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.     

铁(Ⅲ)-4-(2-吡啶偶氮)间苯二酚络合物光化学还原反应的研究

在弱酸性溶液中,Fe3 -PAR络合物可发生光化学还原反应生成Fe2 -PAR络合物。研究了溶液酸度、光强度、有机酸、PAR溶液浓度对Fe3 -PAR络合物光化学还原反应的影响,并对反应机理作了初步探讨。在pH4.5HAc-NaAc缓冲溶液中,PAR浓度为1.8×10?4mol/L,125W高压汞灯照射15min,Fe3 -PAR络合物的光化学还原反应趋于完全。Fe2 浓度在0.12～3.2mg/L范围内符合比尔定律;检出限为0.025mg/L。     

Extraction and spectrophotometric determination of vanadium with 4-(2-thiazolylazo)resorcinol and tetraphenylarsonium and phosphonium chlorides

Extraction of vanadium-4-(2-thiazolylazo)resorcinol complexes by quaternary salts such as triphenylmethylarsonium iodide, tetraphenylarsonium chloride, and tetraphenylphosphonium chloride has been studied. Quantitative extraction is achieved with tetraphenylarsonium and tetraphenylphosphonium chlorides in the pH region between 3.5 and 5. The optimum conditions for the extraction and spectrophotometric determination of vanadium in the extract are: pH 3.8–4.0, the concentration of vanadium 0.1–0.4 μg/ml. Effective molar absorptivity at λ_max = 555 is (2.55 ± 0.05) × 10⁴ liters mol⁻¹ cm⁻¹. Beer's law is obeyed. Relative standard deviation is 2–10% depending on the concentration level. The composition of the extracted complexes was studied in the solution and in the solid state. For their characterization chemical and spectral evidence and comparison with the vanadium-PAR complexes have been combined.     

Spectrophotometric determination of acidity constants of 4-(2-pyridylazo)resorcinol in binary methanol-water mixtures

The acidity constants of 4-(2-pyridylazo)resorcinol (PAR, Scheme 1) in binary mixtures of methanol-water at 25 °C and an ionic strength of 0.1 M have been determined spectrophotometrically. DATa ANalysis (DATAN) program applied for determination of acidity constants. As percent of methanol increases in solvent mixtures the pK_a constants also increased. There is linear relationship between acidity constants and the mole fraction of methanol in the solvent mixtures. Effect of solvent composition on acidity constants and pure spectrum of each component are also discussed.     

2-(2-喹啉偶氮)-5-二甲氨基酚分光光度法测定钒

研究了新试剂2 (2 喹啉偶氮) 5 二甲氨基酚(QADMAP)与钒的显色反应,在pH3.5的柠檬酸 NaOH缓冲介质中,溴化十六烷基三甲基胺(CTMAB)存在下,QADMAP与钒反应生成2∶1稳定络合物,络合物最大吸收波长为580nm,摩尔吸光系数ε=1 12×105L·mol-1·cm-1,钒质量浓度在0～0 6μg mL内符合比尔定律。方法已用于几种合金样品中钒的分析。     

Multiwavelength spectrophotometric determination of protolytic constants of 4-(2-pyridylazo) resorcinol (PAR) in binary DMF-water mixtures

A multiwavelength spectrophotometric titration method was applied to study the protolytic constants of 4-(2-pyridylazo) resorcinol(PAR), in binary DMF + water mixtures. UV-vis absorption spectra of PAR solution were recorded in the course of pH-metric titration of acidic solutions of PAR with standard base solution. The protolytic equilibrium constants, spectral profiles, concentration diagrams and also the number of components have been calculated from the fitting of the pH-spectral titration data with appropriate mass balance equations by a home written program according to an established target factor analysis. To precise determination of number of absorptive components a recently developed statistical indicator function (IND function) was used. A glass electrode calibration procedure based on a four-parameter equation pH=α+SpcH+JH⁺[H⁺]+JOH⁻Kw/[H⁺] based on the Gran's plots was used to obtain pH readings in the concentration scale (p_cH). It has been observed that there is an inverse relationship between second and third protolytic constants and mole fraction of DMF. The effect of the solvent on the protolytic constants was discussed.     

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.     

Spectrophotometric study of acid-base equilibria of 4-(2-benzothiazolylazo)resorcinol and 4-(2-benzothiazolylazo)salicylic acid in water-organic solvent media

The visible absorption spectra of 4-(2-benzothiazolylazo)resorcinol (BTAR) and 4-(2-benzothiazolylazo)salicylic acid (BTAS) have been recorded in water-organic solvent mixtures in the pH range 0.5–12.0. The organic solvents used are methanol, ethanol,n-propanol, iso-propanol, acetone, dioxane and dimethyl formamide. The spectral changes have been explained in terms of shifts in equilibria among different molecular and ionic species of BTAR and BTAS existing in solution. The pK _a values corresponding to the different ionization steps have been determined at 25°C and I=0.1M (KNO₃) by graphic analysis of the absorbance-pH curves. The results obtained are discussed in terms of the molecular structure of the reagents and the nature of the organic co-solvent used.     

Spectrophotometric determination of thallium with 4-(2-pyridylazo)resorcinol and 4-(2-thiazolylazo)resorcinol

Thallium(III) gives sensitive reactions with PAR and TAR (epsilon = 2 x 10(4) at 520 nm), forming 1:1 complexes at pH approximately 1-2, and a mixture of 1:1 and 1:2 complexes at higher pH values; hydrolysis sets in above pH approximately 3. The stability constants are evaluated.     

Determination of Nb(V), V(V), Co(II), Fe(III), Ni(II), Ru(III) and Pd(II) as their 4-(5-nitro-2-pyridylazo) resorcinol chelates by reversed-phase high performance liquid chromatography

This paper reports the separation and determination of Nb(V), V(V), Co(II), Fe(III), Ni(II), Ru(III) and Pd(II) by reversed-phase HPLC using the new reagent, 4-(5-nitro-2-pyridylazo) resorcinol (5-NO₂-PAR) as a precolumn derivatization reagent. On a C₁₈ column, the seven metal chelates can be separated quantitatively with methanol/water (5248, v/v) containing 15 mmol/l pH 5.0 acetate buffer and 10 mmol/l tetrabutylammonium bromide (TBA·Br). The detection limits for Nb(V), V(V), Co(II), Fe(III), Ni(II), Ru(III) and Pd(II) are 0.65 ppb, 0.94 ppb, 0.10 ppb, 0.15 ppb, 0.18 ppb, 3.02 ppb and 2.35 ppb, respectively when the ratio of signal to noise (S/N) is 3. This method is simple and rapid, and has been used in the analysis of rain and liquor with satisfactory results.     

Liquid-liquid extraction and cloud point extraction for spectrophotometric determination of vanadium using 4-(2-pyridylazo)resorcinol

Liquid-liquid extraction (LLE) and cloud point extraction (CPE) of vanadium(V) ternary complexes with 4-(2-pyridylazo)resorcinol (PAR) and 2,3,5-triphenyl-2H-tetrazolum chloride (TTC) were investigated. The optimal conditions for vanadium extraction and spectrophotometric determination were identified. The composition (V: PAR: TTC) of the extracted species was 1:2:3 (optimal conditions; LLE), 2:2:2 (low reagents concentrations; LLE), 1:1:1 (short heating time;CPE), and 1: 1: 1 + 1: 1: 0 (optimal extraction conditions; CPE). LLE, performed in the presence of 1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid and NH₄F as masking agents, afforded the sensitive, selective, precise, and inexpensive spectrophotometric determination of vanadium. The absorption maximum, molar absorptivity, limit of detection, and linear working range were 559 nm, 1.95 × 10⁵ dm³ mol^?1 cm^?1,0.7 ng cm^?3, and 2.2–510 ng cm^?3, respectively. The procedure thus developed was applied to the analysis of drinking waters and steels. The relative standard deviations for V(V) determination were below 9.4 % (4–6 × 10^?7 mass %; water samples) and 2.12 % (1–3 mass %; steel samples).     

Flotation and spectrophotometric determination of silver with 4-(p-nitrophenylazo)-2-amino-3-pyridinol

A sensitive flotation-spectrophotometric method, based on the complex formed between Ag(I) and 4-(p-nitrophenylazo)-2-amino-3-pyridinol is described. The complex precipitates when the aqueous solution is shaken with benzene, and the solid formed is then dissolved in dimethylformamide. The molar absorptivity of the resulting solution is 10.7×10⁴l·mole^–1·cm^–1 at 605 nm. Beer's law is obeyed between 0.08 and 1 ppm of silver. The molar ratio of Agreagent in the separated complex is 12. The effect of foreign ions has been determined and the proposed method can be applied to determination of silver in an exhausted photographic developing solution.     

5-(4-Carboxylphenylazo)-8-aminoquinoline as an analytical reagent for the spectrophotometric determination of gold

The synthesis and analytical application of 5-(4-carboxylphenylazo)-8-aminoquinoline (CPAQ) are described. A simple, rapid, selective, and sensitive spectrophotometric method for the determination of microgram amounts of gold is developed, based on the colour reaction between the metal ion and CPAQ in the presence of cetyltrimethyl ammonium bromide. Gold (III) reacts with the reagent in the ratio 1 3 (metal to ligand) in alkaline solution to form a blue-green complex with an absorption maximum at 608 nm. Beer's law is obeyed over the concentration range 0–1.8 g · ml^–1 (ppm) of gold. The molar absorptivity and Sandell's sensitivity of the method are 9.11 × 10⁴ l · mole^–1 · cm^–1 and 0.00216 g · cm^–2, respectively. The interference of various ions has been studied and conditions were developed for the determination of gold in an ore and anode slimes.     

锰与4-(2-噻唑偶氮)间苯二酚络合吸附波的研究及应用

本文研究了在0.01mol/L NaOH—0.32％乙二胺—0.05mol/L酒石酸钾钠介质中,锰与4-(2-噻唑偶氮)间苯二酚(TAR)络合吸附波的极谱行为。当介质中含有0.003％TAR时,Mn会产生灵敏的导数极谱波,其峰电位为-0.75V(相对银汞齐电极,下同),方法检出限为1.5×10~(-9)mol/L,线性范围为3.6×1.0~(-9)mol/L～2.7×10~(-6)mol/L。研究了极谱波的性质、机理以及络合物的组成。方法成功地应用于某些植物叶中微量锰的含量测定。     

2-(4-羧基苯偶氮)苯并噻唑固相萃取分光光度法测定铂的研究

根据新试剂2-(4-羧基苯偶氮)苯并噻唑(CPABT)与铂的显色反应及C8固相萃取小柱对显色络合物的固相萃取,建立了一种测定痕量铂的新方法,在pH为3.8~5.5的乙酸-乙酸钠缓冲介质中,在Tween-80存在下,铂与CPABT发生反应形成1∶1的稳定络合物,该络合物可用C8固相萃取小柱富集,小柱上富集的络合物用二甲基甲酰胺洗脱后用分光光度法测定,在富集后的测定液中,络合物最大吸收波长为508 nm,摩尔吸光系数ε=2.29×105L.mol-1.cm-1,Pt4 量在0.1~1.2μg/mL内符合比尔定律,方法已用于测定催化剂中的铂。     

Complexing Properties of Uranium and Lanthanoids With 4-(2-Thiazolylazo)-6-Chlororesorcinol

Abstract

4-(2-Thiazolylazo)-6-chlororesorcinol (TAR-Cl) reacts sensitively with uranyl(II) and lanthanoids(III), and forms reddish-brown 1:1 and 1:2 complexes. The complexing behaviors were examined spectrophotometrically. The absorption maxima of the complexes are focused near 553 nm and the optimum pH for complexation lies between 6.5–8.8. Beer's law holds up to about 2 × 10^?5 mol 1^?1, with a molar absorptivity of 3.00 × 10⁴ 1 mol^?1 cm^?1 for uranium and 6 × 10⁴ 1 mol^?1 cm^?1 level for each lanthanoid. The absorptivities are increased with the atomic number, especially in light lanthanoids, that are correlative both to the lanthanoid contraction and the basicity of ortho hydroxyl group in the resorcinol ring, but such effects are not clearly recognized in heavy lanthanoids. Effect of masking agents was also examined, and uranium could be determined selectively in the presence of lanthanoid mixtures by the addition of CyDTA.     

2-(2-Thiazolylazo)-pcresol (TAC) as a reagent for the spectrophotometric determination of titanium (IV)

The reaction between titanium(IV) and 2-(2-thiazolylazo)-p-cresol-(TAC) in aqueous methanol media at apparent pH 4.0–5.6 results in a intensely coloured complex that is stable for at least 2 h. The combining ratio is 1 1 cation TAC. Beer's law is obeyed up to 5.0 g/ml titanium(IV) at 580 nm. The apparent molar absorptivity at 580 nm is 9.82.10³ l.mole^–1.cm^–1 and the detection limit obtained was 5 ng/ml titanium (IV). A spectrophotometric method for the simultaneous determination of titanium and iron with TAC is proposed.     

Reactions of 3-(4-Aryl-2-thiazolyl)- and 3-(2-Benzothiazolyl)-2-iminocoumarins with N-Nucleophiles

The reaction of 3-(4-aryl-2-thiazolyl)- and 3-(2-benzothiazolyl)-2-iminocoumarins with N-nucleophiles was studied. This reaction gives 2-N-substituted 3-(4-aryl-2-thiazolyl)- and 3-(2-benzothiazolyl)iminocourmarins. N-Nucleophiles such as arylamines, heterocyclic amines, and hydrazine derivatives undergo this reaction.