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     

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.     

Determination of formaldehyde by its catalytic effect on the oxidation of pyrogallol red by bromate using flow-injection spectrophotometric detection

This paper reports a simple and sensitive flow-injection method for the spectrophotometric determination of formaldehyde based on the catalytic effect of formaldehyde on the oxidation of pyrogallol red with bromate in acidic media. The decrease in absorbance of the reaction mixture was measured at 470 nm. The calibration graph was linear in the range of 0.47 to 40.0 μ/mL formaldehyde for a sample rate of 30±5 samples per hour. The limit of detection is 0.36 μ/mL. The relative standard deviations for ten replicate measurements of 2.5, 5.0, and 20.0 μ/mL formaldehyde were 3.9, 2.1, and 0.7%, respectively. The method was applied to the determination of formaldehyde in river water, shampoo, and melamine-formaldehyde resin. The text was submitted by the authors in English.     

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 iodide by its catalytic effect on oxidation of sodium pyrogallol-5-sulfonate by hydrogen peroxide.

The kinetic method is based on a catalytic effect on the oxidation of sodium pyrogallol-5-sulfonate by hydrogenperoxide. The reaction is followed spectrophotometrically at 436.8 nm. The kinetic parameters of the reaction are reported and a rate equation is suggested. The calibration graph is linear in the range 10-200 ng cm(-3). The effects of certain foreign ions upon the reaction rate were determined for the assessment of the selectivity of the method. This method has high sensitivity and good selectivity when anions are concerned as well. That is why it can be successfully applied to determination of iodide in real samples (mineral water and soil) directly after the elimination of cations, which interfere. The method was applied to determine iodide in natural waters and soil.     

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).     

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.     

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 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 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.     

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.     

酶催化动力学光度法测定H2O2

H2O2能够氧化偶氮染料刚果红使之褪色,而模拟酶—血红蛋白对其具有催化作用。据此建立了一种以刚果红为指示剂的H2O2-刚果红-血红蛋白酶催化反应体系测定痕量H2O2的新方法。确定了反应的最佳条件,体系的酸度为pH10.7的NH3-NH4Cl缓冲溶液,最大吸收波长为497 nm。该法的线性范围为8.0×10^-8-8.0×10^-5mol/L,检出限为1.97×10^-9mol/L,表观摩尔吸光系数为4.6×10^4L.mol-1.cm^-1。该方法可用于雨水及消毒水中H2O2的测定。     

过氧化氢存在下平行催化氢波法测定奥沙普秦

在0.2mol/LKH2PO4-Na2HPO4(pH5.5±0.1)支持电解质中,奥沙普秦产生一催化氢波,峰电位Ep=-1.25V(vs.SCE)。当1×10-2mol/LH2O2存在时,该催化氢波的峰电流增加12倍,峰电位基本不变,产生一较灵敏的平行催化氢波。其二阶导数峰峰电流ip″与奥沙普秦浓度在1.0×10-7~2.6×10-5mol/L范围内呈线性关系(r=0.9995,n=10),检出限为5.0×10-8mol/L。该方法可用于药物制剂中奥沙普秦含量的测定。     

Spectrofluorimetric determination of tannins based on their activative effect on the Cu(II) catalytic oxidation of rhodamine 6G by hydrogen peroxide

A simple and highly sensitive kinetic fluorimetric method is proposed for the determination of trace tannins, based on the activation of tannins on the oxidation of rhodamine 6G (Rh 6G) by hydrogen peroxide catalyzed by Cu(II) ion. The calibration graph was rectilinear in the range 0.08-1.28 mg l⁻¹ for tannin, the 3σ detection limit for tannin is 0.0455 mg l⁻¹. The relative standard deviation for 11 determinations of 0.4 mg l⁻¹ tannin is 0.96%. The proposed method has been successfully used to determine tannins in tea and Chinese gall. The results obtained were compared with those provided by the Folin-Ciocalteu method. This is the first procedure to be reported for the determination of tannins based on fluorimetric measurements.     

Determination of iron by catalytic oxidation of p-aminophenol by hydrogen peroxide

The oxidation reaction of p-aminophenol by hydrogen peroxide was studied in the presence of ferric ions, which catalyzes it. The corresponding rate constants were calculated and the activation energy was determined. A method for ultramicrodetermination of ferric ion was developed using the method of tangents. Determination of ferric ions from 0.5 × 10^?1 up to 4.5 × 10^?2 μg/ml is possible with a relative mean error of ± 1.55%. The influence of several ions was also investigated.