Spectrophotometric determination of iron(III) and total iron by sequential injection analysis technique

A procedure for determination of concentrations of iron(III) and total iron by sequential injection analysis is described. The method is based on the strong blue-colored complexes formed between iron(III) and tiron. The absorbance of the complexes is measured spectrophotometrically at 635 nm. Oxidation of iron(II) and masking of interfering fluoride is simultaneously done by injecting one zone of hydrogen peroxide and one of thorium(IV) between the sample and reagent zones. Concentration of iron(III) and total iron, in the range 0.002–0.026 M, in diluted samples from a pickle bath were determined. The relative standard deviation was 0.4% (n=7). The method was also used in a pilot plant of a zinc process for determination of iron(III) in the range 0.2–3.0 g l⁻¹. The sample throughput is approximately 17 samples per hour, including three repetitive determinations of each sample.     

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.     

Design of two channel flow cells for simultaneous determination of copper and iron

Two compact double and serial flow cells were designed for simultaneous determination of trace copper and iron ions. 2-(5-Bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)aniline(5-Br-PSAA) was used as a chromogenic reagent. 5-Br-PSAA reacted with Cu(II) and Fe(II) to form red chelate compounds and did not react with Cu(I) and Fe(III). Based on these characteristics, a three-lines flow system using two channel flow cells was assembled for the simultaneous determination of trace amounts of copper and iron and applied to the assay of ground water.     

Ion-chromatographic analysis of mixtures of ferrous and ferric iron

Determinations of the aqueous iron species Fe(II) and Fe(III) are essential for a fully-informed understanding of redox processes involving iron. Most previous methods for speciation of iron have been based on the calorimetric determination of Fe(II) followed by reduction of Fe(III) and analysis for total iron. The indirect determination of Fe(III) and the consumption of relatively large sample volumes have limited the accuracy and utility of such methods. A method based on ion-chromatography has been developed for simultaneous direct determination of Fe(II) and Fe(III). Sample pretreatment involves only conventional filtration and acidification. No interferences with the iron(II) determination were found; in determination of iron(III) the only interference observed was an artifact peak (of unknown origin) that occurred only when iron(II) was present, and had an area that was a function of the iron(II) concentration and could hence be corrected for. Solutions of iron(II) free from iron(III) can be prepared by treatment with a mixture of hydrogen and nitrogen in the presence of palladium black as catalyst, to reduce the iron(III). Photoreduction of iron(III) in acidified samples increases the Fe(II)/Fe(III) ratio; no means of circumventing this effect is known, other than storing the samples in the dark and analysing them as soon as possible.     

Sorption-spectrophotometric determination of iron(II, III) with the use of organic reagents immobilized in a polymethacrylate matrix

The interaction of iron(II) with 2,2′-dipyridyl and 1,10-phenanthroline immobilized in a polymethacrylate matrix was studied. The optimum conditions of the complexation of iron(II) with the immobilized reagents and the chemical analytical properties of the complexes in the polymethacrylate matrix were determined. A sorption-spectrophotometric procedure was developed for the determination of iron(II) and the total of iron(II, III) after the reduction of iron(III) by ascorbic acid. The procedure with 2,2′-dipyridyl was used for the analysis of samples of tap, well, and mineral water and a solution of glucose.     

Separation of selenite,sulkate and iron by cation-exchange resin

Selenite, sulfate and iron(III) are separated by cation-exchange resin. Microgram amounts of selenite in iron(III) sulfate solution at pH 2 are completely adsorbed on the resin together with the large excess of iron(III). while sulfate passes through. Selenite is eluted with 0.5 N hydrochloric acid, leaving iron(III) in the resin. The procedure is applied to the determination of these elements in natural iron sulfides.     

Chelate adsorption for trace voltammetric measurements of iron(III)

Summary A very sensitive electrochemical stripping procedure for trace measurements of iron(III) is described. The chelate of iron with Solochrome Violet RS is adsorbed on the hanging mercury drop electrode, and the reduction current of the accumulated chelate is measured by voltammetry. The adsorption and redox behaviours are explored by cyclic voltammetry. The height of the chelate peak, which is about 0.28 V more negative than the peak of the free dye, is shown to be proportional to the iron concentration. Optimal experimental conditions include a preconcentration potential of –0.40 V, solution pH of 5.1 and a linear scan mode. The sharp chelate peak, associated with the effective interfacial accumulation, coupled with the flat baseline, facilitates measurements at the nanomolar and submicromolar concentration levels using short preconcentration times. The limit of detection after 1 min preconcentration is 0.04 gl^–1 (7 × 10^–10 M), and the relative standard deviation at the 10^–7 M level is 4.7%. The effects of possible interferences, due to coexisting metal ions or organic surfactants, are evaluated. The ability of measuring iron(III) in the presence of iron(II) is illustrated. Actual analyses of sea and tap waters are reported.

---

Chelat-Adsorption für voltammetrische Spurenanalyse von Eisen(III)

     

Spectrophotometric determination of iron with ferrozine by flow-injection analysis

Two methods for the determination of iron by normal FIA and reversed FIA were developed using sodium 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine-4',4'-disulphonate (ferrozine). The reagent formed a chelate with Fe(II) in hexamethylentetramine buffered medium at pH 5.5. In one previous reaction coil Fe(III) was reduced to Fe(II) by ascorbic acid and in the other reaction coil the complexation reaction was developed. The linear range of the determination was 0.5-6 and 0.1-5 mug ml(-1) of iron for normal FIA and reversed FIA respectively. The proposed method was sensitive (detection limit 0.012 and 0.010 mug ml(-1)), rapid and reproducible (RSD 0.3 and 0.28%). The method was satisfactorily applied to the determination of iron in waste water, toadstool tissue, potato leaves, human hair and bauxites at a sampling rate of 90 and 50 samples h(-1) for normal FIA and reversed FIA respectively.     

Multi-pumping flow system for the determination, solid-phase extraction and speciation analysis of iron

A multi-pumping flow system (MPFS) for the spectrophotometric determination, solid-phase extraction (SPE) and speciation analysis of iron at a wide range of concentrations is proposed. Chelating (iminodiacetic groups) disks have been used as solid phase. A solenoid valve allows the deviation of the flow towards the chelating disk to carry out SPE procedures. The possibility to combine solenoid micro-pumps with solenoid valves increases the versatility of MPFS. Ammonium thiocyanate has been chosen as chromogenic reagent for Fe(III). The determination of total iron is achieved by the on-line oxidation of iron(II) to iron(III) with a hydrogen peroxide stream.

A mass calibration was run within the range 0.01–1.75 μg. The detection limit (3s_b/S) was 0.01 μg. The repeatability (R.S.D.) was estimated as 1.6% after 10-fold processing of 2 ml of 0.5 mg l⁻¹ Fe solution. When SPE was not required, two linear calibration graph within the ranges 0.05–10 and 0.2–15 mg l⁻¹ for the determination of iron(III) and total iron, respectively, were obtained. The proposed procedure was validated by analysis of certified reference materials. The analytical features were compared with those obtained exploiting MSFIA.     

Speciation of Fe(III) and Fe(II) in water samples by liquid–liquid extraction combined with low-temperature electrothermal vaporization (ETV) ICP-AES

The use of 1-phenyl-3-methyl-4-benzoylpyrazolone (PMBP) as extractant for separation of Fe(III) and Fe(II) and low-temperature vaporization of the Fe(III)–PMBP chelate into ICP-AES for their speciation analysis was investigated. The factors affecting the formation of Fe(PMBP)₃ chelate and its vaporization behavior were investigated in detail. PMBP was used not only as the extractant for the separation of Fe(III) and Fe(II) but also as the chemical modifier for the low-temperature ETV-ICP-AES determination of iron. Under the optimized conditions, the detection limit for iron(III) and iron(II) are both 3.2?ng/mL, with relative standard deviations of 3.9 and 4.5%, respectively. The proposed method was applied to the determination of trace iron in biological standard reference materials and the species in East Lake water samples, and the results obtained were satisfactory.     

停流流动注射-诱导动力学光度法同时测定微量铁和锑

依据诱导反应的基本原理, 提出了一种同时测定多元素的方法; 研究了Fe(II)、Sb(III)诱导的Cr(VI)-I^-氧化还原反应体系, 并据此建立了停流-诱导动力学光度法同时测定微量铁和锑的工作条件。线性范围分别为0~1.2μg.mL^-1Fe(II)和0~2.0μg.mL^-1Sb(III); 检测限为0.012μg/mL^-1Fe(II)和0.014μg.mL^-1Sb(III)。除Ti(III)、V(IV)及As(III)外, 其余共存离子不影响测定。用本法测定了锌标准物及模拟样品中的铁和锑含量, 结果满意。     

Mechanism of binding of iron to potential therapeutic chelating agents

To aid in designing new therapeutic iron chelating agents, the mechanism of iron binding to prototypic heterocyclic carboxaldehyde thiosemicarbazones has been studied. Based on molecular orbital and spectroscopic studies, iron (II) is found to bind in a covalent manner, while iron(III) seems to interact ionically. However, with both iron(II) and iron(III), chelate formation is dependent on charge interaction between the metal and the coordinating atoms of the ligand.     

Spectrophotometric determination of macroquantities of iron and titanium in real-world objects

The conditions of formation of Fe(III) and Ti(IV) ethylenediaminetetraacetate chelates were optimized. A new rapid spectrophotometric procedure for determination of iron and titanium as EDTA complexes in real-world objects was developed.     

Separation and accurate determination of iron and aluminium in a single sample of silicate rock

A procedure for the separation and subsequent determination of iron and aluminium in silicate samples is given. The anion-exchange separation of iron(III) from vanadium was studied under the conditions of rock analysis. The salt content of the sample solution and the applicability of resins were studied to determine the optimum conditions for the separation of iron and aluminium. The proposed procedure was tested by determining iron and aluminium in the Geological Standards S1 and W1.     

Simultaneous determination of ferric, ferrous and total iron by extraction differential pulse polarography: application to the speciation of iron in rocks

The voltammetric characteristics of Fe(III) oxinate at a mercury electrode, in the presence of 0.2 M tributylammonium perchlorate (tri-BAP) and 0.2 M tributylamine (tri-BA) as the supporting electrolyte have been studied in chloroform. With this supporting electrolyte a two electron quasi-reversible process for the reduction of Fe(III) oxinate was observed. Preceded by a solvent extraction of Fe(III) oxinate in chloroform, differential pulse polarography (DP) was used for the determination of iron. The calibration graph was linear over the concentration range 0.5–50 μM Fe(III) oxinate in chloroform and the detection limit was 1.5 μM. The proposed DP method has been used for the determination of ferric, ferrous and total iron in a mixture and successfully applied to the speciation of iron in rocks.     

Application of redox reactions in spectrophotometry-II Detection and spectrophotometric determination of phenolic compounds with the iron(III)/1,10-phenanthroline complex

To test the utility of the iron(III)/1,10-phenanthroline reagent system for the determination of organic compounds, its reaction with phenolic compounds has been characterized. By a redox reaction the reagent forms the chelate [Fe(phen)(3)](2+), which is extractable as ion-association complexes. Determinations based on these complexes are very sensitive.     

A simple flow injection spectrophotometric determination method for iron(III) based on O-acetylsalicylhydroxamic acid complexation

A simple and rapid flow-injection spectrophotometric method for the determination of iron(III) and total iron is proposed. The method is based on the reaction between iron(III) and O-acetylsalicylhydroxamic acid (AcSHA) in a 2 % methanol solution resulting in an intense violet complex with strong absorption at 475 nm. Optimum conditions for the determination of iron(III) and the interfering ions were tested. The relative standard deviation for the determination of 5 μg L⁻¹ iron(III) was 0.85 % (n = 10), and the limit of detection (blank signal plus three times the standard deviation of the blank) was 0.5 μg L⁻¹, both based on the injection volumes of 20 μL. The method was successfully applied in the determination of iron(III) and total iron in water and ore samples. The method was verified by analysing a certified reference material Zn/Al/Cu 43XZ3F and also by the AAS method.     

Spectrophotometric determination of trace amounts of iron(III) with norfloxacin as complexing reagent

The complexation of iron(III) with norfloxacin in acidic solution at 25 degrees C, at an ionic strength of about 0.3 M and a pH of 3.0 has been studied. The water-soluble complex formed, which exhibits an absorption maximum at 377 nm, was used for the spectrophotometric determination of trace amounts of iron(III). The molar absorptivity was 9.05 x 10(3) I mol-1 cm-1 and the Sandell sensitivity 6.2 ng cm-2 of iron(III) per 0.001 A. The formation constant (Kf) was determined spectrophotometrically and was found to be 4.0 x 10(8) at 25 degrees C. The calibration graph was rectilinear over the range 0.25-12.0 p.p.m. of iron(III) and the regression line equation was A = 0.163c - 0.00042 with a correlation coefficient of 0.9998 (n = 9). Common cations, except cerium (IV), did not interfere with the determination. The results obtained for the determination of iron(III) using the described procedure and the thiocyanate method were compared statistically by means of the Student t-test and no significant difference was found.     

A flow-through fluorescent sensor to determine Fe(III) and total inorganic iron

A flow-through fluorescent sensor for the consecutive determination of Fe(III) and total iron is described. The reactive phase of the proposed sensor, which has a high affinity for complexed Fe(III), consists of pyoverdin immobilized on controlled pore glass (CPG) by covalent bonding. This pigment selectively reacts with Fe(III) decreasing its fluorescence emission. Total inorganic iron is determined as Fe(III) after on-line oxidation in a mini-column containing persulphate immobilized on an ion exchange resin. The developed method allows the determination of Fe(III) in the 3-200 (g l(-1) range. The relative standard deviations of 10 determinations of 60 (g l(-1) of Fe(III) and 20 (g l(-1) of Fe(III)+Fe(II) are 3 and 5%, respectively. The sensor has been satisfactorily applied to speciate iron in synthetic, tap and well waters and wines. There were no significant differences for total inorganic iron determination between this new method and the atomic absorption spectroscopy reference method at the 95% confidence level. The sensor allows the concentration of Fe(II) to be calculated as the difference between total inorganic iron and Fe(III). The lifetime of the sensor is at least 3 months in continuous use or the equivalent of 1000 determinations.     

Application of redox reactions in spectrophotometry-I The iron(III)/1,10-phenanthroline complex as a reagent for the determination of some anions and organic compounds

It is shown that the complex of iron(III) with 1,10-phenanthroline(phen) is suitable as a reagent for determination of some anions and organic compounds. By a redox reaction with the analytes the reagent forms the intensely coloured chelate [Fe(phen)(3)](2+), which is extractable as an ion-association complex with a suitable counter-ion and allows the development of sensitive spectrophotometric methods of determination. Besides the fundamentals, some remarks on analytical applications are given.