Sensitive spectrophotometric determination of vanadium with 2-(5-bromo-2-pyridylazo)-5-diethyl-aminophenol (5-Br-PADAP)

A new sensitive and highly selective method is described for the spectrophotometric determination of microgram amounts of vanadium(V). First, vanadium is isolated by extraction withN-benzoyl-N-phenylhydroxylamine (BPHA) in chloroform from about 4M hydrochloric acid medium. Then, chloroform is evaporated and the residue mineralized with mixture of cone. perchloric and nitric acid. Finally, a colour reaction of vanadium(V) separated with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) in an acetate buffer (pH 4.5) gives a molar absorptivity of 5.48×10⁴l·mol^–1·cm^–1 at 585 nm. The proposed method was applied for the determination of traces of vanadium in aluminium samples. The results obtained show a good precision and accuracy of the method.     

Solvent Extraction of Vanadium(V) as a Ternary Complex with N-Hydroxy-N-p-Chlorophenyl-N′-(2-Methyl-5-Chloro)-Phenyl-p-Toluamidine Hydrochloride and p-Chlorophenol

N-Hydroxy-N-p-chlorophenyl-N′-(2-methyl-5-chloro)-phenyl-p-toluamidine hydrochloride (HCPMCPTH) reacts with vanadium(V) to form a 1:2 (metal:reagent) blue-violet complex which can be quantitatively extracted into chloroform from acetic acid solutions. The deep blue adduct having 1:2:1 (V:HCPMCPTH:PCP) stoichiometry gets quantitatively extracted into chloroform from 0–2.5 M acetic acid media. The formation of the ternary complex has been made the basis for the development of a simple, rapid, sensitive and selective extractive-photometric method for the determination of microamounts of vanadium(V). The method has been applied to the determination of vanadium in steels.     

Selective and sensitive extraction spectrophotometric method for the determination of vanadium (V) as a mixed ligand complex withN-phenyl benzohydroxamic acid and 4-(2-pyridylazo)resorcinol in non-aqueous media

A selective, sensitive and direct method for the spectrophotometric determination of vanadium in steels is developed in which vanadium is extracted withN-phenyl benzohydroxamic acid (PBHA) into chloroform from 5M hydrochloric acid medium followed by colour development by addition of 4-(2-pyridylazo)resorcinol (PAR) inN,N-dimethyl formamide (DMF). The vanadium(V)-PBHA-PAR mixed ligand complex shows maximum absorbance at 560 nm with a molar absorptivity 3.6 × 10⁴ l mol^–1 cm^–1 and obeys Beer's law up to 2.0 g/ml of vanadium. The composition of the mixed ligand complex is determined by Job's method of continuous variations which revealed a 1 1 1 ratio for V(V) PBHA PAR. This method can be directly applied for the determination of vanadium in steels, while in the case of titanium base alloys, after separation of titanium matrix it gives good results even at 50–200 g of vanadium per gram level.     

Formation of oxoperoxo complexes of vanadium(V) with aminopolycarboxylates in acidic aqueous solutions

Summary The electronic spectra of KVO₃–H₂O₂–L–HClO₄(KOH) aqueous solutions, where L is ethylenediaminetetraacetate (edta), 1,2-cyclohexanediaminetetraacetate (cdta),N-(carbamoylethyl)-iminodiacetate (keida) or iminodiacetate (ida) ion were measured and, based on their pH dependence changes (ca. 0.5–7.0) and time, the formation of carboxylato-oxoperoxo complexes of vanadium(V) and their stabilities at room temperature were studied. The monoperoxo complexes with edta, keida and ida are formed immediately after mixing stock solutions, whereas the monoperoxo complex with cdta is formed only by slow decomposition of the stable diperoxo complex. The stabilities of the monoperoxo complexes decrease in following order: cdta>edta>keida>ida.     

Ethylisobutrazine hydrochloride as a selective and sensitive reagent for the spectrophotometric determination of vanadium(V) and its application to vanadium-bearing minerals and alloys

Ethylisobutrazine hydrochloride is proposed as a selective and sensitive reagent for the spectrophotometric determination of vanadium(V). It forms a red-colored species with vanadium(V) in 3.5–6.5 M phosphoric acid medium. An eight-fold molar excess of reagent is necessary for the full development of the color. The red species exhibits an absorption maximum at 518 nm with a molar absorptivity of 9.75 × 10³ liters mol⁻¹ cm⁻¹. Sandell's sensitivity is 5.2 ng cm⁻². Beer's law is obeyed over the range 0.1–6.2 ppm of vanadium(V) with an optimum concentration range of 0.4–6.0 ppm. The effects of acidity, time, temperature, order of addition of reagents, reagent concentration, and the interferences from various ions, are reported. The method has been used successfully for the determination of vanadium in ilmenite and vanadium steels that contain chromium, molybdenum, manganese, nickel, copper, tungsten, and titanium.     

Spectrophotometric determination of vanadium(IV) in the presence of vanadium(V) using Br-PADAP

In the present paper, a simple and sensitive method is proposed for vanadium(IV) determination in the presence of vanadium(V). This is based on the oxidation of vanadium(IV) present in the sample to vanadium(V) by addition of iron(III) cation, followed by a complexation reaction of iron(II) with the spectrophotometric reagent 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP). The iron(II) reacts with Br-PADAP immediately, forming a stable complex with a large molar absorptivity. The vanadium(IV) determination is possible, with a calibration sensitivity of 0.549 g ml^–1, for an analytical curve of 18.8 ng ml^–1 to 2.40 g ml^–1, molar absorptivity of 2.80 × 10⁴ 1 mole^–1 cm^–1 and a detection limit of 5.5 ng ml^–1. Selectivity was increased with the use of EDTA as a masking agent. The proposed method was applied for the vanadium(IV) determination in the presence of several amounts of vanadium(V). The results revealed that 200 g of vanadium(V) do not interfere with determination of 5.00 g of vanadium(IV). The precision and the accuracy obtained were satisfactory (R. S. D.<2%).     

2-(5-Nitro-2-Pyridylazo)-5-(N-Propyl-N-Sulfopropylamino)Phenol as a new analytical reagent for flow-injection spectrophotometric determination of trace vanadium(V)

A flow injection method using 2-(5-nitro-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol-(Nitro-PAPS) as a new chromogenic reagent is presented for sensitive and rapid determination of vanadium. Nitro-PAPS reacts with vanadium(V) in weakly acidic medium to form a water soluble complex of molar absorptivity of 8.0 × 10⁴L mol^–1 cm^–1 at 592 nm (maximum absorption wavelength), which permits the straightforward application of a flow injection system to the sensitive determination of vanadium. Under the optimum conditions established, a linear calibration graph was obtained in the range 1–120 ng mL^–1. The relative standard deviation for 60 ng mL^–1 vanadium was 2.2% (n = 5) and the limit of detection was 1 ng mL^–1. The sample throughput is about 40 h^–1. Most inorganic and organic anions examined did not interfere even at concentrations of 3000–6000 times of vanadium. Interference from cobalt(II), copper(II) and nickel(II) at 200ng mL^–1 levels can be overcome by the addition of N-(dithio-carboxy)sarcosine. The recoveries for each 20 and 10 ng mL^–1 vanadium added to the river water were 98 and 97%, respectively.The authors express their thanks to Miss Miho Suzuki and Miss Hiroyo Yamada for their experimental assistance in part.     

Spectrophotometric study of vanadium(V)-phenylfluorone complex

Spectrophotometric studies of the reaction between vanadium(V) ions and phenylfluorone are presented and used for spectrophotometric determination of vanadium(V). The absorbance at 520 nm obeys Beer's law in the range of 2–15 μg vanadium/10 ml at pH 4. The relative standard deviation is 2% and the molar absorptivity based on vanadium is 2.1 × 10⁴ liters/mol cm. The composition of the complex in solution is of the 1:1 type with stability constant values to 2.5 × 10⁴. Analysis of the solid complex shows that its formula agrees with the formula (C₁₉ H₁₁ O₅)VO₂ · 5H₂O.     

Spectrophotometric determination of vanadium(V) with p-Sulphobenzeneazo-4-(2-amino-3-hydroxypyridine)

Summary p-Sulphobenzeneazo-4-(2-amino-3-hydroxypyridine) reacts with vanadium to form an orange-red coloured complex having maximum absorbance at 530 nm. The reaction is slow at room temperature, it is complete at 40–45° C in 5 min. The effects of temperature, time, pH, reagent concentration, and other variables have been studied. The system obeys Beer's law over the concentration range of 1–12g vanadium(V) ml^–1. The molar absorptivity is 5.453 x 10³l·mole^–1·cm^–1. The metal:ligand ratio of 12 was confirmed by Job's continuous variation and mole ratio methods.

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Spektrophotometrische Bestimmung von Vanadin(V) mit p-Sulfobenzolazo-4-(2-amino-3-hydroxypyridin)

Zusammenfassung p-Sulfobenzolazo-4-(2-amino-3-hydroxypyridin) bildet mit Vanadin(V) einen orange-roten Komplex, dessen Absorptionsmaximum bei 530 nm liegt. Bei Zimmertemperatur verläuft die Reaktion langsam, bei 40–45° ist sie in 5 min vollständig. Der Einfluß von Temperatur, Zeit, pH, Reagenskonzentration und anderer variabler Faktoren wurde untersucht. Im Konzentrationsbereich 1–12g Vanadin/ml entspricht die Reaktion dem Beer-schen Gesetz. Die molare Absorptivität ist 5,453 x 10³l·mol^–1·cm^–1. Das Verhältnis Metall:Ligand wurde nach Job bestimmt und beträgt 12.

     

Rapid extraction and spectrophotometric determination of vanadium(V) with 2′-hydroxy-4-methoxy-5′-methyl chalkone oxime (HMMCO)

2′-Hydroxy-4-methoxy-5′-methyl chalkone oxime (HMMCO) is used for the extraction and spectrophotometric determination of microgram quantities of vanadium. HMMCO forms a green colored complex with vanadium at 9 M HCl extracted into chloroform. The complex absorbs maximum at 630 nm. Beer's law holds good over the concentration range of 2.7 to 94.0 μg of vanadium per ml. The Ringbom plot shows the effective working range of 4.5 to 67.0 μg of vanadium per ml. The extracted species shows the composition to be 1:2 (V:HMMCO). Vanadium can be extracted quantitatively without any serious interference of the foreign ions. It is possible to extract and determine vanadium quantitatively from binary mixtures that contain niobium, tantalum, or titanium. The method is also applicable to some ores.     

Determination of traces of vanadium with the catalytic maximum wave in differential pulse polarography

Summary A differential pulse-polarographic method has been studied for the determination of vanadium employing the catalytic maximum wave. A well-defined differential pulse polarographic peak is observed in the potential range from –0.2 to –0.7 V vs. SCE for vanadium(V) in 10 mmol 1^–1 NaCl containing 10 mmol 1^–1 acetic acid, 40 mmol 1^–1 pyrocatechol, and 2.5 mmol 1^–1 KBrO₃. The peak current is very large and proportional to the concentration of vanadium(V) between 1×10^–7 and 1×10^–6 mol 1^–1. The relative standard deviation at 0.5 mol l^–1 vanadium(V) was 2.06% (n=7). This method has been successfully applied to the determination of vanadium in standard materials such as pond sediment.

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Spurenbestimmung von Vanadium mit Hilfe der katalytischen Maximumsstufe in der Differential-Puls-Polarographie

Zusammenfassung Ein gut definierter differentialpuls-polarographischer Peak wurde für Vanadium(V) in 10 mmol/l NaCl-Lösung, die 10 mmol/l Essigsäure, 40 mmol/l Brenzcatechin und 2,5 mmol/l KBrO₃ enthielt, beobachtet (Potentialbereich –0,2 bis –0,7 V gegen SCE). Der Peakstrom ist sehr groß und die Vanadiumkonzentration im Bereich von 1×10^–7 bis 1×10^–6 mol/l proportional. Die relative Standardabweichung betrug 2,06% (n=7) bei 0,5 mol/l Vanadium(V). Das Verfahren wurde mit gutem Erfolg zur Vanadiumbestimmung in Standardproben (z.B. Teichsediment) eingesetzt.

     

Extraction-spectrophotometric determination of vanadium with 5,5′-dithiodisalicylhydroxamic acid (DTDSHA)

A new method for the extraction-spectrophotometric determination of V(V) is proposed. The violet complex V(V)-5,5′-dithiodisalicylhydroxamic acid formed in aqueous medium (pH 5.0) is extracted into a solution of trioctylmethylammonium chloride (Adogen 464) in toluene, and its spectrophotometric characteristics are studied. The stoichiometry of the complexes formed is 1:1 and 2:1 (reagent:vanadium), and 1:3 for the ionic association complex (2:1):trioctylmethylammonium ion. The system follows Beer's law at pH 5.0 (λ = 550 nm) over the concentration range 0.4 to 2.0 ppm (ε = 7.34 × 10³ liter · mol⁻¹ · cm⁻¹). The method is applied for the determination of vanadium in steel.     

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%.     

Homogeneous and heterogeneous olefin epoxidation catalyzed by a binuclear Mn(II)Mn(III) complex

The synthesis and characterization of a binuclear carboxylated bridged manganese complex containing the heptadentate ligand N,N′-bis(2-hydroxybenzyl)-N,N′-bis(2-methylpyridyl)-2-ol-1,3-propanediamine (H₃bbppnol) is reported. This complex was characterized by elemental analysis; infrared, electronic (UV–vis) and EPR spectroscopy; and conductivity measurements. The complex was immobilized on silica by either adsorption or entrapment via a sol–gel route. The obtained solids were characterized by thermogravimetric analyses (TG and DSC), UV–vis and infrared spectroscopy, and X-ray diffraction. The catalytic performance of the binuclear manganese complex in epoxidation reactions was evaluated for both homogeneous and heterogeneous systems. The catalytic investigation revealed that the complex performs well as an epoxidation catalyst for the substrates cyclohexene (26–39%) and cyclooctene (29–74%). The solids containing the immobilized complex can be recovered from the reaction medium and reused, maintaining good catalytic activity.     

Extraction-spectrophotometric determination of uranium(VI) with PAR and N-octylacetamide

A new and simple method for selective spectrophotometric determination of uranium(VI) with 4-(2-pyridylazo)resorcinol (PAR) and N-octylacetamide into benzene over pH 7.0–9.0 is described. The molar absorptivity of the complex with 9 different amides is in the range of (0.40–3.2)·10⁴ 1·mol^–1·cm^–1 at the absorption maximum. Out of these, the most sensitive compound N-octylacetamide (OAA) was chosen for detailed studies in the present investigation. The detection limit of the method is 0.008 g U·ml^–1. The system obeys Beer's law in the range of 0–5 g U·ml^–1. The method is free from interferences of most of the common metal ions except vanadium(V) and copper(II), which are masked by proper masking agents. The composition of the complex is determined by curve-fitting method. The method has been applied for the recovery of the metal from rock samples and synthetic mixtures.     

Spectrophotometric determination of vanadium(V) with oxine in isoamyl alcohol

A new method for the spectrophotometric determination of vanadium(V) with 8-hydroxyquinoline in isoamyl alcohol is described. The spectra show broad absorption maxima between 450 and 490 nm. The effects of amount of reagent, acidity, time, and temperature were also studied. The optimal interval of Beer's law application is 0.75–3.50 μg vanadium/ml. The nature of the complex in solutions, as well as the interference, reproducibility, and precision of the method, was investigated. The method has been applied to the determination of vanadium in foods.     

Selective Sorption–Spectrometric Determination of Nanogram Amounts of Vanadium(IV) and Vanadium(V)

Conditions of the selective sorption–spectrometric determination of vanadium(IV) and vanadium(V) using sulfonitrophenol M were found. The determination of vanadium (visual test (RSD = 30%) using a reference color scale or quantitative determination (RSD < 10%) by diffuse reflectance spectra is performed immediately after the dynamic-mode sorption of its colored complexes with sulfonitrophenol M at pH 3.5 (vanadium(IV)) or with sulfonitrophenol M and hydroxylamine at pH 1.5 (vanadium(V), 650 nm) at the surface of polyamide membrane disks (d= 1 cm, l= 0.1 mm, m= 2.7 mg). The flow rate is 10–20 mL/min. The detection limit is 5–7 ng of vanadium in the support zone or 0.2–0.5 ng/mL. The determination of 0.5–5 ng/mL vanadium(V) at pH 1.5 does not interfere with 20-fold amounts of V(IV) and 1000-fold amounts of Ni, Zn, Cd, Mg, Co, Cr(III), Mn, PO^3- ₄, and F^–.     

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     

An X-ray study of the complex anionbis(N-hydroxy-iminodiacetate) vanadate(IV), a model for a vanadium-containing biologic compound

The structure of ammonium tetramethylammoniumbis(N-hydroxy-iminodiacetate)vanadate(IV) was determined by x-ray analysis. One independent anion and two cations were found in the asymetric unit. The crystal is monoclinic, space group C2/c, with a=15.820(9), b=16.450(6), c=16.311(4) å,=118.92(3) deg., V=3715(3) å³, Z=8, D_x=1.56g cm^–3,(M_o-K_a)=5.59 cm^–1, F(OOO)=2028, M=434.9 for C₁₂H₂₄N₄O₁₀V. The structure was solved and refined to R(F)=0.029 and R_w(F)=0.040.The complex anion does not contain the oxovanadium(IV) group, but contains vanadium(IV) as the central atom. This is the first example of a vanadium(IV) complex octacoordinated to nitrogen and oxygen atoms exhibiting a highly distorted dodecahedral geometry. The chelation is along twoa and fourg edges. As the angles ones are bonding distances (N—O, 1.381(3), 1.382(4) å) the angles around the central atom are very different from those usually observed in the dodecahedral complexes. The V—O distances range from 1.973(3) to 2.071(3) å and the V—N distances range from 2.002(3) to 2.003(4) å.     

Colorimetric determination of palladium (II) by means of promazine hydrochloride

In acetate buffer medium palladium(II) ions form with promazine hydrochloride (PM) two complexes: an orange one of a formula [Pd(C₁₇H₂₀N₂S)]²⁺ (λ_max = 460 nm, ε = 4.5 × 10³, at 20 °C and pH = 2) and a violet one of a formula [Pd(C₁₇H₂₀N₂S)₂]²⁺ (λ_max = 540 nm, ε = 8.8 × 10³ at 20 °C and pH = 2).The values for instability constants determined by Bjerrum's method amount to pK₁ = 3.95; pK₂ = 3.07; pβ₁ = 3.95; pβ₂ = 7.02, respectively.A colorimetric method of the determination of palladium(II) has been elaborated. The method consists in a measurement of the absorbance of the violet complex of palladium(II) with promazine hydrochloride at λ = 540 nm. The method permits the determination of 2–17 μg Pd/ml with an error of ±2%. The time of the determination is 20 min. Iron(III), Ce(IV), Pt(IV), V(V), Cr(VI), and HNO₃ interfere with the determination.