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.     

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

Summary A spectrophotometric method for the determination of palladium is described using 4-(2-pyridylazo)-resorcinol as reagent. The method involves the formation of two red coloured chelates of palladium-PAR at p_H 4.0 and 10.5 respectively. The colour reactions have sensitivity of 0.0085g cm^–2 and 0.0071g cm^–2 for logI ₀/I= 0.001. The effects of p_H, time, order of addition of reagents, temperature etc. have been investigated. The composition of the complexes (metalreagent) have been confirmed by two methods as 11 (at p_H 4.0) and 32 (at p_H 10.5).

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Zusammenfassung Eine spektrophotometrische Methode zur Palladiumbestimmung mit PAR [4-(2-Pyridylazo)-resorcin] wurde beschrieben. Zwei rotgefärbte Chelate werden bei p_H 4,0 bzw. 10,5 gebildet. Die Empfindlichkeit der beiden Reaktionen beträgt 0,0085 bzw. 0,0071g · cm^–2. Der Einfluß von p_H, Zeit, Reihenfolge der Reagenzien, Temperatur usw. wurde untersucht. Die Zusammensetzung der Komplexe entspricht dem Molverhältnis Pd: Reagens= =11 bei p_H 4,0 bzw. 32 bei p_H 10,5.

     

The extraction-spectrophotometric determination of chromium(III) with 4-(2-pyridylazo)-resorcinol

The extraction-spectrophotometric determination of chromium(III) with 4-(2-pyridylazo)-resorcinol (PAR) is described. PAR(H₂R) forms a 1:3 complex with chromium(III) in a boiling acetate buffer solution at pH 5. The complex forms an ion-association compound with tetradecyldimethylbenzylammonium ion (TDBA⁺):Cr(R)(HR)₂^--TDBA⁺ which can be extracted into chloroform, the molar absorptivity being 4.7 ·10⁴ at 540 nm. If EDTA is added as a masking agent after the Cr(HR)₃ has been formed, only iron, cobalt and nickel interfere seriously, and the method can be made specific for chromium by a preliminary extraction of these metals with cupferron. The sensitivity of the method is seven times higher than that of the diphenylcarbazide method.     

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%.     

Spectrophotometric extractive determination of thiolactams with 4-(2-pyridylazo)-resorcinol and copper

The thiolactams: thiopyrolidon, thiopiperidon, thiocaprolactam, thioenantolactam and thiocaprylolactam form a complex with the ion Cu(II) and PAR in which the ratio Cu:PAR:T1 = 1:2:4. The formation of a ternary complex was used in the spectrophotometric determination of thiolactams in a concentration range of 0.25-4.0 μg/ml thiolactam.     

Spectrophotometric determination of diethyllead and diethyltin ions with 4-(2-pyridylazo)-resorcinol

A study was made of the reaction of diethyllead and diethyltin ions with 4-(2-pyridylazo)-resorcinol; the compositions and the molar extinction coefficients of the compounds formed were determined. Methods are outlined for the determination of these organometallic cations. A method is described for the determination of lead chloride in the presence of (C₂H₅)₂PbCl₂.     

Chelating ion-exchangers containing 4-(2-pyridylazo)-resorcinol as the functional group

The synthesis of a cross-linked polystyrene-azo-PAR resin, and its chelating ion-exchange properties with nine ionic species, are described. A resin structure, containing both PAR and azophenol chelating groups is proposed. The effects on capacity of varying ionic concentration and the nature of the co-ion were studied.     

Metal complexes of 4-(2'-thiazolylazo)-resorcinol A comparative study with 4-(2'-pyridylazo)-resorcinol

The acid dissociation constants of 4-(2'-thiazolylazo)-resorcinol (TAR) and the formation constants of the metal complexes formed by this reagent with Cu(II), Ni(II), Co(II), Zn(II) and Mn(II) have been determined potentiometrically at 25° in 50% v/v mixtures of dioxane and water. The values obtained for TAR and the metal complexes are contrasted with similar values for the reagent 4-(2'-pyridylazo)-resorcinol (PAR). Differences and similarities between the co-ordinating tendencies of these two reagents are revealed in terms of the proton displacement constant and the acid dissociation constants of the metal complexes. Evidence is presented which suggests that both TAR and PAR may act as terdentate ligands toward some bivalent metal ions.     

Extraction-spectrophotometric determination of zinc(ii) with 4-(2-pyridylazo)-resorcinol and a quaternary ammonium salt

A simple and sélective extraction spectrophotometric determination of zinc is described. The complex [Zn(PAR)(2)](CDBA)(2), where PAR is the 4-(2-pyridylazo)resorcinol anion and CDBA is cetyldimethylbenzylammonium ion, is extracted from a solution buffered at pH 9.7 with carbonate/bicarbonate. Beer's law is obeyed over the range 0.2-1.2 ppm zinc, the molar absorptivity being 9.2 x 10(4) 1 .mole(-1).cm(-1). The precision in this range is 0.0056 ppm. Cadmium in up to a 50-fold w w ratio may be masked with diethyldithiocarbamate.     

Spectrophotometric studies on the simultaneous determination of cadmium and mercury with 4-(2-pyridylazo)-resorcinol

A new method for direct spectrophotometric determination of cadmium with 4-(2-pyridylazo)-resorcinol is reported. Absorption maximum, molar absorptivity and Sandell's sensitivity of the 1:1 (M:L) complex are 510 nm, 2.5 x 10(5) l mol(-1) cm(-1) and 3.55 ng cm(-2), respectively. A linear calibration graph is obtained up to 4.49 microg ml(-1). The zero-crossing measurement technique is found suitable for the direct measurement of the first-derivative value at the specified wavelengths. Cadmium(II) (0.42-9.2 microg ml(-1)) and mercury(II) (0.35-7.4 microg ml(-1)) in different ratios have been determined simultaneously. A critical evaluation of the proposed method is performed by statistical analysis of the experimental data. The developed method was applied to the simultaneous spectrophotometric determination of Cd and Hg in some synthetic mixtures and was found to give satisfactory results.     

Extraction studies on the group VB–VIIB and VIII elements using 1-(2-pyridylazo)-2-naphthol as chelating reagent

Extraction behaviour of the chelates of group VB–VIIB and VIII elements using 1-(2-pyridylazo)-2-naphthol (PAN) has been studied as a function of pH. Studies have been made to back-extract the metal ions from the organic phase into the aqueous solution containing the optimum concentration of KCN and HClO₄ and buffers of appropriate pH. The masking agents such as citrate, cyanide, thiosulphate, fluoride and thiourea were used to achieve more specific separations. The studies indicate the potentiality of PAN as a useful solvent extracting reagent in devising group chemical separation procedures for activation analysis.     

Spectrophotometric determination of chromium(III) with 4-(2-thiazolylazo)-resorcinol

Summary The red complex formed between chromium(III) and 4-(2-thiazolylazo)-resorcinol (1 2) at pH 5.0, on heating the reactants to 90° for 45 minutes, is used for Spectrophotometric determination of chromium, the absorbance being measured at 525 nm. Beer's law is obeyed for chromium concentration of 0.06 to 1.1g per ml. Molar absorptivity is 4.98×10⁴ and Sandell sensitivity 0.001g cm^–2. This method has been applied to the determination of chromium content in steel samples.

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Zusammenfassung Der 1 2-Komplex von Chrom(III) mit 4-(2-Thiazolylazo)resorcin bildet sich bei pH 5,0 und 90° C in 45 min. Er eignet sich zur spektrophotometrischen Chrombestimmung. Die Extinktion wird bei 525 nm gemessen. Das Beersche Gesetz ist zwischen 0,06 und 1,1g Cr/ml erfüllt. Die molare Extinktion beträgt 4,98 · 10⁴, die Empfindlichkeit nach Sandell 0,0001g · cm^–2. Die Methode wurde zur Chrombestimmung in Stahlproben angewandt.

     

Preparation and analytical characterization of a chelating resin coated with 1-(2-pyridylazo)-2-naphthol

A chelating sorbent was obtained by deposition of 1-(2-pyridylazo)-2-naphthol on Amberlite XAD-4. The analytical characteristics of the sorbent were established and optimum sorption conditions for Cu, Zn, Fe, Cd, Ni, and Pb under static and dynamic conditions were determined. The sorbent was applied to analysis of river water. After group separation of traces of metals on the sorbent and subsequent elution with hydrochloric add, the metals were determined in the effluent by atomic-absorption spectrophotometry.     

Preparation of a carbon ceramic electrode modified by 4-(2-pyridylazo)-resorcinol for determination of trace amounts of silver

A 4-(2-pyridylazo)-resorcinol (PAR)-modified carbon ceramic electrode (CCE) prepared by the sol-gel technique has been reported for the first time in this paper. By immersing the CCE in aqueous solution of PAR (0.001 mol L⁻¹), after a short period of time, a thin film of PAR was rapidly formed on the surface of the electrode due to its strong adsorption properties. A differential pulse anodic stripping voltammetric (DPASV) method was developed for determination of Ag(I) at the modified carbon ceramic electrode. The analysis procedure consisted of an open circuit accumulation step in a sample solution which was continuously stirred for 12 min. This was followed by replacing the medium with a clean solution where the accumulated Ag(I) was reduced for 15 s in −0.6 V. Then, the potential was scanned from −0.2 to +0.2 V to obtain the voltammetric peak. The detection limit of silver(I) was 0.123 μg L⁻¹, and for seven successive determinations of 10, 100 and 200 μg L⁻¹ Ag(I), the relative standard deviations were 2.1, 1.4 and 1.03%, respectively. The calibration curve was linear for 0.5-300 μg L⁻¹ silver(I). The procedure was applied to determine silver(I) in X-ray photographic films and super-alloy samples.     

Determination of thiosulfate ions by the complexation of lead thiosulfate with 4-(2-pyridylazo)-resorcinol on the PANF-AV-17 solid phase

A procedure was developed for determining thiosulfate ions; the procedure involved their adsorption as a complex with lead ions at pH 4 on disks of polyacrylonitrile fiber filled with an AB-17 anion exchanger and determination by the reaction with 4-(2-pyridylazo)-resorcinol at pH 10. The analytical range was (0.2–0.8) × 10^?4; the detection limit was 2 μg/mL. The determination did not interfere with metal cations at the level of the maximum permissible concentrations for potable water, as well as 2–15-fold amounts of sulfites, sulfides, and iodides; 100–200-fold amounts of sulfates, pyrosulfates, and bromides; and 1000-fold amounts of chlorides. The developed procedure was used in the analysis of tap water by the “added-found” method (RSD < 20%).     

Formation of MSeO4(aq) complexes (M2+ = Mg2+, Co2+, Ni2+, Cu2+, Cd2+) studied as a function of temperature by affinity capillary electrophoresis

Complexation of divalent cations (Mg²⁺, Co²⁺, Ni²⁺, Cu²⁺, Cd²⁺) by selenate ligand was studied by ACE (UV indirect detection) in 0.1 mol/L NaNO₃ ionic strength solutions at various temperatures (15, 25, 35, 45 and 55°C). For each solution, a unique peak was observed as a result of a fast equilibrium between the free ion and the complex (labile systems). The migration time corresponding to this peak changed as a function of the solution composition, namely the free and complexed metal concentrations, according to the complexation reactions. The results confirmed the formation of a unique 1:1 complex for each cation. The thermodynamic parameters were fitted to the experimental data at 0.1 mol/L ionic strength: (25°C) = ?(6.5 ± 0.3), ?(7.5 ± 0.3), ?(7.7 ± 0.3), ?(7.7 ± 0.3), and –(8.1 ± 0.3) kJ/mol and = 2.5 ± 0.2, 4.7 ± 0.4, 4.5 ± 0.6, 8.4 ± 1.1, and 7.2 ± 0.6 kJ/mol for M²⁺ = Mg²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Cd²⁺, respectively. Complexes with alkaline earth and transition metal cations could be distinguished by their relative stabilities. The effect of the ionic medium was treated using the specific ion interaction theory and the thermodynamic parameters at infinite dilution were compared to previously published data on metal–selenate, metal–sulfate, and metal–chromate complexes.