Kinetic-spectrophotometric determination of trace amounts of As(III) based on its inhibitory effect on the redox reaction between bromate and hydrochloric acid

A simple, sensitive, rapid and reliable method has been developed for spectrophotometric determinations of As(III) in the presence of As(V) based on its inhibition effect on the redox reaction between bromate and hydrochloric acid. The decolorization of methyl orange by the reaction products was used to monitor the reaction spectrophotometrically at 525 nm. The method allows the determination of arsenic in the range of 6-1000 mug l(-1). The relative standard deviation for 10 determinations of 40 mug l(-1) of As(III) was 1.43% and the limit of detection, corresponding to a signal to noise ratio of three, was 3.4 mug l(-1). The proposed method was applied to the determination of As(III) in water samples with satisfactory results.     

Kinetic-spectrophotometric determination of trace amounts of vanadium

A simple and sensitive kinetic-spectrophotometric method is described for the determination of vanadium and the possible mechanism of catalytic reaction is proposed. The method is based on the vanadium(V)-catalyzed oxidation of 1,8-diaminonaphthalene (DNA) by potassium bromate (Tiron as activator) at pH 3.8 and 40 degrees C. The reaction was monitored spectrophotometrically by measuring the increase in absorbance of oxidation products at 505 nm after a fixed time (6 min). The proposed method allowed the determination of vanadium in the range 0.025-15 ng ml(-1) with good precision and accuracy and the detection limit was down to 0.01 ng ml(-1). The method was found to be relatively selective and was applied successfully to the determination of vanadium in food and hair samples without previous separations. Recovery experiments have also been performed; excellent results were obtained.     

Kinetic-spectrophotometric determination of traces of vanadium(V) by its catalytic effect on the oxidation of 1,4-dihydroxyphthalimide dioxime with bromate

A kinetic-spectrophotometric method for the determination of trace amounts of vanadium(V) is described. It is based on the catalytic action of this ion on the oxidation of 1,4-dihydroxyphthalimide dioxime by bromate, which yields a red-violet product in acidic medium. The reaction is followed spectrophotometrically by measuring the rate of change in absorbance at 500 nm and 30°C. Using several kinetic methods (tangent, fixed-time and fixed-absorbance), vanadium(V) in the range 10–400 ng ml^?1 can be determined. The proposed methods are hardly subject to interferences. The tangent method was used for the determination of vanadium in atmospheric particulate matter, human serum and synthetic mixtures. The kinetic parameters of the catalysed and uncatalysed reactions are reported.     

Flow-injection spectrophotometric determination of trace vanadium based on catalysis of the gallic acid bromate reaction

High sensitivity is obtained by using high concentrations of gallic acid and bromate, although the uncatalyzed reaction is significant. Various reactant concentrations, reaction temperature, pH and residence times can be used to alter the linear calibration ranges and sensitivity for vanadium. With reagent streams of 1.76 M bromate and 0.06 M gallic acid at pH 3.8 (each at 1 ml min^?1), 0.2–20 ng of vanadium (20-μl injections) can be determined at 30°C. Oxidized gallic acid is detected at 380 nm. When the bromate concentration is decreased to 0.5 M and the temperature is 65°C, 0.05–4 ng of vanadium can be determined; the relative standard deviation is ca. 5% for 0.6 ng of vanadium. The toleranes for Al(III), Fe(III), Mo(VI) and iodide are 10 ng, 10 ng, 50 ng and 200 ng, respectively, for the determination of 1 ng of vanadium. About 12 samples can be injected per hour.     

Spectrophotometric determination of trace nitrite based on catalytic oxidation of thionine by potassium bromate

A kinetic method for the determination of trace nitrite (7 × 10^?9–1.2 × 10^?6 M) based on its catalytic effect on the reaction between potassium bromate and thionine in strongly acidic media is reported. The reaction is monitored spectrophotometrically by measuring the decreasing colour of thionine at 602 nm by the fixed-time method. At a given time of 5 min at 30°C, the detection limit is 2 × 10^?9 M (0.001 absorbance ratio, b = 1 cm) and the relative standard deviation for 1 × 10^?6 M nitrite is 2.6% (n = 6). The method is free from most interferences, especially from large amounts of nitrate. The procedure was successfully applied to the determination of trace nitrite in natural water and sausage samples without preconcentration and separation.     

Highly sensitive spectrofluorimetric kinetic determination of ultratrace amounts of vanadium(V) based on the oxidation of 1,8-diaminonaphthalene by bromate

A highly sensitive catalytic quenching spectrofluorimetric method was described for the determination of V(V) based on its catalytic effect on the oxidation of 1,8-diaminonaphthalene by potassium bromate with Tiron as an activator in weakly acidic medium and the reaction mechanism was investigated. The reaction was followed spectrofluorimetrically by measuring the fluorescence intensity of 1,8-diaminonathphlene (DAN) (λ_ex=356 nm, λ_em=439 nm) at a fixed time of 5 min from initiation of the reaction. Under the optimum conditions, vanadium(V) can be determined in the range 0.05-50.0 ng ml⁻¹ with a S.D.=0.024 for 15 times measurements. The detection limit of the method was down to 0.0088 ng ml⁻¹ and the catalytic reaction activation energy was found to be 43.92 kJ mol⁻¹. The proposed method was tested for the determination of vanadium(V) in rice and natural water samples.     

Spectrophotometric kinetic determination of copper(II) trace amounts based on its catalytic effect on the reaction of the reduced 2,6-dichlorophenolindophenol and hydrogen peroxide

A catalytic spectrophotometric method is presented for the determination of Cu(II), based on the oxidation of the leucocompound of the 2.6-dichlorophenolindophenol (DCPI)(r), in the presence of hydrogen peroxide and the catalytic effect of Cu(II) on this reaction in ammonia-ammonium chloride buffer solution of pH 10.5. The above reaction is followed spectrophotometrically at 562 nm. The study was carried out with a filter spectrophotometer equipped with a fiber optic and an immersed type optical cell of 1 cm. The optimum operating conditions regarding concentration of the reagents involved, pH and temperature were established. The interference effect of several metallic species was also investigated. It was found that the proposed method shows fairly good selectivity and sensitivity, simplicity and rapidity compared to other kinetic methods. The working curve of the recommended reaction-rate method is linear in the concentration range 5-300 ng/ml. The relative standard deviation for a standard solution of 30 ng/ml Cu(II) is better than 2.5%. The method was applied successfully on the determination of Cu(II) in a wide variety of real samples such as alloys, pharmaceuticals, foodstuffs and environmental samples. The results were compared to those received with official methods. Good agreement was attained.     

Kinetic-spectrophotometric determination of Sb(V) based on its reaction with iodide in the presence of methylene blue

A rapid, simple, and sensitive kinetic method is developed for the determination of trace amounts of Sb(V). The method is based on the reaction of Sb(V) with iodide in acidic media in the presence of methylene blue. The reaction was monitored spectrophotometrically by measuring the decrease in the absorbance at 664 nm by a fixed-time technique of 60 s. The method allowed the determination of Sb(V) at concentrations between 0.01 and 2.2 μg/mL. The limit of detection was 0.006 μg/mL and the relative standard deviation for ten replicate measurements of 0.5 μg/mL Sb(V) was 1.2%. The method was applied to the determination of Sb(V) in tap water and spring water with satisfactory results. The text was submitted by the authors in English.     

偶氮胂M-溴酸钾催化动力学光度法测定痕量钒

钒是人体中重要的微量元素之一,测定痕量钒的催化光度法已有许多报道[1～5],但利用偶氮胂M试剂褪色为指示反应测定痕量钒目前尚未见报道.研究发现,在硫酸介质中,V(Ⅴ)对KBrO3氧化偶氮胂M(AM)的褪色反应有强烈的催化作用,且反应速率在一定条件下与溶液中V(Ⅴ)的浓度成正比,据此建立了一个测定痕量钒的新催化光度法并测定了催化反应的反应级数,确定了反应的速度方程.     

KBrO3氧化甲基紫褪色动力学光度法测定食品中痕量钒

基于0.004 mol/L的柠檬酸介质中,痕量V(Ⅴ)催化KBrO3氧化甲基紫的褪色反应,建立了测定痕量V(Ⅴ)的动力学光度法。方法的检出限为1.23μg/L,线性范围为0～0.16μg/mL。讨论了酸度、反应物浓度、温度、反应时间、干扰离子等因素的影响,确定了该体系反应的最佳条件。在25 mL溶液中,测定2.0μg V(Ⅴ)的RSD为1.9%(n=11)。方法可用于测定小麦和苹果中的痕量V(Ⅴ),RSD为1.1%～2.7%,标准加入回收率为97.6%～99.0%。     

Kinetic-spectrophotometric method for the determination of trace amounts of bromide in seawater

A novel simple, sensitive and rapid kinetic-spectrophotometric method is proposed for the determination of trace amounts of bromide. The method is based on its catalytic effect on the oxidation of methylene blue (MB) by hydrogen peroxide in strongly acidic solution. The oxidation reaction is activated by large amounts of chloride and can be monitored spectrophotometrically by measuring the decrease in the absorbance of MB at 746 nm. The determination of bromide is performed by a fixed-time method at the first 100 s from the initiation of the reaction. Unlike other kinetic-spectrophotometric methods for the determination of bromide, the proposed method does not require heating the solution. Bromide can be determined in the range from 80 to 960 μg l⁻¹ with the detection limit of 35 μg l⁻¹. The relative standard deviation of ten replicate determination of 480 μg l⁻¹ bromide was 1.4%. The influence of potential interfering ions was studied. The proposed method was satisfactorily applied to the determination of bromide in seawater without interfering effect from chloride ion.     

Sequential injection spectrophotometric determination of trace amounts of iodide by its catalytic effect on the 4,4'-methylenebis(N,N-dimethylaniline)-chloramine-T reaction

A simple and sensitive sequential injection spectrophotometric procedure is proposed for the determination of trace amounts of iodide in pharmaceutical preparations. The method is based on the catalytic effect of iodide on the (tetra base) 4,4′-methylenebis(N,N-dimethylaniline)-chloramine-T reaction in acidic solution. The method involves a sequential aspiration of 255 μl sample/standard followed by 170 μl tetra base and then 128 μl chloramine-T solutions into a carrier stream to be stacked inside a holding coil and flow reversed through a reaction coil towards a detector. The resulting colored compound is measured at 600 nm using an UV/Vis-spectrophotometer. All the parameters that affect the reaction were evaluated and the calibration curve is linear over a range of 0.1–6.0 μg l⁻¹ of iodide concentration with detection limit of 0.05 μg l⁻¹. A sample throughput of 80 samples per hour and relative standard deviation of less than 2.0% was achieved. The method is successfully applied for the determination of iodide in three different samples (tablets).     

Catalytic determination of trace amounts of vanadium

Summary Some new oxidation reactions of arylamines catalysed by traces of vanadium have been found. It is shown that phenolic compounds have a favourable effect on these processes. Investigations were carried out on the oxidation ofp-phenetidine citrate by potassium chlorate in the presence of vanadium as catalyst and of phenol as activator. A colorimetric method for the determination of 0.1–8g of vanadium, based on this process, is reported.

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Zusammenfassung Einige neue, durch Vanadiumspuren katalysierte Oxydationsreaktionen von Arylaminen wurden gefunden. Phenolische Verbindungen haben auf diese Reaktionen erheblichen Einfluß. Die Oxydation vonp-Phenetidincitrat durch Kaliumchlorat bei Gegenwart von Vanadium als Katalysator und Phenol als Aktivator wurde untersucht. Eine kolorimetrische Methode zur Bestimmung von 0,1 bis 8g. Vanadium wurde auf dieser Grundlage ausgearbeitet.

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Résumé On a trouvé quelques nouvelles réactions d'oxydation des arylamines catalysées par des traces de vanadium. On montre que les composés phénoliques ont un effet favorable sur ces processus. On a effectué des recherches sur l'oxydation du citrate dep-phénétidine par le chlorate de potassium en présence de vanadium comme catalyseur et de phénol comme activateur. On présente une méthode colorimétrique pour le dosage de 0,1 á 8g de vanadium, fondée sur_ce procédé.

     

Kinetic determination of trace amounts of thiosulfate based on its inhibitory effect

The sulfur containing ligand viz., thiosulfate is found to inhibit the Ag(I) catalyzed substitution of cyanide in hexacyanoferrate(II) by phenylhydrazine. The inhibitory effect of thiosulfate is attributed due to its tendency to form complexes with Ag(I), leading to the production of inhibitor-catalyst complexes. The reactions, followed spectrophotometrically in aqueous medium at 488 nm, was possible by the increase in absorbance of the cherry-red product, [Fe(CN)₅PhNHNH₂]^3- at pH 2.8 (±0.02), at 30 (±0.1) °C, and an ionic strength (μ) of 0.02 M (KNO₃). The linear calibration curves were obtained using the absorbance measured at different times (A_t) and thiosulfate concentrations under specified conditions. The calculated detection limit was 4.9 × 10^-7 M. The Michaelis-Menten constant (K_m) and equilibrium constants for the formation of complexes between catalyst and inhibitor (K_CI), and the catalyst and substrate (K_S) were computed from the kinetic data. A general mechanistic scheme is proposed for this reaction.     

Catalytic determination of trace amounts of vanadium by means of the chromotropic acid-bromate reaction

A catalytic reaction-rate method is described for the determination of trace amounts of vanadium; the method is based on the vanadium-catalysed oxidation of chromotropic acid by bromate. The reaction was followed spectrophotometrically by measuring the rate of change in absorbance of chromotropic acid at 430 nm. The method is sensitive, rapid and simple, and allows determination of as little as 5 ng of vanadium. Of the many ions examined, iron(III), copper and tungsten(VI) interfered seriously at 100-fold concentrations. The relative standard deviation for 20 ng of vanadium (10 determinations) was 2.5%.     

Kinetic determination of silver at trace level based on its catalytic effect on a ligand substitution reaction

It is observed that Ag(I) catalyzes the rate of substitution of phenylhydrazine (PhNHNH₂) into hexacyanoferrate(II), producing a cherry red colored complex, [Fe(CN)₅PhNHNH₂]³⁻. The reaction was monitored at 488 nm leading to the formation of the complex under the conditions: [Fe(CN)₆]⁴⁻ (5.0 × 10⁻³ mol dm⁻³), PhNHNH₂ (2.0 × 10⁻³ mol dm⁻³), temperature (25 ± 0.1 °C), pH (2.8 ± 0.02), and ionic strength, I (0.02 mol dm⁻³), (KNO₃). Under optimum conditions, absorbance at fixed times (A _t ) is linearly related to Ag(I) in the concentration range 10.79–97.08 ng cm⁻³, in the presence of several diverse ions. The highest percentage error and relative standard deviations in the entire range of Ag(I) determination are found to be 2.5% and 0.16, with a detection limit of 8.75 ng cm⁻³ of silver(I). The experimental accuracies expressed in terms of percentage recoveries are in the range of 97.87–102.50. The method was successfully applied for the determination of Ag(I) in a few synthetic samples and found to be in good agreement with those obtained from atomic absorption spectrophotometry (AAS). The validity of the proposed method has also been tested for Ag(I) determination in spiked drinking water samples. The present catalytic kinetic method (CKM) is highly sensitive, selective, reproducible, and inexpensive. A review of recently published catalytic spectrophotometric methods for determination of Ag(I) has also been presented for comparison.     

Kinetic determination of uranium(IV) based on its catalytic effect on the phosphomolybdic acid-iodide reaction

A kinetic spectrophotometric method has been developed for the determination of trace amounts of uranium(IV) based on its catalytic effect on the phosphomolybdic acid iodide reaction. A significant feature of the proposed procedure is the selectivity for uranium(IV); it enables the determination of trace amount of uranium in the presence of large excess of rare metalions and other cations and anions. The method can be applied to the determination of uranium within the concentration range of 0–12μg· cm^?3, and the detection limit of the method is 0.02μg·cm^?3. Trace amounts of uranium in thorium nitrate and scandium oxide had been determined by the procedure and the results are satisfactory.     

Simultaneous polarographic determination of micro amounts of vanadium(V) and molybdenum(VI)

A simple and sensitive polarographic method has been developed for the determination of micro quantities of vanadium(V) and molybdenum(VI), based on the reduction of bromate, which is catalysed by these metal ions in the presence of 2,4-dihydroxyacetophenone oxime. Interference by various cations and anions has been investigated.     

柠檬酸-孔雀石绿系统催化动力学光度法测定痕量钒

钒是一种重要的微量元素[1,2],是人体不可缺少的微量元素之一.适量的钒有利于身体健康,但含量过多或过少都会引起某些器官的病变.同时,钒的类胰岛素作用使得生命有机体中钒的生化机理研究和开发治疗糖尿病钒口服药成为当前钒化学研究热点之一.另外,钒可以改善钢的性能,能增强钢的强度、弹性以及抗磨损和抗爆裂性,并且能耐高温又能抗奇寒.钒的氧化物已成为化学工业中最佳催化剂之一,有化学面包之称.因此,寻求一种对痕量钒准确检测的方法具有十分重要的意义.