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.     

Separation of vanadium, niobium and tantalum as ternary mixed-ligand complexes by capillary electrophoresis using chelation with 4-(2-pyridylazo)resorcinol and tartaric acid

Vanadium(V), niobium(V) and tantalum(V) were separated as ternary mixed-ligand complexes by capillary electrophoresis using 4-(2-pyridylazo)resorcinol (PAR) as the color chelating reagent. Four carboxylic acids such as tartaric acid (Tart), oxalic acid, citric acid and acetic acid were investigated as the additional ligand. The first was chosen as the best. Other parameters such as the concentration ratio of Tart to PAR, buffer concentration, injection time and applied voltage were also optimized. Under the optimized conditions, a complete separation of the three metal complexes was accomplished within 10 min. A linear calibration curve in the range of two orders of magnitude was obtained.     

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.     

Separation of vanadium, niobium and tantalum as ternary mixed-ligand complexes by capillary electrophoresis using chelation with 4-(2-pyridylazo)resorcinol and tartaric acid

Vanadium(V), niobium(V) and tantalum(V) were separated as ternary mixed-ligand complexes by capillary electrophoresis using 4-(2-pyridylazo)resorcinol (PAR) as the color chelating reagent. Four carboxylic acids such as tartaric acid (Tart), oxalic acid, citric acid and acetic acid were investigated as the additional ligand. The first was chosen as the best. Other parameters such as the concentration ratio of Tart to PAR, buffer concentration, injection time and applied voltage were also optimized. Under the optimized conditions, a complete separation of the three metal complexes was accomplished within 10 min. A linear calibration curve in the range of two orders of magnitude was obtained.     

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.     

Separation of V(V)-4-(2-pyridylazo)resorcinolato complex from a large excess reagent using an ODS cartridge for high-performance liquid chromatography.

A selective off-line preconcentration technique for the V(V) complex with 4-(2-pyridylazo)resorcinol has been developed and successfully applied to the determination of V(V) in an air-borne sample. The target complex was separated from excess reagent using an ODS cartridge and water as the eluent. The complex was then concentrated on another ODS cartridge using tetrabutylammonium bromide and eluted with methanol; the eluate was applied to a one-drop concentration/HPLC. A detection limit as low as (6.05 +/- 0.82)x 10(-11) M (5 ppt) was achieved.     

Novel poly(methimazolyl)borate complexes of niobium(V) and tantalum(V)

The reactions of [MCl4(eta-C5H5)](M = Nb, Ta) with Ph3Sn{HB(mt)3} (mt = methimazolyl) provide structurally characterised complexes of the new chlorobis(methimazolyl)borate ligand, [MCl3(eta-C5H5){kappa2-S,S'-HClB(mt)2}].     

Ultrasonic-assisted supramolecular solvent-based liquid phase microextraction of mercury as 1-(2-pyridylazo)-2-naphthol complexes from water samples

A separation-preconcentration method based on supramolecular solvent ultrasonic-assisted liquid-phase microextraction (Ss-USA-LPME) for spectrophotometric determination of mercury as 1-(2-pyridylazo)-2-naphthol (PAN) chelates has been established. Red coloured Hg(II)-PAN hydrophobic complex was extracted into the supramolecular phase (1-decanol/THF) at pH 9.5. The extract was separated from aqueous phase by centrifugation, diluted with ethanol and determined by UV–Vis spectrophotometer at λ_max = 560 nm. The influences of important analytical parameters such as pH, amount of PAN, 1-decanol and THF, sample volume and matrix effects for the quantitative recoveries were examined and optimised. Under the optimised experimental conditions, the amount of ligand, 1-decanol and THF were 1.0 × 10^–4 M, 200 µL and 300 µL, respectively. The optimum time of ultrasonic bath and centrifugation were found as 2 min and 5 min. A linear calibration graph was obtained linearly in the concentration ranges of 8.3–1000 µg L^?1. The preconcentration factor was obtained as 20. The limit of detection (LOD) was 2.6 µg L^?1 with the relative standard deviation (RSD) of 2.4% for mercury (C = 100 µg L^?1, n = 7). The validity of the developed Ss-USA-LPME technique was checked with a certified reference material of NIST 1641d. The presented method has been successfully applied to the determination of mercury in water samples.     

Composition of 2-(3,5-dibromo-2-pyridylazo) diethylaminophenol chelates by liquid chromatography

Summary The composition of 3,5-diBr-PADAP metal chelates was determined by liquid chromatography employing appropriate eluents and non-polar bonded stationary phase. The metal-to-ligand ratios were 12, 12 and 12 for Cu(II), Co(III) and Cr(III) respectively, and the V(V)-to-ligand ratio found to be 111 in V(V)-3,5-diBr-PADAP-H₂O₂ in the presence of H₂O₂. The results are in agreement with literature data.     

Spectrophotometric determination of niobium in steels with 4-(2-pyridylazo)-resorcinol

A direct method is presented for the spectrophotometric determination of niobium with PAR in mild and alloy steels. Interference is caused only by tantalum and large amounts of copper. A compensating solution is used to correct for coloured ions and for the copper-PAR complex. The method covers the range 0–100 mg of niobium, and Beer's law is obeyed from 0 to 2.0μg Nb/ml. A molar absorptivity of 14,400 at 536 nm was found for the niobium-PAR complex, with a relative standard deviation of ±0.6%.     

Simultaneous determination of vanadium, niobium and tantalum by high-performance liquid chromatography equipped with on-line enrichment using 2-[2-(5-bromoquinolinylazo)]-5-diethylaminophenol as pre-column derivatization reagent

The chelator 2-[2-(5-bromoquinolinylazo)]-5-diethylaminophenol (5-Br-QADEAP) was synthesized. A method was developed for the simultaneous determination of vanadium, niobium and tantalum as metal–5-Br-QADEAP chelates using rapid column high performance liquid chromatography along with an on-line enrichment technique. Vanadium, niobium and tantalum were pre-column derivatized with 5-Br-QADEAP to form colored chelates. The chelates were separated on a 4.6 × 10 mm, 1.8 μm rapid analytical column with acetonitrile–water (50:50, v/v) containing pH 4.5 phosphate buffer and 0.01 mol L⁻¹ of citrate as the mobile phase. The chelates were separated completely within 2.5 min. The detection limits (S/N = 3) of vanadium, niobium and tantalum are 1.6, 1.6, and 1.8 ng L⁻¹, respectively. This method was applied to the determination of vanadium, niobium and tantalum in alloy steel, water, and geologic samples with good results.     

高效液相色谱法分离2-(4-羟基苯氧基)丙酸酯的对映体

采用高效液相色谱法在手性柱上分离芳氧基苯氧基丙酸类除草剂中间体(±)-2-(4-羟基苯氧基)丙酸酯的对映体。实验结果表明,在三苯甲酸纤维素酯的手性柱上,以无水乙醇为流动相能较好地分离(±)-2-(4-羟基苯氧基)丙酸乙酯和甲酯,其分离因子α值分别为1.44和1.29;同时还发现在三苯甲酸纤维素酯的手性柱上2-取代芳氧基或芳基丙酸酯结构中的酯基团的大小对其对映体的分离有明显的影响,其中以乙基为最佳。并通过对照试验证实了2-(4-羟基苯氧基)丙酸乙酯的右旋体先流出,其左旋体后流出。     

Use of 1-(2-pyridylazo)-2-naphthol as the post column reagent for ion exchange chromatography of heavy metals in environmental samples

Ion exchange chromatography (IEC) using a bi-functional column (quaternary ammonium and sulfonate groups), followed by post-column reaction (PCR) with 1-(2-pyridylazo)-2-naphthol (PAN), was used to separate and quantitate Cu(II), Ni(II), Zn(II), Co(II), Cd(II), Mn(II) and Hg(II) at low concentration levels. IEC-PCR separation was achieved within 14 min using the mobile phase containing 3 mmol L^− 1 2,6-pyridinedicarboxylic acid (PDCA) and 3 mmol L^− 1 oxalate at pH 12.5. Effects of pH as well as PAN, detergent and chloride ion concentrations during post-column reaction on detector response were examined. Detection limits were less than 4.5 μg L^− 1 for all metals except Hg(II) (19 μg L^− 1) using spectrophotometric measurements at 550 nm. Analytical validations showed good linearity for detection up to 6.0 mg L^− 1, with R² higher than 0.99. Precisions based on retention time evaluation for intra-day and inter-day measurements with the relative standard deviation (RSD) were less than 2.9% and 3.6%, respectively. The method gave good accuracy with the recoveries ranged from 80.5 to 105% for all metal ions studied. The proposed method was applied to the analysis of metal ions in environmental samples (leachate, soil and sediment) in Northeastern Thailand. The results were in good agreement with atomic spectroscopic measurements on the same samples.     

Spectrophotometric determination of niobium in zirconium with 4-(2-pyridylazo)resorcinol

The direct spectrophotometric determination of niobium in zirconium alloys with 4-(2-pyridylazo)resorcinol is described. Samples are dissolved in hydrofluoricsulphuric acid mixture and the colour developed without the removal of fluoride. In the presence of EDTA only Co²⁺, Ta⁵⁺ and V⁵⁺ cause serious interference. The molar absorptivity is 3.67 .10⁴ in the presence of 1 /smg of zirconium, and Beer's law is obeyed up to 1.0μg Nb/ml. The method can be applied to zirconium alloys containing as little as 0.005% niobium.     

Co-ordination complexes of niobium and tantalum. XVIII. Peroxo-EDTA Niobates(V) and Tantalates(V)

Preparation and Properties of peroxoethylenediaminetetraacetato niobates(V) and tantalates(V) are reported. These stable, crystalline complexes can be recrystallized from aqueous and hydrogen peroxide solutions. According to chemical and spectral evidence the complexes correspond to the formula M[M^V (O₂)₃EDTA] nH₂O₂, M^I = K, NH₄; M^V = Nb, Ta; n ≤ 1. Niobium and tantalum compounds are isomorphous.     

Determination of bis(2-ethylhexyl) phthalate in water by high-performance liquid chromatography with direct on-column preconcentration

A technique for the direct preconcentration of bis(2-ethylhexyl) phthalate (DEHP) on a reversedphase analytical column was proposed for the analysis of water samples by high-performance liquid chromatography (HPLC). A procedure for determining DEHP in surface-water and atmospheric precipitations in the laboratory and in the field was developed (the limit of detection is 0.1 Μg/L, the limit of determination is 0.3 Μg/L, and the relative standard deviation is 20 or 6% at a DEHP concentration of 0.3 or 10 Μg/L, respectively). The concentration levels of DEHP as a chemical tracer for the transfer and migration of air and water masses were examined in Lake Baikal water and in the snow cover of the Baikal region.     

Separation of Co(II), Ni(II) and Pd(II) with 2-(5-nitro-2-pyridylazo)-5-dimethylaminobenzoic acid by high-performance liquid chromatography

Summary 2-(5-Nitro-2-pyridylazo)-5-dimethylaminobenzoic acid has been found to be a suitable precolumn derivatization reagent for the separation of Co, Ni and Pd. The detection limit for Pd at 665 nm is 0.64 ppb; the linear calibration range is 8–400 ppb.