A newly synthesized graft copolymer for magnetic solid phase microextraction of total selenium and its electrothermal atomic absorption spectrometric determination in food and water samples

A hydrophobic deep eutectic solvent-based microextraction for the determination of ultra-trace arsenic in foods by an electrothermal atomization atomic absorption spectrometry

A hydrophobic deep eutectic solvent-based liquid-phase microextraction approach for the determination of ultra-trace arsenic (total) in foods by an electrothermal atomization atomic absorption spectrometry was developed. Various deep eutectic solvents based on tetraoctylammonium bromide and fatty acids (heptanoic, octanoic, nonanoic, decanoic acids) were studied as extraction solvents for preconcentration of arsenic (V) from mineralizates obtained after a microwave digestion of food samples. Phenomenon of ion-pairs formation between dihydroarsenate and precursor of deep eutectic solvent (tetraoctylammonium) and mass-transfer of the ion-pairs into deep eutectic solvent phase was presented for the first time. The proposed approach allowed to preconcentrate analyte into the deep eutectic solvent phase without the use of additional organic solvents (emulsifier agents or dispersive solvent), chelating and reducing agents. It was found, that the deep eutectic solvent based on tetraoctylammonium bromide and heptanoic acid provided more effective preconcentration of analyte from mineralizates (95% extraction recovery, 57-fold enrichment factor). The obtained limit of detection, calculated as a triple signal-to-noise ratio, was 10 ng L-1. The microextraction procedure was applied for the determination of trace arsenic in rice and wheat grains samples.

A systematic review and meta-analysis of validated analytical techniques for the determination of total selenium in foods and beverages

The intricate balance between the beneficial and harmful effects of selenium (Se) intake means that its quantification in food needs to be done correctly. Therefore, in this review, we systematized 105 articles to identify the most studied methodologies, analytical techniques, and food matrices. Among the analytical techniques employed, inductively coupled plasma mass spectrometry (ICP-MS) (n = 29) emerged as the most commonly used method. The most prevalent hydrolysis methodology to digest Se in food matrices involved the use of nitric acid combined with ultrasound, which improved both the yield and digestion time. Optimal recovery values were achieved when total Se quantification accounted for the sum of Se(IV) and Se(VI) (94.4-99.4%) and for SeCys (88-96.5%). These findings are relevant for advancing methodological approaches, and their results emphasize the importance of developing alternative, faster, and lower-cost protocols for Se quantification in foods and beverages.

A modified selective optical sensor for selenium determination based on incorporating xylenol orange in a poly(vinyl chloride) membrane

A novel optical sensor has been developed to measure selenium ions. The sensor membrane was created by mixing xylenol orange (XO) and sodium tetraphenylborate (NaTPB) with a plasticized poly(vinyl chloride) membrane that contained o-nitrophenyl octyl ether (o-NPOE) as a plasticizer. XO was previously established for use in a colorimeter to measure selenium in water and other media. At pH 6.6, the color of the detecting membrane changed from orange to pink when in contact with Se4+ ions. Various variables affecting the uptake efficiency were evaluated and optimized. Under optimum conditions (i.e., 30% PVC, 60% o-NPOE, and 5.0% of both XO and NaTPB for 5.0 min as the response time), the proposed sensor displayed a linear range 10-175 ng mL-1 with the detection and quantification limits of 3.0 and 10 ng mL-1, respectively. Also, the precision (RSD%) was better than 2.2% for six replicate determinations of 100 ng mL-1 Se4+ in various membranes. For the detection of Se4+, the selectivity of the sensor membrane was investigated for a number of possible interfering inorganic cations, but no appreciable interference was found. With the use of a 0.3 M HCl solution, the sensor was successfully restored, and the response that may have been reversible and reproducible exhibited an RSD% of less than 2.0%. The sensor has been successfully used to analyze Se4+ ions in environmental and biological materials.

Research Progress of Selenium-Enriched Foods

Selenium is an essential micronutrient that plays a crucial role in maintaining human health. Selenium deficiency is seriously associated with various diseases such as Keshan disease, Kashin-Beck disease, cataracts, and others. Conversely, selenium supplementation has been found to have multiple effects, including antioxidant, anti-inflammatory, and anticancer functions. Compared with inorganic selenium, organic selenium exhibits higher bioactivities and a wider range of safe concentrations. Consequently, there has been a significant development of selenium-enriched foods which contain large amounts of organic selenium in order to improve human health. This review summarizes the physiological role and metabolism of selenium, the development of selenium-enriched foods, the physiological functions of selenium-enriched foods, and provides an analysis of total selenium and its species in selenium-enriched foods, with a view to laying the foundation for selenium-enriched food development.

Chemical association of copper and selenium in coals of Sindh by time saving single step strategy and their impact on groundwater

The aim of the present study is to estimate the different chemical fractionations of copper (Cu) and selenium (Se) in coal samples of different coal mining areas. The Cu and Se bound to various chemical fractions of coal collected from two mining fields of Sindh, Pakistan, have been determined by BCR sequential extraction scheme (BCR-SES). The long duration of the BCR sequential scheme (51 h) was reduced by a time-saving shaking device (ultrasonic bath) termed as ultrasonic-assisted extraction (USE) depending on the same operating conditions and extracting solutions used for BCR sequential extraction scheme. The both trace elements were determined in aquifer water, sampled from different depth of both coal mining fields. In addition, the groundwater of dug well in the vicinity of coal mining areas were also analyzed for Cu and Se using reported extraction methodologies. The partitioning of Cu and Se bound with different chemical fractions of coal was successfully made by proposed USE, within 2 h as compared to long duration of BCR-SES (51 h). The Cu and Se concentrations in acid-soluble fractions of coal samples were > 10%, enhanced by USE extraction procedure than those values gained via BCR-SES (p < 0.01). About 67 to 69% of Cu were found in the first three fractions, whereas their remaining amount corresponding to 31 to 33%, respectively bound with crystalline/residual fraction, while up to 66.1 to 71.1% of total Se contents extracted in three extractable phases, followed up to 28.9 to 33.8% of it was bound with residual phase. The concentrations of Cu and Se in groundwater of different aquifers were found in decreasing order as AQ1 > AQII > AQIII; the same trend was observed for two aquifers of Lakhra coal mining, whereas the groundwater samples have two to three folds higher levels of Se than WHO limit. The Cu levels in water samples were significantly lower than the recommended limit of WHO for drinking water (p < 0.01).

A critical review of selected preconcentration techniques used for selenium determination in analytical samples

Selenium (Se) is considered to be an essential trace element needed for all living organisms. The importance, deficiency, and toxic effects of Se mainly depend on its quantity and chemical nature. It has been observed that the inorganic versions of Se are more hazardous than the organic versions. This review is mainly focused on the application of different extraction methods used for Se extraction and determination such as microextraction, solid-phase extraction (SPE), and their modified modes in the last 12 years. The use of different dispersive medium (magnetic field, ultrasonic radiation, and vortex agitator) to enhance Se separation is also part of this review. The usage of environmentally friendly solvents such as supramolecular solvents, hydrophobic deep eutectic solvents (DESs), and ionic liquids (ILs) are also the focus of attention in this review. This review is also emphasized the application of advanced microextraction methods, particularly liquid-phase microextraction (LPME). The most recent advances in LPME extraction techniques for Se in various environmental samples, as well as their prospects, are reviewed. Additionally, a summary of cheap, simple, and accurate techniques that have not yet been used to determine small amounts of Se has been provided.

Speciation and determination of inorganic selenium species in certain fish and food samples by gold-coated W-coil atom trap hydride generation atomic absorption spectrometry

A very sensitive, selective, rapid and easy gas-phase preconcentration based method is presented for the determination and speciation of inorganic selenium in chicken meat, poultry eggs, mullet fish (Mugil Cephalus) and sea bass fish (Dicentrarchus Labrax) samples. Gold-coated W-coil atom trap was used to increase the sensitivity of conventional HG-AAS. LOD and LOQ values were calculated to be 0.021 μg/L and 0.070 μg/L, respectively. RSD% was found as 3.24. The sensitivity was increased 20 times more with the method used in the current study than the HG-AAS method. The interference effects of other metals on Se signal were significantly reduced by trap. SEM and EDX images of both bare and gold coated W-coil atom trap were screened. In order to check the accuracy of the method, "DOLT-5: Dogfish Liver" standard reference material was used and there was a good agreement between certified and found values at the 95% confidence level.

Synthesis of polystyrene-polyricinoleic acid copolymer containing silver nano particles for dispersive solid phase microextraction of molybdenum in water and food samples

Polystyrene-polyricinoleic acid copolymer containing silver nano particles (AgPSrici) was synthesized and used in separation of molybdenum from different aqueous and foodstuff samples during a dispersive-µ-solid phase extraction approach. The synthesized nano particles were verified using Fourier transform infraredspectroscopy. An electrothermal atomic absorption spectrometry has been used for measurement of the studied ions. AgPSrici amount pH, sample volume, elution solvent kind, and the time of extraction were the effective parameters that were optimized by one-variable-at-one-time method. Analytical data of the method was calculated and limit of detection, relative standard deviation, limit of quantification were 0.022 µg L^-1, 2.9%, 150, and 0.066 µg L^-1, respectively. The synthesized adsorption capacity was obtained 170 mg g^-1.Accuracy of the method was studied by performing the method on certified reference materials and the presence of different interfering ions was studied. Molybdenum content of different water and foodstuffs was determined by the introduced method.

Trace Selenium Measurement in Water Using Laser-Induced Fluorescence Assisted by Laser Ablation

Selenium detection and removal from industrial and mining effluents have gained attention recently due to the negative effects of this trace element on aquatic life. However, the current methods for the detection of selenium in effluents are off-line by nature. In order to fill this gap, we investigated the use of laser ablation-assisted laser-induced fluorescence (LA-LIF) to measure trace amount of selenium in aqueous solutions. LA-LIF measurements are real time, label-free, standoff, and require no consumables as well as no sample preparation. They can provide a field-amenable, versatile tool for the measurement of selenium in the whole water treatment chain. We describe the system utilized, the temporal and fluence optimization studies, and the resulting calibration curve, which is linear over a wide dynamic range from parts-per-billion to tens of parts-per-million concentration levels. We also show that the achieved limit of detection of selenium can reach 32 µg/L using LA-LIF, without any kind of preconcentration or matrix transfer.

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.

Development of a magnetic dispersive solid phase extraction method by employing folic acid magnetic nanoparticles as an effective, green, and reliable sorbent followed by dispersive liquid-liquid microextraction for the extraction and preconcentration of seven pesticides from fruit juices

Folic acid magnetic nanoparticles have been prepared and utilized as an effective and reliable sorbent in magnetic dispersive solid phase extraction combined with dispersive liquid-liquid microextraction for the extraction of seven pesticides from different juices before their determination by gas chromatography-flame ionization detector. The sorbent is prepared through ball milling process using a proper mixture of folic acid and magnetic iron oxide. Characterization of the sorbent was done with X-ray diffraction pattern, scanning electron microscopy, and vibrating sample magnetometry. In the current study, limits of detection were in the range 0.12-0.33 μg L^-1. Relative standard deviations at a concentration of 40 μg L^-1 of each analyte were in the ranges of 2.15-5.14% for intra-day (n = 6) and 3.78-6.91% for inter-day (n = 4) precisions. Extraction recoveries and enrichment factors were obtained in the ranges of 70-88 % and 566-708, respectively. The performance of the method was evaluated by determination the selected pesticides in different samples. Graphical Abstract.

A simple and green ultrasound liquid-liquid microextraction method based on low viscous hydrophobic deep eutectic solvent for the preconcentration and separation of selenium in water and food samples prior to HG-AAS detection

A simple and green ultrasound liquid-liquid microextraction method based on low viscous hydrophobic deep eutectic solvent (ULLME-LV-HDES) was proposed for the preconcentration and separation of selenium prior to HG-AAS detection. Six different DESs were prepared for the extraction of selenium. Quercetin was used complexing agent for Se(IV) ions. Various analytical parameters such as pH, quercetin amount, DES type and its volume, sonication time, sample volume were optimized. Tolerance limits of anion, cation and transition metal ions were studied. Preconcentration and enhancement factor were found 62.5 and 121. Under the optimum conditions, limit of detection was found 0.25 ng L^-1 with calibration range of 0.8-120 ng L^-1. Relative standard deviation was found 3.2%. The accuracy of the method was confirmed with certified reference materials (NIST 1567a Wheat flour and NIST 1548a Typical diet). Finally, the developed method was successfully applied to food and water samples.

In-site and solvent-free exfoliation of porous graphene oxide from pencil lead fiber for solid-phase microextraction of cadmium ion before GF-AAS determination

Graphene oxide (GO)-functionalized pencil lead fiber was prepared for the first time by in situ oxidation and exfoliation of graphite contained in pencil lead fiber to porous graphene oxide structure via a one-step solvent-free dielectric barrier discharge (DBD) microplasma treatment. This new fiber was demonstrated as a highly efficient and low-cost solid-phase microextraction (SPME) fiber for the determination of toxic metal ions. The fiber extraction performance was evaluated by using cadmium as a model analyte in a direct immersing SPME mode. Unlike most commercially available and other lab-built fibers, the preparation of the graphene oxidized pencil lead fiber is environmentally friendly, low cost, and non-toxic without using any organic solvents. The fiber is robust due to its coating-free configuration. Furthermore, high extraction efficiency and high sensitivity for cadmium can be obtained due to the abundant oxygen-containing functional groups on the surface of the novel fiber. After extraction, the cadmium adsorbed on the fiber was desorbed to 150-μL solution. Graphite furnace atomic absorption spectrometry (GF-AAS) with low sample consumption was used to determine cadmium. The calibration curve for cadmium ions was linear in a range 0.04-0.26 μg L^-1 with a detection limit of 0.005 μg L^-1. A relative standard deviation (RSD, n = 5) of 2.1% was obtained at 0.1 μg L^-1 of cadmium. The sensitivity enhancement factor (EF) value of the proposed SPME method was 25. The SPME fiber was successfully applied to determine cadmium in tap water, river water, and pond water with spike recoveries ranging from 94 to 105%. Pipe network water samples were also analyzed to evaluate the cadmium release to drinking water due to the corrosion of tubes.

Selenium-Containing Proteins/Peptides from Plants: A Review on the Structures and Functions

Selenium is an essential microelement required for biological processes. Traditional selenium supplements (selenite and selenomethionine mainly) remain concerns due to toxicity and bioavailability. In recent decades, biofortification strategies have been applied to produce selenium-enriched edible plants to address the challenges of superior nutritional quality requirements. Plant-derived selenium-containing proteins/peptides offer potential health benefits beyond the basic nutritional requirements of Se. Highly nucleophilic seleno-amino acids, special peptide sequences, and favorable bioavailability contribute to the biological activities of selenium-containing proteins/peptides, such as antioxidant, antihypertensive, anti-inflammatory, and immunomodulatory effects. However, their applications on a commercial scale are insufficient owing to the complexity of purification and identification techniques and the sparse information on bioavailability and metabolism. In this review, selenium status, structural features, bioactivities, structure-activity relationships, and bioavailability, as well as the mechanisms underlying the bioactivities and metabolism of plant-derived selenium-containing proteins/peptides, are summarized and discussed for their nutraceutical use.

Selenium treatment modulates fluoride distribution and mitigates fluoride stress in tea plant (Camellia sinensis (L.) O. Kuntze)

Tea plants (Camellia sinensis (L.) O. Kuntze) can hyperaccumulate fluoride (F). The accumulation of F in tea leaves may induce serious health problems in tea consumers. It has been reported that selenium (Se) could reduce the accumulation of heavy metals in plants. Thus, the aim of this study was to investigate whether exogenous Se could reduce F accumulation in tea plant. The results showed that Se treatment could decrease F content in tea leaves, increase F accumulation in roots, decrease the proportion of water-soluble F in tea leaves and increase the Se content. Low F levels promoted the accumulation of Se in tea plants. Se treatment could modulate F-induced oxidative injury by decreasing malondialdehyde level and increasing the activities of superoxide dismutase, peroxidase and catalase. Moreover, Se inhibited F-induced increase in leaf iron, calcium, aluminum, leaf and root magnesium and lead contents. These results showed that Se application could decrease F content and increase Se content in tea leaves, which may be served as a novel strategy for production of healthy tea.

Review: Microextraction Technique Based New Trends in Food Analysis

Food chemistry is the study and classification of the quality and origin of foods. The identification of definite biomarkers and the determination of residue contaminants such as toxins, pesticides, metals, human and veterinary drugs, which are a very common source of food-borne diseases. The food analysis is continuously demanding the improvement of more robust, sensitive, highly efficient, and economically beneficial analytical approaches to promise the traceability, safety, and quality of foods in the acquiescence with the consumers and legislation demands. The traditional methods have been used at the starting of the 20th century based on wet chemical methods. Now it existing the powerful analytical techniques used in food analysis and safety. This development has led to substantial enhancements in the analytical accuracy, precision, sensitivity, selectivity, thereby mounting the applied range of food applications. In the present decade, microextraction (micro-scale extraction) pays more attention due to its futures such as low consumption of solvent and sample, throughput analysis easy to operate, greener, robotics, and miniaturization, different adsorbents have been used in the microextraction process with unique nature recognized with wide range applications.

Zirconium nanoparticles based dispersive solid phase extraction prior to slotted quartz tube-flame atomic absorption spectrophotometry for the determination of selenium in green tea samples

In this study, a novel, easy, rapid and green zirconium nanoparticles (Zr-NPs) based dispersive solid phase extraction (DSPE) method is presented for the precise and sensitive determination of selenium by slotted quartz tube-flame atomic absorption spectrophotometry (SQT-FAAS). Influential parameters of the extraction procedure were optimized by altering one parameter while keeping the other parameters constant. The optimum conditions were selected as 10 mg of Zr-NPs, 75 s vortex period, and 200 µL of concentrated HCl for 30 mL of sample/standard solution. The linear range of the developed method was found to be between 25 and 100 µg/L, and the respective limits of detection and quantification were 5.3 and 18 µg/L. About 415 folds enhancement in detection power was achieved by the optimized method relative to the conventional FAAS. Green tea samples were spiked and used for recovery experiments and the results obtained were between 92 and 102%.

Developing a highly selective method for preconcentration and determination of cobalt in water and nut samples using 1-(2-pyridylazo)-2-naphthol and UV-visible spectroscopy

BACKGROUND

Heavy metal contamination in water and agricultural products is a major concern that causes risks for human health. This article describes a highly selective approach to preconcentrate cobalt(II) (Co(II)) ions based on the standard UV-visible measurement of Co(II)-1-(2-pyridylazo)-2-naphthol complex at λ = 628 nm in water and nut samples. In this method, magnetic silica (mSiO₂ ) was utilized as a practical sorbent and 1-(2-pyridylazo)-2-naphthol was employed as a complexing agent in the elution step. The adsorbent was characterized via X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy. The effects of the main variables (pH, adsorption time, sorbent amount, pH of eluent, ligand volume, and desorption time) were investigated and established.

RESULTS

The maximum recovery was achieved at pH 7 ± 0.3, adsorption time of 60 min, sorbent amount of 40 mg, eluent pH 8 ± 0.2, ligand volume of 2 mL (16.95 × 10^-4  mol L^-1 ) and desorption time of 30 min. The linearity of dynamic range (10-500 μg L^-1 ), limit of detection (0.32 μg L^-1 ), relative standard deviation (3.04%), and preconcentration factor (25) show the reliability of the method. The sorbent was reusable 12 times. Selectivity and the effect of interference ions were successfully examined. The adsorption process of Co(II) ions on mSiO₂ was investigated based on Langmuir and Freundlich isotherms. The Freundlich model was fitted with the system and the maximum capacity adsorption of mSiO₂ for Co(II) adsorption is 2.35 mg g^-1 . Then, the kinetics study revealed that the adsorption process of Co(II) ions on the mSiO₂ follows the pseudo-first-order model. The thermodynamics parameters ΔG, ΔS, and ΔH were calculated.

CONCLUSION

The method was fruitfully applied to preconcentrate Co(II) ions in water and nut samples. This method offers high selectivity and precision for determining Co(II) ions. © 2020 Society of Chemical Industry.

Alcohol-DES based vortex assisted homogenous liquid-liquid microextraction approach for the determination of total selenium in food samples by hydride generation AAS: Insights from theoretical and experimental studies

This research article proposes a simple, quick, green and cheap approach for the determination of total selenium in food samples using alcohol-DES based vortex-assisted homogenous liquid-liquid microextraction (alcohol-DES-VA-HLLME) combination with hydride generation atomic absorption spectrometry (HG AAS). Analyte, complexing agent and working pH were Se(IV), Sudan-II and pH 4.0, respectively. In order to analyze the nature of the chemical interaction between Se(IV) ion and Sudan-II ligand, experimental results were supported with computational chemistry tools calculating quantum chemical descriptors like frontier orbital energies, hardness, softness, electronegativity, electrophilicity, nucleophilicity, transferred electron from the ligand to ion, electron donating power, electron accepting power, complexation energy, molecule-ion interaction energy. In addition, the alcohol-DES-VA-HLLME method was earned a good detection limit of 3.5 ng L^-1 and a wide calibration curve in the concentration range of 12-300 ng L^-1 (r: 0.9981). The validity of the method was evaluated by analyzing the two standard reference material (SRMs). The recoveries and relative standard deviations for 25 and 100 ng L^-1 of Se(IV) (N:5) were in the range of 1.2-2.5% and 92.1-103.7% respectively, which proved acceptable. The analytical results showed that the proposed method had important features such as cheapness, green, quick extraction and reuse, which made it attractive for the determination and efficient extraction of total selenium in the food samples.

Development of an efficient sample preparation method for the speciation of Se(iv)/Se(vi) and total inorganic selenium in blood of children with acute leukemia

In this study, a new solidified deep eutectic solvent microextraction (SDES-ME) method was applied for the speciation of Se(iv), Se(vi) and total inorganic selenium in the blood of children with leukemia from Kermanshah, Iran, prior to analysis by iridium-modified tube graphite furnace atomic absorption spectrometry (GFAAS).