Arsenic speciation in environmental samples by hydride generation and electrothermal atomic absorption spectrometry

Colorimetric differentiation of arsenite and arsenate anions using a bithiophene sensor with two binding sites: DFT studies and application in food and water samples

Chemosensor N7R1 with two acidic binding sites was synthesized, and the ability of the sensor to differentiate arsenite and arsenate in the organo-aqueous medium was evaluated using colorimetric sensing methods. N7R1 distinguished arsenite with a peacock blue color and arsenate with a pale green color in a DMSO/H2O (9 : 1, v/v) solvent mixture. The specific selectivity for arsenite was achieved in DMSO/H2O (7 : 3, v/v). The sensor demonstrated stability over a pH range of 5 to 12. The computed high binding constant of 9.3176 × 1011 M-2 and a lower detection limit of 11.48 ppb for arsenite exposed the chemosensor's higher potential for arsenite detection. The binding mechanism with a 1 : 2 binding process is confirmed using UV-Vis and 1H NMR titrations, electrochemical studies, mass spectral analysis and DFT calculations. Practical applications were demonstrated by utilizing test strips and molecular logic gates. Chemosensor N7R1 successfully detected arsenite in real water samples, as well as honey and milk samples.

Alendronate-Functionalized Graphene Quantum Dots as an Effective Fluorescent Sensing Platform for Arsenic Ion Detection

Alendronate-functionalized graphene quantum dots (ALEN-GQDs) with a quantum yield of 57% were synthesized via a two-step route: preparation of graphene quantum dots (GQDs) by pyrolysis method using citric acid as the carbon source and post functionalization of GQDs via a hydrothermal method with alendronate sodium. After careful characterization of the obtained ALEN-GQDs, they were successfully employed as sensing materials with superior selectivity and sensitivity for the detection of nanomolar levels of arsenic ions (As(III)). According to the mechanistic investigation, arsenic ions can quench the fluorescence intensity of ALEN-GQDs through metal-ligand interaction between the As(III) ions and the surface functional groups of the fluorescent probe. This probe provided a rapid method to monitor As(III) with a wide detection range (44 nM-1.30 µM) and a low detection limit of 13 nM. Finally, to validate the applicability, this novel fluorescent probe was successfully applied for the quantitative determination of As(III) in rice and water samples.

Recent Developments in Colorimetric and Fluorometric Detection Methods of Trivalent Metal Cations (Al3+, Fe3+ and Cr3+) Using Schiff Base Probes: At a Glance

This review basically concerned with the application of different Schiff bases (SB) based fluorimetric (turn-off and turn-on) and colorimetric chemosensors for the detection of heavy metal cations particularly Al(III), Fe(III), and Cr(III) ions. Chemosensors based on Schiff bases have exhibited outstanding performance in the detection of different metal cations due to their facile and in-expensive synthesis, and their excellent coordination ability with almost all metal cations and stabilize them in different oxidation states. Moreover, Schiff bases have also been used as antifungal, anticancer, analgesic, anti-inflammatory, antibacterial, antiviral, antioxidant, and antimalarial etc. The Schiff base also can be used as an intermediate for the formation of various heterocyclic compounds. In this review, we have focused on the research work performed on the development of chemosensors (colorimetric and fluorometric) for rapid detection of trivalent metal cations particularly Al(III), Fe(III), and Cr(III) ions using Schiff base as a ligand during 2020-2022.

Dynamics of land cover changes and condition of soil and surface water quality in a Mining-Altered landscape, Ghana

This study investigated the dynamics of mining effects on land use land cover changes and the chemical and physical characteristics of soil and surface water in the Ahafo mining area in Ghana. Landsat imagery was used to analyze land use-land cover changes (LULC) using a supervised classification technique. Soil samples were collected within 600 m from active mining operations and at depths of up to 75 cm, as well as surface water samples from upstream and downstream of the mine. Atomic Absorption Spectrometry was used to determine the concentration of heavy metals in the soil and water samples. The results demonstrated a significant loss of forest and other vegetation covers, which decreased from 44% to 31% to 8% and 20%, respectively, with corresponding increases in the mining site, mine water, settlement/bare surface, cropland and plantation. Organic matter, organic carbon, exchangeable bases, cation exchange capacity, available phosphorus, and pH were all moderate in the soil surrounding the mine. Except for As (4.027 mg/kg) and Hg (1 mg/kg), all heavy metals found in the soil were within FAO/WHO guidelines. Total Dissolved Solids (TDS) (416.18 mg/L), Total Suspended Solids (55.08 mg/L), Turbidity (54.49 NTU), Ca (84.49 mg/L), Mg (31.97 mg/L), nitrate (10.23 mg/L), and sulphate (606.83 mg/L) in the downstream water were higher than those in the upstream and USEPA/WHO limits for drinking water except for TDS. Because of the geology of the area, there were high concentrations of iron, manganese, and aluminum in the surface water. The results show that mining induced severe land cover changes and impaired surface water and soil quality in the mine's vicinity. The findings have implications for stakeholder education, appropriate community water interventions, and company-community-regulator participatory monitoring to avoid health risk exposure and further water and soil quality and vegetation degradation.

A novel strategy for arsenic removal from acid wastewater via strong reduction processing

Due to the high-acidic arsenic-containing wastewater pollution greatly threatening human health and ecological safety, a simple and efficient method for reducing arsenic was proposed in this paper to solve this problem. By using potassium borohydride (KBH₄) as a reducing agent, the soluble arsenic was converted into the gaseous arsine (AsH₃) or solid arsenic (As⁰) to achieve the purpose of removing arsenic in wastewater. By exploring the reaction kinetics of the arsenic removal process, it was found that the fast reaction stage (0-2 min) conformed to pseudo-first-order kinetics. The removal rate of arsenic increased to over 73% in 0.5 min, and reaction equilibrium was reached after 30 min. Various influence factors including arsenic valence, aeration, addition method, concentrations of reducing agent, and hydrogen ion (H⁺) were investigated. The results showed that As(III) was easier to be removed by reduction than As(V), while adding KBH₄ in multiples and aeration were both favorable to the removal of arsenic. Increased concentration of KBH₄ also enhanced the removal of arsenic. Appropriate H⁺ concentration contributed to the arsenic removal, but excessive H⁺ concentration conversely has an inhibitory effect. The maximum removal rate of arsenic was 95.87%, with the maximum removal capacity of 45.50 mg/g. Based on the XRD and SEM-EDS analysis of residue, amorphous arsenic (As⁰) with a mass ratio of more than 94.52% was generated after the reduction of soluble arsenic. Our study demonstrated that the reaction mechanism of reductive degradation is soluble arsenic with hydrogen radicals (H•) to form arsenic (As⁰) and arsine (AsH₃) (in the molar ratio of 6:1). Although the generated solid arsenic (As⁰) is convenient for the soluble arsenic removal from wastewater, attention must be paid to the formation of AsH₃, and strategies for AsH₃ treatment should be considered.

Laser-induced graphene-based electrochemical biosensors for environmental applications: a perspective

Biosensors are miniaturized devices that provide the advantage of in situ and point-of-care monitoring of analytes of interest. Electrochemical biosensors use the mechanism of oxidation-reduction reactions and measurement of corresponding electron transfer as changes in current, voltage, or other parameters using different electrochemical techniques. The use of electrochemically active materials is critical for the effective functioning of electrochemical biosensors. Laser-induced graphene (LIG) has garnered increasing interest in biosensor development and improvement due to its high electrical conductivity, specific surface area, and simple and scalable fabrication process. The effort of this perspective is to understand the existing classes of analytes and the mechanisms of their detection using LIG-based biosensors. The manuscript has highlighted the potential use of LIG, its modifications, and its use with various receptors for sensing various environmental pollutants. Although the conventional graphene-based sensors effectively detect trace levels for many analytes in different applications, the chemical and energy-intensive fabrication and time-consuming processes make it imperative to explore a low-cost and scalable option such as LIG for biosensors production. The focus of these potential biosensors has been kept on detection analytes of environmental significance such as heavy metals ions, organic and inorganic compounds, fertilizers, pesticides, pathogens, and antibiotics. The use of LIG directly as an electrode, its modifications with nanomaterials and polymers, and its combination with bioreceptors such as aptamers and polymers has been summarized. The strengths, weaknesses, opportunities, and threats analysis has also been done to understand the viability of incorporating LIG-based electrochemical biosensors for environmental applications.

Cell-free arsenic biosensors with applied nanomaterials: critical analysis

Arsenic is a ubiquitously found metalloid in our ecosystem because of natural and anthropogenic activities. People exposed to a higher level of arsenic become susceptible to several disorders, including cancer. According to current statistics, the population chronically exposed to arsenic has surpassed 200 million. Therefore, its detection in our environment is of great importance. There are many analytical techniques for the assessment of arsenic in different kinds of environmental samples. Among these techniques, the biosensor is considered a convenient platform and a widely applied analytical device for rapid qualitative and quantitative analysis in the field of environmental monitoring, food safety, and disease diagnosis. Today, there is a trend of including nanomaterials in sensors and biosensors because it empowers researchers to explore new arsenic detection methods and to enhance their analytical capabilities. In this review article, we summarized the latest developments in arsenic biosensors in particular with emphasis on the works based on cell-free approaches that are protein/enzyme-based, DNA-based, and aptamer-based utilizing various transduction platforms. In the meantime, we compared the capabilities that were related to these cell-free arsenic biosensors. This review article also highlights the development and application of novel nanomaterials for arsenic detection.

Speciation of inorganic arsenic in aqueous samples using a novel hydride generation microfluidic paper-based analytical device (µPAD)

The development of the first microfluidic paper-based analytical device (µPAD) for the speciation of inorganic arsenic in environmental aqueous samples as arsenite (As(III)) and arsenate (As(V)) which implements hydride generation on a paper platform is described. The newly developed µPAD has a 3D configuration and uses Au(III) chloride as the detection reagent. Sodium borohydride is used to generate arsine in the device’s sample zone by reducing As(III) in the presence of hydrochloric acid or both As(III) and As(V) (total inorganic As) in the presence of sulfuric acid. Arsine then diffuses across a hydrophobic porous polytetrafluoroethylene membrane into the device’s detection zone where it reduces Au(III) to Au nanoparticles. This results in a color change which can be related to the concentration of As(III) or total inorganic As (i.e., As(III) and As(V)) concentration. Under optimal conditions, the µPAD is characterized by a limit of detection of 0.43 mg L⁻¹ for total inorganic As (As(III) + As(V)) and 0.41 mg L⁻¹ for As(III) and a linear calibration range in both cases of 1.2–8.0 mg As L⁻¹. The newly developed µPAD-based method was validated by applying it to groundwater and freshwater samples and comparing the results with those obtained by conventional atomic spectrometric techniques.

Fluorescence "Turn-Off" and Colorimetric Sensor for Fe2+, Fe3+, and Cu2+ Ions Based on a 2,5,7-Triarylimidazopyridine Scaffold

Two cyanoimidazopyridine-based sensors (SS1 and SS2) were explored for the colorimetric and fluorometric detection of Fe2+, Fe3+, and Cu2+ ions in the semi-aqueous medium. The "turn-off" fluorescence response of both sensors to these ions was due to the restriction in internal charge transfer. Job's plot and semi-empirical calculations revealed that SS1 and SS2 complexed with Cu2+ ions in a 1:1 ratio and Fe2+/3+ ions in a 2:1 ratio, respectively. The sensors were found to have high binding constant (K a) values and low detection limit values. FMO analysis using the semi-empirical quantum mechanics method revealed the decrease in energy gap after complexation with metal ions. Sensor-coated filter paper strips were prepared and analyzed, where the color changes in the strips could be utilized for the real-time detection of Fe2+, Fe3+, and Cu2+ ions.

L-cysteine functionalized graphene quantum dots for sub-ppb detection of As (III)

Here, we report functionalized graphene quantum dots (GQDs) for the optical detection of arsenic at room temperature. GQDs with the fluorescence of three fundamental colors (red, green, and blue) were synthesized and functionally capped with L-cysteine (L-cys) to impart selectively towards As (III) by exploiting the affinity of L-cys towards arsenite. The optical characterization of GQDs was carried out using UV-vis absorption spectroscopy, Fourier transform infrared spectroscopy, and fluorescence spectrometry, and the structural characterizations were performed using transmission electron microscopy. The fluorescence results showed instantaneous quenching in intensity when the GQDs came in contact with As (III) for all test concentrations over a range from 0.025 to 25 ppb, which covers the permissible limit of arsenic in drinking water. The experimental results suggested excellent sensitivity and selectivity towards As (III).

Applied Analytical Methods for Detecting Heavy Metals in Medicinal Plants

For thousands of years, medicinal plants (MPs) have been one of the main sources of drugs worldwide. However, recently, heavy metal pollution has seriously affected the quality and safety of MPs. Consuming MPs polluted by heavy metals such as Pb, Hg, and Cu significantly threaten the health of consumers. To manage this situation, the levels of heavy metals in MPs must be controlled. In recent years, this field has attracted significant attention, but few researchers have systematically summarized various analytical methods. Therefore, it is necessary to investigate methods that can accurately and effectively detect the amount of heavy metals in MPs. Herein, some important analytical methods used to detect heavy metals in MPs and their applications have been introduced and summarized in detail. These include atomic absorption spectrometry, atomic fluorescence spectrometry, inductively coupled plasma mass spectrometry, inductively coupled plasma atomic emission spectrometry, X-ray fluorescence spectrometry, neutron activation analysis, and anodic stripping voltammetry. The characteristics of these methods were subsequently compared and analyzed. In addition, high-performance liquid chromatography, ultraviolet spectrophotometry, and disposable electrochemical sensors have also been used for heavy metal detection in MPs. To elucidate the systematic and comprehensive information, these methods have also been briefly introduced in this review.

Unique photoluminescence response of MoS2quantum dots over a wide range of As (III) in aqueous media

We report the solvothermal synthesis of MoS₂based quantum dots (QDs) and the performance evaluation of bare QDs for the detection of aqueous As (III) oxidative state at room temperature and neutral pH over a vast range (0.1-1000 ppb). Concentration-dependent photoluminescence (PL) of the QDs enhances up to 50 ppb and then suppresses till 1000 ppb. It shows two distinctive slopes for enhancement and suppression. The enhancement is possibly due to the passivation of trap states or defects. The formation of tiny glassy As₂S₃particles on the QD surface may be the possible reason for suppression. The pattern of optical absorption of QDs follows the similar patterns of PL. Still, it shows an enhanced absorbance in the near UV range below ≤300 nm, which increases with As (III) concentration up to 50 ppb and then decreases following the PL pattern. The MoS₂QDs were characterized by using transmission electron microscopy, x-ray diffraction, UV-Vis, and PL spectroscopy. The enhancement and suppression results were excellently fitted with the modified Stern-Volmer equation. The detection of arsenic is possible using these linear fit equations as calibration curves.

Anthranilic Acid Schiff Base as a Fluorescent Probe for the Detection of Arsenite and Selenite: A Detailed Investigation of Analytical Parameters and Mechanism for Interaction

The exploration of an anthranilic acid based Schiff base SB as a "Turn-ON" fluorescent probe for the detection of highly toxic selenite (Se^IV) and arsenite (As^III) species in an aqueous medium is described. The selectivity of SB towards Se^IV and As^III in the presence of other ions was investigated by some spectrofluorimetric and ¹H NMR spectroscopic experiments. The studies revealed the interaction between SB and As^III via the deprotonation of phenolic -OH, which enhanced the conjugation in phenolate ion and in turn enhanced the emission response. The SB has analytical prospects for the quantification of As^III and Se^IV with good sensitivity (LODs; 5.15 ppb for Se^IV and 3.12 ppb for As^III calculated by S/N = 3σ/K). Furthermore, it can be used to evaluate real and synthetic samples for the presence of Se^IV and As^III species as well as the fabrication of on-spot recognition devices (in the form of silica gels SB@SiO₂ and silica coated TLC aluminium strips SB@SiO₂@Al).

Non-chromatographic Speciation of As by HG Technique-Analysis of Samples with Different Matrices

The applicability of the hydride generation (HG) sample introduction technique combined with different spectrochemical detection methods for non-chromatographic speciation of toxic As species, i.e., As(III), As(V), dimethylarsinate (DMA) and monomethylarsonate (MMA), in waters and other environmental, food and biological matrices is presented as a promising tool to speciate As by obviating chromatographic separation. Different non-chromatographic procedures along with speciation protocols reported in the literature over the past 20 year are summarized. Basic rules ensuring species selective generation of the corresponding hydrides are presented in detail. Common strategies and alternative approaches are highlighted. Aspects of proper sample preparation before analysis and the selection of adequate strategies for speciation purposes are emphasized.

Hollow fiber liquid phase microextraction combined with total reflection X-ray fluorescence spectrometry for the determination of trace level inorganic arsenic species in waters

In the present study, we investigated the possibilities and drawbacks of hollow fiber liquid phase microextraction (HF-LPME) combined with total reflection X-ray fluorescence (TXRF) spectrometry for the determination of low amounts of inorganic arsenic (As) species in water samples. The obtained results showed that a three-phase HF-LPME system was more suitable to be used in combination with TXRF than the two phase configuration, since lower detection limit and better precision for As determination can be attained. Relevant experimental parameters affecting As extraction (i.e. types of extractant, organic solvent, agitation speed, pH and extraction time) and TXRF analysis (deposition volume and drying mode) were systematically evaluated. It was found that As(III) was more efficiently extracted at pH 13, whereas, optimum pH for As(V) extraction was at pH 8.5. Limits of detection (LOD) achieved using the best analytical conditions meet the requirements of current legislation and allow the determination of inorganic As(V) and As(III) in water. The proposed method was also applied to different spiked environmental water samples for the preconcentration and subsequent determination of trace inorganic As species.

Trace Arsenic Determination in a TiO2 Pigment Matrix Using Electrothermal Atomic Absorption Spectrometry

This work describes the use of electrothermal atomic absorption spectrometry in combination with a pyrolytic graphite-coated tube with a platform for trace arsenic (As) determination in titanium dioxide (TiO₂) pigment. This type of matrix is challenging, as complete digestion in hydrofluoric acid-containing solution is needed. First, closed-vessel microwave digestion was performed for the full-sample decomposition. Next, a temperature program was optimized for drying, pyrolysis, and atomization temperatures. Furthermore, the use of a chemical modifier mixture was proposed that reduced the background contribution and prevented significant analyte loss and therefore improved the analytical procedure. The optimized method was validated for the detection (LOD) and quantification (LOQ) limits, the linear concentration range, accuracy, and precision. Special attention was devoted to the matrix-matching solutions in the calibration procedure. Linearity was confirmed in the 5.0 to 100.0 µg/L concentration range (R² = 0.999). The average recovery for 16 different real TiO₂ pigment samples was 92.0%, and the relative standard deviation value for six replicate measurements was ≤10.4%. Moreover, the LOD and LOQ in terms of the TiO₂ pigment mass was determined to be 0.2 µg/(g TiO₂) and 0.7 µg/(g TiO₂), respectively. The latter complies with Commission Directive 2008/128/EC, which does not allow more than 3 µg As/(g product) as the specific criteria of purity. Finally, based on scanning electron microscopy analysis of unused and several times used pyrolytic graphite-coated tubes, usage of the tube 250 times before replacement is recommended.

A ZnS quantum dot-based super selective fluorescent chemosensor for soluble ppb-level total arsenic [As(iii) + As(v)] in aqueous media: direct assay utilizing aggregation-enhanced emission (AEE) for analytical application

This study brings out a novel, superselective detection employing thiosalicylic acid-capped ZnS-based quantum dots that display photoluminescence "turn-on" characteristics only in the presence of arsenic in the aquatic medium for the first time. It shows a splendid limit of detection of soluble arsenic down to a few ppb level, much below than the MCL reported value, without being interfered by any other ions.

As(III) and Cr(VI) oxyanion removal from water by advanced oxidation/reduction processes-a review

Water pollution by human activities is a global environmental problem that requires innovative solutions. Arsenic and chromium oxyanions are toxic compounds, introduced in the environment by both natural and anthropogenic activities. In this review, the speciation diagrams of arsenic and chromium oxyanions in aqueous solutions and the analytical methods used for their detection and quantification are presented. Current and potential treatment methods for As and Cr removal, such as adsorption, coagulation/flocculation, electrochemical, ion exchange, membrane separation, phyto- and bioremediation, biosorption, biofiltration, and oxidative/reductive processes, are presented with discussion of their advantages, drawbacks, and the main recent achievements. In the last years, advanced oxidation processes (AOPs) have been acquiring high relevance for the treatment of water contaminated with organic compounds. However, these processes are also able to deal with inorganic contaminants, mainly by changing metal/metalloid oxidation state, turning these compounds less toxic or soluble. An overview of advanced oxidation/reduction processes (AO/RPs) used for As and Cr removal was carried out, focusing mainly on H₂O₂/UVC, iron-based and heterogeneous photocatalytic processes. Some aspects related to AO/RP experimental conditions, comparison criteria, redox mechanisms, catalyst immobilization, and process intensification through implementation of innovative reactors designs are also discussed. Nevertheless, further research is needed to assess the effectiveness of those processes in order to improve some existing limitations. On the other hand, the validation of those treatment methods needs to be deepened, namely with the use of real wastewaters for their future full-scale application. Graphical abstract ᅟ.

Aqueous removal of inorganic and organic contaminants by graphene-based nanoadsorbents: A review

Various graphene-based nanoadsorbents, including graphenes, graphene oxides, reduced graphene oxides, and their nanocomposites, have been widely studied as potential adsorbents due to their unique physicochemical properties, such as structural variability, chemical strength, low density, and the possibility of large scale fabrication. Adsorption mechanisms are governed largely by the physicochemical properties of contaminants, the characteristics of nanoadsorbents, and background water quality conditions. This review summarizes recent comprehensive studies on the removal of various inorganic (mainly heavy metals) and organic contaminants by graphene-based nanoadsorbents, and also discusses valuable information for applications of these nanoadsorbents in water and wastewater treatment. In particular, the aqueous removal of various contaminants was reviewed to (i) summarize the general adsorption capacities of various graphene-based nanoadsorbents for the removal of different inorganic and organic contaminants, (ii) evaluate the effects of key water quality parameters such as pH, temperature, background major ions/ionic strength, and natural organic matter on adsorption, (iii) provide a comprehensive discussion of the mechanisms that influence adsorption on these nanoadsorbents, and (iv) discuss the potential regeneration and reusability of nanoadsorbents. In addition, current challenges and future research needs for the removal of contaminants by graphene-based nanoadsorbents in water treatment processes are discussed briefly.

Inorganic arsenic contents in infant rice powders and infant rice snacks marketed in Korea determined by a highly sensitive gas chromatography-tandem mass spectrometry following derivatization with British Anti-Lewisite

Toxic inorganic arsenic (iAs) has been reported to be present in high quantity in rice and rice-based products. The inorganic arsenic contents in infant foods (n = 59) of ready-to-cook infant rice powders and infant rice snacks marketed in Korea were determined by a highly sensitive gas chromatography-tandem mass spectrometry (GC-MS/MS). The mean iAs contents in the infant rice powder and infant rice snacks were 65.6 and 54.0 μg/kg, respectively. The percentages of rice powders and rice snack containing iAs over the maximum level (100 μg/kg) set by EU for the infant foods were found to be 21, and 6%, respectively. This result clearly suggested that regulation regarding the maximum limit of iAs levels for the baby rice products is urgently needed to be set in Korea. This represents the first report on the iAs levels in ready-to-cook infant rice powder products and infant snacks marketed in Korea.

Inorganic arsenic contents in ready-to-eat rice products and various Korean rice determined by a highly sensitive gas chromatography-tandem mass spectrometry

Rice and rice products have been reported to contain high contents of toxic inorganic arsenic (iAs). The inorganic arsenic contents in microwavable ready-to-eat rice products (n=30) and different types of Korean rice (n=102) were determined by a gas chromatography-tandem mass spectrometry (GC-MS/MS). The method showed low limit of detection (0.015pg), high intra- and inter-day repeatability (<7.3%, RSD), and recovery rates (90-117%). The mean iAs content in the ready-to-eat rice products was 59μgkg^-1 (dry weight basis). The mean iAs contents in polished white, brown, black, and waxy rice were 65, 109, 91, and 66μgkg^-1, respectively. The percentages of ready-to-eat rice products, white, brown, black, and waxy rice containing iAs over the maximum level (100μgkg^-1) set by EU for the infant foods were 17, 4, 70, 36 and 0%, respectively.

Critical evaluation of strategies for single and simultaneous determinations of As, Bi, Sb and Se by hydride generation inductively coupled plasma optical emission spectrometry

A systematic study of hydride generation (HG) of As, Bi, Sb and Se from solutions containing As(III), As(V), Bi(III), Sb(III), Sb(V), Se(IV) and Se(VI) was presented. Hydrides were generated in a gas-liquid phase separation system using a continuous flow vapor generation accessory (VGA) by mixing acidified aqueous sample, HCl and sodium borohydride reductant (NaBH₄) solutions on-line. For detection, a simultaneous axially viewed inductively coupled plasma optical emission spectrometer (ICP-OES) was applied. Effects of the HCl concentration (related to sample and additional acid solutions) and type of the pre-reducing agents used for reduction of As(V), Sb(V) and Se(VI) into As(III), Sb(III) and Se(IV) on the analytical responses of As, Bi, Sb and Se were studied and discussed. Two compromised HG reaction conditions for simultaneous measurements of As+Bi+Sb (CC1) or As+Sb+Se (CC2) were established. It was found that choice of the pre-reductant prior to formation of the hydrides is critical in obtaining the dependable results of the analysis. Accordingly, for a As(III)+As(V)+Bi(III)+Sb(III)+Sb(V) mixture and using CC1, thiourea/thiourea-ascorbic acid interfered in Bi determination and hence, total As+Sb could be measured. If L-cysteine/L-cysteine-ascorbic acid were used, measurements of total Bi+Sb was possible in these HG reaction conditions. For a As(III)+As(V)+Sb(III)+Sb(V)+Se(IV)+Se(VI) mixture and using CC2, thiourea/thiourea-ascorbic acid and L-cysteine/L-cysteine-ascorbic acid influenced HG of Se but ensured total As+Sb determination. In contrast, heating a sample solution with HCl, although did not pre-reduce As(V) and Sb(V), assured quantitative reduction of Se(VI) to Se(IV). Finally, considering all favorable pre-reducing and HG conditions, methodologies for reliable determination of total As, Bi, Sb and Se by HG-ICP-OES were proposed. Strategies for single-, two- and three-element measurements were evaluated and validated, obtaining the detection limits (DLs) below 0.1ngg^-1 and precision typically in the range of 1.4-3.9% RSD.

Reactivity, vibrational spectroscopy, internal rotation and thermochemical aspects of methylarsine

The aim of this investigation was to perform a characterization of the spectroscopic and thermodynamic properties of methylarsine (CH₃AsH₂). Post-Hartree-Fock, 29 DFT methods and eight different composite methodologies were employed in these analyses. A comparison between harmonic and anharmonic frequency accuracies in reproducing the observable frequencies was performed here. In addition, the CH₃AsH₂→CH₂AsH₃ isomerization barrier energy was estimated in 100kcalmol^-1, whereas the H₂-release routes barrier heights were in the 45-107kcalmol^-1 range. A rate constant of 10^-66s^-1 was predicted regarding the isomerization route, while the CH₂AsH₃ hydrogen elimination mechanism is faster than the methylarsine one. The transition state structure of the CH₃AsH₂ internal rotational barrier energy varied between 1.0 and 1.4kcalmol^-1. For the CH₂AsH₃ internal rotation the estimated barrier heights varied 0.6-2.5kcalmol^-1. The adiabatic ionization energy and the heat of formation each structure was also calculated here.

Inorganic Arsenic Determination in Food: A Review of Analytical Proposals and Quality Assessment Over the Last Six Years

Here we review recent developments in analytical proposals for the assessment of inorganic arsenic (iAs) content in food products. Interest in the determination of iAs in products for human consumption such as food commodities, wine, and seaweed among others is fueled by the wide recognition of its toxic effects on humans, even at low concentrations. Currently, the need for robust and reliable analytical methods is recognized by various international safety and health agencies, and by organizations in charge of establishing acceptable tolerance levels of iAs in food. This review summarizes the state of the art of analytical methods while highlighting tools for the assessment of quality assessment of the results, such as the production and evaluation of certified reference materials (CRMs) and the availability of specific proficiency testing (PT) programmes. Because the number of studies dedicated to the subject of this review has increased considerably over recent years, the sources consulted and cited here are limited to those from 2010 to the end of 2015.

One step derivatization with British Anti-Lewsite in combination with gas chromatography coupled to triple-quadrupole tandem mass spectrometry for the fast and selective analysis of inorganic arsenic in rice

We developed a new fast and selective analytical method for the determination of inorganic arsenic (iAs) in rice by a gas chromatography - tandem mass spectrometry (GC-MS/MS) in combination with one step derivatization of inorganic arsenic (iAs) with British Anti-Lewsite (BAL). Two step derivatization of iAs with BAL has been previously performed for the GC-MS analysis. In this paper, the quantitative one step derivatization condition was successfully established. The GC-MS/MS was carried out with a short nonpolar capillary column (0.25 mm × 10 m) under the conditions of fast oven temperature ramp rate (4 °C/s) and high linear velocity (108.8 cm/s) of the carrier gas. The established GC-MS/MS method showed an excellent linearity (r(2) > 0.999) in a tested range (0.2-100.0 μg L(-1)), ultra-low limit of detection (LOD, 0.08 pg), and high precision and accuracy. The GC-MS/MS technique showed far greater selectivity (22.5 fold higher signal to noise ratio in rice sample) on iAs than GC-MS method. The gas chromatographic running time was only 2.5 min with the iAs retention time of 1.98 min. The established method was successfully applied to quantify the iAs contents in polished rice. The mean iAs content in the Korean polished rice (n = 27) was 66.1 μg kg(-1) with the range of 37.5-125.0 μg kg(-1). This represents the first report on the GC-tandem mass spectrometry in combination with the one step derivatization with BAL for the iAs speciation in rice. This GC-MS/MS method would be a simple, useful and reliable measure for the iAs analysis in rice in the laboratories in which the expensive and element specific HPLC-ICP-MS is not available.

Lysosomal membrane response of the earthworm, Eisenia fetida, to arsenic species exposure in OECD soil

The NRRT assay was sensitive for toxicity assessment of inorganic arsenic pollution and it was affected more by As(iii) than by As(v).

Fluorometric sensing of ultralow As(III) concentrations using Ag doped hollow CdS/ZnS bi-layer nanoparticles

Arsenic poisoning from drinking water has been an important global issue in recent years. Because of the high level toxicity of arsenic to human health, an easy, inexpensive, low level and highly selective detection technique is of great importance to take any early precautions. This study reports the synthesis of Ag doped hollow CdS/ZnS bi-layer (Ag-h-CdS/ZnS) nanoparticles for the easy fluorometric determination of As(iii) ions in the aqueous phase. The hollow bi-layer structures were synthesized by a sacrificial core method using AgBr as the sacrificial core and the core was removed by dissolution in an ammonium hydroxide solution. The synthesized nanoparticles were characterized using different instrumental techniques. A good linear relationship was obtained between fluorescence quenching intensity and As(iii) concentration in the range of 0.75-22.5 μg L(-1) at neutral pH with a limit of detection as low as 0.226 μg L(-1).

Fast voltammetry of metals at carbon-fiber microelectrodes: copper adsorption onto activated carbon aids rapid electrochemical analysis

Rapid, in situ trace metal analysis is essential for understanding many biological and environmental processes. For example, trace metals are thought to act as chemical messengers in the brain. In the environment, some of the most damaging pollution occurs when metals are rapidly mobilized and transported during hydrologic events (storms). Electrochemistry is attractive for in situ analysis, primarily because electrodes are compact, cheap and portable. Electrochemical techniques, however, do not traditionally report trace metals in real-time. In this work, we investigated the fundamental mechanisms of a novel method, based on fast-scan cyclic voltammetry (FSCV), that reports trace metals with sub-second temporal resolution at carbon-fiber microelectrodes (CFMs). Electrochemical methods and geochemical models were employed to find that activated CFMs rapidly adsorb copper, a phenomenon that greatly advances the temporal capabilities of electrochemistry. We established the thermodynamics of surface copper adsorption and the electrochemical nature of copper deposition onto CFMs and hence identified a unique adsorption-controlled electrochemical mechanism for ultra-fast trace metal analysis. This knowledge can be exploited in the future to increase the sensitivity and selectivity of CFMs for fast voltammetry of trace metals in a variety of biological and environmental models.

Determination of total arsenic using a novel Zn-ferrite binding gel for DGT techniques: Application to the redox speciation of arsenic in river sediments

A new laboratory-made Zn-ferrite (ZnFe2O4) binding gel is fully tested using Diffusive Gradient in Thin films (DGT) probes to measure total As [including inorganic As(III) and As(V), as well as MonoMethyl Arsenic Acid (MMAA(V)) and DiMethyl Arsenic Acid (DMAA(V))] in river waters and sediment pore waters. The synthesis of the binding gel is easy, cheap and its insertion into the acrylamide gel is not problematic. An important series of triplicate tests have been carried out to validate the use of the Zn-ferrite binding gel in routine for several environmental matrixes studies, in order to test: (i) the effect of pH on the accumulation efficiency of inorganic As species; (ii) the reproducibility of the results; (iii) the accumulation efficiency of As species; (iv) the effects of the ionic strength and possible competitive anions; and (v) the uptake and the elution efficiency of As species after accumulation in the binding gel. All experimental conditions have been reproduced using two other existing binding gels for comparison: ferrihydrite and Metsorb® HMRP 50. We clearly demonstrate that the Zn-ferrite binding gel is at least as good as the two other binding gels, especially for pH values higher than 8. In addition, by taking into consideration the diffusion rates of As(III) and As(V) in the gel, combining the 3-mercaptopropyl [accumulating only As(III)] with the Zn-ferrite binding gels allows for performing speciation studies. An environmental study along the Marque River finally illustrates the ability of the new binding gel to be used for field studies.

Arsenic and antimony in water and wastewater: overview of removal techniques with special reference to latest advances in adsorption

Arsenic and antimony are metalloids, naturally present in the environment but also introduced by human activities. Both elements are toxic and carcinogenic, and their removal from water is of unquestionable importance. The present article begins with an overview of As and Sb chemistry, distribution and toxicity, which are relevant aspects to understand and develop remediation techniques. A brief review of the recent results in analytical methods for speciation and quantification was also provided. The most common As and Sb removal techniques (coagulation/flocculation, oxidation, membrane processes, electrochemical methods and phyto and bioremediation) are presented with discussion of their advantages, drawbacks and the main recent achievements. Literature review on adsorption and biosorption were focused in detail. Considering especially the case of developing countries or rural communities, but also the finite energy resources that over the world are still dependent, recent research have focused especially readily available low-cost adsorbents, as minerals, wastes and biosorbents. Many of these alternative sorbents have been presenting promising results and can be even superior when compared to the commercial ones. Sorption capacities were accurately compiled for As(III,V) and Sb(III,V) species in order to provide to the reader an easy but detailed comparison. Some aspects related to experimental conditions, comparison criteria, lack of research studies, economic aspects and adsorption mechanisms were critically discussed.

A nanogold resonance Rayleigh scattering method for determination of trace As based on the hydride nanoreaction

In H2 SO4 solution, As(III) was reduced to arsine (AsH3 ) by NaBH4 , and was absorbed in HAuCl4 solution to form nanogold particles (NGs) that exhibited a resonance Rayleigh scattering (RRS) effect at 370 nm. Under the selected conditions, when the As(III) concentration increased the RRS peak also increased due to the formation of more NGs. There was a linear correlation between RRS intensity and As(III) concentration in the range 6-1000 ng/mL, with a detection limit of 3 ng/mL. This new hydride generation-nanogold reaction RRS (HG-NG RRS) method was applied to determine trace amounts of As in milk samples, with satisfactory results.