Iron Speciation Analysis Research Articles

Advancements in Portable Voltammetry: A Promising Approach for Iron Speciation Analysis.

Iron, a crucial element in our environment, plays a vital role in numerous natural processes. Understanding the presence and concentration of iron in the environment is very important as it impacts various aspects of our planet's health. The on-site detection and speciation of iron are significant for several reasons. In this context, the present work aims to evaluate the applicability of voltammetry for the on-site determination of iron and its possible speciation using a portable voltammetric analyzer. Voltammetry offers the advantage of convenience and cost-effectiveness. For iron (III) determination, the modification of a glassy carbon electrode (GCE) with an antimony-bismuth film (SbBiFE) using the acetate buffer (pH = 4) as a supporting electrolyte was used. The technique adopted was Square Wave Adsoptive Cathodic Stripping Voltammetry (SW-AdCSV), and we used 1-(2-piridylazo)-2-naphthol (PAN) as the iron (III) ligand. Linearity, repeatability, detection limit, and accuracy were determined using synthetic solutions; then, a Standard Reference Material (SRM) of 1643f Trace Elements in Water (iron content: 93.44 ± 0.78 µg L-1) was used for validation measurements in the real matrix. the accuracy of this technique was found to be excellent since we obtained a recovery of 103.16%. The procedure was finally applied to real samples (tap, lake, and seawater), and the results obtained were compared via Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). The amount of iron found was 207.8 ± 6.6 µg L-1 for tap water using voltammetry and 200.9 ± 1.5 µg L-1 with ICP-OES. For lake water, 171.7 ± 3.8 µg L-1, 169.8 ± 4.1 µg L-1, and 187.5 ± 5.7 µg L-1 were found using voltammetry in the lab both on-site and using ICP-OES, respectively. The results obtained demonstrate the excellent applicability of the proposed on-site voltammetric procedure for the determination of iron and its speciation in water.

Iron species determination by high performance liquid chromatography with plasma based optical emission detectors: HPLC–MIP OES and HPLC–ICP OES

The paper presents an independent application of two hyphenated techniques, wherein an identical chromatographic system i.e. high performance liquid chromatography (HPLC) was coupled to microwave induced plasma optical emission spectrometry (MIP OES) or inductively coupled plasma optical emission spectrometry (ICP OES). A cation–exchange column and a mobile phase based on pyridine–2,6–dicarboxylic acid (PDCA) were employed to separate Fe(II) and Fe(III) within 300 s. Additionally, two methods of sample preparation were employed. Optimization and validation of both methods were conducted parallel. The applicability was presented with different sample matrix types: post–glacial sediments, archaeological pottery, soils located in the proximity of industry wastes disposal site, river sediments and yerba mate (Ilex paraguariensis). Obtained results were compared in terms of the excitation source (microwave induced or inductively coupled) and supplied gas (nitrogen or argon). The research introduces HPLC–MIP OES for iron speciation analysis and its applicability were critically evaluated with HPLC–ICP OES.

Novel ionic reverse mixed micelle supramolecules in dispersive liquid-liquid microextraction for the successive/individual sensitive speciation analysis of iron in natural water by UV–Vis spectrophotometry

A sensitive UV–Vis spectrophotometry based procedure is delineated for ultra-trace speciation analysis of iron in natural waters. This study prepares and utilizes new ionic reverse mixed-micelles (i-RMMs) supramolecules for the coacervate microextraction of iron species successively or independently on field. The anionic dioctylsulfosuccinate-capric acid (DOSS-CA) and cationic Aliquat-336-capric acid (Aliquat-336-CA) RMMs are used as dispersing, ion-pairing and extractant, respectively for Fe(II) and Fe(III). In successive speciation, Fe(II) forms colourless Fe(II)-(phen)32+ at ng mL−1 level in weak acidic medium that reacts with anionic head groups of RMM and configurates as Fe(II)-(phen)32+-(DOSS-CA)2 ion-pair in inner hydrophilic core. This coloured ion-pair settles on the top as coacervate and leaves unreacted Fe(III) in bulk aqueous solution, which is extracted in the similar way as Fe(III)-(SCN)63−-(Aliquat-336-CA)3 ion-pair in strong acidic medium. The above strategy can be applied individually to Fe(III)/Fe(II). The iron species stabilized in coacervates are transported to laboratory for UV–Vis spectrophotometry detection. The pre-concentration and detection limits are 16 and 28; and 0.1 and 0.4 ng mL−1, respectively for Fe(II) and Fe(III). The recoveries are between 92 and 100% for both Fe(II) and Fe(III) at 100 ng mL−1. The accuracy is established by correlating the summation of discrete species concentration obtained with certified total iron of NIST CRMs 1643e and 1643f trace elements in water. This field oriented speciation is applied to real natural waters.

Total metal content and chemical speciation analysis of iron, copper, zinc and iodine in human breast milk using high-performance liquid chromatography separation and inductively coupled plasma mass spectrometry detection

The aim of this research was to quantify essential trace elements (iron, copper, zinc and iodine) and establish their speciation in human milk. Both the element and the species are important in new-born nutrition. Colostrum, and transitional and mature milks (25) were collected from 18 mothers of pre-term or full-term infants. Concentrations of the target elements were determined using ICP-MS. For speciation, HPLC coupled to ICP-MS was employed. Total contents of the micronutrients varied in mothers of pre-term (Fe = 0.997, Cu = 0.506, Zn = 4.15 and I = 0.458 mg L−1) and mothers of full-term (Fe = 0.733, Cu = 0.234, Zn = 2.91 and I = 0.255 mg L−1) infants. Fe, Cu and Zn were associated with biomolecules with high molecular mass compounds, such as immunoglobulins, albumin and lactoferrin whilst iodine was only found as iodide.

Fast iron speciation in seawater by catalytic Competitive Ligand Equilibration-Cathodic Stripping Voltammetry with tenfold sample size reduction

Iron speciation analysis in seawater is a fundamental step to understand the cycling of this element in oceanic waters, in view of its central role in regulating primary productivity and its connection to global planetary cycles. At present, analytical procedures are the bottleneck for speciation analysis, in term of both time and sample size requirement. Here we present a novel instrumental configuration for the speciation analysis of iron by the Competitive Ligand Equilibration - Cathodic Stripping Voltammetry (CLE-CSV) procedure. The new system features a 1 mL microcell and a silver wire pseudoreference enabling a tenfold reduction of the sample volume. 2,3-dihydroxynaphthalene was used as the complexing ligand and atmospheric oxygen as the catalytic enhancer because they ensured the best analytical performances in terms of detection capabilities. The side reaction coefficient for the FeDHN complex αFe’DHN was calibrated against EDTA and an average value of 9.25 for logK’Fe’DHN was calculated. The method was successfully validated in UV digested seawater using diethylenetriaminepentaacetic acid (DTPA), which has known stability constant for iron. The method was lastly applied to six samples from the Ross Sea water column (Antarctica), demonstrating its fit for purpose for the detection of trace amounts of iron ligands in seawater. Thanks to the employed instrumental configuration and the high sensitivity, the proposed method achieved a tenfold reduction in sample size, a tenfold increase in sensitivity compared with other methods employing DHN and halved the analysis time with respect to the fastest method reported in the literature. Half an hour is enough to measure a 12 point titration, making the analysis of at least three titrations per day feasible. It is expected that the application of this procedure will foster the sample throughput, thanks to the reduced analysis time, and make possible the analysis of limitedly available and challenging samples, like porewater and vent fluids via the tenfold reduction in sample size.

Evidence for the development of local anoxia during the Cambrian SPICE event in eastern North America.

The later Cambrian Steptoean Positive Carbon Isotope Excursion (SPICE) event was an episode marked by pronounced changes to the global biogeochemical cycles of carbon and sulfur and significant extinctions on several paleocontinents including Laurentia (North America). While the exact cause(s) of these events remains debated, various lines of evidence suggest an increase in the areal extent of anoxia at the seafloor was a likely feature. Here, we explore whether changes in local oxygenation accompanied the onset of the SPICE in southern Laurentia using cores of the Nolichucky and Eau Claire Formations from Ohio and Kentucky, USA, that represent a transect into the Rome Trough/Conasauga intrashelf basin. At our study locations, the initial positive δ13 C shift of the SPICE occurs in conjunction with increases in the abundance and δ34 S of sedimentary pyrite. Further local redox conditions, tracked using iron speciation analysis, indicate anoxic conditions developed at the two proximal locations after the start of the paired isotopic excursions. However, the location near the basin center shows no indication for anoxia before or during the onset of the SPICE. While this signal may reflect the structure of local redox conditions within the basin, with the development of anoxia limited to the basin margins, we argue that authigenic iron enrichments were muted by sedimentary dilution and/or the enhanced authigenesis of iron-bearing sheet silicates near the basin center, masking the signal for anoxia there. Regardless of the areal extent of anoxia within the basin, in either scenario the timing of the development of anoxic bottom waters was concurrent with local faunal turnover, features broadly consistent with a global expansion of anoxia playing a role in driving the isotopic trends and extinctions observed during the event.

Speciation analysis based on digital image colorimetry: Iron (II/III) in white wine

This work proposes an analytical strategy utilizing digital images (DI) for the iron inorganic speciation in white wine. The method was established by the reaction of iron(II) ions with 1,2 ortho-phenanthroline as a chromogenic reagent. Total iron was determined using the same reagent after the addition of hydroxyl ammonium chloride as a reducing agent. In both cases, digital images of the standards/chromogenic reagent and samples were acquired and stored in JPEG format. The region of interest (ROI) was determined with a constant square shape for all images. The ROI was submitted to decomposition in color values according to the RGB additive color model. However, the data obtained by the blue channel was the one used in the construction of the analytical curves because it presented the highest sensitivity. The optimization of the experimental conditions of the procedure was performed by employing multivariate techniques. The precision was evaluated using a wine sample with iron (II) and total iron contents of 0.41 and 0.69 mg L−1, respectively. The results expressed as relative standard deviations were 3.57% for iron (II) and 4.76% for total iron contents. A comparison between the results obtained for total iron by the DI method with the results found using flame atomic absorption spectrometry confirmed the method accuracy. The DI procedure was applied for speciation analysis in six white wine samples and the contents found varied from 0.41 to 1.67 mg L−1 for iron (II) and from 0.69 to 1.71 mg L−1 for total iron. These results are in agreement with those found for speciation analysis of iron in wine samples. Iron (III) contents can be found by the difference between the total iron and iron (II) contents.

Speciation Analysis of Iron in Long Distance Transported Aerosols in Wet Deposition Collected from Remote Mountain Area Using a Laboratory X-ray Absorption Spectrometer

Speciation Analysis of Iron in Long Distance Transported Aerosols in Wet Deposition Collected from Remote Mountain Area Using a Laboratory X-ray Absorption Spectrometer

Activation of Persulfate by Nanosized Zero-Valent Iron (NZVI): Mechanisms and Transformation Products of NZVI.

The mechanisms involved in the activation of persulfate by nanosized zero-valent iron (NZVI) were elucidated and the NZVI transformation products identified. Two distinct reaction stages, in terms of the kinetics and radical formation mechanism, were found when phenol was oxidized by the persulfate/NZVI system. In the initial stage, lasting 10 min, Fe0(s) was consumed rapidly and sulfate radicals were produced through activation by aqueous Fe2+. The second stage was governed by Fe catalyzed activation in the presence of aqueous Fe3+ and iron (oxyhydr)oxides in the NZVI shells. The second stage was 3 orders of magnitude slower than the initial stage. An electron balance showed that the sulfate radical yield per mole of persulfate was more than two times higher in the persulfate/NZVI system than in the persulfate/Fe2+ system. Radicals were believed to be produced more efficiently in the persulfate/NZVI system because aqueous Fe2+ was supplied slowly, preventing sulfate radicals being scavenged by excess aqueous Fe2+. In the second stage, the multilayered shell conducted electrons, and magnetite in the shell provided electrons for the activation of persulfate. Iron speciation analysis (including X-ray absorption spectroscopy) results indicated that a shrinking core/growing shell model explained NZVI transformation during the persulfate/NZVI process.

Iron detection and speciation in natural waters by electrochemical techniques: A critical review

Summary Developments in iron detection and speciation in natural waters by electrochemical methods are reviewed considering latest, post 2010, evolutions. Voltammetric and potentiometric methods have been employed to detect iron and iron species in natural waters, potentiometric methods being devoted to redox speciation only. Regarding iron detection by voltammetry on the mercury electrode, several improvements have been introduced since 2014, leading to a very low detection limit (LOD, 5 pM), reduced analysis time, elimination of the UV pretreatment and a 20-fold reduction in sample size. Chemically modified, mercury free, electrodes have started to be introduced. Among bulk electrodes, bismuth and bismuth alloy offer the best performances in term of detection limit (0.2 nM). Gold or gold nanoparticle electrodes modified with self-assembled monolayers of different thiols are the most promising among chemically modified electrodes: thiols bear an iron complexing moiety that efficiently preconcentrate iron onto the electrode surface with a claimed LOD of 30 pM. Regarding iron speciation analysis, no substantial advances have been recently achieved. Several ionophores were synthesised and tested in potentiometric electrodes for iron redox speciation (for the detection of both Fe(III) and Fe(II) species), but their use is limited to acidic solutions due to sensitivity limitations. Finally, the voltammetric detection of iron complexation by competitive ligand—cathodic stripping voltammetry has made limited methodological progresses since its introduction in 1994, although improved data treatment procedures have been conveniently implemented.

Identification, separation and component analysis of reddish brown and non-reddish brown iron plaque on rice (Oryza sativa) root surface

Iron plaque (IP) on rice (Oryza sativa) root surface consists of reddish brown IP (RIP) and non-reddish brown IP (NRIP), however, their extraction and characterization need further studies. A reliable method combining chemical and X-ray diffraction (XRD) analysis was introduced to discriminate RIP and NRIP on root surface of rice plants subjected to different phosphate (P) treatments. RIP appeared only on P-deficient rice root surface, and NRIP occurred on both P-deficient and P-sufficient rice root surface. Both RIP and NRIP could be extracted by dithionite-citrate-bicarbonate while only NRIP could be extracted by 0.1 M tetrasodium pyrophosphate (Na4P2O7) specifically. NRIP on P-sufficient root surface was 2.42 times of that on P-deficient plants. Iron speciation analysis showed that the total, amorphous and crystalline iron on P-deficient root surface were 1.47-, 1.50- and 1.35-times of those of P-sufficient plants, respectively. XRD analysis further confirmed that IP on both P-sufficient and P-deficient root surface presented as amorphous features. Dominant minerals of NRIP were iron phosphates, while those of RIP were ferric (hydr)oxides. The specific removal effect of 0.1 M Na4P2O7 for NRIP was also verified by XRD. In this study, phosphate levels in nutrient solution significantly influence the formation of RIP and NRIP on rice root surface. Main components of RIP and NRIP are ferric (hydr)oxides and iron phosphates, respectively. They can be separated by 0.1 M Na4P2O7.

Double-sided Microfluidic Device for Speciation Analysis of Iron in Water Samples: Towards Greener Analytical Chemistry.

Microfluidics minimize the amounts of reagents and generate less waste. While microdevices are commonly single-sided, producing a substrate with microchannels on multiple surfaces would increase their usefulness. Herein, a polymethymethacrylate substrate incorporating microchannel structures on two sides was sandwiched between two polydimethylsiloxane sheets to create a multi-analysis device, which was used for the spectrophotometric analysis of the ferrous ion (Fe(2+)) and the ferric ion (Fe(3+)), by utilizing colorimetric detection. To monitor the signals from both channel networks, dual optical sensors were integrated into the system. The linear ranges for Fe(2+) and Fe(3+) analyses were 0.1 - 20 mg L(-1) (R(2) = 0.9988) and 1.0 - 40 mg L(-1) (R(2) = 0.9974), respectively. The detection limits for Fe(2+) and Fe(3+) were 0.1 and 0.5 mg L(-1), respectively. The percent recoveries of Fe(2+) and Fe(3+) were 93.5 - 104.3 with an RSD < 8%. The microdevice demonstrated capabilities for simultaneous analysis, low waste generation (7.2 mL h(-1)), and high sample throughput (180 h(-1)), making it ideal for greener analytical chemistry applications.

Method development for the redox speciation analysis of iron by ion chromatography–inductively coupled plasma mass spectrometry and carryover assessment using isotopically labeled analyte analogues

An ion chromatography–inductively coupled plasma mass spectrometry (IC-ICP-MS) method was developed for the redox speciation analysis of iron (Fe) based on in-column complexation of Fe2+ and Fe3+ by dipicolinic acid (DPA). The effects of column type, mobile phase composition and molecular ion interference were studied in the method optimization. The carryover of the target species in the IC-ICP-MS method was uniquely and effectively evaluated using isotopically enriched analogues of the analytes (54Fe2+ and 57Fe3+). Standard solutions of the enriched standards were injected into the system following analysis of a sample, and the ratios of the isotopes of iron in the enriched standards were calculated based on the chromatographic peak areas. The concentrations of the analytes carried over from the sample to the enriched standards were determined using the quantitative relationship in isotope dilution mass spectrometry (IDMS). In contrast to the routine way of evaluating carryover effect by injecting a blank solution after sample analysis, the use of isotopically enriched standards identified significant analyte carryover in the present method. Extensive experiments were carried out to systematically identify the source of the carryover and to eliminate the problem; the separation column was found to be the exclusive source. More than 95% of the analyte carryover was eliminated by reducing the length of the column. The detection limit of the IC-ICP-MS method (MDL) for the iron species was 2ngg-1. The method was used to determine Fe2+ and Fe3+ in synthetic aqueous standard solutions and a beverage sample.

Evidence from iron speciation analysis for redox stratification of the Archean ocean 2.7 billion years ago

Evidence from iron speciation analysis for redox stratification of the Archean ocean 2.7 billion years ago

Iron speciation in coal fly ashes—chemical and Mössbauer analysis

Iron speciation analysis of fly coal ashes was performed using transmision Mossbauer spectrometry as well as chemical methods. The investigated samples of ashes came from stoker-fired boiler and pulverized-fuel boiler (of significantly higher combustion temperature). The Mossbauer spectra show noticeable differences in iron-bearing phases content. In the first case aluminosilicate glass dominates, whereas in the second one—a spinel-type phase.

Trace-element and multi-isotope geochemistry of Late-Archean black shales in the Carajás iron-ore district, Brazil

The 250–300-m-thick Carajás Formation in the Carajás mineral province, northern Brazil, consists of banded iron formation (including giant high-grade iron-ore deposits) and minor black shale, overlying a thick pile (2–3km) of about 2.75-Ga-old metabasalt. Carbonaceous shale with pyrite- and locally pyrrhotite-rich patches from drillcore of the Serra Sul exploration project has up to 29ppm Mo; iron-speciation analysis indicates essentially ferruginous and for some samples likely euxinic depositional conditions. Positive δ34S-isotope ratios of TRIS are between +0.3 to +10.7‰, with heavy data restricted to pyrrhotite-free samples. The data suggest microbial sulfate reduction under, at least partially, sulfate-limiting conditions with later overprint by migrating solutions. The black shale is affected by pronounced low-temperature potassium metasomatism (K2O/Na2O>100; up to 10wt.% K2O as adularia) related to diagenetic processes at <100°C, and low-grade metamorphic overprint. We studied a 20-cm-black-shale drillcore interval from the middle part of the Serra Sul BIF sequence in detail. Five samples with the most euxinic signature give a Re–Os regression of 2710±38Ma (2σ) with an initial ratio of −0.37±0.40 (MSWD=3.3), whereas the full data set (n=11), including black-shale samples from the top and bottom of the BIF sequence, gives a regression of 2661±110Ma (MSWD=121). Molybdenum-isotope patterns suggest mixing between a clastic end member, with about 0.2‰ δ98/95Mo for continental input (TDM of 2.8–3.1Ga according to Nd-isotope data), and 0.9‰ δ98/95Mo for a hydrogenous component. Black-shale samples from the bottom of the BIF sequence have heavy Mo-isotope composition of up to 1.8‰ δ98/95Mo. The significant Mo-isotope fractionation is either the result of an early and transient “whiff of oxygen” at 2.7Ga, or the result of hydrothermal fluid overprint.

1,10-Phenanthroline Modulated Redox Potentials Explored for Benign Iron Speciation Analysis

The objective of this study is to develop a simple, environmentally benign alternate analytical method for simultaneous estimation of iron oxidation states. This proposed method of iron speciation is based on 1,10-phenanthroline (phen) modified redox potential of transition metal ions. In a pre-step ex- cess cerium(IV) oxidizes iron(II) in sample to iron(III). Initial back titration of un-reacted cerium(IV) with cobalt(II) in presence of phen gives amount of iron(II) in sample, reduction of iron(III) with cobalt(II) is then used to estimate total iron as iron(III). The potentiometric titration method has been successfully test- ed for determinations of iron(II) and total iron in synthetic and natural samples and represents a distinc- tively green alternative to other reported protocols of iron speciation analysis. (doi: 10.5562/cca2167)

Determination of Fe2+ and Fe3+ species by FIA-CRC-ICP-MS in Antarctic ice samples

Iron is an element of great interest due to its role in primary production and in oceanic carbon cycle regulation, such that past changes in iron deposition may have influenced oceanic sequestration of atmospheric CO2 on millennial time scales. The behavior of iron in biological and environmental contexts depends strongly on its oxidation state. Solubility in water and the capacity to form complexes are just two important characteristics that are species dependent. Distinguishing between the two iron species, Fe(II) and Fe(III), is necessary to evaluate bioavailability, as Fe(II) is more soluble and therefore more readily available for phytoplankton uptake and growth. Here, we present a novel analytical method for iron speciation analysis using Collision Reaction Cell-Inductively Coupled Plasma-Mass Spectrometry (CRC-ICP-MS) and apply it to ice core samples from Talos Dome, Antarctica. The method detection limit is 0.01 ng g−1. A chelating resin, Ni-NTA Superflow, was used to separate the Fe species. At pH 2 the resin is capable of retaining Fe3+ with no retention of Fe2+. After the initial separation, we oxidized the Fe2+ using H2O2, and determined the Fe2+ concentration as the difference between the two measurements. Our preliminary results demonstrate higher Fe2+ concentrations during glacial periods than during interglacial periods. This elevated concentration of Fe2+ suggests that more iron was available for phytoplankton growth during the Last Glacial Maximum, than would be expected from measurements of proxies such as dust mass or total Fe.

Rapid speciation of iron by on‐line coupling of short column capillary electrophoresis and inductively coupled plasma mass spectrometry with the collision cell technique

A method for rapid speciation analysis of iron was developed by on-line coupling of short column capillary electrophoresis and inductively coupled plasma mass spectrometry. The collision cell technique was used to eliminate argon-based polyatomic interferences and a Micromist nebulizer was employed to increase the nebulization efficiency. Rapid speciation analysis of Fe(II) and Fe(III) was achieved within 1 min by short column capillary electrophoresis in a 14 cm x 50 microm id capillary at 28 kV voltage with a mixture of 15 mmol/L tris(hydroxymethyl)aminomethane + 1 mmol/L 1,10-phenanthroline + 1 mmol/L EDTA (pH 8.6) as running electrolyte. The precisions (RSD, n = 5) of migration time and peak area for Fe(II) and Fe(III) were in the range of 1.0 - 2.6 and 1.9 - 3.9%, respectively. The limits of detection (3sigma) of Fe(II) and Fe(III) were 10.0 and 8.3 microg/L, 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 (3 s 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.