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.     

Sequential determination of iron(II) and iron(III) in pharmaceutical by flow-injection analysis with spectrophotometric detection.

A flow injection procedure for the sequential spectrophotometric determination of iron(II) and iron(III) in pharmaceutical products is described. The method is based on the catalytic effect of iron(II) on the oxidation of iodide by bromate at pH = 4.0. The reaction was monitored spectrophotometrically by measuring the absorbance of produced triiodide ion at 352 nm. The activating effect for the catalysis of iron(II) was extremely exhibited in the presence of oxalate ions, while oxalate acted as a masking agent for iron(III). The iron(III) in a sample solution could be determined by passing through a Cd-Hg reductor column introduced in the FIA system to reduce iron(III) to iron(II), which allows total iron determination. Under the optimum conditions, iron(II) and iron(III) could be determined over the range of 0.05 - 5.0 and 0.10 - 5.0 microg ml(-1), respectively with a sampling rate of 17 +/- 5 h(-1). The experimental limits of detection were 0.03 and 0.04 microg ml(-1) for iron(II) and iron(III), respectively. The proposed method was successfully applied to the speciation of iron in pharmaceutical products.     

Simultaneous differential rate determination of iron(II) and iron(III) by flow-injection analysis

Flow-injection procedures for the simultaneous spectrophotometric determination iron(II) and iron(III), relying on the different kinetic-catalytic behaviour of iron(II) and iron(III) in the redox reaction between leucomalachite green and peroxodisulphate with and without the presence of the activator 1,10-phenanthroline, are described. Exploiting the fact that one of the chemical reactions is very rapid whereas the other one is comparatively slower, two experimental procedures are presented. In the first, two individual zones of sample solution are injected simultaneously into separate carrier streams of reagent in a two-line system. Taking advantage of the different residence times of the samples in the manifold lines, the resulting colour formation is measured by a single optical detector with two separate flow cells aligned within the same optical path. The second approach is based on the use of a single-line flow-injection system, exploiting the formation of a double peak as a result of injecting a large sample zone, sandwiched between reagent zones of appropriate composition. In this manner two time-resolved signals for the kinetically governed processes can be obtained and thus used for quantification of the individual species.     

A simple and selective flow-injection spectrophotometric determination of copper(II) by using acetylsalicylhydroxamic acid

A new simple, and rapid flow-injection spectrophotometric method is developed for the determination of trace amounts of Cu(II) by using a new chromogenic reagent acetylsalicylhydroxamic acid (AcSHA). The method is based on the formation of colored Cu(II)-(AcSHA)₂ complex. The optimum conditions for the chromogenic reaction of Cu(II) with AcSHA is studied and the colored (green) complex is selectively monitored at λ_max 700 nm. With the reagent carrier solvent (dimethylsulfoxide (DMSO) and acetate buffer, pH 4.2) flow-rate of 1 ml min⁻¹, a detection limit (2S) of 1 μg l⁻¹ Cu(II) was obtained at a sampling rate of 80 sample h⁻¹. The calibration graph was linear in the Cu(II) concentration range 5-120 μg l⁻¹. The relative standard deviation (n=10) was 0.64% for a sample containing 60 μg l⁻¹ Cu(II). The detailed study of various interferences confirmed the high selectivity of the developed method. The method was successfully applied to determine trace amounts of copper(II) in river and seawater samples. The accuracy of the method was demonstrated by the analysis of standard reference materials C12X3500 and C14XHS 50.     

The spectrophotometric determination of iron(III) in a flow-injection system with a mixed solvent

A fast and sensitive flow-injection procedure is described for the determination of iron(III). The complexing agent is ammonium diisopropyldithiophosphate in a 1:1 (v/v) isopropanol/water carrier stream. The linear range is 0.05–15 mg 1^?1 iron(III) with a detection limit of 0.01 mg 1^?1 and the injection rate is about 400 h^?1.     

Potentiometric flow-injection determination of trace chlorine based on its redox reaction with an iron(III)/iron(II) buffer

A very sensitive and rapid potentiometric determination of trace chlorine in water is described. The method is based on the transient potential changes which appears during the reduction of dissolved chlorin with an iron(III)/iron(II) potential buffer containing chloride and sulfuric acid. The sample is injected into a water carrier stream and merged with a stream of this potential buffer solution; chlorine is reduced during passage through a short reaction coil. The potential change from the baseline is measured with a flow-through ORP (oxidation-reduction potential) electrode. Potential changes (peak heights) are proportional to chlorine concentrations from 10^?7 M to 10^?5 M. The detection limit is 5 × 10^?8 M (3.5 μgl^?1 as Cl₂). The sample throughput is 45 h^?1. Reproducibility is in the range 2.5–1.1%. Results for potable water agree with those obtained by the o-tolidine method.     

Sequential determination of iron and titanium by flow-injection analysis

A flow-injection method has been developed for the sequential spectrophotometric determination of iron and titanium using 3,4 dihydroxybenzoic acid as chromogenic reagent. The system involves the sequential measurement of the absorbances of the complexes at 380 and 570 nm. The system is designed using a simultaneous injection of sample and reagent into separate carrier streams. The proposed method is characterized by a precision of about 2%, a sampling rate of about 50 samples per hour, and a reagent consumption of 200 mul (0.50% solution) per sample. It is relatively free of interferences and was used for the sequential determination of titanium and iron in rocks.     

Ultraviolet spectrophotometric determination of copper in copper ores by flow-injection analysis

A flow-injection analysis (FIA) method for the ultraviolet spectrophotometric determination of copper in copper ores is described. The ore samples are dissolved in concentrated perchloric acid, the excess acid is neutralized with ammonia solution, and the resulting solution is used for the determination of copper. The UV-FIA system is based on the reaction of copper (II) ions with pyrophosphate and subsequent measurement of the absorbance of the dipyrophosphatocuprate (II) complex at 240 nm. The main factors which control the formation of this complex and the FIA variables influencing the system are discussed. The calibration graph is linear from 2-50 ppm copper. At a sampling rate of about 70 samples h(-1) with 50 mul sample injections, precision was about 1% relative standard deviation. Results obtained compare well with those obtained by atomic absorption spectrometry.     

Diformylhydrazine as analytical reagent for spectrophotometric determination of iron(II) and iron(III)

The bidentate ligand diformylhydrazine (OHC-HN-NH-CHO), DFH, combines with iron(II) and iron(III) in alkaline media in the pH range 7.3-9.3 to form an intensely colored red-purple iron(III) complex with an absorption maximum at 470 nm. Beer's law is obeyed for iron concentrations from 0.25 to 13 microg mL(-1). The molar absorptivity was in the range 0.3258x10(4)-0.3351x10(4) L mol(-1) cm(-1) and Sandell's sensitivity was found to be 0.0168 microg cm(-2). The method has been applied to the determination of iron in industrial waste, ground water, and pharmaceutical samples.     

Detection and spectrophotometric determination of copper(III) with p-anisidine

Copper(III) solutions are found to give an instantaneous stable pink-coloured product with 0.2% aqueous p-anisidine in the presence of 0.03N acetic acid. The wavelength of maximum absorption is 533 nm and obeys Beer's law up to 0.89408 g copper(III). It is also recommended as a spot test for copper(III).     

Selective spectrophotometric determination of iron(III) with EDTA

A spectrophotometric determination of iron as its iron (III)-EDTA-H₂O₂-NH₃ complex is described; up to 10-fold amounts of metals that form EDTA complexes absorbing at the same wavelength do not interfere because hydrogen peroxide reacts with thciron(IIl)-EDTA complex but does not affect the EDTA complexes of coppcr(II), nickel(II), cobalt(ltl) and chromium(Ilt).     

Simultaneous determination of iron(II), iron(III), and titanium(IV) by flow injection analysis using kinetic spectrophotometry with Tiron

Summary Two flow injection analysis systems have been worked out for the simultaneous determination of Fe(III), Fe(II), and Ti(IV) based on the kinetic spectrophotometry with Tiron. The first system uses a silver reductor column and a single detector with two flow cells aligned in the same optical path to yield two peaks corresponding to (a) Ti(IV)-Tiron and (b) Ti(IV) plus total iron(III)-Tiron complexes. An another sample injection without the silver column yields a single peak which corresponds to Ti(IV) plus Fe(III)-Tiron complexes. With the two sample aliquot injections the system permits simultaneous determinations with throughput of 30 samples/h in the g to several tens g range of each species. The second system is a multidetection system with or without the silver reductor column using the same spectrophotometry with Tiron, in which the entrapment of the sample plug into a closed system allows its repetitive passage through a single detector. With the advantage of much simpler instrumentation, the system permits 6 samples/h to be analyzed for the three metal species with somewhat lower precisions than the first system.     

Simultaneous spectrophotometric determination of copper(II) and zinc(II) based on their kinetic separation in flow-injection systems

Flow-injection methods are developed for the spectrophotometric analysis of binary copper(II) and zinc(II) mixtures. They are based on measurements of a differential kinetic signal caused by ligand-exchange reactions that occur in the flow between the complexes of these metals with the same chromogenic reagent (4-(2-pyridylazo)-resorcinol or zincon) and aminopolycarboxylic acids. Two different approaches are used for the kinetic separation (or masking) of these metals followed by the on-line processing of the recorded signal by regression analysis. One of them is monitoring an indicator reaction in the stopped-flow mode, and the other is recording the separated peaks in the flow-injection system with two reaction zones reaching the detector over certain periods. The optimum detection conditions were found (c _min = 0.03 μg/mL), which allow the detection of the studied metal ions in mixtures in a ratio of no more than 1: 5 with a relative error of no more than 5%, good precision (RSD < 10%, n = 6, P = 0.95), and high throughput (90 h^?1). The developed procedures were tested in the analysis of model mixtures and pharmaceutical preparations.     

Micro-fusion and spectrophotometric determination of iron(II) and iron(III) in chrome spinels and other refractories

Spectrophotometric determination of FeO in milligram samples of chrome spinels and related refractory minerals after high-frequency micro-fusion with lithium tetraborate in an inert atmosphere is described. Anomalous responses (apparent reduction or oxidation of FeO depending on the ferroïn-type reagent)_rendered the procedure highly unreliable. All the fluxes containing structural oxygen, as well as phosphoric acid, acted as oxidants even when atmospheric oxidation was rigorously excluded. However, the method is suitable for micro-determination of total iron in spinels. Spectrophotometric measurements gave an average relative standard deviation of 0.73%.     

Kinetic flow-injection determination of hydrogen peroxide by use of iron(III)-catalyzed coloration and its application to the determination of biological substances.

A kinetic flow-injection (FI) method is described for the determination of hydrogen peroxide. This method is based on an iron(III)-catalyzed oxidative coupling of 4-aminoantipyrine with N,N-dimethylaniline by hydrogen peroxide. By measuring the change in the absorbance of the dye formed at 560 nm, 1 x 10(-6) - 6 x 10(-4) M hydrogen peroxide could be determined with a sampling rate of 15 h(-1). The relative standard deviation (n = 30) was 0.8% for 5 x 10(-5) M hydrogen peroxide. There was little interference of the co-existing ions and compounds. After introducing some immobilized enzyme reactors to the FI system, the proposed method allowed the determination of glucose and uric acid ranging from 1 x 10(-6) to 6 x 10(-4) M with relative standard deviations of below 2%. The applicability of the method was demonstrated by determining these substances in serum samples.     

Sequential injection lab-on-valve simultaneous spectrophotometric determination of trace amounts of copper and iron

A sequential injection (SI) method in a lab-on-valve (LOV) format for simultaneous spectrophotometric determination of copper and iron has been devised. The detection chemistry is based on the complex formation of 2-(5-bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]aniline (5-Br-PSAA) with copper(II) and/or iron(II) at pH 4.6. Copper(II) reacts with 5-Br-PSAA to form the complex which has an absorption maximum at 580 nm but iron(III) does not react. In the presence of a reducing agent only iron(II)-5-Br-PSAA complex is formed and detected at 558 nm. Under the optimum experimental conditions, the determinable ranges are 0.1-2 mg l⁻¹ for copper and 0.1-5 mg l⁻¹ for iron, respectively, with a sampling rate of 18 h⁻¹. The limits of detection are 50 μg l⁻¹ for copper and 25 μg l⁻¹ for iron. The relative standard deviations (n = 15) are 2% for 0.5 mg l⁻¹ copper and 1.8% for 0.5 mg l⁻¹ iron when determined in standard solutions. The recoveries range between 96 and 105% when determining 0.25-2 mg l⁻¹ of copper and 0.2-5 mg l⁻¹ of iron in artificial mixtures at copper/iron ratios of 1:10 to 5:1. The proposed SI-LOV method is successfully applied to the simultaneous determination of copper and iron in multi-element standard solution and in industrial wastewater samples.     

Use of acetohydroxamic acid in the direct spectrophotometric determination of iron(III) and iron(II) by flow injection analysis

The direct spectrophotometric determination of iron(III) and iron(II) by flow injection analysis with acetohydroxamic acid and 1,10-phenanthroline as reagents is reported. The working ranges are 0.5–10 and 10–60 mg l^?1, respectively. Results obtained for synthetic mixtures of Fe(III) and Fe(II) and for acid extracts of haematite samples were accurate. Interference studies indicate that the method is highly selective.