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 and sequential determination of chromium(VI) and chromium(III) by unsegmented flow methods

Summary Several different configurations for simultaneous and sequential photometric speciation of Cr(VI) and Cr(III) based on the reversed flow injection analysis and completely continuous modes are proposed in this paper. The determination of these species at theg · ml^–1 level is achieved with sampling frequencies between 30 and 100 h^–1 and an r.s.d. of less than ±1% for simultaneous methods and of less than ±3% for the sequential method. The proposed methods are suitable for chromium speciation in waters. A simulation of the continuous monitoring of Cr(VI) and periodical of Cr(III) in natural and waste waters has been performed. The most frequent interferents in these types of samples have been investigated.

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Simultane und sequentielle Bestimmung von Chrom(VI) und Chrom(III) durch unsegmentierte Durchflußmethoden

Zusammenfassung Verschiedene Arten der simultanen und sequentiellen photometrischen Cr(III)- und Cr(VI)-Bestimmung nach der Technik der reversed-flow Injektionsanalyse werden beschrieben. Die relative Standardabweichung für die Bestimmung dieser Chromspezies im g/ml-Bereich bei einer Probenfrequenz von 30 bis 100 je Stunde beträgt weniger als +1% für die Simultan- und weniger als +3% für die sequentiellen Methoden. Eine simulierte kontinuerliche Überwachung von Chrom(VI) sowie eine periodische von Chrom(III) in natürlichem Wasser und Abwasser wird beschrieben. Die häufigsten Störungen werden diskutiert.

     

Simultaneous determination of chromium(VI) and chromium(III) by flame atomic absorption spectrometry with a chelating ion-exchange flow injection system

Summary Simultaneous Determination of Chromium(VI) and Chromium(III) by Flame Atomic Absorption Spectrometry with a Chelating Ion-Exchange Flow Injection System A simple method is described for the simultaneous determination of chromium(VI) and chromium(III) in a flow injection system comprising chelating ion-exchange and flame atomic absorption spectrometry. Sampling rates for 2001 and 1 ml sample volumes were 120 and 60 h^–1 (240 and 120 speciations per hour), respectively. Typical relative standard deviations were 0.52% for Cr(VI) (0.50g ml^–1 and 0.67% for Cr(III) (0.10,g ml^–1) and the corresponding limits of detection were 85 ng ml^–1, and 16 ng ml^–1, respectively.On leave from University of Belgrade.     

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.     

Speciation studies by capillary electrophoresis- Simultaneous determination of chromium(III) and chromium(VI)

A method for the simultaneous determination of chromium(III) and chromium(VI) by capillary electrophoresis (CE) has been developed. The chromium(III) has been chelated with 1,2-cyclohexanediaminetetraacetic acid (CDTA) in order to impart a negative charge and similar mobility to both the chromium(III) and the chromium(VI) species. The effects of the amount of the reagent, pH and heating time required to complete the complexation have been studied. Factors affecting the CE behaviour such as the polarity of electrodes and the pH of electrophoretic buffer have been investigated. The separated species have been monitored by direct UV measurements at 214 nm. The detection limits achieved are 10 microg/l for Cr(VI) and 5 microg/l for Cr(III) and linear detector response is observed up to 100 mg/l. The procedure has been applied to the determination of both chromium species in industrial electroplating samples and its accuracy was checked by comparing the results (as total chromium) with those of atomic absorption spectrometry. No interference occurred from transition metal impurities under optimized separation conditions. The method is also shown to be feasible for determining Cr(III) as well as other metal ions capable to form complexes with CDTA (like iron(III), copper(II), zinc(II) and manganese(II)) in pharmaceutical preparations of essential trace elements.     

Speciation studies by capillary electrophoresis- Simultaneous determination of chromium(III) and chromium(VI)

A method for the simultaneous determination of chromium(III) and chromium(VI) by capillary electrophoresis (CE) has been developed. The chromium(III) has been chelated with 1,2-cyclohexanediaminetetraacetic acid (CDTA) in order to impart a negative charge and similar mobility to both the chromium(III) and the chromium(VI) species. The effects of the amount of the reagent, pH and heating time required to complete the complexation have been studied. Factors affecting the CE behaviour such as the polarity of electrodes and the pH of electrophoretic buffer have been investigated. The separated species have been monitored by direct UV measurements at 214 nm. The detection limits achieved are 10 g/l for Cr(VI) and 5 g/l for Cr(III) and linear detector response is observed up to 100 mg/l. The procedure has been applied to the determination of both chromium species in industrial electroplating samples and its accuracy was checked by comparing the results (as total chromium) with those of atomic absorption spectrometry. No interference occurred from transition metal impurities under optimized separation conditions. The method is also shown to be feasible for determining Cr(III) as well as other metal ions capable to form complexes with CDTA (like iron(III), copper(II), zinc(II) and manganese(II)) in pharmaceutical preparations of essential trace elements.     

Hydrazine sulphate as reagent for titrimetric determination of vanadium(V) and chromium(VI)

Conditions have been developed for the direct titration of vanadium(V) and chromium(VI) with hydrazine sulphate, barium diphenylaminesulphonate being used as indicator and osmium tetroxide as catalyst.     

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.     

Simultaneous determination of iron(III) and vanadium(V) with N-phenylcinnamohydroxamic acid and thiocyanate by extraction-spectrophotometry

N-Phenylcinnarnohydroxamic acid (PCHA) reacts with iron(III) and vanadium(V) in the presence of thiocyanate to form water-insoluble orange and green complexes, respectively. The iron(III)-PCHA and vanadium(V)-PCHA-thiocyanate complexes can be quantitatively extracted into toluene and other common organic solvents at pH 1.5–2.0. The absorption spectra and composition of both complexes are described. The effects of foreign ions and of experimental variables on the extraction and determination of the two metal ions are studied. A simple, selective method is described for the simultaneous determination of iron(III) and vanadium(V) by extraction-spectrophotometry; absorbances are measured at 440 and 580 nm. Mixtures can be determined over the range 10^?4–10^?5 M in each metal. The method was applied successfully to the analysis of standard steels for iron and vanadium.     

Simultaneous determination of chromium (III) and chromium (VI) by reversed-phase ion-pair HPLC with chromium-specific detection

A method for the simultaneous determination of Cr(III) and Cr(VI) with reversed-phase ion-pair HPLC employing chromium-specific detection by flame atomic absorption spectrometry (FAAS) and inductively-coupled plasma mass spectrometry (ICP-MS) is presented. Experimental parameters of the chromatographic separation, such as concentration of the ion-pairing reagent, pH and polarity of the mobile phase have been optimized for two different ion-pairing reagents, tetrabutylammonium phosphate (TBA) and tetraethylammonium nitrate (TEA). Best chromatographic conditions have been obtained with a polymer-based reversed-phase column (Hamilton PRP1) and mobile phases containing either TBA (1 mmol/l) in methanol-water (60:40, v/v) or TEA (2 mmol/l) in water at a pH between 3 and 4. With FAAS the detection limits (3) have been found to be 24 g/l for Cr(III) and 40 g/l for Cr(VI). A detection limit of 0.3 g/l Cr(3) for both chromium species has been obtained when ICP-MS has been used for detection. The method has been applied to analyze tap- and groundwater and to investigate the behaviour of Cr(III) and Cr(VI) in spiked tap-water, as well as to analyze aqueous extracts of coal fly ash (NIST SRM 1633a) and of an ash from a wood treatment company.     

Simultaneous determination of chromium(VI) and chromium(III) at trace levels by adsorptive stripping voltammetry

A new methodology was proposed for the speciation of chromium by differential pulse adsorptive stripping voltammetry (DPAdSV) using pyrocatechol violet (PCV) and N-(2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid (HEDTA) as complexing agents. In this procedure, a partial least squares (PLS) regression was used for the resolution of the strongly overlapping voltammetric signals from mixtures of Cr(III) and Cr(VI) in the presence of PCV and HEDTA. The relative error in absolute value was <6% when concentrations of several mixtures were calculated. The analysis of the possible effect of the presence of foreign ions in the solution was performed. The procedure was successfully applied to the speciation of chromium in different samples of natural water.     

Chemiluminescence determination of iron(II) and titanium(III) by flow injection analysis based on reactions with and without luminol

Titanium(III) and iron(II) are shown to stimulate luminol chemiluminescence in the absence of added oxidant. Down to 10^?9 M titanium can be determined. Both metal ions also produce chemiluminescence when injected into 0.1 M carbonate buffer (pH 10.4), allowing >10^?6 M of each to be determined. The intensities are greater when the solutions have been deoxygenated by a stream of nitrogen, and when rhodamine B is used as a sensitizer.     

Structure and stability of hexa-aqua V(III) cations in vanadium redox flow battery electrolytes

The vanadium(III) cation structure in mixed acid based electrolyte solution from vanadium redox flow batteries is studied by (17)O and (35/37)Cl nuclear magnetic resonance (NMR) spectroscopy, electronic spectroscopy and density functional theory (DFT) based computational modelling. Both computational and experimental results reveal that the V(III) species can complex with counter anions (sulfate/chlorine) depending on the composition of its solvation sphere. By analyzing the powder precipitate it was found that the formation of sulfate complexed V(III) species is the crucial process in the precipitation reaction. The precipitation occurs through nucleation of neutral species formed through deprotonation and ion-pair formation process. However, the powder precipitate shows a multiphase nature which warrants multiple reaction pathways for precipitation reaction.     

Flavin mononucleotide chemiluminescence in cationic micellar media for determination of chromium(III + VI) by flow injection

The flavin mononucleotide chemiluminescence system, originally developed for the determination of copper(II), is modified with cationic surfactant micelles for the determination of chromium(III + VI). In order for chromium to be detected predominantly, the copper-induced luminescent reaction is significantly suppressed by virtue of the cationic micellar effect. The limit of detection (signal-to-noise ratio = 2) is 5 × 10^?8 M chromium (50-μl sample injection).     

Iodometric microgram determination of chromium(III) and (VI) by use of chemical amplification reactions

A simple, rapid and sensitive method is described for the iodometric determination of microgram amounts of chromium(III), based on the oxidation of chromium(III) with periodate at pH 3.2, removal of the unreacted periodate by masking with molybdate and subsequent iodometric determination of the liberated iodate. Chromium(VI) can be determined by this method after prior reduction to chromium(III) with sodium sulphite. The method can also be used for the analysis of organochromium compounds.     

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 determination of chromium(III) and chromium(VI) in aqueous solutions by ion chromatography and chemiluminescence detection.

A method for the simultaneous determination of chromium(iii) and chromium(vi) in a flow system based on chemiluminescence was developed. A Dionex cation-exchange guard column was used to separate chromium(iii) from chromium(vi), and chromium(vi) was reduced by potassium sulfite, whereupon both species were detected by use of the luminol-hydrogen peroxide chemiluminescence system. Linear calibration for both species was established over the concentration range 1-1000 micrograms l-1. The precision at the 20 micrograms l-1 level was 3.5% for chromium(iii) and 3.3% for chromium(vi), respectively. The detection limit was 0.5 micrograms l-1 for both species. Data were in agreement with Zeeman-effect background corrected atomic absorption spectrometry measurements.     

Individual and sequential flow injection spectrophotometric determination of vanadium(V) and titanium(IV)

Summary Methods for the individual and sequential flow injection spectrophotometric determination of vanadium(V) and titanium(IV) are proposed, based on the formation of peroxo complexes. The detection limits are 1.0 × 10^–5 mol/l V (120 l) and 2.5 × 10^–6 mol/l Ti (80 l). A cation exchange resin mini-column is incorporated on-line into the vanadium manifold to remove the titanium complex and allow the vanadium to be determined selectively. A normal injection valve is used for the individual determinations, but it is modified for determination of V(V)/–Ti(IV) mixtures in order to introduce two samples sequentially into the reagent stream. One passes through a cation exchanger minicolumn, the other through an empty column, before reaching the detector. The former allows V alone to be measured, the latter V+Ti.

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Individuelle und sequentielle spektralphotometrische Fließinjektionsbestimmung von Vanadium(V) und Titan(IV)

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Dedicated to Prof. Dr. G. Tölg on the occasion of his 60th birthday