On-column complexation and simultaneous separation of vanadium(IV) and vanadium(V) by capillary electrophoresis with direct UV detection

An on-column complexation method has been developed for the simultaneous determination of V(IV) and V(V). Vanadium species were chelated with aminopolycarboxylic acids to form anionic complexes which were separated by capillary zone electrophoresis (CZE) with direct UV detection. Ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentacetric acid (DTPA), nitrilotriacetic acid (NTA), and N-2-hydroxyethylethlendiaminetriacetric acid (HEDTA) were investigated as both ligand and running electrolyte. Of the ligands studied the complexes of EDTA with V(IV) and V(V) resulted in the highest selectivity and UV response.The conditions used for on-column complexation and separation, including pH, and electrolyte ligand concentration, were examined to achieve reasonable separation selectivity and detection sensitivity. The optimum separation of the anionic forms of V(IV) and V(V) was obtained by use of CZE with UV detection at 185 nm and an electrolyte containing 5 mmol L(-1) EDTA at pH 4.0. Linear calibration plots were obtained in the concentration range10-300 micro mol L(-1); detection limits were 3 micro mol L(-1) for V(IV) and 1 micro mol L(-1) for V(V). The proposed method was demonstrated for the determination of vanadium in groundwater spiked with V(IV) and V(V).     

The polarography of molybdenum,titanium and niobium in solutions of organic acids

Further work on the polarographic reduction of molybdenum(VI), niobium(V) and titanium(IV) in base electrolytes containing organic acids is reported. A base electrolyte of 0.5 M citric acid-0.025 M sulphuric acid-0.05 M thorium nitrate proved suitable for the determination of molybdenum and titanium in the presence of niobium, tantalum, tungsten and zirconium. A direct polarographic method using this base electrolyte is described for the determination of molybdenum in a niobium base alloy.     

Liquid-liquid extraction of niobium(V) in the presence of other metals with high molecular mass amines and ascorbic acid

A novel method is proposed for the solvent extraction of niobium(V). A 0.1M solution of Aliquat 336S in xylene quantitatively extracts microgram quantities of niobium(V) from 0.01M ascorbic acid at pH 3.5-6.5. Niobium from the organic phase is stripped with 0.5M nitric acid and determined spectrophotometrically in the aqueous phase as its complex with TAR. The method permits separation of niobium not only from tantalum(V) but also from vanadium(IV), titanium(IV), zirconium(IV), thorium(IV), chromium(III), molybdenum(VI), uranium(VI), iron(III), etc. Niobium from stainless steel was determined with a precision of 0.42%.     

Extractive-spectrophotometric determination of molybdenum with 4-unsubstituted-5-pyrazolones

A fairly sensitive and selective method for rapid determination of tracer amounts of molybdenum(V) as mixed-ligand complexes with thiocyanate and 4-unsubstituted-5-pyrazolones is described. The red complexes are extractable into chloroform from 1-5M hydrochloric or perchloric acid or 1-3M sulphuric arid media. The molar absorptivities are in the range 1.72-2.15 x 10(4)l.mole(-1).cm(-1) at 455 nm (lambda(max)). The method has been applied to the estimation of molybdenum in various synthetic and alloy-steel samples. In presence of excess of the reagent, Cu(II), Co(II), Mn(II), Fe(II), Fe(III), Al(III), Cr(III), Cr(VI), Ti(III), Ti(IV), Zr(IV), Hf(IV), V(III), V(IV), V(V), Nb(V), Ta(V), W(VI) and U(VI) do not interfere.     

Spectrophotometric and derivative spectrophotometric determination of aluminium with Hydroxynaphthol Blue

The reaction of aluminium(III) with Hydroxynaphtol Blue (HNB) in aqueous media at apparent pH 5.5 results in a red complex that is stable for at least 4 hr. Beer's Law is obeyed up to 1.6 microg/ml of aluminium(III) with an apparent molar absorptivity of 1.66 x 10(4) l.mol(-1). cm(-1) at 569 nm. This paper proposes procedures for aluminium(III) determination by ordinary and first-derivative spectrophotometry. The results demonstrated that the linear dynamic range is 0.03-1.60 microg/ml for ordinary spectrophotometry and 11.8-320.0 ng/ml for first derivative spectrophotometry. The HNB is not selectivity for aluminium, but the addition of EDTA allows the aluminium determination in the presence of accepted amounts of Ca(II), Mg(II), Mn(II), Ba(II), Sr(II), Cd(II), Pb(II), La(III), In(III), Bi(III) and Zn(II). The interference of Cu(II) and Hg(II) can be masked by thiosulphate. Ions such as UO(2)(II), Mo(VI), Co(II), Ti(IV) and PO(4)(III) do interfere seriously. This method was applied for aluminium determination in copper-base alloy, zinc-base alloy, magnesium-base alloy, iron ore, manganese ore, cement, dolomite, feldspar and limestone. The results indicated high accuracy and precision.     

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.     

2,3,7-Trihydroxyfluorones immobilized on cellulose matrices in test methods for determining rare elements

It was shown that 2,3,7-trihydroxyfluorones immobilized by adsorption on cellulose matrices can be used as reagents for the test determination of Mo(VI), Ti(IV), Ge(IV), Hf(IV), Nb(V), Ta(V), W(VI), Bi(III), V(IV), and Zr(IV). The change of the protolytic and complexing properties of trihydroxyfluorones immobilized on cellulose matrices was considered in comparison to corresponding properties in a solution. It was found that the reactions of trihydroxyfluorones with rare elements on cellulose matrices and in a solution exhibit similar effects upon the addition of cetylpyridinium. These effects are the bathochromic shift of the absorption maxima of the reagents and their complexes with analytes and the extension of the range of optimum acidity for complex formation. The complexation of salicylfluorones with the titanium(IV) in solution and on cellulose paper was studied by IR spectrometry. Phenylfluorone immobilized on a mixed-fiber cloth as used in test determinations of (mg/L) 0.05–5 Ti(IV), V(IV), Hf(IV), Nb(V), and Mo(VI); 0.01–5 Ge(IV) and Zr(IV); 0.05–1 Bi(III) and W(VI); and 0.1–5 Ta(V) by the color intensity of the indicator matrix after passing through 20 mL of a test solution. It was shown that phenylfluorone immobilized on cellulose paper can be used to determine (mg/L) 0.05–50 Ti(IV), 0.5–1000 Ge(IV), 0.5–500 Zr(IV), 5–200 Bi(III), 0.1–50 Mo(VI), 0.1–1000 V(IV), 0.1–100 Nb(V), 0.1–800 Hf(IV), 1–100 Ta(V), and 1–800 W(VI) by the length of the colored zone of a test strip after it was brought into contact with a test solution.     

Polarographic analytical determination of Hg(II), Cu(II), Cd(II), As(III), Sb(III), Ti(IV) and U(VI) in the presence of Fe(III)

The analytical determination of Hg(II), Cu(II), Cd(II), As(III), Sb(III), Ti(IV) and U(VI) in the presence of Fe(III) and 1 M H₂SO₄ are investigated using the polarographic technique. The wave corresponding to the reduction of Fe(III) to Fe(II) was found to be completely suppressed by the addition of 1% pyrogallol. Thus, different mixtures of these elements, viz. Hg(II), Cu(II), Cd(II), As(III) and Fe(III)-mixture (A), Cu(II), Cd(II), Sb(III), As(III) and Fe(III)-mixture (B), and Cu(II), Cd(II), Ti(IV), U(VI) and Fe(III)-mixture (C), were quantitatively determined using 1% pyrogallol and 1 M H₂SO₄ as supporting electrolyte. The i₁/c results give excellent correlations in each case, as indicated from the results of leastsquares regression analysis.     

The polarographic determination of thallium

A polarographic method is described for the determination of thallium in sodium triphosphate supporting electrolyte. The incorporation of 0.1% camphor in the electrolyte displaces the cathodic steps of many interfering ions, e.g., lead(II), copper(II), iron(III) and bismuth(III) to a more negative potential (1?.0 V), well away from the thallium step which remains unaffected.     

Application of capillary electrophoresis for inorganic selenium speciation in the frame of high-level waste management

Capillary electrophoresis (CE) with direct UV detection is proposed for speciation of inorganic Se in high-level liquid waste. In this aim, the optimal conditions of measurements (pH, electrolyte buffer concentration) and the influence of nitrate excess on the quantitative determination of Se(IV) and Se(VI) were studied. Different electrolyte buffers were considered: carbonate, phosphate and citrate. It was found, that citrate buffer is the most suitable for the application under consideration. Under the chosen optimal conditions (20 mmol L(-1) citrate buffer, pH 2.5), calibration curves for Se(IV) and Se(VI) are linear in the concentration range 10(-4)-10(-3) mol L(-1). The detection limits are 4x10(-6 )for Se(IV) and 2x10(-5) for Se(VI). The accuracy of the procedure was checked by calculating the recovery by spiking simulation solutions. Relative standard deviation (S(r)) is less than 10%.     

Polarography of molybdenum in aspartic acid solution

The polarographic behaviour of Mo(VI) in solutions of aspartic acid is reported. In 0.01M acid, two waves are obtained, but at pH 4 only one, and they are diffusion controlled. The determination is possible in the presence of Ni, Cr(VI), W(VI), Mn(II), Co(II), Cu(II) or Th, with an accuracy of 2% in the range 10(-5)-10(-3)M.     

Solvent extraction and spectrophotometric determination of palladium(II) with 7-iodo-8-hydroxyquinoline-5-sulphonic acid

An extractive spectrophotometric procedure has been developed for the determination of palladium (II) at microgram levels. The palladium(II) chelate of 7-iodo-8-hydroxyquinoline-5-sulphonic acid is extracted into n-butanol. Extraction is maximal (95%) from 0.2M perchloric acid. Beer's law is valid at 430 nm over a wide range of palladium concentration from 2.5 ppm. The molar absorptivity is 958 1.mole(-1).mm(-1). The system can tolerate a large excess of Co(II), Ni(II), Rh(III), Pt(IV), Cr(III), W(VI), chloride, phosphate, citrate and tartrate. Small quantities of Ru(III), IR(III) and EDTA do not interfere, but serious interference is caused by Fe(III), V(V), Mo(VI) and Os(VIII).     

辛可尼丁的催化氢波

在浓度为０．２ｍｏｌ／Ｌ ＮＨ３·Ｈ２Ｏ－０．２ｍｏｌ／Ｌ ＮＨ４Ｃｌ（ｐＨ＝９．２０）的底液中,辛可尼丁在单扫示波极谱上有一灵敏的催化氢波。导数波峰电位于－１．４２Ｖ（ｖｓ,ＳＣＥ）附近。该峰具有一定吸附性。     

Sine-wave polarographic determination of zirconium or niobium in aqueous media

The sine-wave polarographic determination of zirconium in aqueous media was investigated using solutions which were 0.55 – 5.5·10^-3M in zirconyl chloride and 1 M in potassium chloride and had been adjusted to pH 2.0 with hydrochloric acid. It was possible to determine zirconium in the concentration range of 0.05 to 0.4 mg per ml. The sine-wave polarographic behavior of zirconium in aqueous solutions in the pH range 2–3 is discussed. The sine-wave polarographic determination of niobium in aqueous media was investigated using concentrated sulfuric acid containing 5 to 0.1 mg of niobium per ml in a supporting electrolyte of citric acid; the determination of niobium was possible down to 0.1 mg of niobium per ml of concentrated sulfuric acid although the D.C. polarographic method was impractical for the determination of less than 0.5 mg of niobium per ml.     

Differential pulse polarographic determination of trace selenium(IV) and molybdenum(VI) using the catalytic hydrogen wave

In the presence of selenium(IV) and molybdenum(VI) a new polarographic peak appears which corresponds to a hydrogen catalytic wave. By differential pulse polarography a single, sharp peak at about -1.1 V is obtained, allowing trace determination of selenium(IV) and molybdenum(VI) in the range 1x10(-6)-5.0x10(-9) M with a linear calibration and a detection limit of 1.5x10(-9) M. The optimum conditions are found to be 0.1 M KNO(3) and a pH of about 3.2 (Britton-Robinson buffer). There is no serious interference from some ions when present at 1.0-40 times that of molybdenum. At higher amounts of interfering ions the interference is eliminated by the addition of EDTA.     

Enhanced sensitivity for the differential pulse polarographic determination of Mo(VI) based on adsorption catalytic current

A differential pulse polarographic (DPP) method based on the adsorption catalytic current in a medium containing chlorate and 8-hydroxyquinoline (oxine) is suggested for the determination of molybdenum(VI). Experimental conditions such as pH and the composition of supporting electrolyte have been optimized to get a linear calibration graph at trace levels of Mo(VI). The sensitivity for molybdenum can be considerably enhanced by this method. The influence of possible interferences on the catalytic current has been investigated. The sensitivity of the method is compared with those obtained for other DPP methods for molybdenum. A detection limit of 1.0 × 10^–8 mol/L has been found.     

The spectrophotometric determination of vanadium after extraction as vanadium(III) ferronate by tribenzylamine

Vanadium(III) obtained by dithionite reduction of vanadium(V) can be extracted as its ferron complex with tribenzylamine in chloroform from 0.05 M sulphuric acid. Vanadium (0–5 μg ml^-1) is determined spectrophotometrically at 430 nm with a sensitivity of 0.0028 μg V cm^-2. Al(III), Co(II), Ni(II), Fe(II, III), Hg(II), Si(IV), Be(II), Mg(II), Ca(II), Sr(II), Ba(II), Cr(VI, III), W(VI), Zn(II), U(VI), Mn(II). Pb(II), Cu(II), Cd(II) and Th(IV) do not interfere; only Mo(VI), Ti(IV), Zr(IV). Bi(V) and Sn(II) interfere. A single determination takes only 7 min. The extracted complex is V^III (R-3H.TBA)₃ where R = C₉H₄O₄NSI. The method is satisfactory for the determination of vanadium in steels, alum and other samples without preliminary separations.     

The polarographic determination of traces of titanium-(IV) in the presence of n-benzoyl-n-phenylhydroxylamine

The polarographic behavior of the titanium(IV)-N-benzoyl-N-phenyl-hydroxylamine (BPHA) system in acidic medium and in water-ethanol mixtures has been studied. In (1+3) water-ethanol containing 2 M sulfuric acid and 0.05 M BPHA, titanium(IV) gives a single kinetically controlled wave. Titanium(IV) can be determined at concentrations as low as 5·10^-6M, in the presence of Fe(III), Cu(II), V(V), etc., but Cd(II), Sn(II and IV), As(V), U(VI) and Mo(VI) interfere.     

Separation of rhenium by thin-layer chromatography with polyethyleneimine cellulose in hydrochloric acid media

Summary The thin-layer chromatographic behavior of 49 inorganic ions on polyethyleneimine (PEI) cellulose has been investigated in hydrochloric acid media (0.01–1.0 mol dm⁻³). The sorption on the cellulose decreases with increasing acid concentration for most of the ions, but As(III), Ti(IV) and Te(VI) do not exhibit any R_f variation with the acid concentration. The R_f spectra of TI(I), Cd(II), Pb(II) and Zn(II) have a maximum. Ag(I), Bi(III), Nb(V), Ta(V), Mo(VI) and W(VI) are retained tightly on the layer, due to either insoluble salt formation or extensive hydrolysis. The extremely low R_f values of Hg(II), Pd(II), Au(III), Ru(III) and Pt(IV) are accounted for by stability of their chlorocomplexes. Re(VII) distributes chromatographically, having moderate R_f values between 0.3 and 0.6, so that the selective separation of Re(VII) from the other ions is feasible.     

Square wave Stripping voltammetry of Cobalt Based on Adsorptive accumulation of its Hydroxynaphthol Blue (HNB) Complex at the Static Mercury Drop Electrode

ABSTRACT

A new method is described for the determination of cobalt based on the square wave adsorptive stripping voltammetry of Co(II) complexed with hydroxynaphthol blue (HNB) at the static mercury drop electrode. Optimal conditions were found to be: preconcentration potential, -0.500V vs. Ag/AgCl (KCl 3M); preconcentration time, 30 s (with stirring); pulse height, 50 mV; frequency, 100 Hz; scan increment, 4 mV; step time, 0.010 s; supporting electrolyte, HEPES/HCl (0.1 M, pH 7.0-8.0) or triethanolamine/HCl (0.1 M, pH 7.6); concentration of hydroxynaphthol blue, 5.0 × 10^?6 M. The response of the system was found to be linear in a range of Co(II) concentrations from 2.0 to 10.0 μg/L. The limit of detection was found to be 1.8 × 10^?9 M with 2 minutes of preconcentration time. The effect of various potential interferences were also studied including a variety of cations, anions and organic surfactants. The interferences by Ni(II), and Cr(VI) may be eliminated by addition of EDTA or CDTA and the of Fe(III) and Ti(IV) by fluoride. The merits of the procedure were demonstrated in the analysis of certified and biological samples.