper,we examined catalytic oxidation of benzyl alcohol as a model reaction,especially by infrared spectroscopy.The role of each component is discussed including nitrite,vanadyl,sulphate,and water.Sodium nitrite could be converted into nitrate and nitric acid.The vanadium(IV)could be smoothly oxidized into vanadium(V)under mild and acidic conditions without any organic ligands.The transformation of sulfate and bisulfate,the cessation of an induction period,and the oxidation of benzyl alcohol were closely interrelated.The multiple roles of water are discussed,including reduction of the induction period,participation in redox cycles of nitric compounds,deactivation of vanadium,and as a byproduct of oxidation.This study contributes to further development of aerobic oxidation using vanadium based catalysts.

STUDY OF KINETIC ANALYTICAL METHOD BASED ON CATALYTIC REACTIONS

In this thesis a reviwe is presented for the advances of catalytic spec trophotometric method, three new catalytic reaction systems were presented, and its rela live catalytic spectrophotometric methods have been established by flow injection tech nique. Particulary the relative chemometric methods and theories were used in the field of kinetic - catalytic analysis, in order to solve the problems of multicomponents analysis.

催化动力学光度法测定痕量亚硝酸根

在冰乙酸介质中,利用亚硝酸根催化条件下,溴酸钾氧化茜素红的褪色反应,建立催化动力学光度法,对痕量NO_(2)^(-)进行测定.通过单因素实验得到了各种成分的加入量、反应温度和反应时间等最佳条件.结果发现,在反应体系中,茜素红浓度与NO_(2)^(-)含量之间线性关系良好,在0.02~0.14μg/mL范围内,线性回归方程为ln(A_(0)/A)=1.43 c NO_(3)^(-)(μg/mL)+0.00859,相关系数r^(2)为0.9970,检出限为5.25×10^(-3)μg/mL.该方法操作简单、稳定性好.

亚硝酸还原酶研究进展

亚硝酸还原酶作为一种能催化亚硝酸盐降解的金属酶,在食品、环境等领域具有广泛的应用前景。根据其蛋白质结构及催化机制,亚硝酸还原酶可分为铜型(CuNiRs)、细胞色素cd_(1)型(cd_(1)NiRs)、多聚血红素c型(ccNiRs)和铁氧还蛋白依赖型(FdNiRs)四类。基于此,本文先重点介绍了各类亚硝酸还原酶的结构及催化机制;在此基础上,综述亚硝酸还原酶在工农业制品处理、环境修复、生物传感器等领域取得的应用;此外,分析亚硝酸还原酶的人工酶与模拟酶的研究现状,以期为新型亚硝酸盐酶的开发提供参考。

《饲料中碘的测定》硫氰酸铁-亚硝酸催化动力学法国家标准前处理方法修订解读

对修订的GB/T 13882—2023《饲料中碘的测定》第二法硫氰酸铁-亚硝酸催化动力学法的关于前处理的修订内容进行了解读。该方法相较之前更改了碘标准工作溶液的配制方式、干灰化法并删除了湿法。采用580℃灰化样品,使试样中的碘酸根转换为碘离子,同时使用580℃处理碘标准中间溶液,补偿样品前处理过程中碘的损失。相较于修订前,修订后的前处理样品方法和配制标准系列曲线方式能显著提高方法的准确性。

阻抑动力学光度法测定水样中的痕量铝

基于在CTAC介质中,铝(Ⅲ)对十六烷基三甲基氯化铵(CTAC)催化结晶紫的褪色反应有明显的抑制作用,建立了一种抑制-催化褪色光度法测定痕量铝(Ⅲ)的新方法,研究了影响阻抑褪色反应的因素。结果表明,阻抑反应体系的最大吸收波长为584 nm,方法的线性范围为0.04~0.4μg/mL,线性回归方程为ΔA=0.7227c+0.0687(c的单位为μg/mL),相关系数r=0.9638,检出限为0.063μg/mL,相对标准偏差(RSD)为1.355%。该方法用于环境和工业水样中痕量铝的测定,相对标准偏差为3.7%~4.6%,回收率为96.8%~104.6%。

熟肉食品中亚硝酸盐含量变化分析

目的:分析熟肉食品中亚硝酸盐含量变化,为食品安全提供帮助。方法:选取2022年1月至2022年12月采集到的200份熟肉食品,采用第二法分光光度法对亚硝酸盐含量进行测定,对比不同类型熟肉食品样品(卤肉食品、凉肉食品、烧烤肉食品)、不同来源熟肉食品(超市、农贸市场、流通商贩)、不同季节(春季、夏季、秋季、冬季)采集的熟肉食品样品亚硝酸盐含量、熟肉食品不合格率。结果:不同类型熟肉食品样品、不同来源熟肉食品、不同季节采集的熟肉食品样品亚硝酸盐含量以及熟肉食品不合格率间差异无统计学意义(P>0.05)。结论:本研究中采集到的熟肉食品中亚硝酸盐含量较低,可以放心食用,但在夏季时呈上升趋势。

溴酸钾氧化喹哪啶红催化光度法测定痕量亚硝酸根

基于亚硝酸根对溴酸钾氧化喹哪啶红的催化作用，建立了双波长分光光度动力学测定痕量亚硝酸根的新方法。于４００ ｎｍ测定吸光度△Ａ１，５１０ ｎｍ测定吸光度△Ａ２，以△Ａ＝△Ａ１＋△Ａ２定量。线性范围０．００４～０．１５ ｍｇ／Ｌ；检出限０．００４ ｍｇ／Ｌ０、方法简便，灵敏，准确，选择性好。用于水及蔬菜样品中痕量亚硝酸根的测定，结果满意。

催化光度法测定超痕量亚硝酸根

迄今为止,有关动力学法测定亚硝酸根的报道甚少,笔者实验发现,在磷酸介质中,以溴酸钾氧化中性红,亚硝酸根具有高催化活性,据此,我们研究了适宜的催化反应条件,以及共存离子的影响,从而建立了测定超痕量亚硝酸根的新催化光度法。

藉溴酸钾氧化酸性间胺黄反应催化光度测定痕量亚硝酸根和硝酸根

本文基于NO2-对KBrO3氧化酸性间胺黄而使其褪色的催化作用，以及NO3-经锌粉还原为NO2-，建立了灵敏的催化光度测定痕量NO2-、NO3-的新方法，并讨论了其动力学条件。测定范围10～90μg／L，方法简便快速、选择性好，用于水及食品中痕量NO2-、NO3-的测定，结果满意。

甲基紫动力学催化光度法测定火腿肠中痕量亚硝酸根

基于在稀H3PO4介质中,亚硝酸根对KBrO3氧化甲基紫的褪色反应具有催化作用,建立了一种测定痕量亚硝酸根的催化光度法。该方法在室温下进行,操作方便,大多数离子不干扰。在选择的实验条件下,检出限为2 89×10-3μg/mL,线性范围为0.003～0.28μg/mL,可用于火腿肠样品中亚硝酸根的测定。

溴酸钾氧化茜素绿催化光度法测定痕量亚硝酸根

基于酸性介质溴酸钾氧化茜紊绿反应,提出了测定痕量亚硝酸根新的催化光度法.本法的Sandell灵敏度为9.4×10^(-5)μg/cm^2亚硝酸态氮,测定亚硝酸根量的线性范围为0.01～0.12μg/ml,可用于水样中亚硝酸根测定。

溴酸钾-亚甲蓝催化光度法测定硝酸盐和亚硝酸盐

用镉柱将NO-3 还原为NO-2 ,利用在磷酸介质中NO-2 对溴酸钾氧化亚甲蓝这一褪色反应具有强烈的催化作用而建立了同时测定痕量硝酸盐和亚硝酸盐的新方法。本方法简便、快速、灵敏 ,对亚硝酸盐和硝酸盐测定的线性范围分别为 0～ 2 0 0 μg·L-1和 0 0 0 3～ 310 μg·L-1,用于测定各种水样中痕量NO-2 和NO-3

催化光度法测定水中痕量亚硝酸根

利用在硫酸介质中亚硝酸根催化溴酸钾氧化吖啶橙的褪色反应 ,建立了测定痕量亚硝酸根的新方法。方法检出限为 7.6× 1 0 -8mol/ L,线性范围 0～1 .1 2× 1 0 -6mol/ L。

催化动力学光度法测定蒙药和发样中痕量锌(Ⅱ)

研究了在微酸性介质中 ,过氧化氢氧化钙试剂的褪色反应受Zn(Ⅱ )的催化而加速 ,据此建立了锌的新催化光度法 ,考察了该催化反应的适宜条件及动力学性质。该方法的检出限为 0 6 8μg·L-1,表观活化能为Ea=4 5 1kJ·mol-1,反应速率常量为k =5 80× 10 -3 s-1,测定范围 0 80～ 4 0 0 0 μg·L-1,成功用于蒙药和发样中锌的测定。