Catalytic determination of nanogram amounts from iron(III) using its catalytic effect on the oxidation of sodium pyrogallol-5-sulphonate by hydrogen peroxide

A kinetic method is described for the determination of iron(III) based on its catalytic effect on the oxidation of sodium pyrogallol-5-sulphonate by hydrogen peroxide. The reaction was followed spectrophotometrically by measuring the rate of change in the absorbance of the coloured product at 436.8 nm. Nanogram amounts of iron(III) (2.0-75.0 ng cm(-3)) can be determined with good accuracy and reproducibility. The influence of foreign ions on the results was investigated and the method was found to be adequately selective. It has been applied satisfactorily to the determination of iron(III) in tap water samples. The kinetic parameters of both the catalysed and uncatalysed reactions are reported.     

Kinetic determination of traces of manganese(II) by its catalytic effect on the oxidation of acid blue 45 with hydrogen peroxide

A catalytic method is described for the determination of trace amounts of manganese(II) based on its catalytic effect on the hydrogen peroxide oxidation of an anthraquinone dye, Acid blue 45 (C.I. 63010). The reaction is followed spectrophotometrically by measuring the rate of change in absorbance of the dye at 595 nm. The calibration graph (rate constant (tg α) vs. manganese concentration) is linear in the range 4–25 ng Mn ml^?1, the relative standard deviation being 1.9% at the 13 ng Mn ml^?1 level. There are few interferences. The kinetic parameters of the reaction were investigated and the role of hydrogen peroxide and hydrogencarbonate ions is discussed.     

Kinetic thermometric determination of traces of manganese by its catalytic effect on the reaction between Tiron and hydrogen peroxide

We have developed a highly sensitive kinetic thermometric method for the determination of traces of Mn(II) by its catalytic effect on the oxidation of Tiron by hydrogen peroxide. The reaction is monitored by the initial-rate method, which is applied to temperature-time curves. Under the optimum conditions established in preliminary experiments, manganese can determined over the range 1–120 ng/mL, with an rsd of 5.8% and 1.3% for S ng/mL and 40 ng/mL Mn(II), respectively. The proposed method is subjected to few interferences, the most serious of which is posed by Pb(II), with a tolerated ratio of 201. The method was satisfactorily applied to the determination of Mn(II) in various types of sample (water, beer and wine).

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Zusammenfassung Es wurde eine hochempfindliche kinetische thermometrische Methode zur Bestimmung von Spuren an Mn(II) anhand dessen katalytischen Effektes auf die Oxidation von Tiron mit Wasserstoffperoxid entwickelt. Der Verlauf der Reaktion wurde über die Anfangsgeschwindigkeiten bei den Temperatur-Zeit-Kurven verfolgt. Unter in Vorexperimenten ermittelten optimalen Bedingungen kann Mangan im Bereich 1–120 ng/ml mit einer relativen Standardabweichnung von 5.8% bzw. 1.3% für 5 ng/ml bzw. 40 ng/ml Mn(II) bestimmt werden. Das Verfahren wird von einigen Kreuzwirkungen beeinflußt, von denen die intensivste der Einfluß von Pb(II) mit einem zulässigen Verhältnis von 201 ist. Diese Technik konnte zur Bestimmung von Mn(II) in den verschiedenartigsten Proben (Wasser, Bier, Wein) zufriedenstellend angewendet werden.

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The financial support of DGIC.I (Grant PS 89-0146) is grealfully acknowledged.     

Kinetic determination of traces of copper(ii) by its catalytic effect on the oxidation of 4,4'-dihydroxy-benzophenone thiosemicarbazone by hydrogen peroxide

The kinetic method is based on the catalytic effect of copper(II) on the oxidation of 4,4'-dihydroxybenzophenone thiosemicarbazone by hydrogen peroxide. The reaction is followed spectrophotometrically at 415 nm. The kinetic parameters of the reaction are reported and a rate equation is suggested. Three methods of rate measurement are compared. The calibration graphs are linear in the range 10–90 ng Cu ml^-1. There are few interferences. The method is applied to the determination of copper in waters.     

Kinetic spectrophotometric method for the determination of urinary cobalt based on its catalytic effect on the oxidation of -adrenaline hydrochloride by hydrogen peroxide

A catalytic for determination of nanomolar concentrations of Co(II), i.e., oxidation of -adrenaline hydrochloride with H₂O² in alkaline medium, is proposed. The reaction gives a low limit of detection of 2.5 × 10 ⁻⁹ M Co(II) in the reaction mixture, good reproducibility with a relative standard deviation (R.S.D.) of 4−5% in the Co(II) concentration range 8.0 × 10⁻⁹−8.0 × 10⁻⁸M and good selectivity. On the basis of this indicator reaction, a catalytic-spectrophotometric method for the determination of cobalt in small urine samples (5.00 ml) was elaborated. The analysis of 17 urine samples, taken from healthy persons of different ages, gave cobalt concentrations in the range 0.20–1.50 μmol 1⁻¹. The R.S.D. for ten replicate analyses of a urine sample with an average cobalt content of 0.63 μmol 1⁻¹ was 5.6%. The reliability of the method was verified by a comparative photometric method (r = 0.9755) and by a determination based on known additions of cobalt (r = 0.9894).     

Spectrophotometric determination of osmium based on its catalytic effect on the oxidation of carminic acid by hydrogen peroxide

A highly sensitive spectrophotometric method is described for the determination of trace amounts of osmium(VIII), based on its catalytic effect on the oxidation of carminic acid by hydrogen peroxide. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of carminic acid at 540 nm after 3 min of mixing the reagents. The optimum reaction conditions were 1x10(-4) mol l(-1) carminic acid, 0.013 mol l(-1) hydrogen peroxide and pH 10 at 25 degrees C. By using the recommended procedure, the calibration graph was linear from 0.1 to 1.5 ng ml(-1) of osmium; the detection limit was 0.02 ng ml(-1); the RSD for five replicate determinations of 0.2-1.4 ng ml(-1) was in the range of 1.8-4.7%. The influence of several foreign ions on osmium determination were studied and the effect of interfering ions were removed by extracting osmium into isobuthyl methyl ketone and back extracting into sodium hydroxide solution.     

Kinetic-spectrophotometric determination of palladium in hydrogenation catalyst by its catalytic effect on the oxidation of pyrogallol red by hydrogen peroxide

A new kinetic-spectrophotometric method is described for the determination of ultra trace amounts of Pd(II). The methods based on catalytic action of Pd(II) on the oxidation of pyrogallol red (PGR) with hydrogen peroxide at pH 9.7. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of the PGR at 540 nm, for the first 4.5 min from initiation of the reaction. Calibration curve was linear in the range of 0.02-1.00 microg ml(-1) Pd(II). The limit of detection is 0.017 microg ml(-1) Pd(II). The relative standard deviation (R.S.D.) for ten replicate analyses of 0.03 and 0.60 microg ml(-1) Pd(II) was 1.5 and 0.9%, respectively. The influence of more than 40 potential interfering ions was studied for the selectivity. The proposed method was used for the determination of palladium in catalytic material.     

Kinetic catalytic determination of trace levels of iodide based on the oxidation of basic dyes with hydrogen peroxide monitored potentiometrically using simple PVC electrodes

Four sensitive catalytic potentiometric methods have been developed for trace levels determination of iodide based on its catalytic effects on the oxidation of four dyes: viz. variamine blue (VB), rhodamine B (RB), methylene blue (MB) and malachite green (MG), with H₂O₂ in H₃PO₄ medium at 25 ± 0.5 °C. The catalyzed reaction rates were estimated potentiometrically by monitoring the potential of the corresponding dye-PVC ion selective electrodes. To select the optimized reaction conditions offering the highest sensitivity of the method, parallel studies were carried out on each dye catalyzed reaction including: the effect of reactant concentration, reaction medium and temperature. The working calibration curves were linear over the concentration range from 0.32 to 2.54 mg L⁻¹ iodide for VB method and from 3.2 to 12.7 mg L⁻¹ for other ones. The tolerance limits of more than 20 interfering species were listed indicating the high selectivity of the method. Trace iodide in edible salt and pharmaceutical samples was determined without the need for separation or preconcentration procedures.     

Flow injection determination of iron by its catalytic effect on the oxidation of 3,3',5,5'-tetramethylbenzidine by hydrogen peroxide

A flow injection-photometric method has been developed for the determination of iron(II+III). The method is based on the catalytic effect of iron(III) on the hydrogen peroxide oxidation of 3,3',5,5'-tetramethylbenzidine to form a blue compound (lambda(max)=650 nm). In this catalyzed reaction, 1,10-phenanthroline acted as an effective activator. Iron(II) is also determined, being oxidized by hydrogen peroxide. Calibration graphs for iron(II) and iron(III) obtained under the optimized conditions were identical with each other and linear in the range 0.2-200 ng ml(-1) with a detection limit of 0.05 ng ml(-1) iron. The reproducibility was satisfactory with a relative S.D. of 1.0% for ten determinations of 5 ng ml(-1) iron(III). The proposed method was successfully applied to the determination of iron in river and lake water samples and can be determined free iron species.     

Determination of copper by its catalytic effect on the oxidation of hydroquinone by hydrogen peroxide on supports

The reaction of oxidation of hydroquinone by hydrogen peroxide catalyzed by copper(II) in the presence of 2,2’-dipyridyl is activated by hexamethylenediamino groups that are bonded to the surface of filter paper; additional activating effect is produced by 2,2′-dipyridyl. The introduction of malonic acid dinitrile into the indicator reaction improves the sensitivity of the determination of copper and the contrast of the reaction in solution because of the formation of a blue product. Differently colored compounds are formed on a paper support at different concentrations of copper, which makes it possible to visually distinguish the quantities of copper that differ by an order of magnitude in the range 1 × 10^-5-0.5 μg. Quantitative detection is possible in the range 5 × 10^-6-0.1 μg (c_min = 3 × 10^-6 μg). The concentration of copper (0.2-1.5 μg/mL) is determined in blood serum; the consumption of the sample per one determination is 3 μL     

Kinetic determination of traces of manganese in different materials by its catalytic effect on the methylene green-periodate reaction

The oxidation of Methylene Green by sodium periodate is a slow process. A kinetic method based on the catalytic effect of manganese(II) on this reaction in the presence of 1,10-phenanthroline as activator is described. The reaction is followed spectrophotometrically by measuring the decrease in the absorbance of the dye at 620 nm. Under the optimal experimental conditions [4 x 10(-5)M Methylene Green, 0.2M acetate buffer (pH 4), 2 x 10(-3)M 1,10-phenanthroline, 2.5 x 10(-3)M sodium periodate, 35 degrees ], manganese(II) between 0.2 and 30 ng ml is determined by the tangent method. The accuracy of the method and the influence of 44 foreign ions have been studied and an equation for the kinetics of the catalysed reaction is proposed. The procedure has been applied to the determination of manganese in water, milk and beer with excellent results.     

Spectrophotometric reaction rate method for the determination of molybdenum by its catalytic effect on the oxidation of pyrogallol red with hydrogen peroxide

A kinetic spectrophotometric method for the determination of molybdenum is based on its catalytic effect on the oxidation of pyrogallol red with hydrogen peroxide. The decrease of the absorbance of pyrogallol red in the presence of hydrogen peroxide with time from 0.5 to 4.5 min is proportional to the concentration of Mo(VI) over the range 0.010–0.500 μg/mL. The limit of detection is 0.008 μg Mo/mL. The precision and the effect of the presence of more than forty ions on the molybdenum determination are reported. Probable interferences are completely removed by a cation exchange resin. The procedure was successfully applied to the determination of molybdenum in plant materials and steels. Received: 28 April 1997 / Revised: 16 June 1997 / Accepted: 18 June 1997     

Spectrophotometric reaction rate method for the determination of molybdenum by its catalytic effect on the oxidation of pyrogallol red with hydrogen peroxide

A kinetic spectrophotometric method for the determination of molybdenum is based on its catalytic effect on the oxidation of pyrogallol red with hydrogen peroxide. The decrease of the absorbance of pyrogallol red in the presence of hydrogen peroxide with time from 0.5 to 4.5 min is proportional to the concentration of Mo(VI) over the range 0.010–0.500 μg/mL. The limit of detection is 0.008 μg Mo/mL. The precision and the effect of the presence of more than forty ions on the molybdenum determination are reported. Probable interferences are completely removed by a cation exchange resin. The procedure was successfully applied to the determination of molybdenum in plant materials and steels. Received: 28 April 1997 / Revised: 16 June 1997 / Accepted: 18 June 1997     

Kinetic fluorimetric determination of silver by its catalytic effect on the oxidation of pyridoxal nicotinylhydrazone by potassium peroxidisulphate

Summary The oxidation of pyridoxal nicotinylhydrazone by potassium peroxidisulphate, catalysed by traces of silver(I), has been studied and used for the kinetic determination of this ion. The reaction is followed spectrofluorimetrically by measuring the rate of change in the fluorescence intensity (_ex 365, _em 450 nm). The calibration graph is linear in the silver range 60–720 ng/ml. The variables affecting the method have been optimized and the tolerance levels of foreign ions determined. The solvent extraction method with dithizone is used to eliminate interferences in the determination of silver in synthetic samples.

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Kinetisch-fluorimetrische Bestimmung von Silber auf der Grundlage seiner katalytischen Wirkung bei der Oxydation von Pyridoxal-nikotinylhydrazon durch Kaliumperoxydisulfat

Zusammenfassung Die durch Silberspuren katalysierte Oxydation wurde untersucht und für deren kinetische Bestimmung verwendet. Die Reaktion wird spektrofluorimetrisch ausgewertet, indem man das Ausmaß der Veränderung der Fluoreszenzintensität (_ex=365, _em=450 nm) bestimmt. Die Eichkurve verläuft für 60–720 ng Ag/ml linear. Die das Verfahren beeinflussenden Reaktionsbedingungen wurden optimiert und die Toleranzgrenzen fremder Ionen bestimmt. Störfaktoren bei der Silberbestimmung in synthetischen Proben wurden durch Extraktion mit Dithizon beseitigt.

     

Kinetics of the molybdate catalyzed oxidation of iodide by hydrogen peroxide

The kinetics of the oxidation of iodide by hydrogen peroxide catalyzed by acidic molybdate have been studied by a spectrophotometric stopped-flow method. The results are interpreted in terms of the mechanism and the implied rate law where [mol] is total analytical concentration of molybdate. The values obtained for the rate and equilibrium constants are k₄ = (3.3 ± 1) × 10² 1./mole · s, K₁ = (1.2 ± 0.6) × 10⁴ 1./mole, K₂ = (1.3 ± 0.7) × 10³ 1./mole, and K₃ = (4 ± 3) × 10² 1./mole at 298°K.     

The kinetics of iodide oxidation by hydrogen peroxide in acid solution

The kinetics of the complex reaction between I⁻ and H₂O₂ in acid media was investigated. The particular attention was focused on the determination of the rate constant of the reaction between HIO and H₂O₂ involved in the investigated complex process. The examination of the whole kinetics was performed by simultaneously monitoring the evolution of O₂ pressure, I₃⁻ and I⁻ concentrations. We modeled the behavior of experimentally followed components based on Liebhafsky’s research. Our preliminary results suggest a significantly higher rate constant (3.5 × 10⁷ M⁻¹ s⁻¹) of the reaction between HIO and H₂O₂ as those proposed in the literature.     

Kinetic spectrophotometric determination of traces of molybdenum(VI) by its inhibitory effect on the oxidation of 4-hydroxycoumarine by potassium permanganate.

The present paper describes a simple, selective and sensitive kinetic method for the determination of trace amounts of molybdenum(VI) based on its inhibitory effect on the reaction oxidation of 4-hydroxycoumarine by KMnO(4) in the presence of hydrochloric acid, at pH 1.75 at 25 degrees C. The rate of the indicator reaction was followed spectrophotometrically by measuring the decrease in the absorbance of KMnO(4) at 525 nm. The development method includes optimization of the reagent concentration and temperature. The calibration graph was linear in the range of concentrations from 20 to 200 ng/cm(3) of molybdenum(VI). The probable relative error was in the interval 3.10 - 10.52% for the concentration range of 200 - 20 ng/cm(3) molybdenum(VI), respectively. The interference effects of the foreign ions were determined to assess the selectivity of the method. The developed method was found to have relatively good selectivity, sensitivity, simplicity and rapidity. The proposed method was applied to the determination of molybdenum(VI) in a particular type of steel and alloy (hastelloy).     

Kinetic determination of traces of manganese(II) by its catalytic effect on the autoxidation of 1,4-dihydroxy phthalimide dithiosemicarbazone

A kinetic method is described for the determination of trace amounts of manganese(II) based on its catalytic effect on the aerial oxidation of 1,4-dihydroxyphthalimide dithiosemicarbazone. The reaction is followed spectrophotometrically by measuring the rate of change in absorbance at 594 nm. The calibration graph (rate constant vs. manganese concentration) is linear in the range 10–90 ng Mn ml^-1. The preparation and properties of the reagent are described and the kinetic parameters of the reaction are reported. There are few interferences.     

过氧化氢氧化灿烂甲酚蓝动力学光度法测定痕量铝

基于pH3.6的乙酸 乙酸钠缓冲介质中Al3 对过氧化氢氧化灿烂甲酚蓝(BCB)褪色反应的催化作用,提出了测定痕量铝的新的催化动力学光度法。研究了该法的适宜反应条件,方法的线性范围为0～100ng mL,检出限为0.9ng mL。方法已用于样品中痕量铝的测定。     

Kinetic and mechanistic study of the chlorpromazine-hydrogen peroxide reaction for the catalytic spectrophotometric determination of iodide

Extensive kinetic studies were performed to investigate the mechanism of the chlorpromazine (CP)-hydrogen peroxide reaction utilized in the catalytic determination of iodide. This reaction proceeds by two independent, parallel reactions, one through the formation of a red free radical, another directly to form the colorless product. The red color formation is catalyzed by traces of iodide. The color formation reaction was followed by measuring the increase in absorbance at 525 nm and its kinetic investigations were carried out by the initial rate method. The reaction rate curves for colorless sulfoxide formation were obtained by following the increase in absorbance at 335 nm, and the analysis was carried out by the integration method. The disappearance rate of CP is given by -d[CP]dt = k₃[I⁻[H₂O₂][H⁺] + k₆[CP][H₂O₂][H⁺] + k₉[CP][H₂O₂][H⁺] + k₁₀[CP][H₂O₂], where the first and second terms correspond to the chromogenic reaction and the third and fourth to colorless sulfoxide formation. Mechanisms consistent with each term were proposed and analytical implications of the kinetic studies are discussed.