Iron speciation in natural waters by sequential injection analysis with a hexadentate 3-hydroxy-4-pyridinone chelator as chromogenic agent

Non-transferrin-bound iron determination in blood serum using microsequential injection solid phase spectrometry- proof of concept

Non-transferrin-bound iron (NTBI) is a group of circulating toxic iron forms, which occur in iron overload or health conditions with dysregulation of iron metabolism. NTBI is responsible for increased oxidative stress and tissue iron loading. Despite its relevance as a biochemical marker in several diseases, a standardized assay is still lacking. Several methods were developed to quantify NTBI, but results show high inter-method and even inter-laboratory variability. Thus, the development of a consistent NTBI assay is a major goal in the management of iron overload and related clinical conditions. In this work, a micro sequential injection lab-on-valve (μSI-LOV) method in a solid phase spectrophotometry (SPS) mode was developed for the quantification of NTBI, using a bidentate 3,4-hydroxypyridinone (3,4-HPO) ligand anchored to sepharose beads as a chromogenic reagent. To attain SPS, the functionalized beads were packed into a column in the flow cell, and the analyte, NTBI retained as iron (III), formed a colored complex at the beads while eliminating the sample matrix. The dynamic concentration range was 1.62-7.16 μmol L^-1 of iron (III), with a limit of detection of 0.49 μmol L^-1 and a limit of quantification of 1.62 μmol L^-1. The proposed μSI-LOV-SPS method is a contribution to the development of an automatic method for the quantification of the NTBI in serum samples.

The determination of zinc using flow injection and continuous flow analysis combined with a polymer inclusion film-coated column: Application to the determination of zinc in alloys and commercial lithium chloride

A column coated with a polymer inclusion film (PIF) containing Aliquat 336 as carrier cast on glass beads packed in a glass tube is described for the separation, preconcentration, and determination of zinc(II) in flow injection analysis (FIA) and continuous flow analysis (CFA) systems. In the FIA method, 200 μL of a sample solution containing 2 mol/L lithium chloride is injected into a 2 mol/L lithium chloride stream. This converts zinc(II) ion into its anionic chlorocomplexes which are then extracted into the Aliquat 336-based PIF by anion exchange. The extracted zinc(II) is then back-extracted into a stream of 1 mol/L sodium nitrate solution and determined spectrophotometrically using 4-(2-pyridylazo)resorcinol as the color reagent. The limit of detection (LOD, S/N = 2) was determined as 0.017 mg/L. The usability of the PIF-based FIA method was demonstrated by the determination of zinc in alloys. The PIF-coated column was also employed successfully in the CFA determination of zinc(II) as an impurity in commercial lithium chloride samples. For this, 2 mol/L commercial lithium chloride solution was passed through the column for a predetermined time period followed by stripping in a stream of 1 mol/L sodium nitrate solution.

Facile liquid colorimetric sensor using high-density deep eutectic solvent for trace detection and speciation of iron in milk

An efficient colorimetric sensor was developed using a high-density deep eutectic solvent (HD-DES) for the trace detection and speciation of iron in various milk samples. A liquid colorimetric probe was fabricated by dissolving ferrozine (FZ) in HD-DES prepared from TBABr and PBA. The prederivatization of Fe²⁺ via complexation with FZ on the HD-DES/FZ probe provided the [Fe(FZ)₃]^4- complex, which led to a color change from pale yellow to purple before it was simultaneously extracted by HD-DES. The Fe³⁺ content was calculated by subtracting the amount of Fe²⁺ from the total Fe content following the reduction of Fe³⁺ to Fe²⁺ by L-ascorbic acid in an acid buffer. Under the optimized conditions, the proposed colorimetric sensor exhibited appreciable linearity in the concentration range of 0.003-0.04 mg L^-1, a low limit of detection (0.95 µg L^-1), high enrichment factor (50), and outstanding repeatability. The liquid colorimetric probe was successfully applied for the determination and speciation of iron in milk samples, and the results were compared with those obtained using the standard atomic absorption spectrometry method. Moreover, quantitative analysis was performed on a smartphone using the Image J application to estimate the color intensity change, which eliminated the requirement of sophisticated scientific instruments.

Simultaneous measurement of aqueous redox-sensitive elements and their species across the soil-water interface

The redox-sensitive elements, such as iron, manganese, sulfur, phosphorus, and arsenic, shift their speciation every millimeter (mm) across the soil-water interface in the flooded soil environments. Monitoring of element speciation at this high-resolution (HR) within the SWI is still difficult. The key challenge lies in obtaining sufficient porewater samples at specific locations along the soil gradient for downstream analysis. Here with an optimized inductively coupled plasma mass spectrometry (ICP-MS) method and a HR porewater sampler, we demonstrate mm-scale element profiles mapping across the SWI in paddy soils. High-concentrations of iron and manganese (> 10 mg/L) were measured by ICP-MS in an extended dynamic range mode to avoid signal overflow. The iron profile along the SWI generated by the ICP-MS method showed no significant difference (p < 0.05) compared to that measured independently using a colorimetric method. Furthermore, four arsenic (arsenite, arsenate, monomethylarsonic and dimethylarsinic acid), two phosphorus (phosphite and phosphate) and two sulfur (sulfide and sulfate) species were separated in 10 min by ion chromatography -ICP-MS with the NH₄HCO₃ mobile phase. We verified the technique using paddy soils collected from the field, and present the mm-scale profiles of iron, manganese, and arsenic, phosphorus, sulfur species (relative standard deviation < 8%). The technique developed in this study will significantly promote the measurement throughput in limited samples (e.g. 100 μL) collected by HR samplers, which would greatly facilitate redox-sensitive elements biogeochemical cycling in saturated soils.

Greener and wide applicability range flow-based spectrophotometric method for iron determination in fresh and marine water

A flow-based method for the spectrophotometric determination of iron in recreational waters, both fresh and marine (variable salinity content), was developed. For that purpose, 3-hydroxy-4-pyrydinone ligand functionalized with an ether function was synthetized and used as chromogenic chelator (1-(3'-methoxypropyl)-2-methyl-3-benzyloxy-4-(1H)pyridinone - MRB13) for iron quantification. This water-soluble reagent was previously reported as a greener alternative to quantify iron, due to its low toxicity and a more environmental friendly synthesis. Furthermore, it also displayed a high affinity and specificity for iron. With the main objective of quantifying iron in a variety of water types (different matrices and iron content), two strategies were developed, one of them including on-line solid-phase extraction (SPE), and the other without resorting to a SPE process. Water matrix clean-up and iron enrichment was achieved using a nitrilotriacetic acid resin column. The potential interference of metal ions usually present in water samples was assessed and no significant interference (<10%) was observed. The limits of detection were 11 and 2.9 μg L^-1 without and with SPE, respectively. For one determination (three replicates), the corresponding consumption of MRB13 is 90 μg, sodium hydroxide is 1.4 mg, and boric acid is 5.6 mg. The method was applied to certified water samples and the results were in agreement with certified values. The developed method was also applied to fresh and marine water, and recovery ratios of 103 ± 4 and 101 ± 7 without and with SPE, respectively, were achieved.

Use of an ether-derived 3-hydroxy-4-pyridinone chelator as a new chromogenic reagent in the development of a microfluidic paper-based analytical device for Fe(III) determination in natural waters

This article reports on the development and validation of a disposable microfluidic paper-based analytical device (μPAD) for on-hand, in-situ, and cheap Fe(III) determination in natural waters complying with World Health Organization guidelines. The developed μPAD used 3-hydroxy-4-pyridinone (3,4-HPO) as a colour reagent due to its considerably lower toxicity than traditionally used iron analytical reagents. It was selected among a group of hydrophilic 3,4-HPO chelators containing ether-derived chains in their structure which were prepared using green methods. The relatively high water solubility of these chelators improved the detection limit and applicability as μPAD reagents. Under optimal conditions, the μPAD is characterised by a quantification range between 0.25 and 2.0 mg/L, a detection limit of 55 μg/L and 15 min of analysis time. The signal stability extends up to 4 h and the device is stable for at least one month. The reagent consumption is below 0.2 mg per analysis and the μPAD method was validated by analysis certified reference materials and by comparison with atomic absorption results (RD < 10%). The newly developed μPAD was successfully applied to the determination of iron in river, well and tap waters with no need of any prior sample pre-treatment.

Separation and Determination of Fe(III) and Fe(II) in Natural and Waste Waters Using Silica Gel Sequentially Modified with Polyhexamethylene Guanidine and Tiron

Silica gel, sequentially modified with polyhexamethylene guanidine and pyrocatechin-3,5-disulfonic acid (Tiron), was suggested for sorption separation and determination of Fe(III) and Fe(II). It was found that quantitative extraction of Fe(III) and its separation from Fe(II) were attained at pH 2.5-4.0, while quantitative extraction of Fe(II) was observed at pH 6.0-7.5. An intensive signal with g = 4.27, which is characteristic for Fe(III), appeared in EPR spectra of the sorbents after Fe(II) and Fe(III) sorption. During interaction between Fe(II) and Tiron, fixed on the sorbent surface, its oxidation up to Fe(III) occurred. Red-lilac complexes of the composition FeL₃ were formed on the sorbent surface during sorption regardless of initial oxidation level of iron. Diffuse reflectance spectrum of surface complexes exhibited wide band with slightly expressed maxima at 480 and 510 nm. Procedures for separation and photometric determination of Fe(III) and Fe(II) at the joint presence and total Fe content determination as Fe(II) in waste and natural waters was developed. The limit of detection for iron was 0.05 μg per 0.100 g of the sorbent. The calibration graph was linear up to 20.0 μg of Fe per 0.100 g of the sorbent. The RSD in the determination of more than 0.2 μg of Fe was less than 0.06.

Novel approach to two-component speciation analysis. Spectrophotometric flow-based determinations of Fe(II)/Fe(III) and Cr(III)/Cr(VI)

The proposed approach to two-component speciation analysis relies on simultaneous application of two calibration methods to determination of two different forms of an analyte. One form is determined in extrapolative way, whereas the second form is determined in interpolative way, with the use of the same calibration graph, after appropriate chemical treatment, e.g. oxidation or reduction. The applicability of the approach has been verified on the examples of spectrophotometric determinations of Fe(II)/Fe(III) and Cr(VI)/Cr(III) using 1,10-phenanthroline and 1,5-diphenylcarbazide methods, respectively. In the above methods, ascorbic acid and Ce(IV) have been used to reduce Fe(III) to Fe(II) and to oxidize Cr(III) to Cr(VI), respectively. Lab-In-Syringe and SIA systems (for determination of iron and chromium species, respectively) have been applied to make the implementation of the proposed approach more convenient. The approach was verified on the example of determination of the analytes in synthetic and certified reference materials of ground and waste water samples. Using the developed methods, Fe(II)/Fe(III) and Cr(VI)/Cr(III) were determined within the concentration ranges of 0.06-4.0/0.06-3.0 and 0.03-0.5/0.05-7.0mgL^-1, with precision (RSD, %) less than 3.8/2.0 and 2.2/6.0, and accuracy (RE, %) better than 2.9/4.3 and 6.8/5.2, respectively. The detection limits (mgL^-1) are 0.02/0.02 and 0.01/0.02 for determination of both forms of iron and chromium, respectively. The applicability of the approach has been checked by analysis of artesian water (Fe(II)/Fe(III)) and post-production waste samples (Cr(III)/Cr(VI)).