Micelle mediated extraction of titanium and its ultra-trace determination in silicate rocks

A highly sensitive method for extractive spectrophotometric determination of titanium in silicate rocks is described. Titanium in the range 0-10 microg as TiO2 is extracted into benzene or toluene by the formation of a ternary complex of the metal with thiocyanate (SCN-) and cetyltrimethylammonium bromide (CTA) in the ratio 1:2:2. A deep yellowish-orange ternary complex thus formed is suitable for the determination of titanium at wavelength 421 nm. The optimum colour intensity of this ternary complex was attained when the complex was extracted from an aqueous solution having concentrations of thiocyanate and HCl, in the range, 1.5-2.5 and 1-5 mol L(-1), respectively. The molar absorptivity and Sandell's sensitivity of the extracted species were found to be 1.1-1.0x10(5) L mol(-1) cm(-1) and 0.47 ng cm(-2) (referred to titanium), respectively, at lambda(max) of 421 nm. Except Fe3+, Nb5+ and V5+, no interference was encountered in the estimation of titanium. While up to 10 mg L(-1) Nb and V did not interfere in the determination of titanium, the interference of Fe(3+) was eliminated by reducing it to Fe2+ using SnCl2 solution. The method is highly sensitive and selective. The results obtained for titanium estimation in a host of silicate rock samples have been found to be highly reproducible, accurate and favourably comparable with certified values of reference materials and those obtained from standard methods.     

Separation and simultaneous determination of niobium and tantalum in steel by reversed-phase high-performance liquid chromatography using 2-(2-pyridylazo)-5-diethylamino phenol as a pre-column derivatizing reagent

A method for the simultaneous determination of Nb and Ta in steel and alloy by reversed-phase high-performance liquid chromatography (RP-HPLC) was proposed. 2-(5-Bromo-2-pyridylazo)-5-diethylamino phenol (5-Br-PADAP) was used as a pre-column chelating agent to form a ternary complex with Nb(V) and Ta(V) and tartaric acid. The ternary complexes of Nb(V) and Ta(V) were eluted within 8 min on a C₁₈ column with a mobile phase of methanol-water (55:45, v/v) containing 10 mmol l⁻¹ acetate buffer (pH3.5) and determined with spectrophotometric detection at 598 nm. The detection limits for Nb(V) and Ta(V) were 0.60 and 0.72 μg l⁻¹, respectively, when the ratio of signal-to-noise is 3. The proposed method was used to analyze Nb and Ta in cast iron, alloy and stainless steel.     

The surfactant-sensitized analytical reaction of niobium with 8-hydroxyquinoline-5-sulphonic acid

Cationic surfactants, such as cetylpyridinium bromide (CPB), sensitize the colour reaction of Nb(V) with 8-hydroxyquinoline-5-sulphonic acid (H(2)L). The formation of a ternary complex of stoichiometry 1:3:3 (Nb-L-CPB) is responsible for the observed enhancement in absorptivity and the quenching in the fluorescence of the Nb-L chelate, when a surfactant is present. The ternary complex exhibits maximum absorption at 383 nm ( = 1.46 +/- 0.01 x 10(4) l.mole(-1).cm(-1)) at pH 5.7, and Beer's law is obeyed up to 6-mug ml Nb concentration. Conditional formation constants of the niobium chelate in the presence and absence of CPB have been determined. On the basis of a detailed spectrophotometric and fluorimetric study the nature of the chromophoric reagent-surfactant interaction and the peculiar features of the sensitization by CPB are discussed.     

Spectrophotometric study and analytical applications of the ternary complex Nb-Snazox-H2O2

The possible equilibria of formation for the colored ternary complex of Nb(V), Snazox (azoderivative of 8-hydroxyquinoline), and H₂O₂ are studied. It is shown that an unsaturated coordination complex is formed with a stoichiometric ratio of 1:1:2 and a relatively high conditional stability constant (pK′_d = 13.05 ± 0.55).A detailed account of the optimal experimental conditions for full color development i.e., pH, buffer solutions, ionic strength, rate of color development, order of addition of reagents, etc., is given.Beer's law is obeyed for a final concentration of Nb(V) in the range 1–10 ppm with a precision of about 1%.     

Determination of niobium(V) and tantalum(V) as 4-(2-pyridylazo)resorcinol–citrate ternary complexes in geological materials by ion-interaction reversed-phase high-performance liquid chromatography

A method for the simultaneous separation and determination of Nb(V) and Ta(V) as ternary complexes formed with 4-(2-pyridylazo)resorcinol (PAR) and citrate was developed using ion-interaction reversed-phase high-performance liquid chromatography on a C₁₈ column. Method parameters, such as pre-column complex formation conditions and composition of the complexes were investigated using spectrophotometry and HPLC. Under the optimum conditions, the Nb(V) and Ta(V) complexes were eluted within 12 min with a mobile phase of methanol–water (32:68, v/v) containing 5 mM acetate, 5 mM TBABr and 5 mM citrate buffer at pH 6.5, with detection at 540 nm. A typical separation efficiency was 33 000 and 20 000 theoretical plates per metre for Nb(V) and Ta(V), respectively. The relative standard deviation of retention times for the Nb(V) and Ta(V) complexes were 0.16% and 0.17% and for peak areas were 0.28% and 1.36%, respectively. The detection limits (signal-to-noise ratio=3) for Nb(V) and Ta(V) were 0.4 ppb and 1.4 ppb, respectively. Results obtained for standard reference rock samples agreed well with certified values and results obtained by inductively coupled plasma MS.     

铌(V)-酒石酸-2-(5'-溴-2'-吡啶偶氮)-5-二乙氨基苯酚三元配便物的汞电极上的吸附

本文用线性变势吸附伏安法研究了铌(V)-酒石酸-2-(5'-溴-2'-吡啶偶氮)-5-二乙氨基苯酚三元配合物在汞电极上的电吸附性质, 测定了表面浓度, 讨论了吸附浓度的表达式及其与吸附时间、金属离子浓度、配位体浓度的关系, 验证了吸附量与电极面积及还原峰电流的关系。证明了配合物在电极上的还原是一个可逆吸附的还原过程。     

铌-(5-Br-PADAP)-羟基酸体系混合型络合物的研究

在酒石酸、柠檬酸、草酸和其它羟基酸存在时,研究了铌和2-[(5-溴-2-吡啶)偶氮]-5-(二乙氨基)苯酚(简称5-Br-PADAP)的反应。发现在酒石酸(Tar)存在时,使用5-Br-PADAP测定铌得到最好的结果。本文用吸光光度法研究蓝色的铌-(5-Br-PADAP)-Tar的混合型络合物。在PH为1.0-4.0范围600毫微米处,此蓝色络合物有最大的吸收。摩尔吸光系数是5.7×10⁴。用两种不同的方法研究混合型络合物的组成,Nb:5-Br-PADAP:Tar=1:1:1。在pH为1.0时,Nb的浓度1-32微克/25毫升范围内遵从比尔定律。本文提出高灵敏度和高选择性的吸光光度法测定合金钢中的微量铌。     

Complexation equilibria between niobium(V) and 4-(4'H-1',2',4'-triazolyl-3'-azo)-2-methylresorcinol Extraction-spectrophotometric determination of niobium in pyrochlore-bearing rocks

The complexation equilibria between niobium(V) and 4-(1'H-1',2',4'-triazolyl-3'-azo)-2-methylresorcinol has been studied by spectrophotometric methods and graphical and numerical calculation methods. The 1:2 Nb:R complex species formed at pH 6.2 ( = 2.16 x 10(4) l.mole(-1).cm(-1) at 490 nm) allows the determination of 0.15-2.50 ppm Nb. A 1:1 Nb:R complex species can be extracted into n-butanol from 0.1-1.5M hydrochloric acid ( = 1.28 x 10(4) l.mole(-1) .cm(-1) at 510 nm) and Beer's law is obeyed over the range 0.77-4.64 ppm Nb. Interferences and their elimination have been studied and the methods applied to the determination of niobium in pyrochlore-bearing ores.     

Extraction-spectrophotometric and radiometric investigation of the ternary ion-association complex of niobium(V) with pyrocatechol and triphenyl-tetrazolium chloride

The optimum conditions for extraction of niobium(V) as a ternary ion-association complex with pyrocatechol and triphenyltetrazolium chloride(TTC) have been determined. The investigation of the composition has shown that the ratio Nb:proocatechol:TTC is 1:2:1 K_ex, K_D and have been determined radiometrically, using the chemical model. The influence of foreign ions on the extraction of the ion-association complex has been studied. A method for artifical mixture and steel containing niobium has been used.     

Analytical applications of ternary complexes-VIII An improved reagent system for the spectrophotometric determination of aluminium

Aluminium ions form a ternary complex with Catechol Violet (CV) and cetyltrimethylammonium bromide (CTAB) in which an Al(3)+:CV:CTAB ratio of 1:2:5 is observed. The sensitivity of the binary complex between aluminium and Catechol Violet (615nm) = 1.50 x 10(3) l. mole (-1). mm(-1) is enhanced on ternary complex formation to (670nm) = 5.30 x 10(3) l. mole(-1). mm(-1). The colour is formed instantaneously, stabilizes within 20 min, and may be used for the detection of aluminium in the range O.27-54 pm in the presence of EDTA which prevents the interference of most ions. A benzoate extraction procedure for aluminium is used to prevent interference from hundredfold amounts of Cr(VI), Fe(II), Fe(III), Hg(II), Sb(III), Ti(IV) and acetate, but Be, Cr(III), rare earths, V(V), Zr and tartrate must be absent, as must high concentrations of phosphate and fluoride ions.     

Electrochemical and spectroscopic studies of the chloro and oxochloro complex formation of Nb(V) and Ta(V) in NaCl-AlCl3 melts

The equilibrium constant for the chloro complex formation of Nb(V) NbCl6-<--->NbCl5+Cl- (i) in NaCl-AlCl3 melts at 175 degrees C was found to be pKi = 2.86(5). The oxochloro complex formation of Nb(V) and Ta(V) in NaCl-AlCl3 melts at 175 degrees C could be explained by the following equilibria: MOCl4- <-->MOCl3+Cl- (ii) MOCl3<-->MOCl2(+)+Cl- (iii) where M = Nb and Ta. The equilibrium constants determined by potentiometric measurements with chlorine-chloride electrodes were, for M = Nb, pKii = 2.21(4) and pKiii = 3.95(5) and, for M = Ta, pKii = 2.743(15) and pKiii = 4.521(13). NbCl6- has two bands in the UV-vis region, a strong one at 34.7 x 10(3) cm-1 and a weaker one at 41.6 x 10(3) cm-1. The MOCl4- complexes showed in the case of Nb(V) absorption bands at 32.7 and 42.9 x 10(3) cm-1 and in the case of Ta(V) at 38.6 and 48.1 x 10(3) cm-1.     

A new quasi-one-dimensional ternary chalcogenide: synthesis,crystal structure,and electronic structure of Nb1+xV1-xS5 (x = 0.18)

The new low-dimensional ternary chalcogenide, Nb(1+x)V(1-x)S(5) (x = 0.18), has been prepared and characterized. This compound crystallizes in the monoclinic space group, C2(2h)-P2(1)/m with two formula units in a cell with dimensions a = 9.881(4) A, b = 3.329(1) A, c = 8.775(3) A, and beta = 114.82(3) degrees. The layer is composed of two unique chains of face-sharing Nb-centered bicapped trigonal prisms and edge-sharing M-centered octahedra (M = Nb or V). The electronic structures of the monomeric basic building units, NbS(8) and VS(6), and hypothetical and real one-, two-, and three-dimensional structures making up the compound are examined to understand the nature of inter- and intrachain interactions and orbital overlapping among metals and sulfur atoms. The electronic structure of Nb(1+x)V(1-x)S(5) is essentially given by superimposing those of the individual chains. V d orbitals are found to be crucial for the one-dimensional metallic conductivity along the chain axis.     

Extraction-spectrophotometric determination of iron(II) by ternary complex formation with pyrocatechol violet and cetyltrimethylammonium bromide

A method for iron(II) determination based on reaction with Pyrocatechol Violet to form a 1:2 binary complex at pH 5-7 is described and has been extended to an extraction-spectrophotometric procedure for the determination of iron(II) by formation of the 1:2:2 iron(II)-Pyrocatechol Violet-cetyltrimethylammonium bromide ternary complex. The molar absorptivities of the binary and ternary complexes at 595 and 605 nm are 6.55 x 10(4) and 1.35 x 10(5)1.mole(-1).cm(-1), respectively. The method has been successfully applied to the determination of iron in felspar, Portland cement and sodium hydroxide.     

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.     

On-line preconcentration of niobium(V) and tantalum(V) as 4-(2-pyridylazo) resorcinol-citrate ternary complexes in geological samples by ion interaction high-performance liquid chromatography

4-(2-Pyridylazo) resorcinol (PAR) and citrate were used as pre-column complexing agents for the determination of Nb(V) and Ta(V) as ternary complexes in geological samples. Aliquots of 2 ml of the standard and sample solutions containing the Nb(V) and Ta(V) complexes were loaded onto a concentrator column (C18, 0.4 cm x 4.6 mm) with a carrier mobile phase comprising 20% (v/v) methanol and containing 5 mM acetic acid, 5 mM citric acid and 10 mM tetrabutylammonium bromide (TBABr), pH 6.5 at 2 ml/min for 2 min, with the effluent being directed to waste. An automatic switching valve was then switched to flush both complexes from the concentrator column onto a C18 analytical column using a mobile phase comprising 32% (v/v) methanol and containing 5 mM acetic acid, 5 mM citric acid and 3 mM TBABr, pH 6.5 for 2.5 min. The switching valve was then switched back to the original position, and cleaned with methanol for 7 min to eliminate unwanted species still adsorbed to the concentrator column. This procedure prevented later eluting compounds from reaching the analytical column, which reduced the overall run time. The detection limits of Nb(V) and Ta(V) (determined at a signal-to-noise ratio of 3, detection wavelength of 540 nm and a 2-ml sample volume) were 0.012 and 0.039 ppb for Nb(V) and Ta(V), respectively. Recoveries of Nb(V) and Ta(V) were 99.4 and 96.2%, respectively. The HPLC results obtained from the reference granite and basalt samples agreed well with inductively coupled plasma MS and certified values, but the HPLC method yielded slightly low values of the Nb/Ta ratio.     

Determination of V(V), Nb(V) and Ta(V) as their 2-(5-nitro-2-pyridylazo)-5-diethylaminophenol complexes by reversed-phase high performance liquid chromatography

A method for the reversed-phase liquid chromatographic separation and determination of V(V), Nb(V) and Ta(V) as 2-(5-nitro-2-pyridylazo)-5 diethylaminophenol (5-NO₂-PADAP) complexes is reported. The metal complexes were eluted in 9 min with a mobile phase of methanol-water (54 : 46, v/v) containing 10 mmol L^–1 acetate buffer (pH 3.0) on an ODS column. The detection limits for V, Nb and Ta were 0.09, 0.13 and 1.41 ng mL^–1, respectively, with S/N=3. The analysis of a reference sample of a mineral is discussed. The results corresponded to the certified values, and recoveries of 98.3–101.4% have been obtained.     

Electrochemistry of niobium(V) in sulfuric and methanesulfonic acids: formation of the Nb3O2(SO4)6(H2O)(3)(5-) cluster and designed electrochemical generation of "Nb3O2" core clusters by double potential pulse electrolysis

The electrochemical and spectroelectrochemical properties of niobium(V) and the Nb(3)O(2)(SO(4))(6)(H(2)O)(3)(5-) cluster in sulfuric acid and methanesulfonic acid were investigated using cyclic voltammetry, constant potential electrolysis, and spectroelectrochemistry. These chemical systems were suitable to probe the formation of "Nb(3)O(2)" core trinuclear clusters. In 9 M H(2)SO(4) the cluster Nb(3)O(2)(SO(4))(6)(H(2)O)(3)(5-) exhibited a reversible 1-electron reduction peak at E(pc) = -1.30 V vs Hg/Hg(2)SO(4) electrode, as well as a 4-electron irreversible oxidation peak at E(pa) = -0.45 V. Controlled potential reduction at E = -1.40 V produced the green Nb(3.33+) cluster anion Nb(3)O(2)(SO(4))(6)(H(2)O)(3)(6-). In 12 M H(2)SO(4) Nb(V) displayed two reduction peaks at E(pc) = -1.15 V and E(pc) = -1.30 V. It was determined that the first process involves a quasi-reversible 2-electron reduction. After reduction of Nb(V) to Nb(III) the following chemical step involves formation of [Nb(III)](2) dimer, which further reacts with Nb(V) to produce the Nb(3)O(2)(SO(4))(6(H(2)O)(3)(5-) cluster (ECC process). The second reduction peak at E(pc) = -1.30 V corresponds to further 2-electron reduction of Nb(III) to Nb(I). The electrogenerated Nb(I) species also chemically reacts with starting material Nb(V) to produce additional [Nb(III)](2). In 5 M H(2)SO(4), the rate of the second chemical step in the ECC process is relatively slower and reduction of Nb(V) at E = -1.45 V/-1.2 V produces a mixture of Nb(3)O(2)(SO(4))(6)(H(2)O)(3)(5-) and [Nb(III)](2) dimer. [Nb(III)](2) can be selectively oxidized by two 2-electron steps at E = -0.65 V to Nb(V). However, if the oxidation is performed at E = -0.86 V, the product is Nb(3)O(2)(SO(4))(6)(H(2)O)(3)(5-). A double potential pulse electrolysis waveform was developed to direct the reduction of Nb(V) toward selective formation of the Nb(3)O(2)(SO(4))(6)(H(2)O)(3)(5-) cluster. Proper application of dc-voltage pulses alternating between E(1) = -1.45 V and E(2) = -0.86 V yields only the target trinuclear cluster. Analogous double potential pulse electrolysis of Nb(V) in methanesulfonic acid generates the "Nb(3)O(2)" core cluster Nb(3)O(2)(CH(3)SO(3))(6)(H(2)O)(3)(+).     

A highly selective spectrophotometric determination of niobium (V) using 3-hydroxy-2-[1'-phenyl-3'-(p-chlorophenyl)-4'-pyrazolyl]-4-oxo-4H-1-benzopyran as a complexing agent

3-Hydroxy-2-[1'-phenyl-3'-(p-chlorophenyl)-4'-pyrazolyl]-4-oxo-4H-1benzopyran (HPCPB) is used as an analytical reagent for the spectrophotometric determination of niobium in trace amounts with which it forms a yellow coloured complex (4:1) in perchloric acid medium. The complex is extractable into chloroform and shows absorption maximum at 407-418 nm with a molar absorptivity of 2.79 x 10(4) L mol(-1) cm(-1) and Sandell's sensitivity equal to 0.0033 microg Nb(V) cm(-2), respectively. Beer's law holds good in the range 0-1.2 microg Nb ml(-1), with a standard deviation of +/- 0.0015 absorbance units. The method is free from the interference of a large number of elements and handles satisfactorily the analysis of various samples of varying complexity.     

Separation and determination of vanadium in fertiliser by capillary electrophoresis with a light-emitting diode detector

A method has been developed for determination of vanadium, as an anionic ternary complex of vanadium(V) with 4-(2-pyridylazo) resorcinol (PAR) and hydrogen peroxide, after separation by capillary electrophoresis (CE). The optimum conditions for the formation of the ternary complex were acetate buffer (3 mmol L(-1)) at pH 6 containing 0.15 mmol L(-1) PAR and 7.1 mmol L(-1) H(2)O(2). The CE separation was conducted using 15 mmol L(-1) acetate buffer at pH 6 as the background electrolyte; the separation potential was -30 kV and the injection time 100 s. The vanadium complex was detected photometrically at 568 nm, by use of a light-emitting diode (LED); the detection limit was 19 ppb. The method was applied to the analysis of vanadium in fertilisers. Clean-up of the digested fertiliser sample, with Sep-Pak C(18) coated with tetrabutylammonium hydroxide, before analysis was used to remove matrix ions which otherwise caused electrophoretic de-stacking. Vanadium levels found in the fertiliser samples by use of the CE method were found to be comparable with results obtained by HPLC and ICP-MS.     

RP-HPLC study of redox equilibria in vanadium-PAR binary and ternary systems: Direct determination of vanadium in steel

The reversed-phase high-performance liquid Chromatographic (RP-HPLC) behaviour of the binary chelates of V(V) and V(IV) with 4-(2-pyridylazo) resorcinol (PAR) and ternary chelates of vanadium with PAR and auxiliary ligands: hydrogen peroxide, hydroxylamine, tartrate and citrate were studied using a C₁₈ column. The complex double-peak chromatograms of V(IV)/V(V)-PAR systems were studied and the origin of each peak was proved. Vanadium in ternary systems with PAR and hydrogen peroxide was found exclusively in V(V)-H₂O₂-PAR complex (single peak on the chromatogram) despite its initial oxidation state. The double role of hydroxylamine (complex agent and reductor) in vanadium systems with PAR was confirmed: in the V(V) system three species were identified (V(V)-PAR, V(V)-NH₂OH-PAR and V(IV)-PAR), but in the V(IV) system only two: V(IV)-PAR and V(V)-NH₂OH-PAR. Citrate and tartrate giving single peak were found as auxiliary ligands in ternary V(V) systems of analytical importance. Due to its masking potential towards iron (III) ions, citrate was chosen as the most suitable third component of a ternary vanadium system with PAR, to form the basis of an RP-HPLC method for direct determination of V in steel.