Volumetric studies in oxidation-reduction reactions: Reduction with ferrous ethylenediamine sulphate indirect determinations

Ferrous ethylenediamine sulphate has been. used as a reducing agent in acid medium for the indirect volumetric estimations of potassium chlorate, potassium bromate, potassium metaperiodate, potassium, dichromate, potassium ferricyanide, potassium permanganate, potassium persulphate, hydrogen peroxide and ceric sulphate. The excess of ferrous ethylenediamine sulphate added to each of the substances was titrated with standard potassium permanganate and also with. standard potassium dichromate solution. In case of potassium bromate or potassium metaperiodate the end-point was not sharp in potassium dichromate titrations; while accurate volumetric observations were made with standard potassium permanganate solution.     

A colorimetric determination of thorium

A colorimetric method for the determination of thorium is proposed. It is based upon the precipitation of thorium with a standard solution of oxalic acid and the subsequent reaction of the excess oxalic acid with a standard solution of potassium permanganate. The absorbancy of the remaining permanganate solution is directly proportional to the thorium present. The variables affecting this method have been critically studied. Reliable determinations can be made in the range of 3 to 30 mg of thorium in 1 cm cells when the colored solution is diluted to 250 ml. Most interfering substances can be removed by electrolysis in a mercury cathode cell or by the precipitation of thorium with potassium iodate.     

Analysis of mixtures of citric and oxalic acids based on their oxidation with potassium permanganate and manganese(III) sulfate

A determination of mixtures of citric and oxalic acids has been developed based on quantitative oxidation of the two substances with excess potassium permanganate to carbon dioxide and water and on quantitative oxidation of oxalic acid to carbon dioxide and water and of citric acid to carbon dioxide and formic acid with excess manganese(III) sulfate. The content of the two substances in mixtures can be calculated from the different consumption in these two oxidimetric determinations; a single standard solution of potassium permanganate can also be used for the preparation of manganese(III) sulfate.     

Potentiometric studies in oxidation-reduction reactions: Reduction with ferrous ethylenediamine sulphate indirect determinations

Ferrous ethylenediamine sulphate has been used as a reducing agent to determine indirectly potassium dichromate, hydrogen peroxide, potassium permanganate, potassium persulphate, potassium chlorate, potassium bromate, and ceric sulphate by a potentiometric method. An excess of ferrous ethylenediamine sulphate added to each of the substances in an acid medium is titrated with a standard solution of potassium permanganate, using platinum foil as an oxidation-reduction electrode coupled with a saturated calomel electrode through an agar-agar potassium chloride bridge.     

Oxidation of sulphides with alkaline potassium permanganate

Summary Sulphides are oxidised with potassium permanganate in alkaline medium to give dithionate. A method based upon this reaction is proposed for the determination of sulphides. The method consists in mixing the sulphide solution with an excess of permanganate in presence 1–2 M NaOH and 0.2 g telluric acid. The excess permanganate is then treated with ferrous ammonium sulphate in acid medium and the excess ferrous titrated with permanganate.     

Determination of peroxydiphosphate in acid medium with oxalate (i) with silver(I) as catalyst and (ii) in the presence of excess of manganese(II)

Peroxydiphosphate can be determined with oxalate in acid medium in the presence of silver(I). Excess of oxalic acid along with the sample and silver (I) is heated to boiling and the excess of oxalic acid is titrated against standard permanganate. Another method involves boiling for 2 min a mixture consisting of the sample and excess of manganese(II), followed by titration of the resulting Mn(III) or MnO(2) with standard oxalic acid solution.     

Potentiometric studies in oxidation-reduction reactions: Reduction with ferrous ethylenediamine sulphate ceric sulphate method

Ferrous ethylenediamine sulphate has been used as a reducing agent to determine indirectly potassium permanganate, ceric sulphate, potassium chlorate, hydrogen peroxide, potassium persulphate, potassium dichromate and potassium bromate by a potentiometric method. An excess of ferrous ethylenediamine sulphate added to each of the substances in acid medium was titrated with a standard solution of ceric sulphate, using platinum foil as an oxidation-reduction electrode coupled with a saturated calomel electrode through an agar-agar potassium chloride bridge.     

Potentiometric studies in oxidation-reduction reactions: Oxidation with chloramine-b. indirect determinations

Chloramine-B has been used as an oxidising agent to determine indirectly potassium iodate, potassium metaperiodate, potassium, bromate, potassium dichromate, hydrogen peroxide, chloramine-T and potassium permanganate by a potentiometric method. An excess of potassium iodide added to each of the substances in an acid medium is titrated back with a standard solution of chloramine-B, using platinum foil as an oxidation-reduction electrode coupled with a saturated calomel electrode through an agar-agar potassium chloride bridge.     

Volumetric studies in oxidation-reduction reactions: Reduction with ferrous ethylenediamine sulphate ceric sulphate method

Ferrous ethylenediamine sulphate has been used as a reducing agent in acid medium for the indirect volumetric estimations of potassium chlorate, potassium bromate, potassium metaperiodate, potassium dichromate, potassium ferricyanide, potassium permanganate, potassium persulphate, hydrogen peroxide and ceric sulphate. The excess of ferrous ethylenediamine sulphate added to each of the substances in acid medium was titrated with standard ceric sulphate solution using ferroin as an indicator.     

Differential thermal analysis and temperature profile analysis of pyrotechnic delay systems: mixtures of tungsten and potassium dichromate

The self-propagating combustion reaction between tungsten and potassium dichromate has been studied by differential thermal analysis and temperature profile analysis. Two reaction stages have been distinguished in the combustion where the rate of temperature rise is ? 10⁵ K min^?1: in the first potassium dichromate is reduced by tungsten to form potassium chromate and in the second stage the potassium chromate reacts with more tungsten to form potassium tungstate and chromic oxide.     

食品及生物样品中痕量草酸的荧光动力学法测定

拟定了一个荧光动力学测定痕量草酸根的新方法。在硫酸介质中，草酸催化重铬酸钾氧化罗丹明６Ｇ使其荧光猝灭。方法线性范围为０．８－１４．０ｍｇ／Ｌ，直接用于菠菜，人尿中草酸根的测定，获得满意结果。     

Catalytic kinetic spectrophotometry for the determination of trace amount of oxalic acid in biological samples with oxalic acid-rhodamine B-potassium dichromate system

A new catalytic kinetic spectrophotometric method was proposed for determining trace oxalic acid based on the catalytic effect of oxalate on the oxidation of potassium dichromate with rhodamin B in 0.10 M of sulfuric acid. Good linearity is obtained over the concentration range 0.40-6.0 microg/mL of oxalic acid. After the reactions of the catalytic and non-catalytic systems were terminated by using 2.00 mL of 4 M sodium hydroxide solution, they can be stable for 3 h at room temperature. The apparent activation energy of the catalytic reaction is 12.44 kJ/mol. The effect of 50 coexisting substances was observed. The method was used to determine trace oxalic acid in tea, spinach and urine samples with satisfactory results.     

次亚磷酸钠分离-重铬酸钾容量法测定钨尾矿中砷含量

选矿中产生的钨尾矿长期堆放,经过雨水冲刷,钨尾矿中的砷会进入到水土中,造成环境污染,准确测定钨尾矿中砷含量,利于监测钨尾矿中砷对环境的污染程度。采用硝酸-氯酸钾饱和溶液和氟化铵溶液分解样品,再用硫酸溶液冒烟赶尽硝酸,在盐酸介质中,以硫酸铜为催化剂,用次亚磷酸钠将砷离子还原成元素态,析出的砷过滤分离,除去其他杂质。在硫酸溶液中,用过量的重铬酸钾标准溶液滴定溶解单质砷,过量的重铬酸钾以二苯胺磺酸钠为指示剂,用硫酸亚铁标准溶液反滴定。通过优化样品溶解条件和砷沉淀还原条件,建立了次亚磷酸钠分离-重铬酸钾容量法测定钨尾矿中砷含量的分析方法。通过测定滤液中的砷含量,考察了滤液中砷含量对砷测定结果的影响,可忽略不计,表明实验中砷沉淀完全。通过沉淀单质砷,过滤使砷与杂质元素分离,消除了杂质元素对砷测定的影响。运用重铬酸钾容量法测定3个钨尾矿样品中的砷,并进行加标回收实验,测定结果的相对标准偏差（RSD,n=11）在0.14%～2.1%,加标回收率在97%～101%。方法操作简单、精密度高,适合钨尾矿中高含量砷的测定,测定结果与碱融分离-碘量法结果基本一致。     

Potentiometric stripping analysis for mercury after preconcentration in a potassium permanganate trap

Water samples of total volume 0.5–5 l, containing mercury in the range 0.05–5 μg l^-1 are oxidized with excess of potassium permanganate and then reduced with tin(II) chloride. The mercury is transferred to 5–10 ml of a dilute potassium permanganate trap solution by cycling air through the sample and the trap solution. The mercury(II) content of the trap solution is determined by potentiometric stripping analysis. The accuracy, precision and detection limit of the technique are discussed.     

Low temperature oxidation of oxalic acid with potassium permanganate

Summary Oxidation of oxalate and oxalic acid with permanganate was studied at ordinary temperature. In the presence of mixtures of Mn²⁺ and Cu²⁺ ions the reaction is sufficiently rapid for a visual titration. The end point is attained when a lilac or a faint violet colour appears. A blank experiment is necessary as Cu²⁺ consumes some permanganate before the end point can be perceived. Other catalysts including Zn²⁺, Cd²⁺, Hg²⁺ and Ag⁺ ions were tried but were less efficient.     

Flow Injection Amperometric System Coupled with a Well-Plate for Fast Screening of Total Antioxidant Capacity

A flow injection (FI) system with an amperometric detection in combination with a 96-well-plate has been developed for high throughput screening of total antioxidant capacity. It is based on the reaction between dichromate and antioxidants Chromium reducing antioxidant capacity (CHROMAC) assay. Antioxidant reduces dichromate leading to a decrease of dichromate concentration, in which reacts further with triiodide reagent. The slow reaction between antioxidant and dichromate takes place in parallel in a 96-well microplate, with the reaction time sufficiently long to reach steady state conditions. Microliter volumes of the remaining dichromate solution were manually injected into the FI amperometric system. Reaction with iodide in acidic medium produces triiodide which undergoes electrochemical reduction on a glassy carbon working electrode at 200?mV versus a Ag/AgCl reference electrode. The decrease of electrical current was directly proportional to the antioxidant capacity. The optimum conditions have been achieved as follow: 160?mg?L^?1 of potassium dichromate, pH of dichromate solution of 2.82, 0.005?mol?L^?1 of potassium iodide, 0.20?mol?L^?1 of hydrochloric acid, and 3.0?mL?min^?1 total flow rate. The developed method was applied for the determination of total antioxidant capacity of tea and herbal infusions and fruit juice samples. The results obtained indicated that the developed method had good correlation with the batch CHROMAC spectrophotometric method and 1,1-diphenyl-2-picrylhydrazyl scavenging assay. The proposed method provides fast and high throughput analysis, convenient operation, and low consumption of chemical reagents and samples.     

Kinetic Spectrophotometric Determination of Oxalic Acid Based on the Catalytic Oxidation of Bromophenol Blue by Dichromate

 A sensitive catalytic method is developed for the spectrophotometric determination of oxalic acid. It is based on the catalytic action of oxalic acid on a new indicator reaction – the oxidation of Bromophenol Blue by dichromate in dilute sulfuric acid medium. The reaction rate is monitored spectrophotometrically by measuring the absorbance at 600 nm after quenching the reaction with sodium hydroxide. A calibration graph from 0.1 to 8.0 μg mL⁻¹ of oxalic acid and a detection limit of 0.04 μg mL⁻¹ was obtained. The applicability of this method was demonstrated by the determination of oxalic acid in water extracts from vegetables such as spinach, mushrooms and fresh kidney beans. Received October 18, 1999. Revision June 14, 2000.     

The determination of chemical oxygen demand in waste-waters with dichromate by flow injection analysis

A simple method is described for the continuous determination of chemical oxygen demand (COD) in wastewater samples by flow injection analysis. Samples are injected into a water stream which merges with an acidic dichromate carrier solution. After reaction in a PTFE coil at 120°C, absorbances are measured at 445 nm. D-Glucose is satisfactory as a standard substance for COD in a variety of wastewaters. A sampling rate of 15 samples per hour can be achieved, and the detection limit and precision are 5 mg l^-1 as COD and 0.4%, respectively. Chloride concentrations of ? 100 mg l^-1 interfere slightly unless silver and/or mercury salts are added. COD values for various wastewater samples correlate well with those obtained by standard methods using dichromate or permanganate.     

Flow injection chemiluminescence determination of naftopidil based on potassium permanganate oxidation in the presence of formaldehyde or formic acid

A flow injection method is proposed for the determination of naftopidil based upon the oxidation by potassium permanganate in a sulfuric acid medium and sensitized by formaldehyde and formic acid. The optimum chemical conditions for the chemiluminescence emission were 0.25 mM potassium permanganate and 4.0 M sulfuric acid. Two manifolds were tested and instrumental parameters such as the length of the reactor, injection volume and flow rate were compared. When using the selected manifold in the presence of 0.4 M formaldehyde, naftopidil gives a second-order calibration graph over the concentration range 0.1–40.0 mg L^–1 with a detection limit calculated (as proposed by IUPAC) of 92.5 ng mL^–1 and a standard deviation of 0.12 mg mL^–1 for ten samples of 10.0 mg L^–1 naftopidil. In the presence of 1.15 M formic acid, naftopidil gives a second-order calibration graph over the concentration range 0.05–40.0 mg L^–1 with a detection limit of 14.2 ng mL^–1 and a standard deviation of 0.37 mg mL^–1 for ten samples of 10.0 mg L^–1 naftopidil. In both cases, the determination is free from interferences from common excipients such as sucrose, glucose, lactose, starch and citric acid.     

Determination of iodide with potassium dichromate and sodium vanadate in the presence of acetone

The determination of iodide with potassium dichromate and sodium vanadate in 6-8M phosphoric acid medium by potentiometric or visual titration is described. Ferroin and barium diphenylamine sulphonate (BDAS) are used as the indicators in the visual titration with potassium dichromate and sodium vanadate respectively. Acetone is used to stabilize the iodonium ions liberated, in the visual titration. Iodide can also be determined with sodium vanadate in 2-4M sulphuric acid medium with BDAS as indicator in the presence of oxalic acid as catalyst and acetone to stabilize the liberated iodine cations. The visual procedures are applied for the determination of iodide in tincture of iodine. The formal potentials of the iodine/iodide couple in various phosphoric acid media are reported.