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-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.     

Spectrophotometric reaction rate method for the determination of osmium by its catalytic effect on the oxidation of gallocyanine by bromate

A simple kinetic spectrophotometric method was developed for the determination of osmium. The method is based on the catalytic effect of osmium as osmium tetroxide on the oxidation of gallocyanine by bromate at pH 7. The reaction is monitored spectrophotometrically by measuring the decreasing absorbance of gallocyanine at 620 nm by the fixed-time method. A detection limit of 0.01 ng/ml and linear calibration curve from 0.1 to 100 and from 100 to 1200 ng/ml Os(VIII) is reported. The relative standard deviation for 0.0100 microg/ml Os(VIII) is 0.8% (N = 10). The method is free from most interferences. Osmium in synthetic samples is determined by this method, with satisfactory results.     

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.     

Spectrophotometric study of the reaction rate of 2,4-diaminophenol oxidation by hydrogen peroxide

The noncatalytic oxidation of 2,4-diaminophenol by H₂O₂ was studied. The corresponding rate constants were calculated and the activation energy was found.     

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).     

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.     

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.     

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     

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.     

Spectrophotometric determination of vanadium in different oxidation states with pyrogallol

Determination of vanadium at low concentrations is easily performed with pyrogallol as a ligand which forms a bluish-violet complex with vanadium(III), (IV) or (V). The colour of the bluish-violet complex (lambda(max) = 580 nm) contrasts well with the colour of both pyrogallol and vanadium. The complexes are stable for several hours. Beer's law is obeyed over the range 0-14 mug/ml vanadium at pH 6. The apparent molar absorptivity at 580 nm is (7.75 +/- 0.25) x 10(3)1.mole(-1).cm(-1). The effects of diverse ions on the determination of vanadium have been fully studied. Only Mo(VI) and W(VI) interfere seriously. The method is selective, sensitive and can be applied to the determination of total vanadium in a variety of 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 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 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.     

Spectrophotometric determination of nitrite based on its catalytic effect on the oxidation of carminic acid by bromate

A highly sensitive and selective method is described for the determination of trace amounts of nitrite based on its effect on the oxidation of carminic acid with bromate. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of carminic acid at 490 nm after 3 min of mixing the reagents. The optimum reaction conditions were 1.8×10⁻¹ mol l⁻¹ H₂SO₄, 3.8×10⁻³ mol l⁻¹ KBrO₃, and 1.2×10⁻⁴ mol l⁻¹ carminic acid at 30°C. By using the recommended procedure, the calibration graph was linear from 0.2 to 14 ng ml⁻¹ of nitrite; the detection limit was 0.04 ng ml⁻¹; the R.S.D. for six replicate determinations of 6 ng ml⁻¹ was 1.7%. The method is mostly free from interference, especially from large amounts of nitrate and ammonium ions. The proposed method was applied to the determination of nitrite in rain and river water.     

Copper(II) determination by means of a thermometric method based on its catalytic effect on the hydrazine-hydrogen peroxide reaction

A new catalytic-thermometric method for Cu(II) determination at ppb levels has been established based on the hydrazine-hydrogen peroxide redox reaction. The reaction rate is obtained from the temperature-time curve and shows two linear response zones, between 15–200 ppb and 0.1–0.9 ppm, with a relative standard deviation of 2.0% and 2.2%, respectively. Only 20 ppm of Pb(II) and Fe(III), 1 ppm of Mn(II) and 5 ppb of Co(II) interfere. Interferences of Pb(II) and Fe(III) can be eliminated by the use of maskings. The proposed method can be applied to determine Cu(II) in several samples. In the present paper, this method has been applied to determine Cu(II) in wine.     

Spectrophotometric determination of aluminium and gallium with pyrogallol red and cetyltrimethylammonium ions

Spectrophotometric methods are described for the determination of microgram amounts of aluminium and gallium based on the formation of a ternary complex between the metal, pyrogallol red, and cetyltrimethylammonium bromide. The complexes have absorbance maxima at 610 and 615 nm, respectively, with molar absorptivities of 4.8 × 10⁴(Al)and 1.0 × 10⁵ liter mol^?1 cm^?1 (Ga). Numerous metals interfere. Gallium can be separated by extraction of gallium from 7 M hydrochloric acid with di-isopropyl ether. However, aluminium can be separated by extraction of interfering ions with cupferron.     

Kinetic spectrophotometric determination of low levels of nitrite by catalytic reaction between pyrogallol red and bromate

A kinetic spectrophotometric method for the determination of trace nitrite (0.003-1.000 microg/ml) based on its catalytic effect on the reaction between potassium bromate and pyrogallol red in acidic media is described. The reaction is monitored spectrophotometrically by measuring the decreasing colour of pyrogallol red at 467 nm by the fixed-time method. At a given time of 3.0 min at 30 degrees, the detection limit is 0.001 microg/ml and the relative standard deviation for 0.010 microg/ml nitrite is 1.8% (n = 8). The method is free from most interferences, especially from large amounts of nitrate and ammonium. The procedure was successfully applied to the determination of trace nitrite in natural water without preconcentration.     

Spectrophotometric determination of trace iron by using its catalytic effect on the N-phenylanthranilic acid-potassium periodate reaction.

The analytical features of the reaction between N-phenylanthranilic acid (PAA) and potassium periodate in acidic medium are explored with the aim of improving the catalytic kinetic determination of iron in water samples. In the presence of Fe(II, III), PAA is oxidized by potassium periodate in a formic acid medium to form a violet-colored compound. The reaction is followed spectrophotometrically by measuring the increase in the absorbance of the oxidation product at 525 nm. The variables that affected the reaction rate were investigated and the reaction conditions were established. Calibration graphs are linear in the range of concentrations 2 - 500 ng mL(-1). As low as 10(-8) mol L(-1) Fe(II, III) can be easily determined by the fixed time method. The established catalytic method was successfully applied to the determination of iron in tap water and in pharmaceutical samples.     

Spectrophotometric determination of traces of bromide based on its catalysis of the pyrocatechol violet/hydrogen peroxide reaction

A kinetic-spectrophotometric method for the determination of bromide (0.004–0.3 mg l^?1) based on its catalysis of the oxidation of pyrocatechol violet by hydrogen peroxide in HCl/H₂SO₄ is described. The effect of bromide is greatly increased in the presence of large amounts of chloride. The relative standard deviations are 6.4 and 13% for 0.034 and 0.010 mg l^?1 bromide, respectively (n = 10). Most ions commonly occurring in natural waters do not interfere except for iodide.