Kinetic Spectrophotometric Determination of Vanadium (V) Based on its Inhibitory Effect on the Thionine – Ascorbic Acid Reaction

ABSTRACT

A simple and sensitive kinetic method for the determination of vanadium(V) based on its inhibitory effect on the reduction of thionine by ascorbic acid at pH=5 is described. The reaction rate is monitored spectrophotometrically by measuring the decrease in absorbance of thionine at 598 nm after a fixed time (10 min). The calibration graph is linear in the range of 10 ? 120 ng ml^?1 of vanadium(V) and the detection limit is 6 ng ml^?1. The relative standard deviation (RSD) for 80 ng ml^?1 of V(V) was 0.96% (n=10). The method was successfully applied to the determination of vanadium in a certified reference sample.     

Flow-injection spectrophotometry of vanadium by catalysis of the bromate oxidation of N,N'-bis(2-hydroxyl-3-sulfopropyl)-tolidine

A highly sensitive flow-injection method is proposed for the catalytic determination of vanadium(V) at sub-nanogram per milliliter levels using a new indicator reaction. The method is based on the catalytic effect of vanadium(V) on the bromate oxidation of N,N′-bis(2-hydroxyl-3-sulfopropyl)-tolidine. 1,2-Dihydroxybenzene-3,5-disulfonate was used as an activator in the vanadium(V)-catalyzed reaction and significantly enhanced the sensitivity of the method. Vanadium(V) in the range 0.01-3.0 ng ml⁻¹ was easily determined with sampling rate of about 30 h⁻¹. Vanadium(IV) could be also determined. The limit of detection (S/N=3) was 0.008 ng ml⁻¹ and the relative standard deviations were 1.4 and 1.6% for ten determinations of 0.2 ng ml⁻¹ vanadium(IV) and vanadium(V), respectively. Interferences from metal ions could be suppressed by the addition of ethylenediamine-N,N,N′,N′-tetrakis(methylenephosphonic acid) as a masking agent. The proposed method was successfully applied to the determination of vanadium in water samples.     

Kinetic-Spectrophotometric Determination of Molybdenum(VI) Based on Its Catalytic Effect on the Thionine-Hydrazine Reaction

Abstract

A kinetic method for the determination of trace amounts of Mo(VI) (0.05-4 μg ml^?1) based on its catalytic effect on the reduction of thionine by hydrazine monochloride in strongly acidic media is reported. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of thionine at 605 nm after a fixed time (5 min.). The detection limit of the method is 23 ng ml^?1 and the relative standard deviation (RSD) for 0.05 μg ml^?1 of Mo(VI) is 1.2% (n=7). The method is almost free from interferences, especially from large amounts of tungsten. The procedure was successfully applied to the determination of trace amounts of molybdenum in steel.     

Determination Of SE(IV) in the Presence of SE(VI) at NG ML− Concentration Levels by a Kinetic Spectrophotometric Method

ABSTRACT

The catalytic effect of Se(IV) on the reduction reaction of thionine(TN) by sulfide ion is used for determination of trace amounts of selenium(IV) ion by a kinetic-spectrophotometric method. This new method is simple and highly sensitive. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of the reaction mixture at 598 nm. The fixed time method was used for the first 45s from initiation of the reaction. Under the optimum conditions, in the concentration range of 2-90 ng ml^? of selenium(IV), a quite linear regression equation (r = 0.9984, n = 14) was obtained. The experimental detection limit of the method (S/N = 3) was 1.3 ng ml^?. The relative standard deviation of ten replicate measurements is 2.51% for a 40 ng ml^? solution of selenium. The proposed method is used to the study of selenium (IV,VI) speciation in water at ng ml^? levels. This method was extended for the determination of selenium in real samples.     

Spectrophotometric Catalytic Determination of Trace Amounts of Selenium Based on the Reduction of Azurea by Sulphide

ABSTRACT

A sensitive catalytic kinetic spectrophotometric method for determining ng ml^?1 concentrations of selenium is described. The method, based on the catalytic effect of Se (IV) on the reduction of azureA by sulphide, is monitored spectrophotometrically at 600 nm. The linearity range of the calibration graph is dependent on the concentration of sulphide. The variables affecting the rate of the reaction were investigated and the optimum conditions were established. The method is simple, rapid, precise, sensitive, free from many interferences and is widely applicable. The limit of detection is 2.5ng ml^?1 of Se. The relative standard deviation of seven determinations of 100 ng ml^?1 Se was 1.5%. The method was applied to the determination of selenium in spiked water, Kjeldahl tablets, synthetic samples and health care products.     

The application of the ph-stat method to metal ion-catalyzed reactions

The pH-stat method, which is well known in organic chemistry and biochemistry, is used for the kinetic determination of metal ion catalysts. Indicator reactions that involve protons can be followed by controlled addition of standard base or acid. This is illustrated by the following examples: determination of copper(II) (0.03–0.3 μg ml^-1) with the indicator reaction ascorbic acid—peroxydisulphate; determination of molybdenum(VI) (0.2–2.5 μg ml^-1) with the indicator reaction thiosulphate—hydrogen peroxide; determination of zirconium(IV) (0.2–2 μg ml^-1) with the indicator reaction iodide—hydrogen peroxide; and determination of vanadium(V) (0.2–2 μg ml^-1) with the indicator reaction iodide—bromate. For one example, the copper—ascorbic acid—peroxydisulphate reaction, it is shown that the pH-stat method has distinct advantages over closed systems, giving considerably better sensitivity for the determination of copper (0.5–5 ng ml^-1 ).     

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-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-catalytic determination of vanadium in non-aqueous solvents

Determination of trace vanadium in organic solvents is studied by use of the oxidation of o-dianisdine with t-butyl hydroperoxide. The sensitivity of the catalyzed reaction is optimized by application of a modified simplex method. Under optimum conditions the detection limit is 0.7 ng V ml^?1 in acetonitrile and the relative standard deviation is 0.048. The effect of other metal ions and of co-solvents is discussed. The method is used for trace determinations of vanadium in organic solvents of high purity.     

Kinetic-Spectrophotometric Determination of Traces of Osmium by Its Catalytic Effect on the Oxidation of Pyrogallol Red by Hydrogen Peroxide

Abstract

A Kinetic-spectrophotometric method for the determination of ultra-trace amounts of osmium(VIII) is described. It is based on the catalytic action of osmium(VIII) on the oxidation of pyrogallol red with hydrogen peroxide, yielding a colorless product in neutral medium. The reaction is followed spectrophotometrically by measuring the rate of change in absorbance at 540 nm and 30°C. Os(VIII) in the range 0.005 -100 ng.ml^?1 can be determined. The proposed method is hardly subject to interferences. The relative standard deviation is 1.5% for 1 ng.ml^?1 of Os(VIII). The kinetic parameters of the catalyzed and uncatalyzed reactions are reported. The detection limit is 1 pg.ml^?1.     

FLOW - Injection Determination of Traces of Sulfide by the Brilliant Green - Sulfide Reaction with Spectrophotometry Detection

Abstract

A flow injection system is proposed for the rapid and sensitive determination of trace amounts of sulfide based on the addition reaction of sulfide with Brilliant Green at pH 7 and 25 C°. The effect of important parameters, such as reagent concentration, pH, reagent flow rate, sample volume, temperature and length of the reaction coil are reported. Sulfide in the range of 40 - 2000 ng·ml^?1 can be determined at a rate of 40 ± 5 samples per hour. The limit of detection was obtained as 2.0 ng of sulfide. The relative standard deviation for the determination of 100 ng·ml^?1 of sulfide is 0.8%. A system is proposed for elimination of potential interferences. The method was applied to the determination of sulfide in synthetic samples and in spring water.     

Selective Kinetic Spectrophotometric Determination of Nitrite in Food and Water

Abstract

A highly selective and sensitive method for the kinetic spectrophothometric determination of sub-microgram amounts of nitrite has been development based on its reaction with Nile blue 2B in acidic medium. The reaction is monitored spectrophotometrically at 595 nm at a fixed time of 4.5 min. The change in absorbance at 595 nm is related to the concentration of nitrite in the range 0.005 - 1.100 μg.ml^?1 The detection limit is 0.001 μg.ml^?1. The relation standard deviation is 1% for 0.020 μg.ml^?1 of nitrite for ten replicate measurements. Most common anions and cations do not interfere. The procedure was applied to the determination of trace amounts of nitrite in sausage and water.     

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%.     

Determination of trace platinum by supramolecular catalytic kinetic spectrofluorimetry of β–cyclodextrin–platinum–KBrO3–salicylaldehyde furfuralhydrazone

A supramolecular catalytic kinetic spectrofluorimetric method was developed for the determination of platinum(IV) and the possible mechanism of catalytic reaction was discussed. The method was based on the fluorescence-enhancing reaction of salicylaldehyde furfuralhydrazone (SAFH) with potassium bromate, which was catalysed by platinum(IV) in a water–ethanol medium. β–Cyclodextrin (β-CD) obviously sensitized the determination at pH 5.20 and 25°C. Under optimum conditions, the β-CD–platinum–KBrO₃–SAFH supramolecular kinetic catalytic reaction system had excitation and emission maxima at 372 and 461 nm, respectively. The linear range of this method was 0.60–180 ng ml⁻¹ with a relative standard deviation of 1.2%, and the detection limit was 0.18 ng ml⁻¹. Investigation of the mechanism and the effects of interferences is presented. The proposed method was applied successfully to determine trace platinum(IV) in the chemotherapeutic drug cisplatin and serum from patients with satisfactory results.      

Catalytic Spectrophotometric Determination of Titanium(IV) Using Methylene Blue‐Ascorbic Acid Redox Reaction

A highly selective and sensitive catalytic method for the determination of trace amounts of titanium(IV) was developed. The method is based on the catalytic effect of titanium(IV) on the methylene blue‐ascorbic acid redox reaction. The reaction was followed spectrophotometrically by measuring the change in absorbance of methylene blue at 665 nm, 5 minutes after the initiation of the reaction. In this study experimental parameters were optimized and the effect of the presence of various cations and some anions on the determination of titanium(IV) was examined. The calibration graph was linear in the range of 3‐25 ng mL^?1 of titanium(IV). The relative standard deviation for the determination of 10 and 20 ng mL^?1 of titanium(IV) were 2.64% and 1.51%, respectively (n = 8). The detection limit calculated from three times of standard deviation of blank 3S_b was 0.6 ng mL^?1. The method was successfully applied to the determination of titanium(IV) in tap water and ore samples.     

Spectrophotometric catalytic determination of ultra-trace amounts of selenium based on the reduction of resazurin by sulphide

A sensitive catalytic method for determining ng ml^? concentration of selenium is described. The method is based on the catalytic action of Se(IV) on the reduction of resazurin by sulphide, monitored spectrophotometrically at 605 nm. The linearity range of the calibration graph is dependent on the concentration of sulphide. The variables affecting the rate of the reaction were investigated and the optimum conditions were established. The method is simple, rapid, precise, sensitive and widely applicable. As low as 8.0 × 10^?4 μg ml^?1 of selenium can be determined. The relative standard deviation of seven determination of 10 ng Se was 0.7%. The determination of Se(IV) in the presence of Se(VI) and the determination of total selenium are also described.     

Spectrophotometric determination of vanadium using variamine blue and its application to synthetic, environmental and biological samples

A simple, rapid and accurate spectrophotometric method is described for the determination of trace amounts of vanadium using variamine blue (VB) as a chromogenic reagent. The method is based on the oxidation of variamine blue to form a violetcolored species on reaction with vanadium(V), having an absorption maximum at 570 nm. Beer’s law is obeyed in the range of 0.1–2.0 μg ml^?1. The molar absorptivity and Sandell’s sensitivity were found to be 1.65 × 10⁴ l mol^?1 cm^?1 and 0.003 μg cm^?2, respectively. Optimum reaction conditions were evaluated in order to delimit the linear range. The effect of interfering ions on the determination is described. The proposed method has been successfully applied to the determination of vanadium in steel, pharmaceutical, environmental, and biological samples.     

Determination of trace concentrations of antimony by the introduction of stibine into an inductively-coupled plasma for atomic emission spectrometry

A simple, rapid and sensitive method is described for the determination of trace concentrations of antimony by inductively-coupled plasma atomic emission spectrometry with hydride generation. Hydrochloric acid (1 M) is the best medium for stibine generation, but antimony(III) is also effectively reduced to stibine in 1 M malic acid or 0.5 M tartaric acid, whereas antimony(V) gives no significant signal in either of these acids. This permits the differential determination of Sb(III) and Sb(V). Most of the inter-element interference effects can be minimized by thiourea, bur standard additions are recommended for accurate determinations. Thiourea is also effective in prereducing Sb(V) to Sb(III). The detection limit is 0.19 ng Sb ml^?1 and the calibration graph is linear up to 100 μg ml^?1. The r.s.d, at 1 and 100 ng Sb ml^?1 are 3.8 and 2.1%, respectively. The method is applied to copper metal and to speciation of antimony in waste water.     

Kinetic spectrophotometric determination of trace amounts of selenium based on the catalytic reduction of maxilon blue-SG by sulfide

A simple and sensitive catalytic spectrophotometric method was developed for the determination of trace amounts of selenium. The method is based on the catalytic effect of selenium in form Se(IV) on the reduction of Maxilon Blue-SG by sodium sulfide. Indicator reaction is followed spectrophotometrically by measuring the absorbance change at λ_max=654 nm and constant temperature (30.0±0.1 °C) by fixed time method. Selenium could quantitatively be determined in the range 0.004-0.200 μg ml⁻¹ Se(IV) with a detection limit of 0.205 ng ml⁻¹ Se(IV). All of the variables that affected the reaction rate were investigated and established optimum conditions to give maximum sensitivity. The R.S.D.s of the method (N=12) for the Se(IV) concentrations of 0.004, 0.016, 0.040 and 0.160 μg ml⁻¹ are between 2.27 and 0.32%, respectively, and depended on Se(IV) concentration. The interference effect of various anion and cations on the Se(IV) determination was also fully studied. The selectivity of catalytic reaction was greatly improved with the use of the strong cation exchange resin. The developed kinetic-catalytic reaction was applied to the determination of selenium in real samples as Antioxidant-S, Selsun (which is a healthcare product for the treatment of dandruff) and analytical grade sodium metabisulfite, and in spring water samples without any pre-concentration. The acceptable recoveries were obtained by the method for appropriate standard Se(IV) additions. The method is simple, practical and suitable for using in small laboratories owing to its precision, sensitivity and relative selectivity.     

Integrated Retention/Spectrophotometric Detection Method for the Determination of Formaldehyde

Abstract

An integrated-sensor method for the determination of formaldehyde based on retention of the reaction product of the analyte with p-rosaniline and sulfite in a flow-cell packed with Dowex 1-X-8 anion exchange resin was developed. The method has a good selectivity with a detection limit of 0.3 μg ml^?1 (1 ml sample) or 75 ng ml^?1 (2 ml sample), and a linear range between 1–30 μg ml^?1. The relative standard deviations (n = 11) were 2.8 and 1.3% for 2 and 20 μg ml^?1 formaldehyde, respectively. Depending on the working conditions, the sampling frenquency ranged between 10 and 18 h^?1. The method was applied to the determination of formaldehyde in well water.