Vanadium(III) as an analytical reagent: The titrimetric determination of iron, copper, thallium, molybdenum, uranium, vanadium, chromium and manganese

Vanadium(III) solutions can be used in direct titrations of iron(III), copper(II), thallium(III), molybdenum(VI), uranium(VI), vanadium(V), chromium(VI) and manganese(VII) in milligram amounts. The titrations are done at 70-80 degrees for iron(III), copper(II), thallium(III), molybdenum(VI) and at room temperature for vanadium(V), chromium(VI) and manganese(VII). Uranium(VI) is titrated at 70-80 degrees in presence of iron(II). The vanadium(III) solution is prepared by reduction of vanadium(V) to vanadium(IV) with sulphur dioxide, followed by addition of phosphoric acid and reduction with iodide, and is reasonably stable.     

A new oxidimetric reagent-potassium dichromate in a strong phosphoric acid medium-VIII Potentiometric titration of molybdenum(VI) and vanadium(V)

A new titrimetric method is described for the determination of molybdenum(VI) involving prior reduction to Mo(V) with an excess of Fe(II) in a concentrated phosphoric acid solution, followed by titration with dichromate. The titration can be done at room temperature and without protective atmosphere. Uranium interferes, but vanadium may be determined simultaneously.     

Method of two reagents on a solid phase for the determination of simultaneously present vanadium(V) and molybdenum(VI)

The possibility of the use of two reagents for the determination of two elements from one sample on one disk of fibrous sorbent was studied. Vanadium(V) and molybdenum(VI) are sorbed on a disk of an anionexchange fibrous material and, next, sequentially detected by diffuse reflection spectrometry with 8-hydroxyquinoline-5-sulfonic acid and phenylfluorone. It was demonstrated that vanadium and molybdenum can be determined when present simultaneously in ratios from 1 : 10 to 10 : 1 in the concentration range 0.01-0.15 ώg/mL (RSD < 15%). The detection limit is 0.005 and 0.003 ώg/mL for vanadium and molybdenum, respectively.     

A fluorescence test for vanadium(V) with resorcinol

Summary In continuation of our previous work in which salicylic acid was reported to give a very sensitive and an almost specific colour reaction with vanadium(V), we have now found that vanadium(V) reacts with resorcinol in 20 N sulphuric or phosphoric acid solution to give a blue coloured product, which gives a vivid red fluorescence under filtered ultraviolet light. A sensitive test for vanadium(V) has now been developed making use of this red fluorescence or of the bright blue colour. Dichromate gives a somewhat less sensitive violet colour with the resorcinol reagent under the same conditions, but the product does not fluoresce. Manganese(VII), cerium(IV), iron(III), titanium(IV), uranium(VI), molybdenum(VI) and tungsten(VI) do not interfere with the colour reaction or the fluorescence test for vanadium(V).     

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.     

Extractive separation of molybdenum as Mo(V) xanthate from Iron, vanadium, Tungsten, copper, uranium and other elements

A simple and selective extraction of molybdenum is described. Tungsten is masked with tartaric acid and molybdenum(VI) is reduced in 2M hydrochloric acid by boiling with hydrazine sulphate. Iron, copper and vanadium are then masked with ascorbic acid, thiourea and potassium hydrogen fluoride respectively. The molybdenum(V) is extracted as its xanthate complex into chloroform, from 1M hydrochloric acid that is 0.4M potassium ethyl xanthate. The complex is decomposed by excess of liquid bromine, and the molybdenum is stripped into alkaline hydrogen peroxide solution. The molybdenum is then determined by standard methods. Large amounts of Cu(II), Mn(II), Fe(III), Ti(IV), Zr, Ce(IV), V(V), Nb, Cr(VI), W(VI), U(VI), Re(VII) and Os(VIII) do not interfere. Several synthetic samples and ferromolybdenum have been rapidly and satisfactorily analysed by the method.     

Chromatographic separation of vanadium, tungsten and molybdenum with a liquid anion-exchanger

In acidic solution only molybdenum(VI), tungsten(VI), vanadium(V), niobium(V) and tantalum(V) form stable, anionic complexes with dilute hydrogen peroxide. This fact has been used in developing an analytical method of separating molybdenum(VI), tungsten(VI) and vanadium(V) from other metal ions and from each other. Preliminary investigations using reversed-phase paper chromatography and solvent extraction led to a reversed-phase column Chromatographic separation technique. These metal-peroxy anions are retained by a column containing a liquid anion-exchanger (General Mills Aliquat 336) in a solid support. Then molybdenum(VI), tungsten(VI) and vanadium(V) are selectively eluted with aqueous solutions containing dilute hydrogen peroxide and varying concentrations of sulphuric acid.     

Electroreduction of molybdenum(VI) at a prehydrogenated platinum electrode

The use of hydrogenated platinum electrodes allows observation of the electroreduction of some oxygenated ions, which is otherwise masked by the reduction of the hydrogen ion. The present paper deals with the reduction of molybdenum(VI) at a prehydrogenated platinum electrode in acid solutions. The experimental conditions for the electrode hydrogenation process are the following: 90 min at a cathodic current density of about 7 A/cm(2) for microelectrodes with an area of 0.02-0.03 cm(2); about 120 min at a current density of 1.5-2 A/cm(2) for microelectrodes with an area of 0.25-0.35 cm(2). The reduction of molybdenum(VI) in 0.8-1.6M H(2)SO(4) occurs in two consecutive steps: the more cathodic wave [Mo(V) to Mo(III)] is for the most part masked by the reduction of the solvent; the less cathodic wave [Mo(VI) to Mo(V)] takes place at E(1 2 ) values of about +0.07 V, is well shaped, diffusion-controlled and usable for the determination of molybdenum down to 4 x 10(-5)M or 6 x 10(-5)M if a rotating disk electrode is used. Interferences from diverse ions have been studied. A generalization of the effect of electrode hydrogenation on the reduction of those oxygenated ions so far studied [i.e., vanadium(IV), uranium(VI) and molybdenum(VI)] is presented.     

Polarography of metal-gallic complexes

The polarographic behavior of metal ions in perchlorate media containing gallic acid is described. Tungsten(VI) forms a complex with gallic acid which yields a single wave in these media, useful in the polarographic determination of tungsten. Evidence for complexation of chromium(III), copper(II), iron(III), molybdenum(VI), uranium(VI), vanadium(V), tungsten(VI), praseodymium(III), samarium(III), neodymium(III) and gadolinium(III) is obtained and the behavior of these metal ions is summarized.     

Determination of uranium after its selective extraction as phenylacetate

The method described is based on the extraction of uranium with a chloroform solution of phenylacetic acid from slightly acidic solution containing nitrilotriacetic acid, which masks all interfering metals. After stripping into very dilute hydrochloric acid, uranium is reduced with ascorbic acid and determined complexometrically. The method permits reliable determination of uranium in the presence of all quadri-, ter- and bivalent metals investigated, molybdenum(VI), tungsten(VI), and vanadium(V).     

Extraction and separation of bismuth(III)

Separation of bismuth from beryllium, lead, iron(III), indium, scandium, lanthanum, antimony(III), zirconium, titanium, thorium, vanadium(V), molybdenum(VI), uranium (VI) and chromium(VI) is achieved by selective extraction of bismuth from 0.1M sodium salicylate solution (adjusted to pH 7) into mesityl oxide (MeO). The extracted species is Bi (HOC(6)H(4)COO)(3).3MeO. The results are accurate within +/- 0.5%, with a standard deviation of 0.8%. The separation and determination of bismuth takes only 15 min.     

Solvent extraction of metals with hydroxamic acids

Solvent extraction with hydroxamic acids has been investigated. with comparison of aliphatic and aromatic reagents for the extraction of iron, copper, cobalt and nickel. Caprylohydroxamic acid has been evaluated for use in extraction systems for titanium, vanadium, chromium, molybdenum and uranium, both in terms of acidity of aqueous phase and oxidation state of the metal. It has been established that caprylohydroxamic acid in 1-hexanol is a suitable extractant for the removal of titanium(IV), vanadium(V), chromium(VI), molybdenum(VI) and uranium(VI) from 6M hydrochloric acid.     

Determination of vanadium(V) and chromium(VI) in a single sample on a fibrous ion exchanger disk

The determination of vanadium(V) and chromium(VI) in a single sample on a support disk was studied. Polyacrylonitrile fiber filled with an AV-17 anion exchanger was used as a solid phase. After adsorption, the elements were successively detected in the solid phase by color complexation reactions of vanadium with 8-hydroxyquinoline-5-sulfonic acid and chromium with 1.5-diphenylcarbazide. A procedure was developed for the adsorption-spectroscopic determination of 0.04–0.4 μg/mL vanadium(V) and 0.01–0.05 μm/mL chromium(VI) at V: Cr ratios of 1: 1 to 10: 1 in the dynamic mode. The limits of detections for vanadium and chromium were 0.04 and 0.005 μg/mL, respectively. It was shown that the background salt content of potable water had no appreciable effect; no preliminary sample preparation was required.     

Amperometric and constant-current potentiometric determinations of the Landolt effect

An amperometric method with one platinum indicator electrode as well as the constant-current potentiometric method with one and two indicator electrodes were successfully applied to the Landolt effect determination by means of the hydrogen peroxide-iodideascorbic acid and bromate-bromide-ascorbic acid indicator reactions. The possibilities of application of these methods are illustrated by the determination of small amounts of iron(III), vanadium(V), and molybdenum(VI) with satisfactory accuracy and precision.     

Gravimetric determination of molybdenum and its separation from other metals with n-benzoylphenylhydroxylamine

N-Benzoylphenylhydroxylamine is employed as a precipitant for the determination of molybdenum (VI). The precipitate can be weighed either directly or as molybdenum trioxide after ignition. Molybdenum can be determined in the presence of appreciable amounts of iron(III), cobalt(II), copper(II), chromium(VI) and vanadium (V).     

New gravimetric method for cobalt

A new gravimetric method for the determination of cobalt is described, based on precipitation from acidic solution with a reagent prepared by heating alpha-nitroso-beta-naphthol in a mixture of glacial acetic acid, hydrogen peroxide and syrupy phosphoric acid. The cobalt is weighed, after ignition of the precipitate, as Co(3)O(4). Iron(III), copper, chromium(III), vanadium(V), tungsten(VI), aluminium, molybdenum, nickel, titanium, zirconium, uranium(VI) and cerium do not interfere.     

Flow-injection spectrophotometric determination of molybdenum and vanadium with carminic acid in the presence of cetyltrimethylammonium bromide

The color-forming reactions of molybdenum(VI) and vanadium(IV) with carminic acid (CA) in the presence of cetyltrimethylammonium bromide (CTAB) were used in the flow-injection determination of these metals. The micellar medium enhances the spectrophotometric features of the Mo(VI)-CA and V(IV)-CA binary complexes, and the higher solubility of these complexes when the CTAB concentration is above critical micelle concentration permits the easy application of flow-injection systems. Under the optimum conditions, linear calibration graphs were obtained from 0.76 to 28.8 g/ml for molybdenum and from 0.30 to 9.1 g/ml for vanadium. The detection limits were 0.33 and 0.16 g/ml for molybdenum and vanadium, respectively. The selectivity of the method was investigated and the procedure was successfully applied to the determination of molybdenum in steels and pharmaceuticals and of vanadium in petroleum products.     

Chelating behavior of macroreticular hydroxamic acid resin towards molybdenum(VI), tungsten(VI), uranium(VI) and vanadium(V)

Summary The properties and behaviour of the hydroxamic acid resin have been studied and shown to be an highly selective resin for molybdenum(VI), tungsten(VI), uranium(VI) and vanadium(V) ions. The stability constants of these metal ion complexes with the resin have been determined. The sorption and desorption characteristics of these metal ions on this resin and the methods for the separation of these metal ions from each other on a short column of such resin were also developed.

---

Komplexierungsverhalten von makroretikularem Hydroxamsäureharz gegenüber Molybdän(VI), Wolfram(VI), Uran(VI) und Vanadium(V)

Zusammenfassung Die Eigenschaften und das Verhalten von Hydroxamsäureharz wurden untersucht. Das Harz erwies sich als hochselektiv für Mo(VI), W(VI), U(VI) und V(V). Die Stabilitätskonstanten der Komplexe wurden bestimmt, die Sorptions- und Desorptionscharakteristica wurden untersucht und Trennungsmethoden für die genannten Ionen an einer kurzen Säule entwickelt.

     

Use of N-benzyl-2-naphthohydroxamic acid as a highly selective reagent for solvent extraction and spectrophotometric determination of vanadium(V)

N-Benzyl-2-naphthohydroxamic acid extracts vanadium(V) selectively and quantitatively into chloroform from 2-8.5M hydrochloric acid in the presence of Mo(VI), Zr(IV) and Ce(IV). The extraction takes place quickly and gives a stable reddish-violet extract which shows an absorption maximum at 505 nm with molar absorptivity of (5.34 +/- 0.05) x 10(3) 1.mole(-1).cm(-1). The optimum range for the determination is 2.2-7.4 ppm of vanadium(V) in the final solution. The method has been used for the determination of vanadium in steels.     

Optimization of the conditions of sorption of molybdenum(VI), tungsten(VI), and vanadium(V) on modified silica gels with the use of bromopyrogallol red and surfactants

Sorption of molybdenum(VI), tungsten(VI), and vanadium(V) on amino silica gels in the presence of an anionic dye, bromopyrogallol red, and cationic surfactants fixed on the sorbent surface or present in solution was studied.