Simultaneous kinetic spectrophotometric determination of vanadium(V) and iron(III)

Vanadium(V) and iron(III) can be determined simultaneously at pH 2 and 25 degrees C by a single experiment using their kinetic effect on the oxidation of indigo carmine by bromate which goes through an induction period and then decreases in absorbance, at lambda(max), 612 nm. The rate of the color-fading of indigo carmine is proportional to the concentration of vanadium and is independent of the concentration of iron. The length of the induction period of the reaction is related to the concentration of iron and is independent of the concentration of vanadium. Concentrations of 0.3-2 (mug ml(-1)) vanadium(V) and 6-12 (mug ml(-1)) iron(III) were determined with mean relative errors of 2.7 and 1.6%, respectively. The interference effects of various cations and anions on determination of mixtures of vanadium and iron is reported. Application of the method to real samples and several mixtures of standard solutions are performed which gave acceptable results.     

Simultaneous determination of iron(III) and cobalt(II) withN-phenylcinnamohydroxamic acid and thiocyanate by extraction and spectrophotometry

Simple, precise, sensitive, and highly selective methods for the separate determination of iron(III) and cobalt(II) and for the simultaneous determination of both metal ions are described. Iron(III) and cobalt(II) react with thiocyanate in the presence ofN-phenylcinnamohydroxamic acid (PCHA) to form pinkish red and blue coloured complexes, respectively. Both the iron(III) and cobalt(II) complexes having stoichiometric composition of 122 (FeSCN^–PCHA) and 14 (CoSCN^–), respectively, are quantitatively extractable into ethylacetate from 0.5–1.5 M hydrochloric acid solutions. The spectra of iron(III) and cobalt(II) complexes in the visible region exhibit absorption maxima at 495 and 625 nm, respectively. The coloured systems obey Beer's law in the concentration range of 0.2–4.0g/ml of iron and 2–40g/ml of cobalt. The effects of foreign ions and of various experimental parameters were studied to establish the optimum conditions for the extraction and determination of iron and cobalt. The methods have been applied successfully to the analysis of blood, vitamin B₁₂, and standard steels for iron and cobalt.     

Simultaneous determination of iron(III) and vanadium(V) by use of a kinetic-spectrophotometric and rapid mixing flow system

The quantitative spectrophotometric determination of V(V) by its catalytic effect on the oxidation of chromotropic acid [the disodium salt of 4,5-dihydroxynaphthalene-2,7-disulphonic acid (CS)] by potassium bromate has been adapted to a flow system employing a rapid sample and reagent introduction manifold, in which valves and carrier streams are omitted without decreasing the precision or increasing the sample consumption relative to flow-injection analysis (FIA). Measurements are made at 420 nm. Coexisting Fe(III) can be determined simultaneously at the same wavelength by its more rapid colour chelate formation with CS. An accurate determination of V(V) and Fe(III) in the mixture was developed with a sample throughput of about 60 hr.     

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.     

Deferoxamine-paper for iron(III) and vanadium(V) sensing

The development of a sensor based on the functionalization of common filter paper with deferoxamine (DFO) is proposed with the prospect to produce a solid phase for iron(III) and vanadium(V) sensing. The main features of this sensor are the simplicity of operation, good sensitivity and feasible applicability to real samples without the need of pre-treatment procedures. DFO was selected not only for it is easily anchored to the solid support, but also because it forms colored complexes with iron(III) and vanadium(V); hence, the developing of a simple colorimetric sensor can be considered. In particular, an innovative and economic way to perform colorimetric measurements using a desktop scanner is described. A complete characterization of the functionalized material is also reported.     

Simultaneous spectrophotometric determination of copper(II), vanadium(V), and iron(III) using 2-hydroxy-1-naphthaldehyde benzoylhydrazone

A simple and new simultaneous spectrophotometric method is proposed for the analysis of a three-component system containing Cu(II), V(V) and Fe(III) without separation using 2-hydroxy-1-naphthaldehyde benzoylhydrazone (OHNABH). The reagent reacts with all the three metal ions at pH 5, forming soluble colored species in 30% DMF. The physico-chemical characteristics, statistical analysis and application of the method for the analysis of complex materials are reported. The effect of diverse ions and the stoichiometry and stability constants are also studied. This article was submitted by the authors in English.     

Spectrophotometric determination of vanadium as V(III) oxinate

Vanadium(V) is rapidly reduced by dithionite to V(III) which is extracted as the oxinate into carbon tetrachloride. Vanadium is determined by measuring absorbance of the complex at lambda(max) = 420-425 nm with a sensitivity of 0.004 microg/cm(2) and Beer's law range of 0-7 microg/ml . Several mg of some important elements can be tolerated if they are masked. Molybdenum interferes seriously. The method has been applied to synthetic samples, rutile and ilmenite with satisfactory results. Using ordinary reagents and taking 10 min or less in series for a determination, the method has a sensitivity rarely exceeded by others with a much higher tolerance for other elements.     

Spectrophotometric determination of vanadium (V) with 2-naphthohydroxamic acid

2-Naphthohydroxamic acid in methanol gives an intense and stable red-orange color with vanadium (V), sensitive to 0.009 μg V/cm², for log I₀/I = 0.001 abs. unit at wavelength 450 mμ. The value for σ is ±0.006 a.u., equivalent to ±0.08 p.p.m. V. The colored complex obeys Beer's law over the range 1–10 p.p.m. vanadium. The absorbance (in 1-cm cell) at 10 p.p.m. was so great that no data were obtained at higher concentrations. Under the conditions of the reaction, the combining ratio of vanadium and 2-naphthohydroxamic acid appears to be 1 to 2. Optimum conditions for the use of 2-naphthohydroxamic acid as a spectrophotometric reagent for vanadium-(V) were established; the procedure was applied to the determination of vanadium in steels and non-ferrous alloys with good precision and accuracy.     

Extract-photometric determination of vanadium(V) with 3-indole-acetohydroxamic acid

Summary A spectrophotometric study has been carried out of the violet complex 3-indole-acetohydroxamic acid-vanadium extracted into a solution of trioctylmethyl-ammonium chloride in toluene [_max 525 nm; =5381 l mol^–1 cm^–1; stoichiometry 1:3 (metal:reagent)]. A new method for the extract-spectrophotometric determination of V⁵⁺ in the range of 2–7 g/g is proposed and interferences by foreign ions were investigated. The method has been satisfactorily applied to the determination of vanadium(V) in fuel oil. The relative error is ±2.9%.     

Spectrophotometric determination of vanadium as vanadium(IV) pyridine thiocyanate

A spectrophotometric determination of vanadium as vanadium(IV) pyridine thiocyanate is described. The blue complex is formed in acidic aqueous solution and extracted into pyridine-chloroform. Absorbance is measured at 7.40 mμ. The range of best accuracy for 1-cm cells is from about 80 to 240 μg of vanadium per ml, and sensitivity is 0.4 μg of vanadium per cm² at 7.40 mμ. The vanadium may be present initially as vanadium(IV) or vanadium(V), which is reduced to vanadium(IV) by the large excess of thiocyanate ion added. Several elements interfere in the determination ; a separation procedure involving mercury cathode electrolysis is suggested.     

Simultaneous differential rate determination of iron(II) and iron(III) by flow-injection analysis

Flow-injection procedures for the simultaneous spectrophotometric determination iron(II) and iron(III), relying on the different kinetic-catalytic behaviour of iron(II) and iron(III) in the redox reaction between leucomalachite green and peroxodisulphate with and without the presence of the activator 1,10-phenanthroline, are described. Exploiting the fact that one of the chemical reactions is very rapid whereas the other one is comparatively slower, two experimental procedures are presented. In the first, two individual zones of sample solution are injected simultaneously into separate carrier streams of reagent in a two-line system. Taking advantage of the different residence times of the samples in the manifold lines, the resulting colour formation is measured by a single optical detector with two separate flow cells aligned within the same optical path. The second approach is based on the use of a single-line flow-injection system, exploiting the formation of a double peak as a result of injecting a large sample zone, sandwiched between reagent zones of appropriate composition. In this manner two time-resolved signals for the kinetically governed processes can be obtained and thus used for quantification of the individual species.     

Differential determination of antimony(III) and antimony(V) by solvent extraction-spectrophotometry with mandelic acid and Malachite Green, based on the difference in reaction rates

Highly sensitive and reproducible extraction-spectrophotometric methods for differential determination of antimony(III) and antimony(V) were investigated. It was found that antimony(III) reacts easily with mandelic acid to form a complex anion extractable into chlorobenzene with Malachite Green from weakly acidic media (pH 2.2-3.5) at room temperature, whereas antimony(V) reacts only slowly, and heating for 15 min at 45 degrees is needed to obtain maximum sensitivity. The significant difference between the rates of reaction of mandelic acid with antimony(III) and antimony(V) was applied to the differential determination of these two species. The calibration graph was linear over the range 0.15-6.0 mug for antimony(III), and 0.20-10 mug for antimony(V).     

Simultaneous determination of iron(II) and iron(III) in aqueous solution by kinetic spectrophotometry with tiron

A kinetic spectrophotometric method that requires no prior measurement of rate constants is developed for the simultaneous determination of iron(II) and iron(III). The method is based on the aerial oxidation of iron(II) in the presence of tiron and acetate ions. The iron(III) formed is subsequently complexed with tiron and the absorbance/time relation is evaluated. The concentrations of iron(III) and iron(II) are obtained from the absorbance values at the start and at equilibrium, respectively, calculated by non-linear least-squares fitting. A linear calibration graph is obtained up to 12 μg ml^?1 iron(II)/iron(III). The method is applied to iron-rich ground water.     

Bromometric determination of vanadium (V) by hydrazine

A method for the quantitative determination of vanadium(V), based on the reduction of vanadium(V) by hydrazine, has been described. The reduction is carried out in high concentration of hydrochloric acid and the excess hydrazine back-titrated against standard potassium bromate, using the dead-stop end-point procedure. Hydrazine is preferentially oxidized by bromate in presence of vanadium(IV). Accurate results have been obtained over a wide range of vanadium(V) concentration.     

Simultaneous polarographic determination of micro amounts of vanadium(V) and molybdenum(VI)

A simple and sensitive polarographic method has been developed for the determination of micro quantities of vanadium(V) and molybdenum(VI), based on the reduction of bromate, which is catalysed by these metal ions in the presence of 2,4-dihydroxyacetophenone oxime. Interference by various cations and anions has been investigated.     

Investigation of the vanadium(III)/vanadium(II)/ N-(hydroxyethyl)ethylenediaminetriacetic acid system by cyclic voltammetry and differential pulse polarography

Cyclic voltammetry and differential pulse polarography (d.p.p.) are used to study the influence of pH and metal complex concentration on the voltammetric responses of the V(III)/V(II)/ N- (hydroxyethyl)ethylenediaminetriacetic acid (HEDTA) system. The monomer-dimer equilibrium of V(III)HEDTA gives rise to typical patterns on cyclic voltammograms. The formation constant for (V(III)HEDTA)₂ is evaluated by d.p.p. The dimer-monomer concentration ratios representing the equilibrium in the bulk solution can be obtained only when the drop time of the mercury electrode is ?0.2 s. The pH-independent value of the half-wave potential for the reduction of V(III)HEDTA to V(II)HEDTA is used to evaluate the ratio of the formation constants of V(III)HEDTA and V(II)HEDTA. The suitability of V(III)HEDTA as a model complex for V(III) in ascidians (primitive marine organisms) is discussed.