Nanomaterials in speciation analysis of metals and metalloids

Environmentally friendly nanoflower Al2O3@carbon spheres as adsorbent for dispersive solid-phase microextraction of copper and lead in food and water samples

A fast and simple dispersive solid-phase microextraction method (d-SPμE) was described for the determination of copper and lead in food, water, and sediments using FAAS. Firstly, nanoflower Al2O3@carbon spheres composite (NF Al2O3@CSs) was synthesized and then characterized. The obtained NF Al2O3@CSs was used for the d-SPμE of copper and lead in aqueous solutions. The influence of important parameters like pH, contact time, eluent conditions, volume of sample, and competing ion effects on the d-SPμE efficiency of copper and lead was investigated. They were pH, 7; eluent, 2 mol L-1 HCl (2 mL); sample volume, 250 mL for copper and 150 mL for lead with recoveries ≥90%. The adsorption and elution of analytes on NF Al2O3@CSs were realized quickly without vortexing. The LODs of the d-SPμE for copper and lead were found to be 0.69 μg L-1 and 2.8 μg L-1, respectively, while its PF was 125 for copper and 75 for lead. The intra-day precision and inter-day repeatability (RSD%, n = 7) were 1.3% and 1.6% for Cu(II) and 2.3% and 3.2% for Pb(II), respectively. Finally, the accuracy of the d-SPμE was investigated by determination of the analytes in four certified reference materials (TMDA-53.3 Lake water, NW-TMDA-54.6 Lake water, NIST 1573a Tomato leaves, and NIST RM 8704 Buffalo River Sediment). The analyte recoveries together with analyses of dam water, river water, wastewater, sea water, sumac, tea, chocolate, and lentils were studied. The results indicate that recoveries ranged from 90 to 103% in water samples and 91 to 110% in food samples.

Preconcentration and Removal of Pb(II) Ions from Aqueous Solutions Using Graphene-Based Nanomaterials

Direct determination of lead trace concentration in the presence of relatively complex matrices is often a problem. Thus, its preconcentration and separation are necessary in the analytical procedures. Graphene-based nanomaterials have attracted significant interest as potential adsorbents for Pb(II) preconcentration and removal due to their high specific surface area, exceptional porosities, numerous adsorption sites and functionalization ease. Particularly, incorporation of magnetic particles with graphene adsorbents offers an effective approach to overcome the separation problems after a lead enrichment step. This paper summarizes the developments in the applications of graphene-based adsorbents in conventional solid-phase extraction column packing and its alternative approaches in the past 5 years.

Metal(loid)s in Common Medicinal Plants in a Uranium Mining-Impacted Area in Northwestern New Mexico, USA

The objective of this study was to determine uranium (U) and other metal(loid) concentrations (As, Cd, Cs, Pb, Mo, Se, Th, and V) in eight species of plants that are commonly used for medicinal purposes on Diné (Navajo) lands in northwestern New Mexico. The study setting was a prime target for U mining, where more than 500 unreclaimed abandoned U mines and structures remain. The plants were located within 3.2 km of abandoned U mines and structures. Plant biota samples (N = 32) and corresponding soil sources were collected. The samples were analyzed using Inductively Coupled Plasma−Mass Spectrometry. In general, the study findings showed that metal(loid)s were concentrated greatest in soil > root > aboveground plant parts, respectively. Several medicinal plant samples were found to exceed the World Health Organization Raw Medicinal Plant Permissible Level for As and Cd; however, using the calculated human intake data, Reference Dietary Intakes, Recommended Dietary Allowances, and tolerable Upper Limits, the levels were not exceeded for those with established food intake or ingestion guidelines. There does not appear to be a dietary food rise of metal(loid) ingestion based solely on the eight medicinal plants examined. Food intake recommendations informed by research are needed for those who may be more sensitive to metal(loid) exposure. Further research is needed to identify research gaps and continued surveillance and monitoring are recommended for mining-impacted communities.

Influence of Selenium Biofortification of Soybeans on Speciation and Transformation during Seed Germination and Sprouts Quality

Selenium (Se) biofortification during seed germination is important not only to meet nutritional demands but also to prevent Se-deficiency-related diseases by producing Se-enriched foods. In this study, we evaluated effects of Se biofortification of soybeans on the Se concentration, speciation, and species transformation as well as nutrients and bioactive compounds in sprouts during germination. Soybean (Glycine max L.) seedlings were cultivated in the dark in an incubator with controlled temperature and water conditions and harvested at different time points after soaking in Se solutions (0, 5, 10, 20, 40, and 60 mg/L). Five Se species and main nutrients in the sprouts were determined. The total Se content increased by 87.3 times, and a large portion of inorganic Se was transformed into organic Se during 24 h of germination, with 89.3% of the total Se was bound to soybean protein. Methylselenocysteine (MeSeCys) and selenomethionine (SeMet) were the dominant Se species, MeSeCys decreased during the germination, but SeMet had opposite trend. Se biofortification increased contents of total polyphenol and isoflavonoid compounds and amino acids (both total and essential), especially in low-concentration Se treatment. In conclusion, Se-enriched soybean sprouts have promising potential for Se supplementation and as functional foods.

Speciation analysis of inorganic selenium in wastewater using a highly selective cellulose-based adsorbent via liquid electrode plasma optical emission spectrometry

Speciation of selenium (Se) is typically carried out using a sophisticated technique such as ICP-MS after preconcentration using an adsorbent; however, the separation and preconcentration of inorganic Se has not been realized in the solutions containing high concentrations of SO₄^2-. A dithiocarbamate-modified cellulose (DMC) was used in this study for the selective extraction and preconcentration of inorganic Se in wastewater, with a portable liquid electrode plasma-optical emission spectrometry (LEP-OES) being employed for quantification. DMC was found to selectively and quantitatively adsorb selenite (Se^IV) over a wide range of pH (1.0-8.0); however, less than 3.0% of selenate (Se^VI) was adsorbed in a pH range of 3.0-11. Quantitative extraction of Se^IV was achieved even in the presence of 3.5 mol L^-1 SO₄^2-. The maximum sample volume from which 10 mg of DMC could quantitatively extract Se^IV was found to be 500 mL. KOH (0.60 mL, 1.5 mol L^-1) was found to quantitatively desorb Se^IV retained on the adsorbent and yielded an enrichment factor of 833. The recovery of Se species from synthetic flue-gas desulfurization wastewater containing Se^IV and Se^VI at concentrations of 5.0 µmol L^-1 was 96.2 ± 1.8% and 105.8 ± 1.8%, respectively.

Materials interacting with inorganic selenium from the perspective of electrochemical sensing

Inorganic selenium, the most common form of harmful selenium in the environment, can be determined using electrochemical sensors, which are compact, fast, reliable and easy-to-operate devices. Despite progress in this area, there is still significant room for developing high-performance selenium electrochemical sensors. To achieve this, one should take into account (i) the electrochemical process that selenium undergoes on the electrode; (ii) the valence state of selenium species in the sample and (iii) modification of the sensor surface by a material with high affinity to selenium. The goal of this review is to provide a knowledge base for these issues. After the Introduction section, mechanisms and principles of the electrochemical reduction of selenium are introduced, followed by a section introducing the modification of electrodes with materials interacting with selenium and a section dedicated to speciation methods, including the reduction of non-detectable Se(VI) to detectable Se(IV). In the following sections, the main types of materials (metallic, polymers, hybrid (nano)materials…) interacting with inorganic selenium (mostly absorbents) are reviewed to show the diversity of properties that may be endowed to sensors if the materials were to be used for the modification of electrodes. These features for the main material categories are outlined in the conclusion section, where it is stated that the engineered polymers may be the most promising modifiers.

Magnetic dispersive micro-solid phase extraction coupled with dispersive liquid-liquid microextraction followed by graphite furnace atomic absorption spectrometry for quantification of Se(IV) and Se(VI) in food samples

In this work, magnetic dispersive micro-solid phase extraction (MDMSPE) coupled with dispersive liquid-liquid microextraction (DLLME) was developed for Se(IV) and Se(VI) followed by graphite furnace atomic absorption spectrometry. MDMSPE involved the use of magnetic ZnFe₂O₄ nanotubes for adsorbing Se(VI). The sorbent was isolated from aqueous phase by using an external magnetic field instead of tedious centrifugation or filtration. In the following step, Se(IV) in the upper aqueous phase of MDMSPE was enriched by DLLME. Samples were prepared with artificial gastric juice to avoid the inter-conversion of target species. The main factors affecting the determination of the analytes were studied in detail. the detection limits of this method were 1.0 and 1.3 pg mL^-1 for Se(IV) and Se(VI) with relative standard deviations of 4.6% and 5.1% (c = 1.0 ng mL^-1, n = 9), respectively. An enrichment factor of 200 was obtained. This method was used for the detection of Se(IV) and Se(VI) in food samples without any pre-oxidation or pre-reduction operation. A certified reference material of milk powder was analysed by this method, and the determined values were in good agreement with the certified values. Recoveries of spike experiments were in the range of 91.0-107%.

Application of Metallic Nanoparticles and Their Hybrids as Innovative Sorbents for Separation and Pre-concentration of Trace Elements by Dispersive Micro-Solid Phase Extraction: A Minireview

It is indisputable that separation techniques have found their rightful place in current analytical chemistry, considering the growing complexity of analyzed samples and (ultra)trace concentration levels of many studied analytes. Among separation techniques, extraction is one of the most popular ones due to its efficiency, simplicity, low cost and short processing times. Nonetheless, research interests are directed toward the enhancement of performance of these procedures in terms of selectivity. Dispersive solid phase extraction (DSPE) represents a novel alternative to conventional solid phase extraction (SPE) which not only delivers environment-friendly extraction with less solvent consumption, but also significantly improves analytical figures of merit. A miniaturized modification of DSPE, known as dispersive micro-solid phase extraction (DMSPE), is one of the most recent trends and can be applied for the extraction of wide variety of analytes from various liquid matrices. While DSPE procedures generally use sorbents of different origin and sizes, in DMSPE predominantly nanostructured materials are required. The aim of this paper is to provide an overview of recently published original papers on DMSPE procedures in which metallic nanoparticles and hybrid materials containing metallic particles along with other (often carbon-based) constituent(s) at the nanometer level have been utilized for separation and pre-concentration of (ultra)trace elements in liquid samples. The studies included in this review emphasize the great analytical potential of procedures producing reliable results in the analysis of complex liquid matrices, where the detection of target analyte is often complicated by the presence of interfering substances.

A review on cleaner strategies for extraction of chitosan and its application in toxic pollutant removal

Existence of human beings in this world require a cleaner environment, in which, water is the main requirement for living. Owing to the considerable development in civilisation and considerable population explosion, an increase in the contamination of natural water resources by means of non-biodegradable contaminants like heavy metals is observed thereby increasing the need for treatment of water before usage. Despite the existence of specific limits for disposal of heavy metals in water resources, studies still show high contamination of heavy metals in all these water resources. This review provides a brief note on sources and toxicity of different heavy metals in various oxidation states, their effects as well as highlights the numerous available and advanced techniques for heavy metals removal. Of all techniques adsorption is found to be beneficial as it doesn't inculcate any secondary pollutants to the environment. Additionally, this article has investigated the advantages of polymer nanocomposites in adsorption and mainly focused on biopolymer chitosan owing to its abundance in natural environment. The cleaner techniques for the extraction of chitosan and its functionalisation using different types of nanofillers are comprehensively discussed in this review. This article suggests a better alternative for conventional adsorbents as well as aids in remediation of wastes.

Determination of Mn(II) and Mn(VII) in beverage samples using magnetic dispersive micro-solid phase extraction coupled with solidified floating organic drop microextraction followed by graphite furnace atomic absorption spectrometry

Magnetic dispersive micro-solid phase extraction (MDMSPE) was coupled with solidified floating organic drop microextraction (SFODME) for direct separation and preconcentration of Mn(II) and Mn(VII) before graphite furnace atomic absorption spectrometry determination. MDMSPE involved use of magnetic ZnFe₂O₄ nanotubes for adsorbing Mn(VII). Sorbent was isolated from aqueous phase by an external magnet. Mn(II) in upper solution from MDMSPE was further enriched by SFODME. This method avoids tedious pre-oxidation/pre-reduction operation and time-consuming centrifugation/filtration step. An enrichment factor of 200-fold was obtained. Detection limits of this method were 0.005 and 0.007 ng mL^-1 for Mn(II) and Mn(VII) with relative standard deviations of 4.0% and 4.8% (n = 9), respectively. This method was successfully used for detection of Mn(II) and Mn(VII) in tap water, ice tea, energy drink, mineral water, sprite drink and carbonated drink. A certified reference material of water sample was analyzed with satisfactory results. Recoveries of spike experiments ranged from 92.5 to 106%.

Magnetic Solid Phase Extraction as a Promising Technique for Fast Separation of Metallic Nanoparticles and Their Ionic Species: A Review of Recent Advances

The widespread use of silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) in a wide variety of industrial as well as medical sectors is indisputable. This leads to a new concern about their presence in various environmental compartments. Since their negative effect and potential toxicity impact have been confirmed, analytical chemists focus on the development of different procedures for their reliable detection, identification, characterization, and quantification, not only in homogenous and simple matrices but also in complex environmental matrices. However, nanoparticles and their ionic species can coexist and their toxicity may differ; therefore, novel analytical approaches are necessary to monitor not only the nanoparticles but also their ionic species. The aim of this article is to bring a review of recent works where magnetic solid-phase extraction (MSPE) procedures in connection with spectrometric methods were used for separation/preconcentration and quantification of (1) silver and gold ions in various environmental samples, (2) AgNPs and AuNPs in real water samples in the presence of various coexisting ions, and (3) both species (it means Ag ions and AgNPs; Au ions and AuNPs) in real water samples. The results presented herein show the great analytical potential of MSPE procedures in connection with spectrometric methods used in these fields and can be helpful in guiding analytical chemists who aim to work on this subject.

Hydroquinone-Based Fabrication of Gold Nanorods with a High Aspect Ratio and LSPR Greater than 850 nm to Be Used as a Surface Plasmon Resonance Platform for Rapid Detection of Thiophanate Methyl

The use of gold nanorods (AuNRs) as surface-enhanced Raman scattering (SERS) substrates has gained much attraction due to their remarkably aspect-ratio-dependent plasmonic properties. In this report, we described the development of AuNRs with a high aspect ratio and longitudinal surface plasmon resonance (LSPR) >850 nm through a hydroquinone-based fabrication with minor modifications. The synthesis started with the reduction of chloroauric acid (HAuCl4) by sodium borohydride (NaBH4) to make gold nanoseeds from which AuNRs were grown with the aid of silver nitrate (AgNO3), HAuCl4, cetyltrimethylammonium bromide (CTAB), and hydroquinone (HQ). Scanning electron microscopy coupled with energy-dispersive X-ray (SEM-EDX), Transmission electron microscope (TEM), X-ray diffraction (XRD) and Ultra-violet-Visible spectroscopy (UV-Vis) were performed to study the shape, size, and structural and optical properties of AuNRs, respectively. The results showed that AuNRs with high aspect ratios (AR > 3) were single crystals with a heterogenous size distribution, and that the growth of Au nanoseeds into AuNRs took place along the [001] direction. AuNRs exhibited two plasmon resonance peaks at 520 nm and 903 nm, while gold nanoseeds had only a plasmon resonance peak at 521 nm. The as-synthesized AuNRs also showed SERS effects for thiophanate methyl, a broad-spectrum fungicide, with the limit of detection down to 5 mg/L of the fungicide. AuNR-coated glass can serve as a SERS-based sensing platform for rapid detection of thiophanate methyl with high sensitivity and reproducibility.

Speciation of chromium in waters using dispersive micro-solid phase extraction with magnetic ferrite and graphite furnace atomic absorption spectrometry

The combination of a solid-phase microextraction process with graphite furnace atomic absorption spectrometry provides a very sensitive determination method for determining chromium in waters. Freshly prepared ferrite particles are used to retain the chromium species, and then separated by a magnet without the need for a centrifugation step. The solid phase is suspended in water and directly introduced into the graphite furnace to obtain the analytical signal. The complexation of Cr(III) with ethylenediaminetetraacetate allows the selective retention of Cr(VI), and thus the speciation of the metal. The procedure is sensitive (0.01 µg L⁻¹ detection limit when using a 10 mL sample aliquot) and reproducible (5% relative standard deviation for five consecutive experiments at the 0.3 µg L⁻¹ level). The reliability of the procedure is verified by analysing five certified water samples.