Iron(III) as activator for catalytic fluorimetric microdetermination of V(V)

The activation of the vanadium(V)-catalysed aerial oxidation of sodium 4,8-diamino-1,5 -dihydroxyanthraquinone-2,6-disulphonate by iron(III) is discussed. The oxidation product is intensely fluorescent and allows fluorescence-monitoring of the slow reaction, which is preceded by an induction period. On the basis of this investigation, an accurate method for determination of vanadium(V) at the 1-10 ng/ml level has been developed.     

Simultaneous first-derivative spectrophotometric determination of iron(III) and molybdenum(VI) in cobalt-chromium and nickel-chromium alloys

A method is proposed for the simultaneous determination of iron(III) and molybdenum(VI) by first-derivative spectrophotometry based on the absorption spectra of their complexes with morin in the presence of a cationic surfactant. The zero-crossing measurement technique is found sutiable for the direct measurement of the first-derivative value at the specified wavelengths. Iron(III) (0.9-1.5 mug ml(-1)) and molybdenum(VI) (0.3-4.2 mug ml(-1)) in different ratios have been determined simultaneously. A critical evaluation of the proposed method is performed by statistical analysis of the experimental data. The method was applied to determine iron and molybdenum in different alloys.     

Simultaneous flow injection determination of iron(III) and vanadium(V) and of iron(III) and chromium(VI) based on redox reactions

A flow injection analysis (FIA) method is presented for the simultaneous determinations of iron(III)-vanadium(V) and of iron(III)-chromium(VI) using a single spectrophotometric detector. In the presence of 1,10-phenanthroline (phen), iron(III) is easily reduced by vanadium(IV) to iron(II), followed by the formation of a red iron(II)-phen complex (lambda(max) = 510 nm), which shows a positive FIA peak at 510 nm corresponding to the concentration of iron(III). On the other hand, in the presence of diphosphate the reductions of vanadium(V) and/or chromium(VI) with iron(II) occur easily because the presence of diphosphate causes an increase in the reducing power of iron(II). In this case iron(II) is consumed during the reaction and a negative FIA peak at 510 nm corresponding to the concentration of vanadium(V) and/or chromium(VI) is obtained. The proposed method makes it possible to obtain both positive (for iron(III)) and negative (for vanadium(V) or chromium(VI)) FIA peaks with a single injection.     

Extraction and spectrophotometric determination of vanadium(V) with 8-hydroxyquinoline

The extraction and spectrophotometric determination of vanadium (V) with oxine is investigated at higher acidities than described previously. Under these conditions, n-butanol and other alcohols are found to exert a synergic effect on the extraction of vanadium into benzene. In the presence of alcohol only a 6-fold ligand excess is needed for quantitative extraction in a single operation, the acidity of the aqueous medium being 0.05M with respect to sulphuric or phosphoric acid. The interference of iron(III) in the spectrophotometric determination of vanadium is suppressed by the addition of pyrophosphate. Beer's law is obeyed up to 14.0 mug of vanadium/ml and the sensitivity is 0.008 mug of vanadium/cm(2) at 390 mmu. The composition of the extracted species is found to be vanadium:oxine:n-butanol = 1:2:2.     

Spectrophotometric determination of micro-amounts of vanadium with 5,7-di-iodo-8-hydroxyquinoline

A precise spectrophotometric method for the determination of 2.5-25 mug of vanadium in volumes of up to 500 ml of water was developed. The method is based on the simultaneous concentration (100-1000 fold) and complexation of vanadium(V) with di-iodo-oxine in a water-immiscible phase. Interference from iron is eliminated by masking with phosphoric acid. The standard deviation evaluated was +/-0.04 mug for solutions containing 5 mug vanadium.     

Rapid kinetic determination of silver (I), using in-cuvette mixing and computerized data acquisition

 The determination of silver(I) based on its catalytic effect on the oxidation of indigo carmine with hexacyanoferrate(III) is described. The reaction is monitored spectrophotometrically by means of a home-made rapid system with computer data acquisition. The decrease in absorbance of indigo carmine at 612 nm, pH 6 and at a fixed concentration of hexacyanoferrate(III) and indigo carmine is proportional to the concentration of Ag(I). The acquired data based on the initial rate and fixed time are processed. Up to 100.0 μg/ml of silver are determined. The limit of detection and average relative standard deviation are 0.13 μg/ml and 1.9%, respectively. The effect of foreign ions on the determination of silver is also discussed. The proposed method is applied to the determination of Ag(I) in expired photographic film. Received: 17 June 1996 / Revised: 26 July 1996 / Accepted: 2 August 1996     

Spectrophotometric determination of Sb(III) in Sb(III)/Sb(V) binary mixtures using sodium dodecylsulfate/nonylphenoxy polyethoxyethanol mixed micellar media

Different micellar media had different effects on the absorption spectra of the complexes of bromopyrogallol red with Sb(III) and Sb(V). The mixed micellar medium composed of 0.7 ml of 0.2% sodium dodecylsulfate (SDS) and 0.3 ml of 2% nonylphenoxypolyethoxyethanol (OP) at 80 degrees C could be used for the sensitive determination of Sb(III) in Sb(III)/Sb(V) binary mixtures. Under the optimal conditions, Beer's Law was obeyed over the range 0.1-2.3 mug ml(-1) Sb(III) with molar absorptivity at 538 nm being 4.8 x 10(4) l mol(-1) cm(-1) and detection limit 0.04 mug ml(-1). For 10 mug Sb(III), more than 100 mug Sb(V) could be tolerated (error < 3%) in the presence of SDS/OP micellar medium as compared with 0.1 mug Sb(V) in the absence of SDS/OP micellar medium. In addition, the sensitivity of Sb(III) in the micellar medium was much higher than that in pure water medium. As compared with conventional extraction spectrometry, the proposed method produced a reproducible result. It did not need the conversion of Sb(III) to Sb(V) and a time-consuming extraction process. A detailed discussion on the selection of surfactants, the effect of temperature, and the role played by the mixed surfactants were also made.     

Fluorimetric trace determination of cerium(III) with sodium triphosphate

Sodium triphosphate acts as a specific reagent for enhancing the fluorescence intensity of cerium(III). The purpose of this study was to investigate the spectrofluorimetric determination of trace amounts of Ce(III) in sodium triphosphate solution. The excitation and emission wavelengths are 303.5 nm and 353 nm respectively. Optimum sodium triphosphate concentration is found to be 0.074 g l(-1) at room temperature. The fluorescence varies linearly with the concentration of cerium(III) in the range 0.001-45 mug ml(-1). The detection limit is 9.4 x 10(-4)mug ml(-1). The relative standard deviations for 30 mug ml(-1) and 0.05 mug ml(-1) Ce(III) in 0.074 g l(-1) sodium triphosphate solution are 1.1% and 0.72% respectively. Quenching effects of other lanthanides and some inorganic anions are described. This method is a direct and rapid analytical method for the determination of Ce(III) in rare earth mixtures and cerium concentrates.     

Flow injection analysis for oxidation state speciation of vanadium(IV) and vanadium(V) in natural water.

A sensitive and simultaneous spectrophotometric flow injection method for the determination of vanadium(IV) and vanadium(V) is proposed. The method is based on the effect of ligands such as 2,4,6-tris(2-pyridyl)-1,3,5-triazine (TPTZ) and diphosphate on the conditional redox potential of iron(III)/iron(II) system. A four-channel flow system is assembled. In this flow system, diluted hydrochloric acid (1.0 x 10(-2) mol dm(-3)) as a carrier for standard/sample, acetate buffer (pH 5.5) as a carrier for diphosphate solution, an equimolar mixed solution of iron(III) and iron(II) and a TPTZ solution are delivered, so that the baseline absorbance can be established by forming a constant amount of iron(II)-TPTZ complex (lambda(max) = 593 nm). Vanadium(IV) and/or vanadium(V) (400 microL) and diphosphate (200 microL) solutions are simultaneously introduced into the flow system; in this system the diphosphate solution passes through a delay coil. The potential of the iron(III)/iron(II) system increases in the presence of TPTZ, and therefore vanadium(IV) is easily oxidized by iron(III) to vanadium(V) to produce an iron(II)-TPTZ complex (a positive peak for vanadium(IV) appears). On the other hand, the potential of the redox system decreases in the presence of diphosphate, so that vanadium(V) can be easily reduced by iron(II) to vanadium(IV). In this case, the amount of iron(II) decreases according to the amount of vanadium(V). As a result, the produced iron(II)-TPTZ complex decreases (a negative peak for vanadium(V) appears). In this manner, two peaks for vanadium(IV) and vanadium(V) can be alternately obtained. The limits of detection (S/N = 3) are 1.98 x 10(-7) and 2.97 x 10(-7) mol dm(-3) for vanadium(IV) and vanadium(V), respectively. The method is applied to the simultaneous determination of vanadium(IV) and vanadium(V) in commercial bottled mineral water samples.     

Voltammetric Determination of Indigo Carmine and Amaranth on a Silver-Based Mercury Film Electrode

Abstract

The voltammetric behavior of indigo carmine and amaranth on silver-based mercury film electrodes was studied. At pH 4, reduction current peaks were observed at potential ?0.11 V (indigo carmine) and ?0.24 V (amaranth), respectively. The system showed a linear response to both of the food colorants in a concentration range of 0 to 100 ng/ml. Detected at different reduction potentials, indigo carmine and amaranth could be determined separately without interfering with each other. This method demonstrated a better reproducibility and longer life time than the existing techniques.     

Studies in the complex formation of metal ions with sugars. I. The complex formation of cobalt(II), cobalt(3), copper(II) and nickel(II) with mannitol

The use of elastic polyurethane foam as a support for chloranil was proved successful. Reductions of cerium(IV), vanadium(V) and iron(II) on foam-filled columns were carried out quantitatively and rapidly. The effect of flow-rate and temperature on the reduction of each metal ion was examined in detail. Cerium(IV) was reduced quantitatively on passing through the foam-redox column at flow-rates of 2–11 ml min^-1 at room temperature. The reduction of vanadium(V) and iron(III) was slower; complete reduction occurred only at flow-rates up to 4 and 2 ml min^-1 for V(V) and Fe(III), respectively. At 35°, however, it was possible to use flow-rates of 7 and 6 ml min^-1 for the quantitative reduction of V(V) and Fe(III), respectively.     

First Order Derivative Spectrophotometric Determination of Vanadium(V) and Iron(III) Individually and Simultaneously

A novel, sensitive and highly selective first derivative spectrophotometric method is proposed for the determination of vanadium(V) and iron(III) metal ions separately and simultaneously in a mixture. 2-Hydroxy-1-naphthaldehyde benzoylhydrazone (OHNABH) reacts with vanadium(V) and iron(III) in sodium acetate–acetic acid buffer medium (pH 5.0) forming yellow and yellowish brown colored soluble complexes, respectively. The first derivative curves of these colored solutions show maximum derivative amplitudes at 465 nm (V(V)) and 540 nm (Fe(III)) obeying Beer's law in the range 0.12–2.50 g ml^–1 and 0.14–4.20 g ml^–1, respectively. Large number of foreign ions do not interfere in the present method. A very simple and accurate simultaneous first derivative method is also reported for the determination of V(V) and Fe(III) in mixtures without solving simultaneous equations. The method is applied for the analysis of various natural samples, food and biological materials.     

Preconcentration of 1-(2-pyridylazo)-2-naphthol-iron(III)-capriquat on a membrane filter, and third-derivative spectrophotometric determination of iron(III)

Iron(III) was preconcentrated by collection on an organic solvent-soluble membrane filter (nitrocellulose (NC)) of the iron(III)-1-(2-pyridylazo)-2-naphthol (PAN) complex in the presence of capriquat as an oily quaternary ammonium salt. Third-derivative spectrophotometry was used for measurement of the third-derivative distance (d(3)A/dlambda(3)) between lambda(1) = 520 nm and lambda(2) = 590 nm or lambda(3) = 660 nm and lambda(4) = 724 nm of the iron(III)-PAN-capriquat complex or PAN-capriquat in dimethylsulfoxide (DMSO) following preconcentration. The calibration curve was linear in the range of 1-10 mug iron(III)/5.0 ml DMSO solution. The proposed method was about five-fold more sensitive and more selective than using zero-order spectrophotometry.     

Separation of arsenic(III) and arsenic(V) in ground waters by ion-exchange

The predominant species of arsenic in ground water are probably arsenite and arsenate. These can be separated with a strong anion-exchange resin (Dowex 1 x 8; 100-200 mesh, acetate form) in a 10 cm x 7 mm column. Samples are filtered and acidified with concentrated hydrochloric acid (1 ml per 100 ml of sample) at the sample site. Five ml of the acidified sample are used for the separation. At this acidity, As(III) passes through the acetate-form resin, and As(V) is retained. As(V) is eluted by passage of 0.12M hydrochloric acid through the column (resulting in conversion of the resin back into the chloride form). Samples are collected in 5-ml portions up to a total of 20 ml. The arsenic concentration in each portion is determined by graphite-furnace atomic-absorption spectrophotometry. The first two fractions give the As(III) concentration and the last two the As(V) concentration. The detection limit for the concentration of each species is 1 mug l .     

Simultaneous determination of gallium(III) and indium(III) by derivative spectrophotometry

A simple, selective and sensitive derivative spectrophotometric method is proposed for the simultaneous determination of gallium(III) and indium(III) in mixtures using 1-(2-pyridylazo)-2-naphthol in cationic micellar medium, without any prior separation. Beer's law is obeyed between 2.80x10(-1)-3.63 and 4.60x10(-1)-9.20 mug ml(-1) concentration of Ga(III) and In(III) at 550 and 542 nm, the isodifferential points of indium and gallium complexes in the first-order derivative mode, respectively. The proposed method is successfully applied for the determination of gallium and indium in standard reference materials and synthetic binary mixtures with a relative error of +/-2.07 and +/-2.55%, respectively.     

Preconcentration of iron (III), cobalt (II) and copper (II) nitroso-R complexes on tetradecyldimethylbenzylammonium iodide-naphthalene adsorbent

Iron, cobalt and copper form coloured water soluble anionic complexes with disodium 1-nitroso-2-naphthol-3-6-disulphonate (nitroso R-salt). The anionic complex is retained quantitatively as a water insoluble neutral ion associated complex (M-nitroso R-TDBA) on tetradecyldimethylbenzylammonium iodide on naphthalene (TDBA(+)I(-)-naphthalene) packed column in the pH range of: Fe(III): 3.1-6.5, Co: 3.4-8.5 and Cu 5.9-8.0 when their solutions are passed individually over this adsorbent at a flow rate of 0.5-5.0 ml/min. The solid mass consisting of an ion associated metal complex along with naphthalene is dissolved out of the column with 5 ml dimethylformamide/chloroform and metals are determined spectrophotometrically. The absorbance is measured at 710 nm for iron, 425 nm for cobalt and 480 nm for copper. Beers law is obeyed in the concentration range 9.2-82 mug of iron, 425 nm for cobalt cobalt and 3.0-62 mug of copper in 5 ml of final DMF/CHCl(3) solution. The molar absorptivities are calculated to be Fe: 7.58 x 10(3), Co: 1.33 x 10(4) and Cu: 4.92 x 10(4)M(-1)cm(-1). Ten replicate determinations containing 25 mug of iron, 9.96 mug of cobalt and 3.17 mug of copper gave mean absorbances 0.677, 0.450 and 0.490 with relative standard deviations of 0.88, 0.98 and 0.92%, respectively. The interference of large number of metals and anions on the estimations of these metals has been studied. The optimized conditions so developed have been employed for the trace determination of these metals in standard alloys, waste water and fly ash samples.     

Extractive spectrophotometric determination of trace amounts of iron(III) with benzyltriethylammonium chloride

The ion-association complex formed between a thiocyanato-iron(III) ion and a benzyltriethylammonium ion is extracted into 1,2-dichloroethane, and its absorbance at 476 nm is used for determination of the iron. Beer's law is obeyed up to about 4 mug/ml iron concentration in the final solution. The molar absorptivity is 2.79 x 10(4) l.mole(-1).cm(-1).     

Niobium(III) as an analytical reagent. : Part I. The titrimetric determination of iron,copper, thallium,molybdenum, uranium and vanadium

Niobium(III) solutions can be used in direct titrations of copper(II), iron(III), thallium(III), moIybdenum(VI), vanadium(V) and uranium(VI) in milligram amounts. Phenosafranine is generally satisfactory as the indicator, but potentiometric end-points can also be used. Copper and iron can be determined successively when a mixed indicator containing phenosafranine and méthylene blue is used. Thallium(I) and thallium (III) can be determined in mixtures. The niobium (III) solutions are stable for several days under a carbon dioxide atmosphere.     

Spectrophotometric determination of vanadium(v) and its application to vanadium steels containing chromium, molybdenum, tungsten and manganese

A newly synthesized reagent, N-o-toluoyl-N-o-tolylhydroxylamine is used in a sensitive and selective spectrophotometric method for determination of vanadium(V). The method has been successfully applied to vanadium determination in Mn-Mo-Cr-V steels. The system in 2-6M hydrochloric acid medium obeys Beer's law at 510 nm in the range of vanadium concentration from 0.5 to 10.0 mug ml .     

Ion paired chromatography of iron (II,III), nickel (II) and copper (II) as their 4,7-Diphenyl-1,10-phenanthroline chelates

A reversed phase ion-paired chromatographic method that can be used to determine trace amounts of iron (II,III), nickel (II) and copper (II) was developed and applied to the determination of iron (II) and iron (III) levels in natural water. The separation of these metal ions as their 4,7-diphenyl-1,10-phenanthroline (bathophenanthroline) chelates on an Inertsil ODS column was investigated by using acetonitrile-water (80/20, v/v) containing 0.06 M perchloric acid as mobile phase and diode array spectrophotometric detection at 250-650 nm. Chromatographic parameters such as composition of mobile phase and concentration of perchloric acid in mobile phase were optimized. The calibration graphs of iron (II), nickel (II) and copper (II) ions were linear (r > 0.991) in the concentration range 0-0.5, 0-2.0 and 0-4.0 mug ml(-1), respectively. The detection limit of iron (II), nickel (II) and copper (II) were 2.67, 5.42 and 18.2 ng ml(-1) with relative standard deviation (n = 5) of 3.11, 5.81 and 7.16% at a concentration level of 10 ng ml(-1) for iron (II) and nickel (II) and 25 ng ml(-1) for copper (II), respectively. The proposed method was applied to the determination of iron(II) and iron(III) in tap water and sea water samples without any interference from other common metal ions.