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.     

Spectrophotometric determination of palladium with 4-(2-pyridylazo)resorcinol

Summary A simple photometric method for the determination of palladium has been worked out, employing pyridylazo-resorcinol (PAR) as a complexing ligand for the metal ion. The coloured species is extractable into chloroform in the presence of diethylamine, the absorbance of which is measured at 535 nm. The method is free from the interference of a large number of elements particularly the other platinum metals. It obeys Beer's law in the range of 0–3 g Pd/ml with Sandell's sensitivity of 0.0034 g Pd cm^–2. The ratio of metal to ligand in the complex is found to be 1:1. Analysis of various samples has been carried out with satisfactory and reproducible results (standard deviation ±0.002).     

Relative stabilities of metal complexes of 4-(2-pyridylazo)resorcinol and 4-(2-thiazolylazo)resorcinol

The stability constants of 1:1 complexes of 4-(2-pyridylazo)resorcinol (PAR) and 4-(2-thiazolylazo)resorcinol (TAR) with Mn(II), Ni(II), Cu(II) and Zn(II) have been determined spectrophotometrically at μ = 0.1 and 25°C. The method is based on indirect estimation of the protonated and normal complexes by measuring the ligand absorption peak. Both protonated and normal complexes of these metals with PAR are more stable than those with TAR. The reverse order was previously observed for the pronated complexes of the lanthanides(III). The different behaviour of the 3d transition metals(II) compared to the lanthanides(III) is discussed. The proton dissociation constants of the protonated complexes of PAR or TAR with various metals are also discussed.     

Spectrophotometric study of the reaction of the uranyl ion with 4-(2-thiazolylazo) resorcinol

The uranyl ion forms only 1:1 chelates with 4-(2-thiazolylazo) resorcinol (TAR) in solution, UO(2)(TAR)H(+) being formed below pH 3 and UOS(TAR) above pH 3-5. The latter complex may also be precipitated at pH > 3. The quantitative formation of UO(2)(TAR) at pH 7.5-7.8 in solutions containing a small excess of reagent and some triethanolamine as buffer can be used for the sensitive spectrophotometric determination of uranium. Several interfering ions can be masked with a mixture of sodium fluoride, cyclohexanediaminetetraacetic acid and 5-sulphosalicylic acid. TAR is slightly less sensitive than 4-(2-pyridylazo)resorcinol as a reagent for uranium but is more selective.     

Extraction and spectrophotometric determination of gallium with 4-(2-pyridylazo)resorcinol

A sensitive and selective spectrophotometric determination of gallium is described. It is based on extraction of gallium from 3 M hydrochloric acid solution as a chloro-complex into 1,2-dichlorobenzene and exchange of the chloro ligand with 4-(2-pyridylazo)resorcinol (PAR); the final association complex of Ga—PAR with tetraphenylarsonium ions is measured in the organic phase. The absorption maximum occurs at 510 nm and the effective molar absorptivity is (8.2 ±0.3) ·1O⁴ l mol^-1cm^-1. Beer's law is obeyed over the range 0.2–2 p.p.m. of gallium. Few ions interfere.     

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.     

Determination of titanium by adsorption voltammetry with 4-(2-pyridylazo) resorcinol

Summary Titanium (IV) forms a complex with 4-(2-pyridylazo) resorcinol (PAR) in weakly acidic solutions. This complex can be used to determine titanium by adsorption voltammetry at a stationary Hg-electrode. The experimental conditions for the determination are described. The current-concentration curve is linear from 0.15–4.8 ng/g. Ti at a deposition time of 3 min, the detection limit lies at 0.1 ng/g. The influence of foreign ions was investigated. The determination can be carried out in the presence of a 1000-fold excess of iron by the standard addition method, albeit with decreased sensitivity.     

Spectrophotometric study and analytical application of the reaction between manganese(II) and 4-(2-pyridylazo)resorcinol

A highly sensitive method for spectrophotometric determination of manganese(II) with 4-(2-pyridylazo)resorcinol (PAR) as reagent is described. The molar absorptivity of the complex was found to be 8.65 ± 0·04 x 10⁴. The stability constant of the ML₂ complex was found to be log β₂ = 15·6. Beer's law is obeyed within the range 0·02–0·5 μg of Mn/ml. An application of this reaction for analytical purposes is described.     

Separation and quantitation of metal ions by 4-(2-pyridylazo)resorcinol complexation in capillary electrophoresis-electrospray ionisation mass spectrometry

The possibility of using capillary electrophoresis-electrospray ionisation (ESI)/MS to separate and quantify cobalt and iron was explored. It was necessary to tackle and overcome problems from different sources, some of them being rather unpredictable. The results obtained suggest the occurrence of oxidation processes of metal ions during the formation of the electrospray. The quantitative oxidation of cobalt(II) to cobalt(III), a process at our knowledge never described before, appears particularly interesting. The results obtained, though not optimised for sensitivity appear promising, since a limit of detection of the order of tenths of picograms was obtained. Further, from the comparison with the results obtained by optical detection, the use of CE-ESI/MS appears advantageous.     

Co-ordinating properties of some ligand systems related to 4-(2-pyridylazo)resorcinol

The metal-complexing properties of 2-(8-quinolylazo)-1-naphthol-4-sulphonic acid and the 2-pyridyl-, 2-pyrimidyl- and 8-qumolylhydrazones of salicylaldehyde have been described and compared with those of 4-(2-pyridylazo)resorcmol and related dyes. The sensitive chromophoric action of metal ions on the latter group of dyes is thought to be due to the formation of a resonance-stabilized anion in which the heterocyclic nitrogen atom plays an important part. Ligands capable of forming chelates containing larger rings give on reaction with metals less sensitive colour reactions but more stable complexes.     

Improved spectrophotometric determination of osmium(VIII) with 4-(2-pyridylazo) resorcinol in mixed surfactants

The colour development between 4-(2-pyridylazo)-resorcinol(PAR) and osmium(VIII) in the presence of cationic and nonionic surfactants in a weakly acidic medium was more stable and reproducible than in the absence of surfactant (PAR-alone method). An improved spectrophotometric determination of osmium(VIII) with PAR was investigated in the presence of mixed surfactants of N-hexadecyltrimethylammonium chloride (HTAC) and Brij 58 [poly(oxyethylene)lauryl ether] as cationic and nonionic surfactants at pH 6.0-7.2. The calibration graph was linear in the range 0-110 microg/10 ml osmium(VIII), and the apparent molar absorptivity was 2.4 x 10(4) l.mole(-1).cm(-1) with a Sandell sensitivity of 0.0079 microg/cm(2) osmium(VIII).     

Characterization of complexes involved in the spectrophotometric determination of cobalt with 4-(2-pyridylazo)resorcinol

Complex species involved in the spectrophotometric determination of cobalt with 4-(2-pyridylazo)resorcinol (PAR = H₂R) were studied in solution and in the solid state. An anionic [Co(III)R₂]^- species was extracted from aqueous solution in chloroform by tetraphenylarsonium or tetraphenylphosphonium chloride. Stable tetraphenylarsonium and tetraphenylphosphonium salts of di-4-(2-pyridylazo)resorcinolo cobaltate(III) with the formula [(C₆H₅)₄X][Co(III)R₂] where X=As.P; and R=C₁₁H₇N₃O₂^2-, were isolated from the chloroform phase. The complexes were characterized by elemental analyses, visible, i.r., p.m.r., e.s.r. spectra, x-ray powder photographs, magnetic susceptibility and conductivity measurements. The spectral evidence and magnetic properties indicate a tridentate coordination of two 4-(2-pyridylazo) resorcinol dibasic anions, bonded to cobalt(III) in a symmetric arrangement with both azo groups coordinated to the cobalt atom through a single nitrogen lone pair.     

Kinetics and mechanism of the reaction between bis 4-(2-pyridylazo) resorcinol ferrate(II) complex and cyanide ion

Summary Cyanide ion reacts with [Fe(Par)₂]^2–,i.e. Par=4-(2-pyridylazo)resorcinol to form a 113 mixed cyanocomplex. The reaction has been studied spectrophotometrically at 720 nm _max, pH=11.5±0.02, and I=0.1 M (NaClO₄) at 25±0.1°C. The order with respect to cyanide varies from one to two at high and low cyanide concentrations respectively. The rate constants for respective reactions are k₁=(6.1±0.3)×10^–2 M^–1 s^–1, k₂=(12.6±1.0) M^–2 s^–1. The reverse reaction does not occur at a measurable rate even in presence of a large excess of Par. These observations suggest that [Fe(Par)₂]^2– forms a mixed [FePar(CN)₃]^3– complex in presence of an excess of cyanide ion. The activation parameters for the reaction have been calculated and used to support a three step mechanism consistent with these results. The effect of ionic strength tends further support to the mechanism.     

Kinetics and mechanism of the reaction between bis 4-(2-pyridylazo)resorcinol ferrate(III) complex and cyanide ion

Summary Kinetics and mechanism of formation of a 113 mixed cyano-complex from [Fe^III (Par)₂]^– (where Par represents 4-(2-pyridylazo)resorcional) and cyanide ion has been studied spectrophotometrically at 720 nm [_max=Fe^(III)(Par) ₂ ^– ], pH=10.0±0.02, temp=25±0.1°C and 1=0.1 M (NaClO₄). The order with respect to cyanidevaries from one to two at high and low cyanide concentrations respectively. The rate constants for respective reactions are k₁=10.8±0.6×10^–2 M^–1 s^–1, k₂=7.7±0.5 M^–2 s^–1. The reverse reaction does not occur at a measurable rate even in presence of large excess of par. These observations suggest that Fe^III (Par) ₂ ^– forms a mixed complex, [FePar(CN)₃]^2-, in presence of an excess of cyanide ions. A three-step mechanism consistent with these results is proposed. The activation parameters for the reaction have been derived and used to support the proposed mechanism. The effect of ionic strength lends further support to the mechanism.     

Determination of trace amounts of copper with 4-(2-pyridylazo)resorcinol by solid phase spectrophotometry

A determination method for traces of copper by Solid-Phase Spectrophotometry (SPS) has been developed. It is based on the fixation of copper(II) as 4-(2-pyridylazo)resorcinol complex on a styrene-divinylbenzene anion-exchange resin. The resin phase absorbances at 525 and 800 nm are measured directly, and the determination of copper (with a RSD of 1.8%) is possible in the range of 0.3–4.5 μg L^?1. The method has been applied to the determination of copper in different samples, i.e. mushrooms, tea, drugs and waters.