Sensitive spectrophotometric determination of ascorbic acid in fruit juices and pharmaceutical formulations using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP)

A simple and very sensitive method has been developed for the determination of ascorbic acid based on the oxidation of ascorbic acid to dehydroascorbic acid by iron(III), followed by a complexation of iron(II) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol(Br-PADAP). The iron(II) complex is formed immediately, with absorption maxima at 560 and 748 nm and a molar absorptivity of 1.31 × 10⁵ l mole^–1cm^–1 and 5.69 × 10⁴ l mole^–1cm^–1, respectively. The ascorbic acid determination is possible with a linear range up to 2.4 μg ml^–1, a calibration sensitivity of 0.744 ml μg^–1 at 560 nm and 0.323 ml μg^–1 at 748 nm, and a detection limit of 15 ng ml^–1 and 44 ng ml^–1, respectively. The procedure was used for the ascorbic acid determination in several fruit juices and pharmaceutical formulations. The results demonstrated a good precision (R.S.D. < 1%) and are in agreement with those obtained with others methods. The Br-PADAP method proposed is six times more sensitive than the method using the iron(II)-1,10-phenanthroline system. Received: 7 May 1996 / Revised: 1 July 1996 / Accepted: 8 August 1996     

Spectrophotometric determination of vanadium(IV) in the presence of vanadium(V) using Br-PADAP

In the present paper, a simple and sensitive method is proposed for vanadium(IV) determination in the presence of vanadium(V). This is based on the oxidation of vanadium(IV) present in the sample to vanadium(V) by addition of iron(III) cation, followed by a complexation reaction of iron(II) with the spectrophotometric reagent 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP). The iron(II) reacts with Br-PADAP immediately, forming a stable complex with a large molar absorptivity. The vanadium(IV) determination is possible, with a calibration sensitivity of 0.549 g ml^–1, for an analytical curve of 18.8 ng ml^–1 to 2.40 g ml^–1, molar absorptivity of 2.80 × 10⁴ 1 mole^–1 cm^–1 and a detection limit of 5.5 ng ml^–1. Selectivity was increased with the use of EDTA as a masking agent. The proposed method was applied for the vanadium(IV) determination in the presence of several amounts of vanadium(V). The results revealed that 200 g of vanadium(V) do not interfere with determination of 5.00 g of vanadium(IV). The precision and the accuracy obtained were satisfactory (R. S. D.<2%).     

Solid-phase spectrophotometric microdetermination of iron with ascorbic acid and ferrozine

 A very sensitive and selective method for the determination of trace amounts of iron has been developed, based on the reduction of Fe(III) to Fe(II) by ascorbic acid, followed by chromogenic chelation of Fe(II) with ferrozine. The complex Fe(II)-ferrozine is easily sorbed on a dextran-type anion-exchange gel packed in a 1 mm cell, and the absorbance of the gel is measured directly at 569 and 800 nm. The extended linear range of the determination is 0.5–10 ng ml^-1 of iron (apparent molar absorptivity=4.4×10⁷ l mol^-1 cm^-1) and the precision (RSD) 1.3% for a concentration of 5 ng ml^-1 of iron (n=10). The detection limit for a sample volume of 1000 ml, using 0.040 g of anion-exchanger, corresponds to 0.12 ng ml^-1. The method has been successfully applied to the determination of iron in natural and waste waters, wine, soil extract and previously digested vegetal tissues, drugs and human hair. Received: 20 November 1995/Revised: 23 January 1996/Accepted: 26 January 1996     

Organic solvent-soluble membrane filters for the preconcentration and spectrophotometric determination of iron(II) traces in water with Ferrozine

An organic solvent-soluble membrane filter (MF) is proposed for the simple and rapid reconcentration with subsequent spectrophotometric determination of trace levels of iron (II) in water. Iron (II) is collected on a nitrocellulose membrane filter as ion associate of an anionic complex, which is formed by iron (II) and Ferrozine and a cation-surfactant. The ion-pair compound and the MF can be dissolved in small volumes of 2-ethoxyethanol and the absorbance of the resulting solution is measured at 560 nm against a reagent blank with molar absorptivity of 4.01 × 10⁴ L mol^–1 cm^–1. Beer’s law is obeyed over the concentration range 0–10 μg L^–1 of iron (II) in water and the detection limit is 0.03 μg L^–1 with a 50-fold enrichment factor. The proposed method can satisfactorily be applied to the determination of iron (II) in natural water and sea water. Received: 23 June 1998 / Revised: 21 July 1998 / Accepted: 25 August 1998     

Spectrophotometric determination of iron in alloys and ores with 1-(2-pyridylmethylideneamine)-5-(salicylideneamine)thiourea

Summary A spectrophotometric method for the determination of iron is described. The green Fe(II) complex is formed at pH 4.8 in a medium containing 40% dimethylformamide and 0.8 g/l ascorbic acid, and the absorbance is measured at 635 nm. The molar absorptivity is 5.7×10³lo·mole^–1·cm^–1. The method has been applied with good results to the determination of iron in six alloys and ores.

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Spektrophotometrische Bestimmung von Eisen in Legierungen und Erzen mit 1-(2-Pyridylmethylidenamin)-5-(salicylidenamin)-thioharnstoff

Zusammenfassung Ein spektrophotometrisches Verfahren zur Eisenbestimmung wurde beschrieben. Der grüne Fe(II)-Komplex bildet sich bei pH 4,8 in einem Medium aus 40% Dimethylformamid und 0,8 g/l Askorbinsäure. Die Absorbanz wird bei 635 nm gemessen. Die molare Absorptivität beträgt 5,7× 10³l·mol^–1·cm^–1. Die Methode gab gute Resultate bei der Bestimmung von Eisen in sechs Legierungen und Erzen.

     

Liquid chromatographic determination of chelates of cobalt (II), copper (II) and iron (II) with 2-thiophonaldehyde-4-phenyl-3-thiosemicarbazone

Summary A new chelating reagent 2-thiophenaldehyde-4-phenyl-3-thiosemicarbazone (TAPT) has been examined for high performance liquid chromatographic (HPLC) separations of cobalt (II), copper(II) and iron (II) or cobalt (II), nickel (II), iron (II), copper (II) and mercury (II) as metal chelates on a C₁₈, 5μm column (250×4 mm i.d.) The chelates were eluted isocratically with methanol: acetonitrile: water containing sodium acetate and tetrabutylammonium bromide (TBA), and detected at 254 nm. A solvent extraction procedure was developed for simultaneous determination of the metals with detection limits within 0.02–2.5 μ g.mL⁻¹. The method was applied to the determination of copper, cobalt and iron in natural waters.     

Development of an optical chemical sensor based on 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol in Nafion for determination of nickel ion

An optical chemical sensor based on immobilization of 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol (Br-PADAP) in Nafion membrane is described. The membranes were cast onto glass substrates and were used for the determination of nickel in aqueous solutions by spectrophotometry. The sensor system is highly transparent, mechanically stable and showed no evidence of reagent leaching. The influence of several parameters such as pH, ligand concentration, and type and concentration of regenerating solution were optimized. The sensor system showed good sensitivity in the range 0.5-20 μg ml⁻¹ with a detection limit of 0.3 μg ml⁻¹ Ni(II). The sensor has been incorporated into a home-made flow-through cell for determination of nickel in flowing streams with improved sensitivity, precision and detection limit. The calibration curve in the flow system was linear in the range 0.1-16 μg ml⁻¹ with a detection limit of 0.07 μg ml⁻¹. The sensor is easily regenerated by dilute nitric acid solution. The proposed method was successfully applied to the determination of nickel content in vegetable oil and chocolate samples and the results were compared with those obtained using atomic absorption spectrometry.     

Simultaneous spectrophotometric determination of nickel and iron in copper-base alloy with bromo-PADAP

The reaction of nickel (II) with Br-PADAP, in the presence of tergitol NPX surfactant, forms a complex with absorption peaks at 520 and 560 nm. The iron(II)-Br-PADAP system at the same conditions forms a chelate with absorption peaks at 560 and 748 nm. This allows the simultaneous spectrophotometric determination of nickel and iron by measuring the absorbance at 560 and 748 nm. The proposed method, at ph 4.0-5.7, shows a molar absorptivity of 1.22 x 10(5)l . mole(-1) . cm(-1) for nickel at 560 nm and 8.20 x 10(4)l . mole(-1) . cm(-1) at 560 nm and 3.35 x 10(4)l . mole(-1) . cm(-1) at 748 nm for iron(II). Beer's law is obeyed up to 0.40 mu/ml of nickel(II) and up to 0.65 mu/ml of iron(II). Thiosulphate as masking agent allows the simultaneous determination of iron and nickel in the presence of high concentrations of copper. The ethylene glycol 2-(2-amino-ethyl) tetracetic acid provides the elimination of many other interferences. The method has been applied successfully to the simultaneous determination of nickel and iron in reference samples.     

Simultaneous determination of chromium (III) and copper (II) by using derivative spectrophotometry with MEDTA

The application of derivative spectrophotometry to the simultaneous determination of chromium (III) and copper (II) with MEDTA is described. The procedure is suitable for concentrations of 0.40–2.60 mg ml^–1 of chromium (III) and 0.15–0.60 mg ml^–1 of copper (II). The main interferences, both anionic and cationic, are easily eliminated. The method was applied to different aqueous matrices. It was compared with an atomic absorption method and good results were obtained. Received: 12 June 1996 / Revised: 30 July 1996 / Accepted: 2 August 1996     

Simultaneous First Derivative Spectrophotometric Determination of Palladium and Nickel Using 2-(2-Thiazolylazo)-5-Dimethylaminobenzoic Acid as an Analytical Reagent

 A simple, rapid, selective, sensitive and economical method has been developed for the simultaneous determination of trace amounts of palladium and nickel in aqueous methanolic medium using 2-(2-thiazolylazo)-5-dimethylam inobenzoic acid as an analytical reagent by first derivative spectrophotometr y. Palladium is determined by measuring base to peak distance at λ=695.0 nm while nickel is estimated by zero crossing method in the mixture. The linearity is maintained between 0.12–1.75 μg mL⁻¹ for palladium and 0.07–1.60 μg mL⁻¹ for nickel in the pH range 2.8–7.2 and 3.4–8.8 respectively. Seven replicate determinations of 1.0 μ g mL⁻¹ of palladium and 0.8 μg mL⁻¹ of nickel in a mixture give a mean signal height of 0.391 for Pd and 0.541 for Ni with relative standard deviations of 0.9% and 1.2%, respectively. The sensitivity of the proposed method is 0.391 (dA/dλ)/(μg mL⁻¹) for palladium and 0.685 (dA/dλ)/(μg mL⁻¹) for nickel. Various parameters have been optimised for the simultaneous determination of palladium and nickel in various complex samples. Received March 30, 1999. Revision November 25, 1999.     

Flow injection spectrofluorimetric determination of iron(III) in water using salicylic acid

A simple and fast flow injection fluorescence quenching method for the determination of iron in water has been developed. Fluorimetric determination is based on the measurement of the quenching effect of iron on salicylic acid fluorescence. An emission peak of salicylic acid in aqueous solution occurs at 409 nm with excitation at 299 nm. The carrier solution used was 2 × 10⁻⁶ mol L⁻¹ salicylic acid in 0.1 mol L⁻¹ NH₄⁺/NH₃ buffer solution at pH 8.5. Linear calibration was obtained for 5–100 μg L⁻¹ iron(III) and the relative standard deviation was 1.25 % (n = 5) for a 20 μL injection volume iron(III). The limit of detection was 0.3 μg L⁻¹ and the sampling rate was 60 h⁻¹. The effect of interferences from various metals and anions commonly present in water was also studied. The method was successfully applied to the determination of low levels of iron in real samples (river, sea, and spring waters).     

Simultaneous separation and microdetermination of cobalt(II), nickel(II) and copper(II)

 A sensitive and selective flotation procedure for the separation of microamounts of Co(II), Ni(II) and Cu(II) separately or in admixture is described. The maximum separation rate (∼1) for 0.1 mmol/L of each analyte is achieved using 1 mmol/L of both oleic acid (HOL) surfactant and 4-phenylthiosemicarbazide (HPTS) as a collector in the pH range 6–7. A method for the simultaneous separation and microdetermination of the analytes is elaborated, based on adding excess HPTS and floating the species with HOL at pH ∼6. The filtrate (which is clear brownish-yellow) obtained from the scum is used for the spectrophotometric determination of Co(II) at 350 nm. The formation constants of 1:1 and 1:2 [Co(II):HPTS] species are 6.9×10⁵ and 1.22×10¹⁰ L mol^-1, respectively. Beer’s law is obeyed up to 9 μg/mL of Co(II) with a molar absorptivity of 1.15×10⁴ L mol^-1 cm^-1. The precipitate in the scum layer is quantitatively collected, dissolved in aqua regia and aspirated directly into the flame for the (AAS) determination of Ni and Cu. The procedure is successfully applied to some natural water samples. A mechanism for the separation of the analytes is proposed. Received: 23 January 1996/Revised: 1 April 1996/Accepted: 9 April 1996     

Development of method for the speciation of inorganic iron in wine samples

In this paper, we proposed a procedure for the determination of iron(II) and total iron in wine samples employing molecular absorption spectrophotometry. The ligand used is 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (Br-PADAP) and the chromogenic reaction in absence or presence of ascorbic acid (reducing agent) allows the determination of iron(II) or total iron, respectively. The optimization step was performed using a multivariate technique (Box Behnken design) involving the factors pH, acid ascorbic concentration and reaction time.The method allows the determination of iron(II) and iron(III) in wine samples, with limits of detection and quantification 0.22 and 0.72 μg L⁻¹, respectively. The precision expressed as relative standard deviation (R.S.D.) was 1.43 and 0.56% (both, n = 11) for content of iron(II) in wine samples of 1.68 and 4.65 mg L⁻¹, and 1.66 and 0.87% (both, n = 11) for content of total iron in wine samples of 1.72 and 5.48 mg L⁻¹.This method was applied for determination of iron(II) and total iron in six different wine samples. In these, the iron(II) content varied from 0.76 to 4.65 mg L⁻¹ and from 1.01 to 5.48 mg L⁻¹ for total iron. The results obtained in the determination of total iron by Br-PADAP method were compared with those that were performed after complete acid digestion in open system and determination of total iron employing FAAS. The method of regression linear was used for comparison of these results and demonstrated that there is no significant difference between the results obtained with these two procedures.     

Sequential flow-injection spectrophotometric determination of iron(II) and iron(III) by copper(II)-catalyzed reaction with Tiron

A flow injection method for the sequential determination of iron(II) and iron(III) was developed. It is based on the differential reaction kinetics of iron(II) and iron(III) with Tiron in a double-injection FI system. The proposed method employs the accelerating action of copper(II) for the oxidation of iron(II) in the presence of Tiron. A linear calibration graph is obtained for iron (II) and iron(III) in the concentration range 1.8 × 10^–5– 1.8 × 10^–4 mol/L; the throughput of samples is 30 injections/h. Received: 22 October 1996 / Revised: 4 December 1996 / Accepted: 10 December 1996     

2-(2-Thiazolylazo)-p-cresol(TAC) as a Reagent for the Spectrophotometric Determination of Lead(II)

Abstract

The reaction between lead(II) and 2-(2-Thiazolylazo)-p-Cresol(TAC) in the presence of TERGITOL NPX (4 mg/ml) at an apparent pH 9.0–10.0 results in an intensely colored complex which is stable for at least 4 hr.

The composition of the complex is 1:2 cation: TAC and the log of the formation constant is 11.92 ± 0. 40. Beer's law is obeyed up to 6.0μg.ml^?1 of lead(II) at 650nm.

The apparent molar absorptivity at 650 nm is 2.07 × 10⁴ 1. mole^?1.cm^?1 and the detection limit was obtained as 10.0 ng.ml^?1 of lead(II).

The method is applied to determination of lead(II) in copper-base alloy.     

Spectrophotometric determination of trimethoprim by oxidation in drug formulations

A spectrophotometric determination of trimethoprim is described based on the reaction of its amine group with persulfate which acts as a strong oxidizing agent in alkaline media. The reaction produces a stable yellow colored compound after heating in a boiling water bath for 30 min. At λ_max 355 nm, Beer’s law is obeyed in the concentration range 10–60 μg ml^–1 with a molar absorptivity of 2.7 × 10³ l mol^–1cm^–1. The method is applied to formulations with sulfamethoxazole. Received: 30 July 1996 / Revised: 16 October 1996 / Accepted: 22 October 1996     

Kinetics of Complexation of Uranium with 2-(5-Bromo-2-Pyridylazo)-5-(Diethylamino) Phenol (Br-PADAP) in a 1:1 Water-Ethanol Medium

2-(5-Bromo-2-pyridylazo)-5-(diethylamino) phenol (Br-PADAP) forms a 1:1 complex with the uranyl ion in the presence of sulphosalicylic acid, which acts as stabilizer for this complex in the triethanol amine/perchloric acid buffer system. A change in the stoichiometry of the complex was seen at pH<5. Kinetic measurements were carried out using stopped-flow spectrophotometer in the presence of an excess concentration of U(VI) in the pH range 6.5 to 8. The dependence of the pseudo-first-order rate constant, k(obs), on the concentrations of U(VI), ligand and hydrogen ion showed that Br-PADAP reacts with UO₂(OH)⁺ to form an intermediate species (equilibrium constant = 1.28×10⁴mol.dm⁻³) that then rearranges (rate constant = 5.6×10⁻²s⁻¹) to form the product species. UO₂(OH)⁺ is present in equilibrium with the unreactive species UO₂(OH)₂, as well as with the unreactive sulfosalicylic acid complex.     

Extraction-spectrophotometric determination of trace iron (II) in sea water with 2-[2-(3,5-dibromopyridyl)azo]-5-diethylaminobenzoic acid

An extraction-spectrophotometric method is described for the determination of traces of iron(II) with 2-[2-(3,5-dibromopyridyl)azo]-5-diethyl-aminobenzoic acid. The reagent forms a stable and blue 12 iron/reagent complex that can be extracted into chloroform. The apparent molar absorptivity of the iron(II) complex is 1.09 × 10⁵ 1 mol^–1 cm^–1 at 624 nm in chloroform. The reagent is relatively selective; interferences from cobalt, copper, nickel and vanadium can be removed by using dimethylglyoxime and EDTA. The method is applied to the determination of iron (II) in sea water and aluminium alloys with good precision and accuracy.     

Selenium determination by HG-ICPAES: Elimination of iron interferences by means of an ion-exchange resin in a continuous flow system

 An accurate procedure for the elimination of iron interferences in the determination of selenium in geological materials by the Hydride Generation – Inductively Coupled Plasma Atomic Emission Spectrometry technique (HG-ICPAES) is proposed. A selective removal of iron is achieved by on-line incorporation of a microcolumn filled with strongly acidic cation exchange resin (Dowex 50W-X8). The microcolumn manifold used was interfaced with the hydride generation manifold by a flow injection sample injection valve. After the removal of the iron, a 500 μl sample was injected into a carrier stream of water. This was merged with hydrochloric acid and sodium tetrahydroborate in order to generate the corresponding selenium hydride. The system was found to have a limit of detection of 0.4 ng ml^-1 and a relative standard deviation of 2% for 20 ng ml^-1 selenium. The application of the method on different Geochemical Standard Reference Samples demonstrated that results were statistically indistinguishable from certified values. Received: 7 March 1996 / Revised: 30 May 1996 / Accepted: 4 June 1996     

Speciation of arsenic(V) and arsenic(III) by cathodic stripping voltammetry in fresh water samples

A voltammetric stripping procedure is described for the determination of arsenic(V) in a mannitol-sulphuric acid medium. The arsenic is coprecipitated with copper and selenium and reduced to arsine at the hanging mercury drop electrode. Using an accumulation time of 240 s, the detection limit is 0.52 μg L^–1, the determination limit is 0.9 μg L^–1. The method has been applied to the determination of arsenic in water samples. By varying the composition of the supporting electrolyte it is possible to differentiate between arsenic(III) and arsenic(V). As both oxidation states have different toxicological characteristics, the ability to discriminate between both is an distinct advantage of the proposed method. Received: 25 October 1996 / Revised: 7 February 1997 / Accepted: 12 February 1997