恒电流库仑分析法测定硫酸亚铁铵等基准试剂的纯度

在1．8mol／L硫酸介质中,以恒电流通过含有Mn^2＋的电解质溶液,使工作电极铂阳极上电生出Mn^3＋,Mn^3＋与溶液中待测基准试剂硫酸亚铁铵、草酸钠或草酸定量反应,以永停终点法确定库仑滴定终点,通过测量电解电流及电解时间,利用法拉弟电解定律计算基准试剂的纯度。该方法的相对误差为0．32％～0．36％,测量结果的相对标准偏差为0．045％-0．050％（n=11）。     

库仑滴定法测定烟叶提取物中茄尼醇

本文提出用库仑滴定法测定茄尼醇。以含有1mol·L－1KBr的78％（V／V）醋酸溶液为介质，以5mA恒电流为电解电流，对布尼醇进行库仑滴定，用双铂电极电流法指示滴定终点，得到满意结果．方法简便、准确，不需要标准溶液，不需要昂贵仪器。     

用精密库仑滴定法测定三氧化二砷的纯度

一、前言三氧化二砷是容量分析中常用的一种基准物质。Marinenko和Taylor曾用电解氧化碘离子产生碘的库仑滴定法测定其纯度,同时研究了电解产生碘的电流效率。Newton亦进行过类似的工作,他们都获得了很高的测量精度。在本工作中用积分残余电流的方法进一步研究了电解产生碘的电流效率及其与电解质溶液的pH关系。测定三氧化二砷纯度的精度为31ppm。     

库仑—新极谱电分析法

恒电流库仑滴定时无论用电位法或是用电流法指示终点,恒电流都会影响指示信号的观测;用新极谱分析法指示恒电流库仑滴定终点,同样受恒电流干扰,为了判断滴定终点,需多次断电停止滴定,观测峰高。本文提出根据两次间隔滴定观测到的峰高获得分析结果的方法。     

库仑滴定法快速测定牛磺酸含量

建立了一种快速测定牛磺酸原料药中牛磺酸含量的库仑滴定分析方法。采用曼尼希反应使牛磺酸与甲醛发生反应,释放出相应的H~+,随后通过恒电流电解产生滴定剂OH~-,至滴定终点后,依据法拉第电解定律计算得到牛磺酸含量。探讨了甲醛加入量、滴定终点pH的选择,拟定了具体的电解条件。3种原料药中牛磺酸含量的测定结果与中国药典(二部)推荐的电位滴定法测定结果一致,相对标准偏差RSD在0.40%以下,回收率在99.5%~100.4%之间,可在10 min之内自动完成整个测定过程。     

钨丝电化分离富集电热原子吸收法测定岩矿中的微量金

我们曾报导了钨丝恒电位电解电热原子吸收法测定微量金。该方法虽具有一定特点,但铜有严重干扰,铁有较大干扰,当其含量高时得不到吸收信号。为适于测定各种类型的含金岩矿,对该方法做了如下改进:①改进NF101型定时电解富集仪,研制出NF,102型多功能电解富集仪,增加了定时恒电位阳极溶出及定时恒电流电沉积功能。②电解沉积金以后,将钨丝改作阳极进行恒电位溶出,消除铜的严重     

电解生成亚铁离子返滴定法测定消毒液中过氧化氢含量的数字化实验*

氧化还原与电解的相关知识是中学化学学习的重点内容。应用自主研制的MXLab21先进数字化实验系统电解Fe₂(SO₄)₃溶液,用电解生成的Fe²⁺直接滴定KMnO₄溶液以测定其浓度,再用返滴法测定消毒液中H₂O₂的含量。对恒电流电解的最佳条件如Fe₂(SO₄)₃溶液浓度及电解电流大小进行了优化。该数字化实验系统相比较于常规数字化仪器(或手持技术)的优越性在于其自带电解、搅拌及控制系统,能在电解的同时利用电生物质实现对待测物质的准确测定,测定时间短(不超过4 min)。本实验采用预设终点电势值的方法自动估计滴定终点,不但便捷准确,且呈现出的实时直观的电势和电量随时间变化的动态曲线便于学生理解电解及氧化还原滴定反应的微观本质,对中学化学教学及化学学科核心素养的培养具有重要价值。     

高精密恒电流库仑法测定CCQM-K73国际关键比对盐酸溶液中H+含量

采用高精密恒电流库仑法测量了CCQM-K73国际比对样品盐酸溶液含量。该方法是国际上公认的基准测量方法,根据法拉第电解定律,通过质量、电阻、电动势、时间等基本物理量及法拉第常数来进行样品的测定,直接溯源到国际SI单位,不需要用标准物质进行比对。中国计量科学研究院作为国家化学计量最高溯源,参加了该项关键比对,并取得了等效一致的好成绩。     

库仑滴定法快速测定白酒中总酯的含量北大核心CSCD

提出了库仑滴定法测定白酒中总酯含量的方法。以铂电极为工作电极对,pH复合玻璃电极为指示电极,0.80 mol·L^(-1)硫酸钾溶液为支持电解质,通过恒电流电解生成的H~+滴定预处理后样品中剩余的OH^(-),直至滴定终点pH 7.70,根据法拉第电解定律测得样品中总酯的含量。结果表明:测定过程约10 min完成。按标准加入法进行回收试验,回收率为88.0%~106%。方法用于实际白酒样品中总酯含量的测定,测定结果与国家标准规定的电位滴定法测定结果无显著性差异。     

库仑滴定法测定新洁尔灭溶液中溴化苄烷铵的含量

应用库仑滴定法测定了新洁尔灭溶液中溴化苄烷铵的含量。用0.09mol·L-1硝酸溶液和0.5%(w)明胶溶液以体积比10比1混合的混合溶液作电解液,银棒作阳极进行恒电流电解,电解电流为10mA。电解过程中,从银电极释放出的Ag+与试液中溴化苄烷铵的Br-反应生成沉淀。Br-被完全沉淀时,电流上升,滴定到达终点,根据法拉第定律计算溴化苄烷铵的含量。溴化苄烷铵的质量浓度在0.422 8~1.480g·L-1范围内与所消耗的电量之间呈线性关系。对同一样品的分析,本方法的测定结果与四苯硼钠滴定法的测定结果相符,本方法测定结果的相对标准偏差(n=6)为0.9%。用标准加入法进行回收试验,测得回收率在99.6%~102%之间。     

水为载流-原子荧光光谱法同时测定土壤中痕量砷、汞

改变原子荧光光谱法以稀酸为载流的进样方式,以水为载流在新型双道原子荧光光谱仪上同时测定了土壤中的痕量砷(As)、汞(Hg)。方法采用王水水浴加热溶解样品,用50 g/L硫脲-抗坏血酸混合溶液预先将砷还原为+3价,保持10%(体积分数)以上盐酸浓度,不转移直接定容静置后测定。优化了仪器工作条件,详细考察了以水为载流测定的可行性,选择了同时测定As、Hg所需的硼氢化钾浓度和盐酸浓度。方法节省了酸试剂用量,操作快速,单个样品测定仅需20s左右。方法检出限As为0.005 mg/kg,Hg为0.0008 mg/kg,相对标准偏差(RSD%,n=7)在1.0%～7.4%,经土壤国家标准物质和实际样品验证,适合土壤中痕量As、Hg的同时快速测定。     

水载流-原子荧光光谱法同时测定土壤中痕量砷、汞

改变原子荧光光谱法以稀酸为载流的进样方式,以水为载流在新型双道原子荧光光谱仪上同时测定了土壤中的痕量砷(As)、汞(Hg).采用王水水浴加热溶解样品,用50 g/L硫脲-抗坏血酸混合溶液预先将砷还原为As(Ⅲ),保持10％(体积分数)以上盐酸浓度,不转移直接定容静置后测定.优化了仪器工作条件,详细考察了以水为载流测定的...     

微波消解-氢化物发生原子荧光法同时测定土壤中的砷汞

建立了微波消解-氢化物发生原子荧光法同时测定土壤中As、Hg的分析方法。用体积分数35%的王水作为消解溶剂,在设定的微波消解条件下,可以将土壤中的As、Hg提取完全,有效解决了消解液中剩余酸过多的问题。方法用体积分数5%的HCl作为反应介质,20 g/L NaBH4作为还原剂。通过测定国家标准参考物质和加标回收实验,对方法进行了验证。已用于土壤中As、Hg的测定。     

Analysis of hypobromite solutions by indicator titrations

A rapid titrimetric method is described for the determination of the three oxidizing components in 10^-1 N hypobromite solutions with only arsenic(III) as the standard reagent. Hypobromite is determined by titration with arsenic(III) in alkaline medium, with bromothymol blue, quinoline yellow or epsilon blue as reversible indicator. Bromite is determined by reaction with an excess of iodide in weakly alkaline medium, followed by titration of the formed triiodide with arsenic(III) solution and starch as indicator. Total hypobromite, bromite and bromate is determined by titration of arsenic(III) in hydrochloric acid medium, with quinoline yellow as reversible indicator. Bromate is calculated by difference.     

Neutron activation analysis of arsenic in rocks and sediments by direct evolution with chloride- and bromide-condensed phosphoric acid reagents

A simple method is presented for the determination of arsenic in rocks and in sediments by neutron activation. After irradiating a sample it is, without any other treatment, directly heated in condensed phosphoric acid containing sodium chloride or sodium bromide to evolve arsenic as arsenic(III) chloride or bromide. The distillate is absorbed in distilled water, in which arsenic is later precipitated in elementary form by adding hypophosphite to the solution. From arsenite, arsenic(III) oxide, arsenate and arsenic(III) sulphide, arsenic chloride can be evolved with NaCl-CPA reagent, but elementary arsenic and arsenic(V) oxide do not react with it. However, metallic arsenic is found to react with KIO₃-NaCl-CPA and arsenic(V) oxide with the NaBr-CPA, both both evolving arsenic(III) chloride or bromide. Therefore, successive distillations, the first with NaCl-CPA and the second with NaBr-CPA, give a satisfactory means of differential determination of arsenic(III) and arsenate as well as arsenic(V) oxide. For the elementary arsenic a problem still now remains. The chemical recovery of carrier goes well beyond 95%. Part of this work was performed at the Research Reactor Institute, Kyoto University.     

Co-determination of sodium metabisulfite and starch in corn syrup by flow injection coulometry

During the processing of corn syrup for commercial use, starch, in the form of alpha -amylose, must be completely broken down to its D -glucopyranose units. Sodium metabisulfite is added to the corn syrup as a preservative. Flow Injection Coulometry was used to perform an automated assay of these analytes, both individually and jointly. The sodium metabisulfite concentration, over a range of 3.5 x 10(-4)-2.9 x 10(-2)M, is determined by coulometric flow injection titration with generated iodine, using spectrophotometric endpoint detection at 530 nm. Analysis over this range produced a relative standard deviation of < 1.5% and was found to correlate very well with manual titrations. The determination was performed in the presence of varying amounts of starch, and was found to be independent of the starch concentration. Starch was determined, when no sodium metabisulfite was present, from the absorbance level after the reaction of the sample with a specific amount of iodine. In the presence of sodium metabisulfite, the rate of the accumulation of the starch/iodine interaction product after the metabisulfite titration endpoint, at a constant reagent generation rate, was used. A relative standard deviation of < 1.4% was obtained for all starch analyses, with a very good correlation (correlation coefficients 0.997) with the known relative concentration. The use of the FIC technique to perform analyses by specific amount and excess reagent generation is demonstrated, along with dual analyte determination.     

Differential determination of arsenic (III) and total arsenic with L-cysteine as prereductant using a flow injection non-dispersive atomic absorption device

Speciation of arsenic in environmental samples gains increasingly importance, as the toxic effects of arsenic are related to its oxidation state. A method was developed for the determination of trace amounts of arsenic (III) and total arsenic by flow injection hydride generation coupled with an in-house made non-dispersive AAS device. The total arsenic is determined after prereduction of arsenic (V) to arsenic (III) with L-cysteine in a low concentration of hydrochloric, acetic or nitric acid. The conditions for the prereduction, hydride generation and atomization were systematically investigated. A quartz tube temperature of 800 degrees C was found to be optimum in view of peak shape and baseline stability. Pb(II), Ni(II), Fe(III), Cu(II), Ag(I), Al(III), Ga(II), Se(IV), Bi(III) were checked for interfering with the 2 microg/L As(V) signal. A serious signal depression was only observed for Se(IV) and Bi(III) at a 150-fold excess. With the above system, arsenic was determined at a sampling frequency of about 1/min with a detection limit (3sigma) of 0.01 microg/L using a 0.5 mL sample. The reagent blank was 0.001+/-0.0003 absorbance units and the standard deviation of 10 measurements of the 2 microg/l As signal was found to be 1.2%. Results obtained for standard reference materials and water samples are in good agreement with the certified values and those obtained by ICP-MS     

Determination of arsenic in aqueous solutions by no-reference inversion voltammetry

Electrochemical method for arsenic determination at concentrations characteristic of inversion voltammetry was suggested. The method does not require calibration of the measuring instrument against standard solutions or application of the standard-additive technique. The method of no-reference inversion-volammetric determination is based on calculating the arsenic concentration in solution with the use of the preliminarily determined coulometric constant of an electrochemical cell.     

一次消解土壤样品测定汞、砷和硒

建立了测定土壤中3种挥发性元素(汞、砷、硒)的一次消解方法,确定以程序控温石墨自动消解仪+王水-氢氟酸-硼酸络合敞开体系为最佳消解体系,采用氢化物发生-原子荧光光谱法(HG-AFS)分别测定同一消解液中汞、砷、硒的含量.采用国家标物中心有证标准物质土壤环境样品GSS-1~GSS-8进行了方法验证,结果均符合标准偏差的允许范围.此消解方法相比于现行标准方法,避免了针对各元素的分次处理,简化了消解步骤,节省了前处理时间,减少了试剂消耗,提高了实验效率,适用性广、灵敏度高、检出限低,尤其适合批量样品的微量/痕量元素分析,可作为一种大规模土壤样品中重金属污染监测和治理的快捷方法.     

CZE for the speciation of arsenic in aqueous soil extracts

We developed two separation methods using CZE with UV detection for the determination of the most common inorganic and methylated arsenic species and some phenylarsenic compounds. Based on the separation method for anions using hydrodynamic sample injection the detection limits were 0.52, 0.25, 0.27, 0.12, 0.37, 0.6, 0.6, 1.2 and 1.0 mg As/L for phenylarsine oxide (PAO), p-aminophenylarsonic acid (p-APAA), o-aminophenylarsonic (o-APAA), phenylarsonic acid (PAA), 4-hydroxy-3-nitrobenzenearsonic acid (roxarsone), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenite or arsenious acid (As(III)) and arsenate (As(V)), respectively. These detection limits were improved by large-volume sample stacking with polarity switching to 32, 28, 14, 42, 22, 27, 26 and 27 microg As/L for p-APAA, o-APAA, PAA, roxarsone, MMA, DMA, As(III) and As(V), respectively. We have applied both methods to the analysis of the arsenic species distribution in aqueous soil extracts. The identification of the arsenic species was validated by means of both standard addition and comparison with standard UV spectra. The comparison of the arsenic species concentrations in the extracts determined by CZE with the total arsenic concentrations measured by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) indicated that CZE is suited for the speciation of arsenic in environmental samples with a high arsenic content. The extraction yield of phenylarsenic compounds from soil was derived from the arsenic concentrations of the aqueous soil extracts and the total arsenic content of the soil determined by ICP-AES after microwave digestion. We found that 6-32% of the total amount of arsenic in the soil was extractable by a one-step extraction with water in dependence on the type of arsenic species.