Nanomaterials in analytical atomic spectrometry

Iron oxide xerogels for improved water quality monitoring of arsenic(III) in resource-limited environments via solid-phase extraction, preservation, storage, transportation, and analysis of trace contaminants (SEPSTAT)

Arsenic is a widespread trace groundwater contaminant that presents a range of health risks and has an acceptable level of only 10 μg L-1 in drinking water. However, in many countries arsenic quantification in water is limited to centralized laboratories because it requires the use of elemental analysis techniques with high capital cost. As a result, routine water samples are frequently not tested for trace contaminants such as arsenic. In order to facilitate improved arsenic monitoring, we present the use of iron oxide xerogels for adsorption of arsenic(iii) from water samples at neutral pH, dry storage for over 120 days, and desorption of stored arsenic at elevated pH. Iron oxide xerogels offer high surface area (340 m2 g-1) and an As(iii) adsorption capacity of 165 mg g-1. Using an extraction solution of 100 mM sodium hydroxide and 1 mM sodium phosphate, As(iii) is reliably eluted from iron oxide xerogels for initial As(iii) concentrations from 10 μg L-1 to 1000 μg L-1, with a calculated detection limit of less than 4 μg L-1 and less than 17% difference in recovered As(iii) between test solutions with low and high interfering ion concentrations. By demonstrating the ability for iron oxide xerogels to reliably adsorb, store, and release arsenic, we enable the development of protocols for solid-phase extraction, preservation, storage, transportation, and analysis of trace contaminants (SEPSTAT), where arsenic would be adsorbed from water samples onto xerogel-based sorbents and shipped to centralized laboratories for recovery and quantification.

Characterization of Nanoparticles: Advances

Over the past two decades, the unique properties of engineered nanoparticles (NPs) have placed them at the centre of revolutionary advancements in many sectors of science, technology and commerce. Multi-technique and multi-disciplinary analytical approaches are required to identify, quantify, and characterize the chemical composition, size and size distribution, surface properties and the number and concentration of NPs. In this chapter, an overview of the recent advances in the characterization of NPs will be presented.

Photochemical Vapor Generation for Colorimetric Speciation of Inorganic Selenium

Gold nanoparticles (AuNPs) are widely used as optical probes in colorimetric detection, thanks to their high molar extinction coefficient. However, sample matrixes of high salinity or strong acidity/alkalinity often break the electrostatic repulsion of AuNPs suspension, or/and the surface functionality of AuNPs, causing strong and unfavorable interferences. Photochemical vapor generation (PVG) is an efficient technique for the sample matrix separation. Besides, it possesses distinct features of green reducing reagent, reduced interferences from concomitant elements, and direct speciation by the assistance of photocatalyst. Herein, we developed a photochemical vapor generation (PVG) method for the green and direct speciation analysis of inorganic selenium (i.e., Se(IV) and Se(VI)), by colorimetric or visual monitoring of unmodified AuNPs. The generated Se species from PVG were directed into the AuNPs solution for a reaction to take place, which produced a specific new absorption band at 600 nm for detection. The experimental parameters, including the concentration of organic acid, the sample flow rate, the concentration of AuNPs, and the flow rate of carries gas, were optimized in detail. Under optimized conditions, the limits of detection (LOD) for Se(IV) and Se(VI) were 0.007 and 0.006 μg mL^-1 by UV-vis detection, respectively. It is worth mentioning that 0.08 μg mL^-1 Se can induce an obvious color change, which can be directly observed with the naked eye. Relative standard deviations (RSDs) of 4.5% and 4.3% were obtained from seven replicate measurements of 0.15 μg mL^-1 Se(IV) and Se(VI) standard solution, respectively. The developed assay has been successfully applied for the speciation of Se in a dietary supplement sample and environmental water samples including lake water, seawater, simulated water reference materials, and tap water.

Influence of Al2O3 Nanoparticles on the Soil Elements

The behavior of nanoparticles released to the soil has been extensively studied in recent years; however, the effects of nanoparticles on the distribution of soil elements and on sowing are still unknown. To this end, to examine the distribution of selected elements in soil, soil samples were treated weekly with 1.0 mg and 20.0 mg of Al₂O₃ nanoparticles for 3 weeks. Additionally, different types of plants (including taproot, fibrous root and ornamental bulbous plants) were sowed in the soil samples. After each treatment, surface soil samples were collected and digested with acid digestion. The concentrations of selected elements (Ca, Mg, Fe, Al, Cu, Co, Ni) were determined using a microwave plasma atomic emission spectrometer. Al₂O₃ treatment for 3 weeks, both low and high doses, had no effect on the Al content in soil samples when compared to the controls. Additionally, Al₂O₃ showed desorption properties on the analyte elements.

Characterization of nZVI nanoparticles functionalized by EDTA and dipicolinic acid: a comparative study of metal ion removal from aqueous solutions

Surface modification of nZVI particles by EDTA and PDCA leads to the formation of magnetite and feroxyhyte shell. PDCA capping caused the elongation of spheres into ellipsoids. Metals adsorption was more efficient on smaller ellipsoidal particles.

Efficacy of engineered GO Amberlite XAD-16 picolylamine sorbent for the trace determination of Pb (II) and Cu (II) in fishes by solid phase extraction column coupled with inductively coupled plasma optical emission spectrometry

Graphene oxide (GO) was immobilized innovatively through azo spacer arm onto the surface of polymeric Amberlite XAD-16 resin in order to expose all oxygen functionalities freely available for metal ions coordination and further modification with picolylamine which governs selectivity. The GO Amberlite XAD-16 picolylamine enables the development of SPE column coupled with ICP-OES for preconcentration and determination of Pb (II) and Cu (II) in water and fish samples. Elution was performed by mild acid (2M HCl) no other carcinogenic organic solvent was used, prevents ligand leaching. Under optimized conditions, the preconcentration factors of 150 and detection limits 1.434 and 0.048 µg L⁻¹ for Pb (II) and Cu (II)  were obtained respectively.

Sequential determination of gallium, indium, and thallium in environmental samples after preconcentration on halloysite nanotubes using ultrasound-assisted dispersive micro solid-phase extraction

A preconcentration procedure for gallium, indium, and thallium using HNTs was developed prior to their sequential determination by HR-CS GFAAS.

A simple dispersive-micro-solid phase extraction based on a colloidal silica sorbent for the spectrophotometric determination of Fe(ii) in the presence of tetrabutylammonium bromide

This study demonstrates a simplified dispersive micro-solid phase extraction (d-μ-SPE) using silica sol as the sorbent for the preconcentration of ferrous ions.

Fe3O4/hydroxyapatite/graphene quantum dots as a novel nano-sorbent for preconcentration of copper residue in Thai food ingredients: Optimization of ultrasound-assisted magnetic solid phase extraction

Fe₃O₄/hydroxyapatite/graphene quantum dots (Fe₃O₄/HAP/GQDs) nanocomposite was synthesized and used as a novel magnetic adsorbent. This nanocomposite was characterized using scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, and magnetization property. The Fe₃O₄/HAP/GQDs was applied to pre-concentrate copper residues in Thai food ingredients (so-called "Tom Yum Kung") prior to determination by inductively coupled plasma-atomic emission spectrometry. Based on ultrasound-assisted extraction optimization, various parameters affecting the magnetic solid-phase extraction, such as solution pH, amount of magnetic nanoparticles, adsorption and desorption time, and type of elution solvent and its concentration were evaluated. Under optimal conditions, the linear range was 0.05-1500ngmL^-1 (R²>0.999), limit of detection was 0.58ngmL^-1, and limit of quantification was 1.94ngmL^-1. The precision, expressed as the relative standard deviation of the calibration curve slope (n=5), for intra-day and inter-day analyses was 0.87% and 4.47%, respectively. The recovery study of Cu for real samples was ranged between 83.5% and 104.8%. This approach gave the enrichment factor of 39.2, which guarantees trace analysis of Cu residues. Therefore, Fe₃O₄/HAP/GQDs can be a potential and suitable candidate for the pre-concentration and separation of Cu from food samples. It can easily be reused after treatment with deionized water.

Removal of tetracycline and oxytetracycline from water by magnetic Fe3O4@graphene

In this paper, Fe₃O₄@graphene (Fe₃O₄@G) magnetic nanocomposite was prepared via in situ precipitation method for the removal of oxytetracycline (OTC) and tetracycline (TC) from aqueous solution. The properties of the prepared nanocomposite were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and magnetic property measurement system (MPMS). Adsorption isotherm and kinetics of OTC and TC were studied in batch experiments. The influence of the dosage of Fe₃O₄@G, the solution pH, and ion strength on the adsorption process were also assessed. The results demonstrated that the Langmuir model fitted the adsorption equilibrium data better than did the Freundlich model, and the pseudo-first-order model was more suitable than the pseudo-second-order to describe the adsorption process, with a good adsorption rate constant (k = 0.974 and 0.834 g mg^-1 h^-1, respectively). The adsorption ability reached maximum at pH of 7 with no NaCl. The removal efficiency of Fe₃O₄@G in lake, tap, and pool water were 95.45, 96.68, and 89.82 % for OTC and 98.77, 98.23, and 89.09 % for TC, respectively. The π-π interaction and cation-π bonding of the adsorbent and analytes make it suitable for the removal of OTC and TC. The present study suggests that the prepared composite can be deemed as a promising material for the removal of tetracycline antibiotics from aqueous solution.

Application of a Zn(ii) based metal–organic framework as an efficient solid-phase extraction sorbent for preconcentration of plasticizer compounds

A solid-phase extraction (SPE) sorbent, a Zn(ii) based metal–organic framework, was prepared via a simple, solventless, green and a low-cost mechanosynthesis process.

Extraction and preconcentration of formaldehyde in water by polypyrrole-coated magnetic nanoparticles and determination by high-performance liquid chromatography

In this study, a simple and rapid extraction method based on the application of polypyrrole-coated Fe3 O4 nanoparticles as a magnetic solid-phase extraction sorbent was successfully developed for the extraction and preconcentration of trace amounts of formaldehyde after derivatization with 2,4-dinitrophenylhydrazine. The analyses were performed by high-performance liquid chromatography followed by UV detection. Several variables affecting the extraction efficiency of the formaldehyde, i.e., sample pH, amount of sorbent, salt concentration, extraction time and desorption conditions were investigated and optimized. The best working conditions were as follows: sample pH, 5; amount of sorbent, 40 mg; NaCl concentration, 20% w/v; sample volume, 20 mL; extraction time, 12 min; and 100 μL of methanol for desorption of the formaldehyde within 3 min. Under the optimal conditions, the performance of the proposed method was studied in terms of linear dynamic range (10-500 μg/L), correlation coefficient (R(2) ≥ 0.998), precision (RSD% ≤ 5.5) and limit of detection (4 μg/L). Finally, the developed method was successfully applied for extraction and determination of formaldehyde in tap, rain and tomato water samples, and satisfactory results were obtained.

Fabrication of graphene/Fe3O4@polythiophene nanocomposite and its application in the magnetic solid-phase extraction of polycyclic aromatic hydrocarbons from environmental water samples

Polythiophene (PT) was used as a surface modifier of graphene/Fe3O4 (G/Fe3O4) composite to increase merit of it, and also overcome some limitations and disadvantages of using G/Fe3O4 alone as solid phase extraction (SPE) sorbent. An in-situ chemical polymerization method was employed to prepare G/Fe3O4@PT nanocomposites. Application of this newly designed material in the magnetic SPE (MSPE) of polycyclic aromatic hydrocarbons (PAHs), as model analytes, in the environmental water samples was investigated. The characterization of the hybrid material was performed using transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray analysis, Fourier transform-infrared (FT-IR) spectroscopy and vibrating sample magnetometry. Seven important parameters, affecting the extraction efficiency of PAHs, including: amount of adsorbent, adsorption and desorption times, type and volume of the eluent solvent, initial sample volume and salt content of the sample were evaluated. The optimum extraction conditions were obtained as: 4 min for extraction time, 20 mg for sorbent amount, 100mL for initial sample volume, toluene as desorption solvent, 0.6 mL for desorption solvent volume, 6 min for desorption time and 30% (w/v) for NaCl concentration. Good performance data were obtained at the optimized conditions. Detection limits were in the range of 0.009-0.020 μg L(-1) in the real matrix. The calibration curves were linear over the concentration ranges from 0.03 to 80 μg L(-1) with correlation coefficients (R(2)) between 0.995 and 0.998 for all the analytes. Relative standard deviations were ranged from 4.3 to 6.3%. Appropriate recovery values, in the range of 83-107%, were also obtained for the real sample analysis.

A carboxylated graphene and aptamer nanocomposite-based aptasensor for sensitive and specific detection of hemin

A unique nanocomposite was crafted by grafting hemin-binding-aptamer (HBA) onto carboxylated graphene (COO-GR). Infrared spectroscopy, Raman spectroscopy and diffuse reflectance spectra suggested that -NHCO- covalent bonds were formed between HBA and COO-GR. The resulting COO-GR/HBA functionalized electrode was used as a novel label-free biosensor. The square wave voltammetry was employed to realize the selective and specific detection of hemin. The obtained aptasensor possessed excellent performance with a detection limit of 0.64 nmol L(-1) (S/N=3) and a linear range from 1 to 150 nmol L(-1). Moreover, COO-GR was shown to be a promising candidate in making aptasensors, carrying advantages over graphene in terms of the simplicity of sensor preparation and the reduction of background noise.

Extraction of three nitrophenols using polypyrrole-coated magnetic nanoparticles based on anion exchange process

In this research, the applicability of polypyrrole-coated Fe3O4 nanoparticles (Fe3O4@PPy NPs) as an anion exchange magnetic nanosorbent is demonstrated. For this purpose, three nitrophenols were selected as models which are acidic compounds with low logP values and their extraction in neutral form (only based on hydrophobic interactions) is difficult. The extracted nitrophenols were separated and determined by high-performance liquid chromatography-UV detection. The size, morphology and surface coating of synthesized Fe3O4@PPy NPs have been characterized via different techniques such as Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy and thermo-gravimetric analysis. The important parameters influencing the extraction efficiency were studied and optimized. Under the optimum extraction conditions (300mL sample solution with pH 10, extraction and desorption times of 10 and 2min, respectively, 500μL of 0.1M HNO3 in acetonitrile as eluent, and 40mg of adsorbent), a linear range between 0.75 and 100μgL(-1) (R(2)>0.997), and limits of detection ranging from 0.3 to 0.4μgL(-1) were obtained. Preconcentration factors in the range of 125-180 were achieved and relative standard deviations (RSDs%) were less than 4.9 (n=4) for the three nitrophenols. The analytical method was successfully applied for environmental water samples such as tap water, rain water and river water. The recoveries varied within the range of 84-109% confirming good performance of the method in various waters samples. The results showed that the proposed method is a rapid, convenient and feasible technique for determination of nitrophenols in aqueous samples.