Recent advances and applications of graphene-based extraction materials in food safety

Preparation of an imidazolium-based poly(ionic liquid) functionalized magnetic three-dimensional graphene oxide for magnetic solid phase extraction of pyrethroids from tea samples

In this work, an imidazolium-based poly(ionic liquid) (poly(1-dodecyl-3-vinyl-imidazolium bromide) functionalized magnetic three-dimensional graphene oxide (Fe3O4@3D-GO@poly(ImC12+Br-)) was synthesized via a vacuum freezing-drying method and used as a magnetic solid phase extraction (MSPE) adsorbent for the efficient extraction of pyrethroid pesticides from tea samples. The prepared Fe3O4@3D-GO@poly(ImC12+Br-) was confirmed by scanning electron microscopy (SEM), Fourier transform infrared spectrometry (FT-IR), vibrating sample magnetometer (VSM) and X-ray photoelectron spectrogram (XPS). Due to its large specific surface area and the ability to offer multiple intermolecular interactions, including π-π stacking, hydrophobic and hydrogen bond interactions, the prepared Fe3O4@3D-GO@poly(ImC12+Br-) showed high extraction efficiency for pyrethroids. The experimental parameters were optimized by a combination of single-factor method and Box-Behnken design to improve the extraction efficiency. Under the optimum conditions, coupled with high performance liquid chromatography (HPLC), a sensitive analytical method was developed for the determination of pyrethroids, and the proposed method showed wide linear ranges (1.00-100 μg L-1) with correlation coefficients (R) ranging from 0.9980 to 0.9994, low limits of detection (0.100 μg L-1) and good repeatability with intra-day relative standard deviations (RSDs) in the range of 2.90-5.53 % and inter-day RSDs in the range of 1.83-7.76 %. Moreover, the developed method was successfully applied to the determination of pyrethroids in tea samples and satisfactory recoveries ranging from 82.37 % to 114.34 % were obtained. The results showed that the developed Fe3O4@3D-GO@poly(ImC12+Br-) was an ideal, effective and selective material for the extraction and enrichment of pyrethroids from tea samples.

Two-dimensional hydrophilic imprinted resin-graphene oxide composite for selective extraction and rapid determination of gibberellin traces in licorice samples

This study presents novel methodologies and materials for selectively and sensitively determining gibberellin traces in licorice to address food safety concerns. A novel hydrophilic imprinted resin-graphene oxide composite (HMIR-GO) was developed with fast mass transfer, high adsorption capacity, and exceptional aqueous recognition performance for gibberellin. Leveraging the advantages of molecular imprinting, hydrophilic resin synthesis, and rapid mass transfer characteristics of GO, HMIR-GO was employed as an adsorbent, showing resistance to matrix interference. Coupled with HPLC, a rapid and selective method for determining gibberellin was established. Under optimal conditions, the method exhibited a wide linear range (0.02-5.00 μg g-1, r = 0.9999), low detection limits (3.3 ng g-1), and satisfactory recoveries (92.0-98.4%), enabling the accurate and rapid detection of gibberellin in licorice. This study introduces a pioneering strategy for the selective extraction and determination of trace gibberellin levels, offering insights for similar applications in functional foods.

Low flow-resistance solid phase extraction of fluoroquinolones in water and food samples by high-pressure wet spinning porous polyimide microfibers

In this work, porous polyimide microfibers (PI-μF) were prepared by high-pressure wet spinning method, and successfully applied as adsorbents for solid phase extraction (SPE) of fluoroquinolones (FQs) in water and food samples. The PI-μFs of ∼10, 25, 50, 100 μm in diameter could be controlled by the inner diameter of quartz capillary nozzles. The flow resistance of SPE cartridges packed with 10 μm PI microfiber (10-PI-μF) and 25-PI-μF was comparable to or even lower than that of commercial SPE cartridges, while the flow resistance of 50-PI-μF and 100-PI-μF SPE cartridges was increased obviously due to tiny broken pieces. The 10-PI-μF and 25-PI-μF have a specific surface area of 102 m2 g-1 and 76 m2 g-1, mesopores of 22-32 nm, and large breakthrough volume of 110 mL/5 mg and 85 mL/5 mg for FQs, while the 50-PI-μF and 100-PI-μF had much lower specific surface area and hardly had retention for FQs. FQs from tap water, egg and milk samples were then extracted by PI-μF SPE, and analyzed by high performance liquid chromatography-fluorescence detector (HPLC-FLD). SPE parameters as type of elution solvent, elution solvent volume, pH value of sample solution, flow rate of sample solution, and breakthrough volume were first optimized in detail. Under the optimal conditions, the PI-μF SPE/HPLC-FLD method showed high recoveries (96.8%-107%), wide linearity (0.05-50 μg L-1, or 0.01-10 μg L-1), high determination coefficients (R2 ≥0.9992), and low limits of detection (LODs, 0.005-0.014 μg L-1). For the real tap water, egg and milk samples, the recoveries and RSDs were 81-119% and 0.8-9.8%, respectively. The results show that porous microfiber up to 25 μm in diameter is a promising solid-phase extraction adsorbent with the lowest flow resistance that can be used for trace organic pollutants in water and food samples.

Exploring the potential applications of amphiphilic carbon dots based nanocomposite hydrogel in liquid chromatographic separations

BACKGROUND

Due to their excellent stability, low toxicity, flexible modification and adjustable functionality, carbon dots (CDs) have a promising application prospect in the field of chromatographic stationary phases. Hydrogels are new functional polymer materials with three-dimensional network structure that have excellent hydrophilicity, high porosity and unique mechanical properties, which are also good candidate materials for liquid chromatography. Nevertheless, a review of the literature reveals that CDs based nanocomposite hydrogels have not yet been reported as HPLC stationary phases.

RESULTS

In this work, amphiphilic CDs with multiple functional groups and polyacrylic acid hydrogel were grafted to the surface of silica gel by an in-situ polymerization method, and a CDs/polyacrylic acid nanocomposite hydrogel stationary phase (CDs/hydrogel@SiO2) was prepared. CDs act as the macroscopic cross-linking agents to form a cross-linked network with polyacrylic acid chains through physical cross-linking by hydrogen bonding and chemical cross-linking by amidation and esterification reactions, which not only improve the swelling property of the hydrogel but also increase its stability. Additionally, the introduction of CDs with multifunctional groups modulates the hydrophilic-hydrophobic balance of the hydrogel that also imparts good hydrophobicity to the composite hydrogel. Through the study of retention mechanism and influencing factors, it is certificate that the CDs/hydrogel@SiO2 has mixed-mode chromatographic performance. Furthermore, the CDs/hydrogel@SiO2 column shows great potential for the determination of organic contaminants in environmental water samples.

SIGNIFICANCE

This work confirms the potential application of CDs/hydrogel composite for the separation of various samples and provides the possibility of developing CDs based nanocomposite hydrogel in the field of liquid chromatography. Introducing CDs into hydrogel can open up a new way for nanocomposite hydrogels to be used in HPLC, which expands the advance of hydrogel and CDs in separation field.

Nanoscale Materials Applying for the Detection of Mycotoxins in Foods

Trace amounts of mycotoxins in food matrices have caused a very serious problem of food safety and have attracted widespread attention. Developing accurate, sensitive, rapid mycotoxin detection and control strategies adapted to the complex matrices of food is crucial for in safeguarding public health. With the continuous development of nanotechnology and materials science, various nanoscale materials have been developed for the purification of complex food matrices or for providing response signals to achieve the accurate and rapid detection of various mycotoxins in food products. This article reviews and summarizes recent research (from 2018 to 2023) on new strategies and methods for the accurate or rapid detection of mold toxins in food samples using nanoscale materials. It places particular emphasis on outlining the characteristics of various nanoscale or nanostructural materials and their roles in the process of detecting mycotoxins. The aim of this paper is to promote the in-depth research and application of various nanoscale or structured materials and to provide guidance and reference for the development of strategies for the detection and control of mycotoxin contamination in complex matrices of food.

Automated and semi-automated packed sorbent solid phase (micro) extraction methods for extraction of organic and inorganic pollutants

In this study, the packed sorbent solid phase (micro) extraction methods from manual to automated modes are reviewed. The automatic methods have several remarkable advantages such as high sample throughput, reproducibility, sensitivity, and extraction efficiency. These methods include solid-phase extraction, pipette tip micro-solid phase extraction, microextraction by packed sorbent, in-tip solid phase microextraction, in-tube solid phase microextraction, lab-on-a-chip, and lab-on-a-valve. The recent application of these methods for the extraction of organic and inorganic compounds are discussed. Also, the combination of novel technologies (3D printing and robotic platforms) with the (semi)automated methods are investigated as the future trend.

Recent Trends in Graphene-Based Sorbents for LC Analysis of Food and Environmental Water Samples

This review provides an overview of recent advancements in applying graphene-based materials as sorbents for liquid chromatography (LC) analysis. Graphene-based materials are promising for analytical chemistry, including applications as sorbents in liquid chromatography. These sorbents can be functionalized to produce unique extraction or stationary phases. Additionally, graphene-based sorbents can be supported in various materials and have consequently been applied to produce various devices for sample preparation. Graphene-based sorbents are employed in diverse applications, including food and environmental LC analysis. This review summarizes the application of graphene-based materials in food and environmental water analysis in the last five years (2019 to 2023). Offline and online sample preparation methods, such as dispersive solid phase microextraction, stir bar sorptive extraction, pipette tip solid phase extraction, in-tube solid-phase microextraction, and others, are reviewed. The review also summarizes the application of the columns produced with graphene-based materials in separating food and water components and contaminants. Graphene-based materials have been reported as stationary phases for LC columns. Graphene-based stationary phases have been reported in packed, monolithic, and open tubular columns and have been used in LC and capillary electrochromatography modes.

Determination of polycyclic aromatic hydrocarbons in Chinese herbal medicines by gas chromatography-mass spectrometry with graphene-functionalized nickel foam

Graphene-functionalized nickel foam (NF) sorbent materials were prepared and characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Thermogravimetric analysis. For the separation and detection of polycyclic aromatic hydrocarbons (PAHs) in five Chinese medicine samples, namely dandelion, fructus aurantii, peppermint, mulberry leaf and embryo chrysanthemum, a method combining dispersive micro-solid phase extraction and gas chromatography-mass spectrometry (GC-MS) was developed. Four conditions affecting the extraction efficiency, such as the type of desorption solvent, the amount of sorbent, the extraction time and the volume of water sample, were optimized. The results of the methodological validation showed that NF@SiO₂@G was able to adsorb PAHs well and with good reproducibility. All analytes showed good linearity in the concentration range of 20-2000 ng/mL with coefficient of determination R²≥0.9956. The limit of detection was 0.98-13.34 ng/mL, and the limit of quantification ranged from 3.25 to 44.47 ng/mL. Both the intra-day and inter-day precision were lower than 15.46%, and the spiked recoveries were in the range of 75.5-118.4%. The total contents of the 16 PAHs contained in these five Chinese herbal medicines (CHMs) were varied from 450 to 1557 µg/kg. The results indicated that the graphene-functionalized NF sorbent combined with GC-MS can effectively detect PAHs in CHMs.

ProFlow nano-liquid chromatography with a graphene oxide-functionalized monolithic nano-column for the simultaneous determination of chloramphenicol and chloramphenicol glucuronide in foods

Chloramphenicol (CAP) is an effective antibiotic with broad spectrum against gram-positive and gram-negative bacteria, while it is used to treat various infections in animals. Although CAP is banned for usage in the livestock products including, milk, honey, seafood, and royal jelly, CAP is still often detected in foods of animal origin, posing a threat to consumer health. The use of CAP is restricted in many countries due to its side effect in human metabolic process according to the Expert Committee on Food Additives (ECFA) recommendation. Chloramphenicol glucuronide (CAPG) is also a metabolic product of CAP, which may be a hazardous chemical for human health. Therefore, the development of sensitive separation and quantification method is an important issue, especially for food safety. Herein, we reported the preparation and application of a monolithic nano-column for CAP and CAPG analyses in foods by ProFlow Nano liquid chromatography (ProFlow Nano LC). The monolithic nano-column was prepared by an in situ polymerization using 3-chloro-2-hydroxypropylmethacrylate (HPMA-Cl) and ethylene dimethacrylate (EDMA) and followed graphene oxide (GO) modification. After characterization, the monolithic nano-column was used for the analysis of CAP and CAPG in honey and milk samples by ProFlow Nano LC. The whole method was validated in terms of linearity, sensitivity, precision, recovery, and repeatability, while it led to obtain high sensitivity with limit of quantification was found as 0.02 µg/kg for CAP. Limit of quantification for CAPG was found as 0.08 µg/kg. The developed method with monolithic nano-column was optimized to achieve very sensitive analyses of CAP and CAPG in the food samples. The applicability of the nano-column was successfully demonstrated by the analysis of CAP and CAPG in milk and honey samples. PRACTICAL APPLICATION: This article describes the preparation and application of a monolithic nano-column for the separation and determination of chloramphenicol and chloramphenicol glucuronide in food samples by ProFlow Nano LC. The use of new and advanced techniques is a crucial issue in the food science and technology. In this sense, this study demonstrated a new food analysis method using advanced instrumental technique with a homemade monolithic nano-column.

Synthesis of hypercrosslinked polymers for efficient solid-phase microextraction of polycyclic aromatic hydrocarbons and their derivatives followed by gas chromatography-mass spectrometry determination

Three novel hypercrosslinked polymers (HCPs) were synthesized via Friedel-Crafts reaction employing 1,3,5-tris(bromomethyl)-2,4,6-trimethylbenzene as alkylating agent, and triphenylbenzene, tetraphenylethylene and p-quaterphenyl as the aromatic units, respectively. The prepared HCPs were applied as solid-phase microextraction coatings for direct immersion extraction of polycyclic aromatic hydrocarbons (PAHs) and their oxygenated and nitrated derivatives in environmental water samples. The key factors affecting the extraction efficiency including extraction time, extraction temperature, stirring rate, ionic strength and desorption conditions, were carefully studied. Coupled with gas chromatography mass spectrometry analysis, a new method for determining PAHs and their derivatives was developed. Under the optimized conditions, the limits of detection (S/N=3) and limits of quantitation (the lowest concentration for quantification) of the method were in the range of 2.5-25.0 and 7.5-75.0 ng L^-1, respectively. The recoveries of spiked samples were in the range of 73.1-118.3% with relative standard deviations less than 13.0%. The developed method was applied for the simultaneous determination of nine PAHs and their derivatives in environmental water samples, showing good accuracy and reliability.

Porous chitosan/partially reduced graphene oxide/diatomite composite as an efficient adsorbent for quantitative colorimetric detection of pesticides in a complex matrix

On-site, instrument free quantitative analysis of pesticides is of significant importance for food safety control. However, it is still a great challenge for pesticide detection in food via the current visual detection methods due to the presence of interferents in a complex matrix. In this study, a complex tea matrix had a strong effect on a gold nanoparticles (Au NPs) based colorimetric sensor for the detection of pesticides. Here, a porous chitosan/partially reduced graphene oxide/diatomite (CS/prGO/DM) composite was successfully synthesized via a facile hydrothermal treatment. It could act as an efficient adsorbent for removing different types of tea interferents. A colorimetric sensing platform for the quantitative detection of pesticides in a complex matrix was successfully established. The color changes of the aggregation of Au NPs induced by pesticides were captured using the camera of a smartphone and the images were processed with average RGB (red, green, and blue) values obtained using self-developed software. The G/R values and A700/525 values obtained from UV-vis spectra could be used for quantitative analysis of pesticides. The limits of detection of phosalone and thiram in tea were 90 nM and 13.8 nM, respectively. It is expected that graphene-based materials are attractive for wide application of on-site colorimetric quantitative detection in a variety of fields like environmental protection, food safety and bioanalysis.

Amphipathic carbon quantum dots-functionalized silica stationary phase for reversed phase/hydrophilic interaction chromatography

Carbon quantum dots (CQDs) are considered as good chromatographic separation materials. However, due to the hydrophily of the synthesized CQDs, their applications in HPLC are limited to HILIC for separating strong polar compounds only. In this work, a novel amphipathic CQDs with both hydrophobicity and hydrophily is developed as mixed-mode stationary phase for RPLC/HILIC. To give CQDs certain hydrophobicity, 1,8-diaminooctane is chosen as one of the carbon sources for introducing alkyl chain into CQDs. The amphipathic CQDs modified silica (CQDs/SiO₂) stationary phase has typical characteristic of RPLC/HILIC. Both hydrophobic and hydrophilic compounds including alkylbenzenes, polycyclic aromatic hydrocarbons, nucleosides and bases, amino acids, β-adrenoceptor blockers and agonists, sulfonamides, antibiotics and alkaloids obtain satisfactory separation on this CQDs/SiO₂ column. 14 nucleosides and bases commonly existing in living organisms achieve good separation on this amphipathic CQDs/SiO₂ column within 25 min and the resolutions reach 1.33-13.83 with an average column efficiency of 18,800. The retention mechanism of this novel CQDs/SiO₂ column is investigated by linear solvation energy relationship model. It is found that hydrophobic interaction, π-π stacking, hydrogen-bonding and electrostatic interactions are main retention interactions under RPLC mode. This work provides a new approach for synthesis of amphipathic CQDs. Also, it indicates that amphipathic CQDs with versatile functional properties have great prospect in separation science.

Microextraction Techniques with Deep Eutectic Solvents

In this review, the ever-increasing use of deep eutectic solvents (DES) in microextraction techniques will be discussed, focusing on the reasons needed to replace conventional extraction techniques with greener approaches that follow the principles of green analytical chemistry. The properties of DES will be discussed, pinpointing their exceptional performance and analytical parameters, justifying their current extensive scientific interest. Finally, a variety of applications for commonly used microextraction techniques will be reported.

Magnetic solid-phase extraction of gingerols in ginger containing products

In this study, a graphene oxide/magnetite (GO-Fe₃O₄) nanocomposite was synthesized and used as a sorbent in the magnetic solid-phase extraction (MSPE) of gingerols from fresh ginger rhizomes, ginger extracts, commercial tea samples, ginger candies, thermogenic supplements, and tonic water. An MSPE method was developed, and the main influencing parameters in the sample preparation process were investigated. After GO-Fe₃O₄ based MSPE, 6-gingerol, 8-gingerol, and 10-gingerol were determined by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The whole GO-Fe₃O₄-MSPE-LC-MS/MS method proved high selectivity and consistent analytical confidence. The limits of detection (LOD) ranged between 2 and 3 μg L-1. Intra-day and inter-day RSDs fluctuated between 1.7 - 13.4% and 0.4-10.9%, respectively. Weighted calibration revealed good linearity within the studied range (5-200 μg L^-1) and guaranteed appropriate accuracy (relative residues < 25%). MSPE with GO-Fe₃O₄ demonstrated to be a practical, fast, efficient, high-throughput, and environmental-friendly sample preparation technique for determining of gingerols in commercial products, and its hyphenation with LC-MS/MS analysis yield a valuable analytical tool for the confident quality control of commercial ginger-containing products.

Automated needle-sleeve based online hyphenation of solid-phase microextraction and liquid chromatography

A novel approach for the online coupling of solid-phase microextraction (SPME) and liquid chromatography (LC) is introduced. An innovative Si@GO@βCD coated needle-sleeve extractant device was developed and then employed in the automated online SPME-LC-UV determination of estrogen-like isoflavones from human urine samples. The extractant SPME device is easily attachable at the endpoint of an analytical syringe needle and operated by a lab-made autosampler. Fully automated online SPME-LC is accomplished by proper autosampler programming to perform the following steps: i) the analytes extraction by direct immersion of the extractant device into the stirred sample, ii) a rinsing step iii) the analytes desorption/enrichment, iv) the online transference of the extract to the LC injection valve. Besides allowing the online SPME hyphenation, this extraction modality efficiently addressed the drawbacks associated with the clogging and dispersion of graphene-based microextraction techniques performed in packed-bed and dispersive formats. The main extraction parameters and the performance of the automated online SPME-LC method developed were carefully studied. The results show a good sensitivity, reliability, and straightforward analytical strategy for the determination of organic compounds in complex samples. The detection limit of the method was 20 μg L¹ for DAI and 10 μg L^-1 for GEN, FOR and BIO. The intra-day RSD was below 10% and inter-day RSD was below 13%. The total analysis time was less than 17 min per sample.

Self-Assembled Three-Dimensional Microporous rGO/PNT/Fe3O4 Hydrogel Sorbent for Magnetic Preconcentration of Multi-Residue Insecticides

The purpose of this work was to develop a highly selective, sensitive, and reliable method for multi-residual analysis. A three-dimensional microporous reduced graphene oxide/polypyrrole nanotube/magnetite hydrogel (3D-rGOPFH) composite was synthesized and utilized as a magnetic solid-phase extraction (MSPE) sorbent to preconcentrate thirteen insecticides, including five organophosphorus (isocarbophos, quinalphos, phorate, chlorpyrifos, and phosalone), two carbamates (pirimor and carbaryl), two triazoles (myclobutanil and diniconazole), two pyrethroids (lambda-cyhalothrin and bifenthrin), and two organochlorines (2, 4′-DDT and mirex), from vegetables, followed by gas chromatography-tandem mass spectrometry. This method exhibited several major advantages, including simultaneous enrichment of different types of insecticides, no matrix effect, high sensitivity, and ease of operation. This is ascribed to the beneficial effects of 3D-rGOPFH, including the large specific surface (237 m2 g−1), multiple adsorption interactions (hydrogen bonding, electrostatic, π–π stacking and hydrophobic interaction force), appropriate pore size distribution (1–10 nm), and the good paramagnetic property. Under the optimal conditions, the analytical figures of merit were obtained as: linear dynamic range of 0.1–100 ng g−1 with determination coefficients of 0.9975–0.9998; limit of detections of 0.006–0.03 ng g−1; and the intra-day and inter-day relative standard deviations were 2.8–7.1% and 3.5–8.8%, respectively. Recoveries were within the range of 79.2 to 109.4% for tomato, cucumber, and pakchoi samples at the fortification levels of 5, 25, and 50 ng g−1. This effective and robust method can be applied for determining multi-classes of insecticide residues in vegetables.

The Current Role of Graphene-Based Nanomaterials in the Sample Preparation Arena

Since its discovery in 2004 by Novoselov et al., graphene has attracted increasing attention in the scientific community due to its excellent physical and chemical properties, such as thermal/mechanical resistance, electronic stability, high Young's modulus, and fast mobility of charged atoms. In addition, other remarkable characteristics support its use in analytical chemistry, especially as sorbent. For these reasons, graphene-based materials (GBMs) have been used as a promising material in sample preparation. Graphene and graphene oxide, owing to their excellent physical and chemical properties as a large surface area, good mechanical strength, thermal stability, and delocalized π-electrons, are ideal sorbents, especially for molecules containing aromatic rings. They have been used in several sample preparation techniques such as solid-phase extraction (SPE), stir bar sorptive extraction (SBSE), magnetic solid-phase extraction (MSPE), as well as in miniaturized modes as solid-phase microextraction (SPME) in their different configurations. However, the reduced size and weight of graphene sheets can limit their use since they commonly aggregate to each other, causing clogging in high-pressure extractive devices. One way to overcome it and other drawbacks consists of covalently attaching the graphene sheets to support materials (e.g., silica, polymers, and magnetically modified supports). Also, graphene-based materials can be further chemically modified to favor some interactions with specific analytes, resulting in more efficient hybrid sorbents with higher selectivity for specific chemical classes. As a result of this wide variety of graphene-based sorbents, several studies have shown the current potential of applying GBMs in different fields such as food, biological, pharmaceutical, and environmental applications. Within such a context, this review will focus on the last five years of achievements in graphene-based materials for sample preparation techniques highlighting their synthesis, chemical structure, and potential application for the extraction of target analytes in different complex matrices.

Dispersive micro-solid phase extraction based on a graphene/polydopamine composite for the detection of pyrethroids in water samples

In this study, a simple, rapid, precise, and environmentally friendly microextraction named dispersive micro-solid phase extraction based on a graphene/polydopamine composite as a sorbent was investigated for the analysis of four pyrethroids (fenpropathrin, cyhalothrin, etofenprox and bifenthrin) in water samples. The graphene/polydopamine composite was successfully synthesized using a one-step method, and was characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy and X-ray photoelectron spectroscopy. The simplicity and rapidity of dispersive micro-solid phase extraction and the high surface area and adsorptivity of the graphene/polydopamine composite were combined in the proposed method. Several main parameters, including the amount of the sorbent, extraction time, ionic strength and desorption conditions, were independently optimized and the results were compared to find the best extraction setup for dispersive micro-solid phase extraction. Under the optimal conditions, good linearity was observed for all the target analytes, with the coefficient of determination ranging from 0.9997 to 0.9999. The extraction recoveries obtained using the proposed method ranged from 76.81% to 85.29%, and the limits of detection varied from 1.5 to 3 μg L-1. In addition, the relative standard deviation values for the intra-day precision were between 0.41% and 3.00%, while the inter-day precision showed relative standard deviation values ranging from 1.61% to 5.59%. Overall, the figures of merit of the entire procedure showed that this technique could produce satisfactory results in the detection of pyrethroids in water samples or other organic pollutants in the future.

Reduced graphene oxide-based magnetic composite for trace determination of polycyclic aromatic hydrocarbons in cosmetics by stir bar sorptive dispersive microextraction

This work describes a sensitive and rapid analytical method for trace determination of polycyclic aromatic hydrocarbons (PAHs) in cosmetic samples. The proposed method is based on stir bar sorptive-dispersive microextraction (SBSDME). A magnetic composite made of CoFe₂O₄ magnetic nanoparticles embedded into reduced graphene oxide sheets is used as sorbent phase. After the extraction, the target analytes are desorbed in toluene and then analyzed by gas chromatography-mass spectrometry (GC-MS). The main parameters involved in the extraction procedure (i.e., composite amount, extraction time and desorption time) were evaluated and optimized to provide the best extraction efficiency. The method was successfully validated under the selected conditions, showing a linear range of at least up to 125 ng mL^-1, instrumental and method limits of detection from 0.02 to 2.50 ng mL^-1 and from 0.15 to 24.22 ng g^-1, respectively, and relative standard deviations (RSD) below 10 % for all the target analytes. Standard addition combined with internal standard calibration was employed for quantification. The proposed method was successfully applied to the analysis of ten PAHs in four cosmetic products of different matrix. Several analytes between 14 and 464 ng g^-1 were found, some of them prohibited in cosmetic products. This work expands the analytical potential of SBSDME technique to other analytes and to the use of new sorbent phases, showing the great versatility of this approach depending on the characteristics of the analytes.

Amino-modified Scholl-coupling mesoporous polymer for online solid-phase extraction of plant growth regulators from bean sprouts

A new amino-modified Scholl-coupling mesoporous polymer (NH₂@SMPA)-online solid-phase extraction method, coupled with high-performance liquid chromatography (online SPE-HPLC) was established for the analysis of six plant growth regulators (PGRs) in bean sprouts. NH₂@SMPA was synthesized by acid-catalyzed deacetylation of acetylamino-Scholl-coupling mesoporous polymer (SMPA). The diversity of functional groups, such as aromatic, acetylamino, and NH₂, was conducive to multiple binding interactions between NH₂@SMPA and PGRs. NH₂@SMPA exhibited superior extraction capability for PGRs, compared with SMPA and commercial adsorbents. The extraction conditions, including loading solvent, pH of loading solution, eluting solvent, and flow rates of loading and elution, were optimized. Under the optimized conditions, wide linear ranges (0.01-500 μg kg^-1) and low detection limits (2.34-20.2 ng kg^-1) were obtained. The recoveries were satisfactory, i.e., 86.0% to 109% with relative standard deviations ≤9.8% (n = 3). Finally, the online SPE-HPLC method was successfully used for determination of PGRs in bean sprouts.

Facile synthesis of rGO-MoS2-Ag nanocomposites with long-term antimicrobial activities

The abuse of antibiotics has led to the emergence of numerous super resistant bacteria, which pose a serious threat to public health. Developing nanomaterials with novel modes of bactericidal activity offers the promise of fighting pathogens without the risk of causing drug resistances. Here, we used reduced graphene oxide (rGO), bulk molybdenum disulfide (MoS₂) and silver nitrate (AgNO₃) to synthesize a ternary nanocomposite, rGO-MoS₂-Ag, via a simple one-pot method. The resulting rGO-MoS₂-Ag presented as crumpled and sheet-like structures decorated with Ag nanoparticles. The minimum inhibitory concentration and minimum bactericidal concentration of rGO-MoS₂-Ag against Escherichia coli were 50 and 100 μg ml^-1, while Staphylococcus aureus reacted only to twice higher concentrations of 100 and 200 μg ml^-1, respectively. Notably, rGO-MoS₂-Ag exhibited better antibacterial activity towards E. coli and S. aureus than rGO, MoS₂, or rGO-MoS₂. This result can be attributed to the excellent performance of rGO-MoS₂-Ag in destroying the bacterial cell membrane and inducing the generation of reactive oxygen species. The Ag⁺ ion release of rGO-MoS₂-Ag was delayed, endowing the nanocomposite with long-term antibacterial capabilities and better biosafety. Our results indicate that the as-prepared rGO-MoS₂-Ag has promising potential for application in biomedicine and public health.

New Advanced Materials and Sorbent-Based Microextraction Techniques as Strategies in Sample Preparation to Improve the Determination of Natural Toxins in Food Samples

Natural toxins are chemical substances that are not toxic to the organisms that produce them, but which can be a potential risk to human health when ingested through food. Thus, it is of high interest to develop advanced analytical methodologies to control the occurrence of these compounds in food products. However, the analysis of food samples is a challenging task because of the high complexity of these matrices, which hinders the extraction and detection of the analytes. Therefore, sample preparation is a crucial step in food analysis to achieve adequate isolation and/or preconcentration of analytes and provide suitable clean-up of matrix interferences prior to instrumental analysis. Current trends in sample preparation involve moving towards "greener" approaches by scaling down analytical operations, miniaturizing the instruments and integrating new advanced materials as sorbents. The combination of these new materials with sorbent-based microextraction technologies enables the development of high-throughput sample preparation methods, which improve conventional extraction and clean-up procedures. This review gives an overview of the most relevant analytical strategies employed for sorbent-based microextraction of natural toxins of exogenous origin from food, as well as the improvements achieved in food sample preparation by the integration of new advanced materials as sorbents in these microextraction techniques, giving some relevant examples from the last ten years. Challenges and expected future trends are also discussed.