Use of carbon nanotubes and electrothermal atomic absorption spectrometry for the speciation of very low amounts of arsenic and antimony in waters

Arsenic speciation by using emerging sample preparation techniques: a review

Arsenic is a hazardous element that causes environmental pollution. Due to its toxicological effects, it is crucial to quantify and minimize the hazardous impact on the ecology. Despite the significant advances in analytical techniques, sample preparation is still crucial for determining target analytes in complex matrices. Several factors affect the direct analysis, such as trace-level analysis, advanced regulatory requirements, complexity of sample matrices, and incompatible with analytical instrumentation. Along with the development in the sample preparation process, microextraction methods play an essential role in the sample preparation process. Microextraction techniques (METs) are the newest green approach that replaces traditional sample preparation and preconcentration methods. METs have minimized the limitation of conventional sample preparation methods while keeping all their benefits. METs improve extraction efficacy, are fast, automated, use less amount of solvents, and are suitable for the environment. Microextraction techniques with less solvent consumption, such as solid phase microextraction (SPME) solvent-free methods, and liquid phase microextraction (LPME), are widely used in modern analytical procedures. SPME development focuses on synthesizing new sorbents and applying online sample preparation, whereas LPME research investigates the utilization of new solvents.

Recent advancements in antimony (Sb) removal from water and wastewater by carbon-based materials: a systematic review

Antimony (Sb) has been classified as a high-priority contaminant in the environment. Sb contamination resulting from the use of antimony-containing compounds in industry necessitates the development of efficient methods to remove it from water and wastewater. Adsorption is a highly efficient and reliable method for pollutants removal owing to its availability, recyclability, and low cost. Recently, carbonaceous materials and their applications for the removal of Sb from the aqueous matrices have received special attention worldwide. Herein, this review systematically summarizes the occurrence and exposure of Sb in the environment and on human health, respectively. Different carbon-based adsorbents have been classified for the adsorptive removal of Sb and their adsorption characteristics have been delineated. Recent development in the adsorption performance of the adsorbent materials for improving the Sb removal from the aqueous medium has been outlined. Further, to develop an understanding of the effect of different parameters like pH, competitive ions, and dissolved ions for Sb adsorption and subsequent removal have been discussed. A retrospective analysis of literature was conducted to present the adsorption behavior and underlying mechanisms involved in the removal of Sb using various adsorbents. Moreover, this study has identified emerging research gaps and emphasized the need for developing modified/engineered carbonaceous adsorbents to enhance Sb adsorption from various aqueous matrices.

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.

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.

Fabrication of Sb3+sensor based on 1,1′-(-(naphthalene-2,3-diylbis(azanylylidene))bis(methanylylidene))bis(naphthalen-2-ol)/nafion/glassy carbon electrode assembly by electrochemical approach

A new Schiff base named 1,1′-(-(naphthalene-2,3-diylbis(azanylylidene))bis(methanylylidene))bis(naphthalen-2-ol) (NDNA) was synthesized by condensation reaction and then characterized by spectroscopic techniques for structure elucidation.

Fully-automated magnetic stirring-assisted lab-in-syringe dispersive liquid–liquid microextraction for the determination of arsenic species in rice samples

Fully-automated magnetic stirring-assisted lab-in-syringe dispersive liquid–liquid microextraction (MAS-LIS-DLLME), combined with graphite furnace atomic absorption spectrometry (GFAAS) was developed for the fast and efficient separation and preconcentration of trace levels of inorganic arsenic species in rice samples. This totally automated analytical procedure combines the advantages of lab-in-syringe flow system and dispersive liquid–liquid microextraction (DLLME) aiming at separation of trace arsenite and arsenate species from natural matrix for the first time. With a single syringe pump that is coupled with a multiposition valve, the whole lab-in-syringe microextraction process including cleaning, mixing, microextraction, phase separation, and target analyte collection was implemented in a fully-automated way. Significant factors of the MAS-LIS-DLLME method were sample acidity, concentration of the chelating agent, amounts of ionic liquids (ILs), aspiration speed and matrix interference. Using the present method, the limits of detection (LODs) for As(v) was 0.005 μg L⁻¹. The relative standard deviation (RSDs) for seven replicate measurements of 2.0 μg L⁻¹ of As(v) was 3.7%. The linear dynamic range (LDR) was 0.04–5.0 μg L⁻¹ and the determination coefficients was 0.9990. Under the optimum conditions, the developed totally automated analytical procedure was successfully applied for the trace arsenite and arsenate species studies in natural rice samples and standard reference materials with satisfactory results.

The schematic of the MAS-LIS-DLLME system. D, detection system; SP, syringe pump; SV, three-way solenoid valve; W, waste; MPV, multiposition valve.

Determination of antimony compounds in waters and juices using ion chromatography-inductively coupled plasma mass spectrometry

A method was developed by coupling ion chromatography (IC) and inductively coupled plasma mass spectrometry (ICP-MS) for the speciation of antimony. In this study, antimony species such as antimonite [Sb(III)], antimonate [Sb(V)] and trimethyl antimony(V) (TMeSb) were separated in less than 8min using anion exchange chromatography with a Hamilton PRP-X100 column as the stationary phase. Mobile phase A was 20mmolL^-1 ethylenediaminetetraacetic acid (EDTA), 2mmolL^-1 potassium hydrogen phthalate (KHP) in 1% v/v methanol (pH 5.5) and 20mmolL^-1 EDTA, 2mmolL^-1 KHP, 40mmolL^-1 (NH₄)₂CO₃ in 1% v/v methanol (pH 9.0) formed mobile phase B. Detection limits and relative standard deviations (RSD) were 0.012-0.032ngmL^-1 and 2.2-2.8% respectively. This method was applied to bottled waters and fruit juices purchased in Kaohsiung, Taiwan. In water samples, Sb(V) was the major species where as in juices organometallic Sb species were also present.

Speciation of very low amounts of antimony in waters using magnetic core-modified silver nanoparticles and electrothermal atomic absorption spectrometry

A micro-solid phase extraction procedure for the separation and preconcentration of antimony based in the use of magnetic particles covered with silver nanoparticles functionalized with the sodium salt of 2-mercaptoethane-sulphonate (MESNa) is discussed. After separation by means of a magnetic field, the solid phase is directly introduced into an electrothermal atomizer for antimony determination. Alternatively, the solid can be slurried and then injected into the atomizer. In all cases, palladium nitrate is used as a chemical modifier. The preconcentration factors are close to 205 and 325, with detection limits of 0.02 and 0.03µgL^-1 antimony, for the slurry and solid sampling procedures, respectively. Speciation of Sb(III) and Sb(V) is achieved by means of two extractions carried out at different acidity. The results for total antimony are verified using certified reference materials. Water samples are analyzed for antimony speciation.

Inorganic arsenic speciation in water samples by miniaturized solid phase microextraction using a new polystyrene polydimethyl siloxane polymer in micropipette tip of syringe system

The polymer, polystyrene polydimethyl siloxane was loaded into the micropipette tip of the syringe system as an adsorbent to developed miniaturized solid phase microextraction. Standard solutions of arsenate and arsenite were passed through the adsorbent loaded in micropipette tip to check the adsorption behaviors. It was observed that arsenate adsorbed on the polystyrene polydimethyl siloxane in the pH rang of 6-8, while arsenite was directly passed through the micropipette tip of syringe system. The adsorbed arsenate in micropipette tip of syringe system were eluted by 1.0M hydrochloric acid. The total inorganic arsenic contents were obtained by the addition of oxidizing agent potassium permanganate into the studied samples before passing to the micropipette tip of syringe system. Arsenite concentration in water samples were measured by subtracting arsenate from total inorganic arsenic concentration. Different characteristics which effect the determination of arsenate specie like amount of adsorbent, adsorption capacity, pH, pulled and pushed cycles for adsorption and desorption, volume of sample, eluent type and it volume were also studied in detail. Enrichment factor and detection limit of arsenate by desired method were 218 and 6.9ngL^-1 respectively. The relative standard deviation was 4.1% (n=10, C=0.12µgL^-1). Accuracy of the desired technique was confirmed by analysis of the CRMs (Lake Ontario Water TM-28.3 and Riverine Water NRCC-SLRS-4). Desired technique was significantly useful for determination of the total arsenic, arsenate, and arsenite contents in different natural water samples.

Sampling of dissolved inorganic SbIII by mercapto-functionalized silica-based diffusive gradients in thin-film technique

The mercapto-functionalized silica (MPS) diffusive gradients in thin-film (DGT) devices, for the first time, were characterized by the determination of dissolved inorganic Sb^III.

Using citric acid stabilizing reagent to improve selective hydride generation-ICP-MS method for determination of Sb species in drinking water

Citric acid as the stabilizing reagent to improve the selectivity of HG-ICP-MS for the direct speciation of Sb in drinking water.

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.

Speciation and determination of inorganic arsenic species in water and biological samples by ultrasound assisted-dispersive-micro-solid phase extraction on carboxylated nanoporous graphene coupled with flow injection-hydride generation atomic absorption spectrometry

In this paper, carboxylated nanoporous graphene as a nanoadsorbent was evaluated in two types of ultrasound assisted-dispersive micro-solid phase extraction for speciation of trace As(v) and As(iii) ions in natural water and human biological samples.

Speciation of As(III) and As(V) in water samples by graphite furnace atomic absorption spectrometry after solid phase extraction combined with dispersive liquid-liquid microextraction based on the solidification of floating organic drop

A solid phase extraction (SPE) coupled with dispersive liquid-liquid microextraction based on the solidification of floating organic drop (DLLME-SFO) method, using diethyldithiphosphate (DDTP) as a proper chelating agent, has been developed as an ultra preconcentration technique for the determination of inorganic arsenic in water samples prior to graphite furnace atomic absorption spectrometry (GFAAS). Variables affecting the performance of both steps were thoroughly investigated. Under optimized conditions, 100mL of As(ΙΙΙ) solution was first concentrated using a solid phase sorbent. The extract was collected in 2.0 mL of acetone and 60.0 µL of 1-undecanol was added into the collecting solvent. The mixture was then injected rapidly into 5.0 mL of pure water for further DLLME-SFO. Total inorganic As(III, V) was extracted similarly after reduction of As(V) to As(III) with potassium iodide and sodium thiosulfate and As(V) concentration was calculated by difference. A mixture of Pd(NO3)2 and Mg(NO3)2 was used as a chemical modifier in GFAAS. The analytical characteristics of the method were determined. The calibration graph was linear in the rage of 10-100 ng L(-1) with detection limit of 2.5 ng L(-1). Repeatability (intra-day) and reproducibility (inter-day) of method based on seven replicate measurements of 80 ng L(-1) of As(ΙΙΙ) were 6.8% and 7.5%, respectively. The method was successfully applied to speciation of As(III), As(V) and determination of the total amount of As in water samples and in a certified reference material (NIST RSM 1643e).

Separation/Preconcentration and Speciation Analysis of Trace Amounts of Arsenate and Arsenite in Water Samples Using Modified Magnetite Nanoparticles and Molybdenum Blue Method

A new, simple, and fast method for the separation/preconcentration and speciation analysis of arsenate and arsenite ions using cetyltrimethyl ammonium bromide immobilized on alumina-coated magnetite nanoparticles (CTAB@ACMNPs) followed by molybdenum blue method is proposed. The method is based on the adsorption of arsenate on CTAB@ACMNPs. Total arsenic in different samples was determined as As(V) after oxidation of As(III) to As(V) using potassium permanganate. The arsenic concentration has been determined by UV-Visible spectrometric technique based on molybdenum blue method and amount of As(III) was calculated by subtracting the concentration of As(V) from total arsenic concentration. MNPs and ACMNPs were characterized by VSM, XRD, SEM, and FT-IR spectroscopy. Under the optimal experimental conditions, the preconcentration factor, detection limit, linear range, and relative standard deviation (RSD) of arsenate were 175 (for 350 mL of sample solution), 0.028 μg mL−1, 0.090–4.0 μg mL−1, and 2.8% (for 2.0 μg mL−1,n=7), respectively. This method avoided the time-consuming column-passing process of loading large volume samples in traditional SPE through the rapid isolation of CTAB@ACMNPs with an adscititious magnet. The proposed method was successfully applied to the determination and speciation of arsenic in different water samples and suitable recoveries were obtained.

Iron-complexed adsorptive membrane for As(V) species in water

Selective preconcentration of a target analyte in the solid phase is an effective route not only to enhance detection limit of the conventional analytical method but also for elimination of interfering matrix. An adsorptive membrane was developed for selective preconcentration and quantification of ultra-trace (ppb) amounts of As(V) present in a variety of aqueous samples. The precursor membrane was prepared by UV-initiator induced graft polymerization of sulphate and phosphate bearing monomers (1:1 mol proportion) in pores of the host microporous poly(propylene) membrane. Fe(3+) ions were loaded in the precursor membrane to make it selective for As(V) ions. The presence of phosphate functional groups prevent leaching of Fe(3+) ions from the membrane when it comes in contact with solution like seawater having high ionic strength. The optimized membrane was characterized in terms of its physical structure, chemical structure and experimental conditions affecting As(V) uptake in the membrane. The possibility of quantifying total preconcentration of As content was also explored by converting As(III) to As(V). To quantify As(V), the membrane samples were subjected to instrumental neutron activation analysis (INAA). The studies carried in the present work showed that quantification of inorganic arsenic species in natural water samples is easily possible in 2-3 ppb concentration range.