Advances and Applications of Hybrid Graphene-Based Materials as Sorbents for Solid Phase Microextraction Techniques.

The advancement of traditional sample preparation techniques has brought about miniaturization systems designed to scale down conventional methods and advocate for environmentally friendly analytical approaches. Although often referred to as green analytical strategies, the effectiveness of these methods is intricately linked to the properties of the sorbent utilized. Moreover, to fully embrace implementing these methods, it is crucial to innovate and develop new sorbent or solid phases that enhance the adaptability of miniaturized techniques across various matrices and analytes. Graphene-based materials exhibit remarkable versatility and modification potential, making them ideal sorbents for miniaturized strategies due to their high surface area and functional groups. Their notable adsorption capability and alignment with green synthesis approaches, such as bio-based graphene materials, enable the use of less sorbent and the creation of biodegradable materials, enhancing their eco-friendly aspects towards green analytical practices. Therefore, this study provides an overview of different types of hybrid graphene-based materials as well as their applications in crucial miniaturized techniques, focusing on offline methodologies such as stir bar sorptive extraction (SBSE), microextraction by packed sorbent (MEPS), pipette-tip solid-phase extraction (PT-SPE), disposable pipette extraction (DPX), dispersive micro-solid-phase extraction (d-µ-SPE), and magnetic solid-phase extraction (MSPE).

Magnetic solid-phase extraction based on restricted-access molecularly imprinted polymers for ultrarapid determination of ractopamine residues from food samples by capillary electrophoresis.

An ultrafast, efficient, and eco-friendly method combining magnetic solid phase extraction and capillary electrophoresis with diode array detection have been developed to determine ractopamine residues in food samples. A restricted access material based on magnetic and mesoporous molecularly imprinted polymer has been properly synthesized and characterized, demonstrating excellent selectivity and high adsorbent capacity. Short-end injection capillary electrophoresis method was optimized: 75 mM triethylamine pH 7 as BGE, -20 kV, 50 mbar by hydrodynamic injection during 8 s, and capillary temperature at 25 °C; reaching ultrafast ractopamine analysis (∼0.6 min) with good peak asymmetry, and free from interfering and/or baseline noise. After sample preparation optimization, the conditions were: 1000 µL of sample at pH 6, 20 mg of adsorbent, stirring time of 120 s, 250 µL of ultrapure water as washing solvent, 1000 µL of methanol: acetic acid (7: 3, v/v) as eluent, and the adsorbent can be reused four times. In these conditions, the analytical method showed recoveries around to 100 %, linearity ranged from 9.74 to 974.0 µg kg-1, correlation coefficient (r) ≥ 0,99 in addition to adequate precision, accuracy, and robustness. After proper validation, the method was successfully applied in the analysis ractopamine residues in bovine milk and bovine and porcine muscle.

Synthesis of ionically imprinted Poly(Alylthiourea) in the presence of 1-(2-Pyridylazo)-2-Napthol (PAN) for preconcentration in magnetic dispersive solid phase of nickel ions in water and food samples.

In the present study, a magnetic ion-imprinted polymer based on n-allylthiourea in the presence of 1-(2-pyridylazo)-2-naphthol (MIIP-PAN) was synthesized, characterized, and applied in the preconcentration of nickel ions by dispersive magnetic solid phase extraction (DMSPE) with FAAS detection. For comparison, non-imprinted polymer (MNIP-PAN) and imprinted polymer without PAN were synthesized. The characterization of the polymers was performed by FT-IR, DRX, TEM, TGA, VSM, and BET. Selectivity studies were performed comparing the competitive adsorption of Ni2+ with other cations on MIIP-PAN and MNIP-PAN, achieving higher relative selectivity coefficients for MIIP-PAN than for MNIP-PAN and NIP. Under optimized conditions, the method provided a preconcentration factor of 76.70, detection limit of 0.25 µg/L and intra-day (2.06 - 2.33 %) and inter-day (1.82 - 4.90 %) precision. The developed method was applied to samples of water, teas, and chocolate powder, and its precision was evaluated through tests of recovery and analysis of certified materials.

Magnetic and mesoporous molecularly imprinted polymer synthesized by rational computation design: Sample preparation and analysis of ractopamine.

Through density functional theory calculations was studied theoretically the formation process of a magnetic and mesoporous molecularly imprinted polymer for ractopamine (RAC), evaluating the molecular electrostatic potential map, functional monomers, functional monomer / template stoichiometry and crosslink agents. The results revealed that the best conditions for the synthesis were established with acrylic acid as functional monomer in a 1: 4 stoichiometry using acetonitrile as the solvent and ethylene glycol dimethacrylate as crosslink agent. It was observed that nine hydrogen bonds established between the RAC and acrylic acid play a key role on the pre-polymerization complex. In addition, three analytical methods using HPLC, UHPLC and CE instruments were optimized for rapid analysis. The adsorbent was experimentally synthesized considering the best conditions found at the molecular level and characterized by FTIR, DRX, TGA, SEM, TEM, surface analysis, and wettability. After that, the synthesized material was used in magnetic solid phase extraction combined with capillary electrophoresis in a preliminary RAC recovery study from milk samples. Finally, greenness metric with a score of 0.55 have been obtained for the sample preparation procedure using the online AGREEprep metric.

Magnetic solid phase extraction as a nonchromatographic method for the quantification of ultratrace inorganic arsenic in rice by inductively coupled plasma-optical emission spectrometry (ICP OES).

An alternative analytical method was developed for the quantification of inorganic arsenic (iAs) in rice by ICP OES. Iron nanoparticles modified with an organophosphorus compound were used as the solid phase for MSPE of iAs from the plant matrix. The MSPE procedure was performed using 4 mL of a buffer solution with pH 4.0, 20 mg of the nanomaterial, and a 15-min extraction time. The total As (tAs) by ICP OES was also quantified using the same MSPE procedure after solubilization of the samples by a block digester. The accuracy of tAs and iAs quantification was verified using CRM NIST 1568b (97 % and 101 % recovery, respectively). The precision (RSD < 15 %) and LOD and LOQ (1.08 and 3.70 µg kg-1, respectively) of the proposed method were satisfactory. The rice samples had tAs contents between 0.090 and 0.295 mg kg-1 and iAs mass fractions between 0.055 and 0.109 mg kg-1.

Determination of sunset yellow, allura red, and fast green using a novel magnetic nanoadsorbent modified with Elaeagnus angustifolia based on magnetic solid-phase extraction by HPLC

Abstract Sunset yellow (SY), allura red (AR) and fast green (FG) are frequently used in commercial food products, although they are considered to be hazardous to public health due to their toxic efficacy and high exposure risk potency. In this study, a new, rapid, and reliable method based on a magnetic solid-phase extraction (MSPE) was developed for the simultaneous determination of SY, AR, and FG. Fe3O4 modified with Elaeagnus angustifolia was used for the first time as an adsorbent (Fe3O4-EA) in MSPE. It was characterized with scanning electron microscopy, Brunauer Emmet Teller surface area analysis and X-ray diffraction. MSPE parameters were optimized in terms of pH, adsorption, and elution time and elution volume. High-performance liquid chromatography was used for dye quantitation. Analytical separation was performed by applying ammonium acetate buffer, acetonitrile, and methanol as the mobile phase to a C18 reverse-phase analytical column. Intraday and inter-day repeatability of the method performed at the concentration of 0.2, 1.0 and 2.0 µg/mL exhibited <8.1% RSD (n=3). The limit of detection values was between 0.05-0.1 µg/mL. The adsorption data of SY, AR and FG on Fe3O4-EA were fitted with the Langmuir model with qmax values of 45.0, 70.4 and 73.0 mg/g, respectively.

A fast, low-cost, sensitive, selective, and non-laborious method based on functionalized magnetic nanoparticles, magnetic solid-phase extraction, and fluorescent carbon dots for the fluorimetric determination of copper in wines without prior sample treatment.

A new fluorimetric method for copper(II) determination in wines was developed combining functionalized magnetic nanoparticles (FMNP) and fluorescent carbon dots (FCD). To produce FMNP, Fe3O4 was coated with Al2O3 forming Fe3O4@Al2O3 core-shell magnetic nanoparticles and functionalized with PAN and SDS. FCD was synthesized from pineapple juice through hydrothermal carbonization. For copper determination, aliquots of wine, the FMNP dispersion, and Britton-Robinson buffer (pH = 4.0) were mixed under stirring to allow the adsorption of copper by FMNP. Cu-FMNP complex was attracted by a niobium magnet and, after discarding the non-magnetic material, the copper(II) ions were eluted with an FCD dispersion before fluorescence quenching measurements. The proposed method presented a linear range from 0.020 to 0.100 mg L-1 (r2 = 0.9953), RSD (intraday) < 3.0%, and recovery rates from 96 to 105 %. FMNP and FCD properties permitted extraction/preconcentration/determination of copper within 1 min with an enrichment factor of nine and without prior sample treatment.

Efficient and selective extraction of azamethiphos and chlorpyrifos residues from mineral water and grape samples using magnetic mesoporous molecularly imprinted polymer.

A magnetic mesoporous molecularly imprinted polymers was synthesized on the surface of magnetic nanoparticles silanized with 3-(trimethoxysilyl) propyl methacrylate to introduce reactive methacrylate groups. Subsequently, methacrylic acid monomers were grafted onto the surface of this adsorbent functionalized via polymerization by precipitation. Magnetic mesoporous molecularly imprinted polymer was properly characterized by different techniques and applied as adsorbent in magnetic solid phase extraction for selective determination of two organophosphorus pesticides, azamethiphos and chlorpyrifos, in mineral water and grape samples. After sample preparation optimization, recoveries of 99.56% and 98.86% were obtained for azamethiphos and chlorpyrifos, respectively. The magnetic solid phase extraction coupled to HPLC-UV presented limit of quantification of 5 ng mL-1, linearity ranged of 5 to 1000 ng mL-1, in addition to adequate accuracy, precision and robustness. The pesticides showed stability in the matrix and were satisfactorily quantified in real mineral water and grape samples.

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.

A robotic magnetic nanoparticle solid phase extraction system coupled to flow-batch analyzer and GFAAS for determination of trace cadmium in edible oils without external pretreatment.

A lab-made magnetic-mechanical robotic (MMR) system coupled to a flow-batch analyzer (FBA) for magnetic nanoparticles solid phase extraction (MSPE) is presented. As an illustrative application, an NMR-FBA couple was connected to a graphite furnace atomic absorption spectrometer (GFAAS) for quantification of trace cadmium in edible oils. Factors affecting MSPE, such as the amount of adsorbent, the type, concentration and volume of the eluent and elution time were studied. Under the optimized experimental conditions, the interferents studied did not reveal a significant change in the analytical response, indicating that proposed method is selective. The sampling rate, characteristic mass, working linear range, limits of detection (LOD), and sensitivity were 10h-1, 0.18pg, 0.05-1.0µgkg-1, 0.006µgL-1, and 0.4197, respectively. An enrichment factor of 9 was achieved using a 2.5mL oil sample. In order to evaluate the accuracy, a certified reference material was analyzed by the proposed and a reference method. The values obtained were compared with the one provided from the manufacturer and no statistically significant differences were observed among three values at a confidence level of 95% using paired t-test. In addition, the precision intra-day and inter day of the proposed method and the robustness were assessed and again no statistically significant differences were observed at a confidence level of 95%. The use of a microcolumn to immobilize the MNPs is not needed with the proposed MMR-FBA-GFAAS system, thus avoiding the well-known problem of non-uniform packing of the MNPs presented in previous flow-based automatic methods. Despite a high organic load of edible oils, the method developed is simple, robust and presents satisfactory analytical features when compared with others that have been reported in the literature, suggesting that it is a potentially useful alternative to determine trace analytes in viscous matrices without external pretreatment.

Magnetic solid-phase extraction based on mesoporous silica-coated magnetic nanoparticles for analysis of oral antidiabetic drugs in human plasma.

In the present work, magnetic nanoparticles embedded into mesoporous silica were prepared in two steps: first, magnetite was synthesized by oxidation-precipitation method, and next, the magnetic nanoparticles were coated with mesoporous silica by using nonionic block copolymer surfactants as structure-directing agents. The mesoporous SiO2-coated Fe3O4 samples were functionalized using octadecyltrimethoxysilane as silanizing agent. The pure and functionalized silica nanoparticles were physicochemically and morphologically characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The resultant magnetic silica nanoparticles were applied as sorbents for magnetic solid-phase extraction (MSPE) of oral antidiabetic drugs in human plasma. Our results revealed that the magnetite nanoparticles were completely coated by well-ordered mesoporous silica with free pores and stable pore walls, and that the structural and magnetic properties of the Fe3O4 nanoparticles were preserved in the applied synthesis route. Indeed, the sorbent material was capable of extracting the antidiabetic drugs from human plasma, being useful for the sample preparation in biological matrices.

Magnetic solid phase extraction followed by high-performance liquid chromatography for the determination of sulphonamides in milk samples.

A simple and effective method based on magnetic solid-phase extraction combined with high performance liquid chromatography was used for the determination of nine sulphonamides in milk samples. The extraction and cleanup via silica-based magnetic adsorbent dispersion in milk samples followed by the magnetic isolation and desorption of the analytes using NaOH-methanol. Three different magnetic phenyl silica adsorbents were synthesized by varying the molar ratio of phenyltrimethylsilane and tetramethylorthosilicate; these adsorbents were evaluated for sulphonamides retention in terms of their pH and degree of hydrophobicity. The optimal conditions were a pH of 6.0 and a magnetic:sorbent ratio of 2:1. Under optimal conditions, limits of detection ranging from 7 to 14 µg L(-1) were obtained. The method was validated according with the European Commision Decision 2002/657/EC. The proposed method was applied to analyse sulphonamides in 27 milk samples of different brands. Thirteen samples tested were positive for the presence of sulphonamides.