Arsenite Anions Research Articles

Selective Chromogenic Chemosensors for Arsenite Anion: A Facile Approach to Analyzing Arsenite in Honey, Milk, and Water Samples.

In this study, two chemosensors, N5R1 and N5R2, based on 5-(4-nitrophenyl)-2-furaldehyde, with varying electron-withdrawing groups, were synthesized and effectively employed for the colorimetric selective detection of arsenite anions in a DMSO/H2O solvent mixture (8 : 2, v/v). Chemosensors N5R1 and N5R2 exhibited a distinct color change upon binding with arsenite, accompanied by a spectral shift toward the near-infrared region (Δλmax exceeding 200 nm). These chemosensors established stability between a pH range 6-12. Among them, N5R2 displayed the lowest detection limit of 17.63 ppb with a high binding constant of 2.6163×105 M-1 for arsenite. The binding mechanism involved initial hydrogen bonding between the NH binding site and the arsenite anion, followed by deprotonation and an intramolecular charge transfer (ICT) mechanism. The mechanism was confirmed through UV and 1H NMR titrations, cyclic voltammetric studies, and theoretical calculations. The interactions between the sensor and arsenite anions were further analyzed using global reactivity parameters (GRPs). Practical applications were demonstrated through the utilization of test strips and molecular logic gates. Real water samples, honey, and milk samples were successfully analyzed by both chemosensors for the sensing of arsenite.

Selective chromogenic nanomolar level sensing of arsenite anions in food samples using dual binding site probes

In the present study, two chromogenic probes, N7R2 and N7R3, each containing two binding sites, were designed and synthesized for the selective detection of arsenite in DMSO/H2O (1:1, v/v). The probes exhibited stability across a pH range spanning from 5 to 12. The lower detection limits of 2.01 ppb (18.86 nM) for N7R2 and 1.79 ppb (16.75 nM) for N7R3, which are much lower than the WHO recommended permissible limit of arsenite, confirmed the superior efficiency of the probes in detecting arsenite. The detection mechanism for arsenite was proposed through UV and 1H NMR titrations, electrochemical studies, and DFT calculations. Practical applications were demonstrated through the fabrication of test strips and molecular logic gates. The probes efficiently recognized arsenite in real water, honey, milk samples, and fruit/vegetable juices. Both N7R2 and N7R3 exhibited excellent recovery rates in the analysis of food samples, demonstrating the probes' usefulness in real sample analysis.

Colorimetric sensors for discriminatory detection of arsenite ions: Application in milk, honey and water samples and molecular logic gates

Millions of people are exposed to dangerous arsenic levels in drinking water, highlighting the urgent need for affordable, continuous on-site arsenic monitoring methods. It is crucial to specifically detect arsenite among inorganic arsenic anions because it is more poisonous than arsenate. Addressing these concerns, the present study developed 5-(4-nitrophenyl)-2-furaldehyde based two colorimetric chemosensors, N5R3 and N5R4, with different signaling groups for the selective detection of arsenite anions over arsenate in DMSO/H2O (6:4, v/v). The red-shift in the UV–Vis absorption spectra supported the distinct color changes of sensors N5R3 and N5R4 displayed upon binding with arsenite. Sensors demonstrated stability over a pH range of 6 to 12 and exhibited stability over a considerable time period. Among the chemosensors, N5R3 exhibited the lowest detection limit of 7.41 ppb with a high binding constant of 2.9976 × 106 M−1 for arsenite. The 1:1 binding interactions between the chemosensors and arsenite were confirmed using B-H plot and Job’s plot analysis. The intramolecular charge transfer (ICT) mechanism for detecting arsenite was proposed through UV and 1H NMR titrations, electrochemical studies, mass spectral analysis and DFT calculations. The interactions between the sensor and arsenite anions were further analyzed using global reactivity parameters (GRPs). Practical applications were demonstrated through the utilization of test strips and molecular logic gates. Both chemosensors efficiently recognized arsenite in real water, honey, and milk samples.

Colorimetric chemosensors for the selective detection of arsenite over arsenate anions in aqueous medium: Application in environmental water samples and DFT studies

Novel organic receptors N3R1- N3R3 were developed for the selective colorimetric recognition of arsenite ions in the organo-aqueous media. In the 50% aq. acetonitrile media and 70% aq. DMSO media, receptors N3R2 and N3R3 showed specific sensitivity and selectivity towards arsenite anions over arsenate anions. Receptor N3R1 showed discriminating recognition of arsenite in the 40% aq. DMSO medium. All three receptors formed a 1:1 complex with arsenite and stable for a pH range of 6–12. The receptors N3R2 and N3R3 achieved a detection limit of 0.008 ppm (8 ppb) and 0.0246 ppm, respectively, for arsenite. Initial hydrogen bonding on binding with the arsenite followed by the deprotonation mechanism was well supported by the UV–Vis titration, 1H- NMR titration, electrochemical studies, and the DFT studies. Colorimetric test strips were fabricated using N3R1- N3R3 for the on-site detection of arsenite anion. The receptors are also employed for sensing arsenite ions in various environmental water samples with high accuracy.

Chromogenic detection of fluoride, dihydrogen phosphate, and arsenite anions based on 2,4-dinitrophenyl hydrazine receptors: spectral and electrochemical study

ABSTRACT The colorimetric recognition of biologically relevant fluoride (F−), acetate (AcO−), and dihydrogen phosphate (H2PO4 −) ions, and poisonous arsenite (AsO2 −) ions, was devised and new receptors for these anions synthesised via the Schiff base condensation procedure. UV–visible titration, fluorescence titration, 1H-NMR titration, and cyclic voltammetry were used to explore the interactions of receptors R1–R3 with anions and possible detection mechanisms. The synthesised probes could sense inorganic fluoride, acetate, dihydrogen phosphate, and arsenite in the organo–aqueous medium (H2O/ Dimethylsulphoxide, 1: 9, v/v) and displayed a change in colour detectable to the naked eye. Out of the three synthesised receptors, receptor R1 showed better sensing ability of fluoride, acetate, dihydrogen phosphate, and arsenite ions in the organo–aqueous medium with a lower detection limit of 0.1 ppm, 0.171 ppm, 0.194 ppm, and 0.144 ppm, respectively. All three receptors formed complexes with the anions through H-bonding interaction followed by deprotonation of the NH proton.

Simultaneous reduction and adsorption of arsenite anions by green synthesis of iron nanoparticles using pomegranate peel extract.

Arsenic is a toxic metalloid that is present in the environment as arsenate and arsenite anions. Exposure to arsenic anions caused skin problems, degenerative diseases, kidney, liver, and lung cancer. The synthesized iron nanoparticles (NPs) were examined as a green low-cost adsorbent for the removal of arsenite anions from aqueous solution via batch adsorption procedure. Iron NPs were prepared in a single step by the reaction of Fe+3 0.01M solution with a fresh aqueous solution of 2% w/v pomegranate peel extract (PPE) as both reducing and capping agents. The physicochemical properties of peel were investigated by some experiments and functional groups were determined by the FT-IR spectrum. The electrochemical behavior of PPE was studied using cyclic voltammetry on a glassy carbon electrode as produced a cathodic peak at range 120-400mV. The progress of nZVI production was monitored by a decrease of 372nm wavelength UV-Vis spectra of PPE. The 27 adsorption experiments were carried out as a function of solution pH, initial arsenite concentration, mass adsorbent, and contact time according to DOE. The rapid rate of adsorption was observed at 20-60min, indicating that the principal mechanism dominating the sorption process was reduction and chemical adsorption. The arsenite removal efficiency was found to be dependent on the solution pH, adsorbent dose, and initial concentration, respectively. The experimental data show the ability of the synthesized iron NPs to remove arsenate from solution in both synthetic and polluted natural water. The thermodynamic study suggested the spontaneous and endothermic nature of adsorption of arsenite by green synthesized iron NPs. The iron NPs synthesized with PPE increased the removal of arsenite with an increase in the active surface, indicating some chemical interactions between the adsorbent and oxoanions.

Arsenic (III) Removal from a High-Concentration Arsenic (III) Solution by Forming Ferric Arsenite on Red Mud Surface

Arsenic (As) is considered one of the most serious inorganic pollutants, and the wastewater produced in some smelters contains a high concentration of arsenic. In this paper, we purified the high-concentration arsenic solution with red mud and Fe3+ synergistically. In this system, arsenite anions reacted with Fe(III) ions to form ferric arsenite, which attached on the surface of red mud particles. The generated red mud/Fe1−x(As)x(OH)3 showed a better sedimentation performance than the pure ferric arsenite, which is beneficial to the separation of arsenic from the solution. The red mud not only served as the carrier, but also as the alkaline agent and adsorbent for arsenic treatment. The effects of red mud dosage, dosing order, pH, and molar ratio of Fe/As on arsenic removal were investigated. The efficiency of arsenic removal increased from a pH of 2 to 6 and reached equilibrium at a pH of 7. At the Fe/As molar ratio of 3, the removal efficiency of arsenic ions with an initial concentration of 500 mg/L reached 98%. In addition, the crystal structure, chemical composition, and morphological properties of red mud and arsenic removal residues (red mud/Fe1−x(As)x(OH)3) were characterized by XRD, XPS, X-ray fluorescence (XRF), SEM-EDS, and Raman spectroscopy to study the mechanism of arsenic removal. The results indicated that most of the arsenic was removed from the solution by forming Fe1−x(As)x(OH)3 precipitates on the red mud surface, while the remaining arsenic was adsorbed by the red mud and ferric hydroxide.

Simple Electrochemical Detection Method Employing a Hydrogel Soft Matrix: Application in Tap Water

The proposed method implies the electrochemical detection of an analyte preloaded in a hydrogel. In order to evaluate the potential application of this method, arsenic detection in tap water was performed. Polymeric hydrogels bearing cationic groups poly(N-isopropyacrylamide)-co-3-(acrylamidopropyl)trimethylammonium chloride were used to sorb arsenic ions, at basic pH, from the real and synthetic stock samples. The concentration of arsenic was electrochemically determined using the loaded hydrogel and a modified glassy carbon electrode. Employing a cationic hydrogel, the peak current for the arsenic oxidation was ca. 8 times higher than the peak current measured using poly(N-isopropyacrylamide), a neutral hydrogel, indicating a strong electrostatic interaction between the polymeric cationic groups and arsenite anions. By using this method, values of arsenic comparable to those measured by Atomic Absorption Spectroscopy were obtained for tap water of small cities in Argentina. These results suggest that this new and easy method is suitable to sense a threshold limit of arsenic in real samples since the features of the hydrogel allow the arsenite loading into the matrix. Besides the cationic hydrogels could be employed to sampling on-field and to build a portable analysis system.

FERROCENYL ALKYLAMMONIUM N-SUBSTITUTED POLYPYRROLE CONTAINING Pt AND Pd AND ITS APPLICATION ON ELECTROANALYSIS OF ARSENITE

Arsenic occurs in a variety of forms and oxidation states and is a very toxic element. The main inorganic arsenic species present in natural waters are arsenate (oxidation state V) and arsenite ions (oxidation state III). Arsenite is more toxic and mobile than arsenate. Therefore, it is important the development of new materials for analysis and control of these toxic species. This research proves that polymer-metal composite electrode materials synthesized by incorporation of Pt0 and Pd0 nanoparticles into a poly(pyrrole-ferrocenyl alkylammonium) matrix present electrocatalytic properties towards the oxidation of arsenite to arsenate. The polymer films displayed a stable electrochemical response in aqueous solution. However, when the polymer film modified electrode were transferred to aqueous solution in presence of arsenite anions, the CV curves for polymer films were deeply modified by the decrease in the electroactivity of the film. It can be concluded that the cationic polymer films present a strong affinity toward arsenite anions. The composite films containing Pt0 or Pd0 showed catalytic activity towards oxidation of As(III) to As(V) due to the presence of metal catalyst particles into the polymer films.

Adsorptive removal of As(III) from aqueous solution by waste litchi pericarps.

The present study investigated the removal of arsenite anions (AsO33-, referred to as As(III)) from aqueous solutions by waste litchi pericarps (LPs). Influential factors such as the adsorbent dose, contact time, solution pH, and initial As(III) concentration were investigated. The optimum conditions for As(III) adsorption by the LPs occurred at a contact time of 60 min, adsorbent dose of 10.0 g/L, solution pH of 5.0, and initial As(III) concentration of 1 mg/L. A Box-Behnken design with three variables (adsorbent dose, contact time, and solution pH) at three different levels was studied to identify the correlations between the influential factors and the As(III) adsorption; the results showed a significant interaction between the adsorbent dosage and pH. Additionally, adsorption isotherms, kinetics, and thermodynamics were investigated to explore the As(III) adsorption mechanism. Adsorption by the LPs conformed to the Langmuir, Redlich-Peterson, and Koble-Corrigan isotherm models, suggesting that the process proceeds via monolayer, homogeneous adsorption. In addition, the As(III) adsorption could be characterized by a pseudo-second-order mechanism, revealing that the rate-limiting step might be chemisorption. The thermodynamic studies showed that As(III) adsorption by the LPs was spontaneous and endothermic, and disorder at the solid-liquid interface increased in the adsorption process.

Condensed [OPr4]10+ and Discrete [AsO3]3–Ψ1-Tetrahedra in Pr5O4Cl[AsO3]2

The oxide chloride arsenite Pr5O4Cl[AsO3]2 was obtained as green crystals as a by-product of the synthesis of PrOTAs oxide arsenides (T = late transition metal), starting from Pr6O11, a transition metal oxide, arsenic, and an NaCl/KCl flux. Pr5O4Cl[AsO3]2 crystallizes with the monoclinic Nd5O4Cl[AsO3]2-type structure, space group C2/m. The structure was refined from single-crystal diffractometer data: a = 12.4943(15), b = 5.6884(13) c = 9.0776(19) Å , β = 116.61(1)°, R(F) = 0.0264, wR(F2) = 0.0509, 542 F2 values, and 52 variables. It is built up from corrugated layers of edge- and corner-sharing [OPr4]10+ tetrahedra, which are connected via chloride anions. The space between the layers is filled by these Cl− and discrete arsenite anions [AsO3]3− with lone pairs pointing towards each other. The network of condensed [OPr4]10+ tetrahedra is compared with the different arrays in the oxide pnictides α-PrOZnP, and in β -PrOZnP. Arsenic lone pair energy bands, main interactions, and the spatial distribution were identified precisely using density functional theory (DFT). Among the three crystallographically different sites for praseodymium, one was found non-magnetic in these calculations.

Adsorption of arsenate and arsenite anions from aqueous medium by using metal(III)-loaded amberlite resins

In this paper, we studied the feasibility of using La(III)-, Ce(III)-, Y(III)-, Fe(III)- and Al(III)-loaded 200CT resin as adsorbents for the removal of As(III and V) from aqueous solution. The effects of the contact time, pH of solution and initial concentration of solution on the removal of As(III and V) were investigated in a batch system in order to explain the adsorption mechanism. The removal of As(III and V) by using metal(III)-loaded 200CT resins are strictly pH-dependent. The reaction mechanism was discussed and followed an ion exchange adsorption mechanism. The kinetics of As(III) adsorption with Y(III)-200CT and As(V) adsorption with Fe(III)-200CT can be described well by the pseudo-first-order and second-order models. The equilibrium adsorption data were fitted by four isotherm models. The fitting results suggested that the Y(III)- and Ce(III)-200CT resins are better adsorbents for the As(III) adsorption and the maximum uptakes are 0.4835 and 0.4592 mol/kg, respectively. And Fe(III)-200CT resin is the best adsorbent for the removal of As(V) with the maximum capacity of 1.450 mol/kg. The coexisting ion influence of PO 4 3− was bigger than SO 4 2− on the removal of As(III and V).

Adsorptive separation of arsenate and arsenite anions from aqueous medium by using orange waste

Cellulose and orange waste were chemically modified by means of phosphorylation. The chemically modified gels were further loaded with iron(III) in order to create a suitable chelating environment for arsenate and arsenite removal. The loading capacity for iron(III) on the gel prepared from orange waste (POW) was 1.21 mmol g −1 compared with 0.96 mmol g −1 for the gel prepared from cellulose (PC). Removal tests of arsenic with the iron(III)-loaded gel were carried out batchwise and by using a column. Arsenite removal was favored under alkaline condition for both PC and POW gels, however, the POW gel showed some removal capability even at neutral pH. On contrary, arsenate removal took place under acidic conditions at pH=2–3 and 2–6 for the PC and POW gels, respectively. Since iron(III) loading is higher on the POW gel than on the PC gel greater arsenic removal has been achieved by the POW gel compared with the PC gel. It can be concluded that the POW gel can be used for the removal and recovery of both arsenite and arsenate from arsenic contaminated wastewater.

Calculation of the UV Absorption Spectra of As(III) Oxo- and Thio- Acids and Anions in Aqueous Solution and of PF3 in the Gas-phase

Changes in the UV spectra of As(OH)3 solutions with variations in pH and temperature have recently been used to determine the temperature dependence of the pKa of the acid. In previous studies I used quantum mechanical techniques to study changes in structure and vibrational spectra as a function of pH for arsenites and thioarsenites. I previously calculated UV spectra for ``molecular'' minerals, like realgar As4S4. Here I use a number of different quantum mechanical methods, both Hartree-Fock and density functional theory based, to calculate the UV spectra for both a related simple well-characterized gas-phase molecule PF3 and for As(OH)3 and As(SH)3 and their conjugate anions and some neutral and anionic oligomers in aqueous solution. For the monomeric species small numbers of water molecules have been explicitly included, in a supermolecule or microsolvation approach. I find that UV absorption energies accurate to a few tenths of an eV can be obtained both for gas- phase PF3 and for neutral arsenious acid in aqueous solution, for which the UV absorption maximum is calculated to occur around 6.5 eV, consistent with experiment. Accurate calculation of the UV energies for arsenite anions in aqueous solution is much more difficult, since basis set size and solvation effects are considerably larger than for the neutral molecules, but fairly reliable results can still be obtained. Deprotonation is found to reduce the lowest calculated UV transition energy by about half an eV. Oligomerization also reduces the lowest calculated UV energy by at least half an eV. Replacement of one or all the –OH groups by –SH groups reduces the lowest calculated UV energies by about 2 eV. UV excitation energies have been calculated for oligomeric species as large as As3E3(EH)3 and As4E6, where E = O, S, and may be useful for identifying such species in solution.

Sorption of arsenate and arsenate anions by iron(III)-poly(hydroxamic acid) complex

Iron(III)-poly(hydroxamic acid) resin complex has been studied for its sorption abilities with respect to arsenate and arsenite anions from an aqueous solution. The complex was found effective in removing the arsenate anion in the pH range of 2.0 to 5.5. The maximum sorption capacity was found to be 1.15 mmol/g. The sorption selectivity showed that arsenate sorption was not affected by chloride, nitrate and sulphate. The resin was tested and found effective for removal of arsenic ions from industrial wastewater samples.

Effects of Intracellular Glutathione on Sensitivity ofEscherichia colito Mercury and Arsenite

The effect of intracellular glutathione on sensitivity to mercuric cations and arsenite anions was studied inEscherichia colimutants that lack glutathione (gshA) with or without an additional mutation affecting the osmotregulant trehalose. The absence of glutathione increased cellular sensitivity to both Hg2+and AsO2−. The double mutant was more sensitive to Hg2+than the single mutant strain. The addition of plasmid resistance determinants of Hg2+and AsO2−showed additivity between chromosomal genes and plasmid genes. Mercury resistance was increased in the plasmid-containing cells but not up to the level of wild-type cells. Plasmid arsenite resistance was not expressed in the gshA mutant ofE. coli.

Ligand exchange sorption of arsenate and arsenite anions by chelating resins in ferric ion form: II. Iminodiacetic chelating resin Chelex 100

Arsenate and arsenite are selectively removed by ligand exchange sorption on iminodiacetic chelating resin Chelex 100 used in ferric ion form, the saturation sorption capacities being 45 and 70 mg As / g wet resin with respect to As(V) and As(III) anions, respectively. The liquid sorption of As(V) anions is maximum at pH ∼ 2 and that of As(III) anions at pH ∼ 10. Monovalent anionic species H 2AsO − 3 are mostly involved in ligand sorption on Chelex (Fe 3+), and on average approximately one and two anionic species of As(V) and As(III), respectively, are coordinated to each resin-bound Fe 3+ ion at saturation. The sorbed anionic species are readily stripped with dilute sodium hydroxide into a concentrated form for recovery. An enrichment of more than 40-fold relative to influent concentration (< 100 ppm As) is obtained in ligand exchange column operation for arsenate, as compared to less than 20-fold enrichment for arsenite. Reactivation of the stripped resin is performed in one step by treatment with a mildly acidic solution of ferric chloride (pH ∼ 2), which reconverts the resin to the chelated-Fe 3+ form. The regenerated ligand exchanger exhibits a higher sorption capacity due to additional ion-exchange sorption on the accumulated ferric hydroxide gel. The ligand sorption capacity of the polymer-chelated Fe 3+ ion is, however, several-fold higher than the anion exchange capacity of the ferric hydroxide gel, with respect to both As(V) and As(III) anions.

Ligand exchange sorption of arsenate and arsenite anions by chelating resins in ferric ion form I. Weak-base chelating resin dow XFS-4195

The weak-base chelating resin Dow XFS-4195 has been used in ferric ion form for removal and recovery of arsenate and arsenite anions from dilute aqueous solutions by ligand-exchange sorption. Arsenate and arsenite anions are effectively sorbed by the ferric-form resin in preference to other common anions at low solution concentrations, the saturation sorption capacities being 46 and 51 mg As/g wet resin for arsenate and arsenite, respectively. However, at low concentrations (< 1 mmol/1) the equilibrium sorption of arsenate is several times higher and the rate of sorption is also an order of magnitude greater than those for arsenite. The sorbed species are readily stripped with dilute sodium hydroxide into a concentrated form for recovery. An enrichment of more than 100-fold relative to the influent concentration (<100 ppm As) is obtained in ligand-exchange column operation for arsenate, as compared to less than 20-fold enrichment for arsenite. Reactivation of the stripped resin is performed in one step by treatment with an acidified solution (pH 0.8) of ferric chloride which reconverts the resin to the chelated-Fe 3+ form. The regenerated ligand exchanger exhibits a higher sorption capacity due to additional ion-exchange sorption by the residual ferric hydroxide gel in the resin pores. The ligand sorption capacity of the polymer-chelated Fe 3+ ion is, however, several-fold higher than the anion exchange capacity of the ferric hydroxide gel, with respect to both arsenate and arsenite anions. In ligand sorption, the useful pH range for arsenate anions is 4–7 with the sorption maximum at pH ⋍ 5 , while arsenite anions are effectively sorbed at pH 8–11, the sorption being maximum at pH ⋍ 10 .