Speciation of dissolved iron(III) and iron(II) in water by on-line coupling of flow injection separation and preconcentration with inductively coupled plasma mass spectrometry

A method has been developed for the speciation of trace dissolved Fe(II) and Fe(II) in water by on-line coupling of flow injection separation and preconcentration with inductively coupled plasma mass spectrometry (ICPMS). Selective determination of Fe(III) in the presence of Fe(II) was made possible by on-line formation and sorption of the Fe(III)-pyrrolidinecarbodithioate (PDC) complex in a PTFE knotted reactor over a sample acidity range of 0.07-0.4 mol L(-1) HCl, elution with 1 mol L(-1) HNO3, and detection by ICPMS. Over a sample acidity range of 0.001-0.004 mol L(-1) HCl, the sum of Fe(III) and Fe(II), i.e., Fe(III + II), could be determined without the need for preoxidation of Fe(II) to Fe(III). The concentration of Fe(II) was obtained as the difference between those of Fe(III + II) and Fe(III). With a sample flow rate of 5 mL min(-1) and a 30-s preconcentration time, an enhancement factor of 12, a retention efficiency of 80%, and a detection limit (3s) of 0.08 microg L(-1) were obtained at a sampling frequency of 21 samples h(-1). The relative standard deviation (n = 11) was 2.9% at the 10 microg L(-1) Fe(III) level. Recoveries of spiked Fe(III) and Fe(II) in local tap water, river water, and groundwater samples ranged from 95% to 103%. The concentrations of Fe(III) and Fe(II) in synthetic aqueous mixtures obtained by the proposed method were in good agreement with the spiked values. The result for total iron concentration in the river water reference material SLRS-3 was in good agreement with the certified value. The method was successfully applied to the determination of trace dissolved Fe(III) and Fe(II) in local tap water, river water, and groundwater samples.     

A comparative study for the ion exchange of Fe(III) and Zn(II) on zeolite NaY

The uptake capacity of Fe(III) and Zn(II) ions in NaY zeolite was investigated. Experiments were carried out in a fixed bed column at 30 degrees C, pH 3.5 and 4.5 for Fe(III) and Zn(II), respectively, and an average particle size of 0.180 mm. In order to minimize the diffusional resistances the influence of flow rate on the breakthrough curves at feed concentrations of 1.56 meq/L for Fe(III) and 0.844 meq/L for Zn(II) was investigated. Flow rate of the minimal resistance in the bed according to mass transfer parameter were 2.0 mL/min for iron and 8.0 mL/min for zinc ions. Freundlich and Langmuir isotherm models have been used to represent the column equilibrium data. The iron dynamic isotherm was successfully modeled by the Langmuir equation and this mathematical model described well the experimental breakthrough curves for feed concentrations from 0.1 up to 3.5 meq/L. The zinc dynamic isotherm was successfully modeled by the Freundlich equation. This equilibrium model was applied to mathematical model. Experimental breakthrough curves could be predicted. Experiments were also carried out in a batch reactor to investigate the kinetics adsorption of the ions Fe(III) and Zn(II). Langmuir kinetic model fit well both experimental data.     

Modified aluminosilicates as low-cost sorbents of As(III) from anoxic groundwater

The utilization of low-grade clay materials as selective sorbents represents one of the most effective possibilities of As removal from contaminated water reservoirs. The simple pre-treatment of these materials with Fe (Al, Mn) salts can significantly improve their sorption affinity to As oxyanions. The natural kaolin calcined at 550 degrees C (mostly metakaolin) and raw bentonite (mostly montmorillonite) pre-treated with Fe(II), Fe(III), Al(III) and Mn(II) salts were used to remove of As from the model anoxic groundwater with As(III) concentration about 0.5 and 10 mg L(-1). All the pre-treating methods were appropriate for bentonite; the efficiency of As(III) sorption varied from 92 to >99%, by the sorption capacity higher than 4.5 mg g(-1). In the case of metakaolin, Fe(II)- and Mn(II)-treatments proved the high sorption efficiency (>97%), while only <50% of As was removed after Fe(III) and Al(III) pre-treatment. The sorption capacities of treated metakaolin ranged from 0.1 to 2.0 mg g(-1).     

A new ion-selective electrode based on aluminium tungstate for Fe(III) determination in rock sample, pharmaceutical sample and water sample

An inorganic cation exchanger, aluminum tungstate (AT), has been synthesized by adding 0·1 M sodium tungstate gradually into 0·1 M aluminium nitrate at pH 1·2 with continuous stirring. The ion exchange capacity for Na⁺ ion and distribution coefficients of various metal ions was determined on the column of aluminium tungstate. The distribution studies of various metal ions showed the selectivity of Fe(III) ions by this cation exchange material. So, a Fe(III) ion-selective membrane electrode was prepared by using this cation exchange material as an electroactive material. The effect of plasticizers viz. dibutyl phthalate (DBP), dioctylphthalate (DOP), di-(butyl) butyl phosphate (DBBP) and tris-(2-ethylhexylphosphate) (TEHP), has also been studied on the performance of membrane sensor. It was observed that the membrane containing the composition AT: PVC: DBP in the ratio 2: 20: 15 displayed a useful analytical response with excellent reproducibility, low detection limit, wide working pH range (1–3·5), quick response time (15 s) and applicability over a wide concentration range of Fe(III) ions from 1 × 10⁻⁷ M to 1 × 10⁻¹ M with a slope of 20 ± 1 mV per decade. The selectivity coefficients were determined by the mixed solution method and revealed that the electrode was selective for Fe(III) ions in the presence of interfering ions. The electrode was used for atleast 5 months without any considerable divergence in response characteristics. The constructed sensor was used as indicator electrode in the potentiometric titration of Fe(III) ions against EDTA and Fe(III) determination in rock sample, pharmaceutical sample and water sample. The results are found to be in good agreement with those obtained by using conventional methods.     

Arsenate adsorption and desorption kinetics on a Fe(III)-modified montmorillonite

The adsorption-desorption kinetics of arsenate on a Fe(III)-modified montmorillonite (Fe-M) was studied at different arsenate concentrations, pH and stirring rates. The synthesized solid was a porous sample with Fe(III) present as a mix of monomeric and polymeric Fe(III) species in the interlayer and on the external surface. Adsorption took place in a two-step mechanism, with an initial fast binding of arsenate to Fe(III) species at the external surface (half-lives of 1 min or shorter) followed by a slower binding to less accessible Fe(III) species in pores and the interlayer (half-lives of around 1 h). Desorption kinetics also reflected the presence of externally and internally adsorbed arsenate. At pH 6 the maximum adsorbed arsenate was 52 μmol/g, a value that is low as compared to adsorption on ferrihydrite (700 μmol/g) and goethite (192-220 μmol/g). However, since the Fe(III) content of Fe-M is much lower than that of ferrihydrite and goethite, Fe(III) species in Fe-M are more efficient in binding arsenate than in ferrihydrite or goethite (one As atom is attached every 8.95 iron atoms). This high binding efficiency indicates that Fe(III) species are well spread on montmorillonite, forming small oligomeric species or surface clusters containing just a few iron atoms.     

Arsenic removal by adsorption on iron(III) phosphate

Under natural conditions, arsenic is often associated with iron oxides and iron(III) oxidative capacity towards As(III) is well known. In this study, As(III) and As(V) removal was performed using synthesised iron(III) phosphate, either amorphous or crystalline. This solid can combine (i) As(III) oxidation by iron(III) and (ii) phosphate substitution by As(V) due to their similar properties. Results showed that adsorption capacities were higher towards As(III), leading to Fe2+ and HAsO4(2-) leaching. Solid dissolution and phosphate/arsenate exchange led to the presence of Fe3+ and PO4(3-) in solution, therefore various precipitates involving As(V) can be produced: with Fe2+ as Fe3(AsO4)2.8H2O(s) and with Fe3+ as FeAsO4.2H2O(s). Such formations have been assessed by thermodynamic calculations. This sorbent can be a potential candidate for industrial waste treatment, although the high release of phosphate and iron will exclude its application in drinking water plants.     

Solid-phase extraction of Fe(III), Pb(II) and Cr(III) in environmental samples on amberlite XAD-7 and their determinations by flame atomic absorption spectrometry

This paper describes a simple and accurate procedure for preconcentration of trace amounts of Fe(III), Pb(II) and Cr(III) ions. The preconcentration procedure is based on retention of p-xylenol blue chelates on Amberlite XAD-7. The analytes retained were eluted from Amberlite XAD-7 by using 1 mol L(-1) HCl. The influences of the analytical parameters including amounts of reagents, pH and type of eluent were also investigated. The detection limits of Fe, Pb and Cr were found to be 3.07, 18.6 and 3.27 microg L(-1), respectively. The accuracy of the procedure was checked by the analysis of an electrolytic copper wire sample. The relative error was less than 5%. The presented method was applied to the determination of Fe(III), Pb(II) and Cr(III) in water samples from Denizli, Turkey with good results such as recoveries more than 95%, relative standard deviations below 10%.     

Sorption of Pb(II), Cr(III), Cu(II), As(III) to peat, and utilization of the sorption properties in industrial waste landfill hydraulic barrier layers

In this study, removal of suspended solids (SS) and turbidity from marble processing wastewaters by electrocoagulation (EC) process were investigated by using aluminium (Al) and iron (Fe) electrodes which were run in serial and parallel connection systems. To remove these pollutants from the marble processing wastewater, an EC reactor including monopolar electrodes (Al/Fe) in parallel and serial connection system, was utilized. Optimization of differential operation parameters such as pH, current density, and electrolysis time on SS and turbidity removal were determined in this way. EC process with monopolar Al electrodes in parallel and serial connections carried out at the optimum conditions where the pH value was 9, current density was approximately 15 A/m², and electrolysis time was 2 min resulted in 100% SS removal. Removal efficiencies of EC process for SS with monopolar Fe electrodes in parallel and serial connection were found to be 99.86% and 99.94%, respectively. Optimum parameters for monopolar Fe electrodes in both of the connection types were found to be for pH value as 8, for electrolysis time as 2 min. The optimum current density value for Fe electrodes used in serial and parallel connections was also obtained at 10 and 20 A/m², respectively. Based on the results obtained, it was found that EC process running with each type of the electrodes and the connections was highly effective for the removal of SS and turbidity from marble processing wastewaters, and that operating costs with monopolar Al electrodes in parallel connection were the cheapest than that of the serial connection and all the configurations for Fe electrode.     

Separation,preconcentration and inductively coupled plasma-mass spectrometric (ICP-MS) determination of thorium(IV), titanium(IV), iron(III), lead(II) and chromium(III) on 2-nitroso-1-naphthol impregnated MCI GEL CHP20P resin

A simple and effective method is presented for the separation and preconcentration of Th(IV), Ti(IV), Fe(III), Pb(II) and Cr(III) by solid phase extraction on 2-nitroso-1-naphthol impregnated MCI GEL CHP20P resin prior to their inductively coupled plasma-mass spectrometric determinations. The influence of analytical parameters including pH of the aqueous solution, flow rates of sample and eluent solutions and sample volume on the quantitative recoveries of analyte ions was investigated. Matrix effects caused by the presence of alkali, earth alkali and some metal ions in the analyzed solutions were investigated. The presented solid phase extraction method was applied to BCR-144R Sewage Sludge (domestic origin), BCR-141R Calcareous Loam Soil, NIST 1568a Rice Flour and NIST 1577b Bovine Liver certified reference materials (CRMs) for the determination of analyte ions and the results were in good agreement with the certified values. The separation procedure presented was also applied to the various natural water samples collected from Turkey with satisfactory results.     

Simultaneous separation and speciation of inorganic As(III)/As(V) and Cr(III)/Cr(VI) in natural waters utilizing capillary microextraction on ordered mesoporous Al2O3 prior to their on-line determination by ICP-MS

In this paper, a system of flow injection (FI) capillary microextraction (CME) on line coupled with inductively plasma mass spectrometry (ICP-MS) was proposed for simultaneous separation and speciation of inorganic As(III)/As(V) and Cr(III)/Cr(VI) in natural waters. Ordered mesoporous Al2O3 coating was prepared by sol-gel technology and used as CME coating material. Various experimental parameters affecting the capillary microextraction of inorganic arsenic and chromium species have been investigated and optimized. Under the optimized conditions, the limits of detection were 0.7 and 18 ng L(-1) for As(V) and Cr(VI), 3.4 and 74 ng L(-1) for As(III) and Cr(III), respectively, with an enrichment factor of 5 and a sampling frequency of 8h(-1). The relative standard deviations (R.S.D.) were 3.1, 4.0, 2.8 and 3.9% (C=1 ng mL(-1), n=7) for As(V), As(III), Cr(VI) and Cr(III), respectively. The proposed method was successfully applied for the analysis of inorganic arsenic and chromium species in mineral water, tap water and lake water with the recovery of 94-105%. In order to verify the accuracy of the method, two certified reference of GSBZ50027-94 and GSBZ50004-88 water samples were analyzed and the results obtained were in good agreement with the certified values. The ordered mesoporous Al2O3 coated capillary showed an excellent solvent and thermal stability and could be re-used for more than 30 times without decreasing extraction efficiency.     

Microstructural evolution of Al–Fe powder mixtures during high-energy ball milling

High-energy ball milling has been performed on FexAl1-x powder mixtures with x=0.75, 0.50, 0.25 and 0.20. X-ray diffraction, Mossbauer spectroscopy and electron microscopy have been used to characterize the samples milled for different times and annealed in a differential scanning calorimeter. It is found that, during milling, there is diffusion of both elements into each other, with a prevalence of iron diffusion into aluminium, at least in the early stages of the process. This behaviour is more pronounced in the aluminium-rich samples. The growth of the Fe(Al) and Al(Fe) solid solutions has been observed for x0.5, different from the lower iron concentrations where the Fe(Al) phase has not been detected. The annealing of pre-milled samples favours the formation, depending on the sample composition and on the annealing temperature, of intermetallic phases such as Fe3Al, FeAl, Fe2Al5 and FeAl3. © 1998 Chapman & Hall     

Immobilized gallium(III) affinity chromatography of phosphopeptides.

A novel procedure for micropurification of phosphorylated peptides, as a front end to mass spectrometric analysis, is described. As a result of a systematic study, we propose the use of an immobilized metal affinity chromatography (IMAC) in a microtip (Erdjument-Bromage, H.; et al. J. Chromatogr., A 1998, 826, 167-181) format, more specifically in combination with Ga(III) ions. Manual Ga-(III) IMAC is easy to perform; phosphopeptides are retrieved in a near-quantitative and highly selective manner, to yield a concentrated sample for direct analysis by matrix-assisted laser desorption/ionization time-of-flight and nanoelectrospray ionization mass spectrometry. Ga-(III) ions offer distinct advantages over the use of other metals, such as Fe(III) and Al(III), in terms of both selectivity and versatility, including facile base elution. Selectivity is best illustrated by effective enrichment of phosphopeptides that were present in a molar ratio of approximately 2% on a background of unphosphorylated protein, a situation very typical perhaps for protein phosphorylation states in the cell. The system was also used to retrieve and tentatively identify five previously uncharacterized phosphopeptides from a tryptic digest of human beta 4 integrin, isolated from cell extracts by immunoprecipitation.     

Synthesis and cytocompatibility of manganese (II) and iron (III) substituted hydroxyapatite nanoparticles

Manganese (II) and iron (III) substituted hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂) nanoparticles were synthesized using wet chemical method. All samples were single-phase, non-stoichiometric and B-type carbonated hydroxyapatite. Compared with pure HA, Mn²⁺ substituted (MnHA) and Fe³⁺ doped HA (FeHA) did not demonstrate significant structure deviation. Since ion exchange mechanism was applied for the synthesis process, the morphology and particle size were not significantly affected: all samples were elongated spheroids of around 70 nm. The presence of Fe and Mn was confirmed by energy dispersive X-ray spectroscopy (EDX) while the concentrations were quantified by inductively coupled plasma (ICP). Fe³⁺ ions were more active than Mn²⁺ ions in replacing Ca²⁺ ions in HA lattice structure. The magnetic property of HA was modified by substitution with Fe. The Fe5 (Fe_added/Ca_added = 5% by molar ratio) was paramagnetic while pure HA was diamagnetic. Results of extraction assay from cells cultured in extracted medium for 72 h suggested that both MnHA and FeHA were non-cytotoxic to osteoblast cells. Meanwhile, the presence of Fe³⁺ ions in HA demonstrated significant positive effect on osteoblast cells, where the cell number on Fe5 pellets was twice that of pure HA and MnHA samples.     

Tris(2-aminoethyl) amine functionalized silica gel for solid-phase extraction and preconcentration of Cr(III), Cd(II) and Pb(II) from waters

A new tris(2-aminoethyl) amine (TREN) functionalized silica gel (SG-TREN) was prepared and investigated for selective solid-phase extraction (SPE) of trace Cr(III), Cd(II) and Pb(II) prior to its determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). Identification of the surface modification was characterized and performed on the basis of FT-IR. The separation/preconcentration conditions of analytes were investigated, including effects of pH, the shaking time, the sample flow rate and volume, the elution condition and the interfering ions. At pH 4, the maximum adsorption capacity of Cr(III), Cd(II) and Pb(II) onto the SG-TREN were 32.72, 36.42 and 64.61 mg g(-1), respectively. The adsorbed metal ions were quantitatively eluted by 5 mL of 0.1 mol L(-1) HCl. Common coexisting ions did not interfere with the separation. According to the definition of International Union of Pure and Applied Chemistry, the detection limits (3sigma) of this method for Cr(III), Cd(II) and Pb(II) were 0.61, 0.14 and 0.55 ng mL(-1), respectively. The relative standard deviation under optimum conditions is less than 4.0% (n=11). The application of this modified silica gel to preconcentration trace Cr(III), Cd(II) and Pb(II) of two water samples gave high accurate and precise results.     

Speciation and determination of ultra trace amounts of chromium by solidified floating organic drop microextraction (SFODME) and graphite furnace atomic absorption spectrometry

Solidified floating organic drop microextraction (SFODME) method in combination with graphite furnace atomic absorption spectrometry (GFAAS) has been used for the determination of chromium species in water and urine samples. 1-undecanol containing 2-thenoyltrifluoroacetone (TTA) was used as a selective chelating agent for the extraction of Cr(III). The total Cr was determined after the reduction of Cr(VI) to Cr(III) with hydroxylamine. The concentration of Cr(VI) was determined from the difference between the concentration of total chromium and the Cr(III). Several variables such as the sample pH, concentration of TTA, salt concentration, extraction time and the sample volume were investigated in detail. Under the optimum conditions, the limit of detection of the proposed method was 0.006 μg l(-1) for Cr(III) and the relative standard deviation for six replicate determinations at 0.1 μg l(-1) Cr(III) was 5.1%. The proposed method was successfully applied for the determination of chromium species in tap water, well water, mineral water, and urine samples.     

Spectrophotometric determination of aluminium and indium with 2,2',3,4-tetrahydroxy-3',5'-disulphoazobenzene

2,2',3,4-Tetrahydroxy-3',5'-disulphoazobenzene (tetrahydroxyazon 2S) has been synthesized for the first time. This reagent has been used for the spectrophotometric determination of aluminium and indium ions. The method is very sensitive and selective for the direct determination of aluminium and indium. The optimum pH and absorbance of complexes formed of tetrahydroxyazon 2S with aluminium and indium are 5; 500 nm and 495 nm for Al and In, respectively. The system obeys Beer's law at 0.05-1.6 microg mL(-1) of aluminium and 0.06-2.1 microg mL(-1) of indium concentration. The molar absorptivity is 6.42 x 10(4)L mol(-1)cm(-1) for aluminium and 7.70 x 10(4)L mol(-1)cm(-1) for indium. The molar compositions of the complexes are 1:1 at optimum conditions. Alkaline and alkaline earth elements, halogens, thiourea, ascorbic acid, Cd(II), Pb(II), Mn(II), Zn(II), Co(II), Ni(II), Cr(III), Bi(III), La(III), Si(IV) do not interfere this method. The method can be applied to the direct spectrophotometric determination of trace amounts of aluminium in steel, alloys, waste water, river waters, spring water and ground water. The method was also successfully applied to the indium determination in artificial mixture.     

Preparation, characterization and photoelectrochemical behaviors of Fe(III)-doped TiO2 nanoparticles

Fe(III)-doped TiO₂ nanoparticles with different Fe(III) content (at %, nominal) have been prepared at different pH using hydrothermal method. The products were characterized by X-ray powder diffraction, transmission electron microscope, electron diffraction, diffuse reflectance spectra, XPS and spot EDX analysis. All the studies showed that anatase, brookite and trace of hematite coexisted at lower pH (1.8 and 3.6) when Fe(III) content was as low as 0.5% and the distribution of iron ions was non-uniform between particles. But at higher pH (6.0), the uniform solid solution of iron-titanium oxide formed. The photoelectrochemical properties were studied by measuring photocurrent at different electrode potentials and the results showed the phenomena of p-n photoresponse existence in samples prepared at pH 1.8–6.0.     

Separation of beryllium (II) and aluminium (III) by solvent extraction using Bis-2 ethylhexyl phosphoric acid [HDEHP]

A simple and rapid method for the extraction is described for the separation of beryllium (II) and aluminium (111) from aqueous sulphate solution with Bis-2 ethylhexyl phosphoric acid (HDEHP) in toluene. A systematic study of the solvent extraction of chemically similar elements, beryllium (II) and aluminium (III) was carried out separately and it has been observed that under certain specific conditions beryllium (II) and aluminium (III) can be separated in a short period from their mixture using HDEHP as an extractant.     

Adsorption and aggregation of Fe(III)-hydroxy complexes during the photodegradation of phenol using the iron-added-TiO(2) combined system

The behavior of Fe(III) aquacomplexes in TiO(2) suspensions in the degradation of phenol has been investigated. The most active Fe(OH)(2+) species adsorbed on the surface of TiO(2) retards the conversion of Fe(OH)(2+) into oligomers and therefore increases the percentage of Fe(OH)(2+) with irradiation time, with a consequent enhancement in the catalytic cycle of Fe(III)/Fe(II) and excited charge traps by Fe(III) in the iron-TiO(2) system. The influence of iron addition on TiO(2) was obtained when the regeneration of [Fe(OH)(2+)] remained continuous with irradiation time. In an optimum TiO(2) suspension (0.5g/L) with the addition of 0.1mM Fe(III), the measured k(obs) values for phenol degradation were enhanced for the higher adsorption of Fe(OH)(2+) on the reactive surface of TiO(2) at a specified irradiation time.     

Heterogeneous photo-Fenton degradation of polyacrylamide in aqueous solution over Fe(III)-SiO(2) catalyst

This article presents preparation, characterization and evaluation of heterogeneous Fe(III)-SiO(2) catalysts for the photo-Fenton degradation of polyacrylamide (PAM) in aqueous solution. Fe(III)-SiO(2) catalysts are prepared by impregnation method with two iron salts as precursors, namely Fe(NO(3))(3) and FeSO(4), and are characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) methods. The irradiated Fe(III)-SiO(2) is complexed with 1,10-phenanthroline, then is measured by UV-vis-diffuse reflectance spectroscopy (UV-vis-DRS) and XPS to confirm the oxidation state of Fe in solid state. By investigating the photo-Fenton degradation of PAM in aqueous solution, the results indicate that Fe(III)-SiO(2) catalysts exhibit an excellent photocatalytic activity in the degradation of PAM. Moreover, the precursor species and the OH(-)/Fe mole ratio affect the photocatalytic activity of Fe(III)-SiO(2) catalysts to a certain extent. Finally, the amount of Fe ions leaching from the Fe(III)-SiO(2) catalysts is much low.