Magnetic graphene solid-phase extraction for the determination of carbamate pesticides in tomatoes coupled with high performance liquid chromatography

The synthesis of Zr-metal-organic framework functionalized magnetic graphene nanocomposites as an adsorbent for fast determination of multi-pesticide residues in tobacco samples

In this paper, a simple and reliable method has been established to determine the residues of nine pesticides in tobacco by using GC-MS coupled with magnetic solid phase extraction. A novel magnetic Zr-MOF nanocomposite based on graphene was synthesized, and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy and N2 adsorption-desorption measurements. The prepared material has the advantage of large surface area (178 m2/g), good magnetic response and high thermal stability, which is shown to be suited for the fast enrichment of multi-pesticides in tobacco matrix. The extraction conditions including amount of adsorbent, adsorption time, eluting solvent as well as desorption time were investigated. The whole process of pretreatment is accomplished within 10 min. This method shows low limit of detection, wide linear range and good reproducibility (relative standard deviations <12.7%), satisfactory recoveries were obtained, ranging from 57.9% to 126.3% for tobacco samples.

Simultaneous enantioselective determination of 22 chiral pesticides in fruits and vegetables using chiral liquid chromatography coupled with tandem mass spectrometry

This paper presents a novel multi-residue method for the enantioselective analysis of 22 chiral pesticides in cucumber, tomato, cabbage, grape, mulberry, apple and pear at enantiomeric levels. Pesticides were efficiently extracted by magnetic solid-phase extraction based on graphene as sorbent. Response surface methodology was used to assist the multivariable optimization. The perfect chiral separation of the enantiomers was achieved on a Chiralpak IG column within 47 min by reversed-phase liquid chromatography coupled with tandem mass spectrometry, which is a significant improvement to resolve a large group of chiral compounds under one set of conditions. The method was validated in terms of selectivity, linearity, sensitivity, trueness and precision, which all satisfy the requirement for pesticides residue analysis. The proposed method was successfully applied for monitoring the occurrence and enantiomeric composition of pesticides in different fruits and vegetables, demonstrating its applicability for the routine analysis of chiral pesticide residues in food samples.

A hierarchically porous composite monolith polypyrrole/octadecyl silica/graphene oxide/chitosan cryogel sorbent for the extraction and pre-concentration of carbamate pesticides in fruit juices

A hierarchically porous structured composite monolith sorbent of polypyrrole-coated graphene oxide and octadecyl silica incorporated in chitosan cryogel (PPY/GOx/C18/chitosan) was synthesized and used as solid-phase extraction sorbent for the determination of carbamate pesticides. Various factors affecting the characteristics of the adsorbents (chemistry of the sorbent, polymerization time, concentrations of graphene oxide and octadecyl silica) and the extraction efficiency using the prepared sorbents, such as sample loading, desorption conditions, sample volume, sample flow rate, sample pH, and ionic strength, were investigated and optimized. Under the optimal conditions of sorbent preparation and extraction, the developed composite monolith sorbent provided wide linear responses from 1.0 to 500 μg L^-1 for carbofuran and diethofencarb, from 0.5 to 500 μg L^-1 for carbaryl, and from 2.0 to 500 μg L^-1 for isoprocarb. The limits of detection using HPLC-UV at 203, 220, and 208 nm were in the range of 0.5-2.0 μg L^-1. When the composite monolith sorbent was applied for the pre-concentration and determination of carbamate in fruit juices, good recoveries (84.1-99.5%) were achieved. The developed sorbents were porous and exhibited low back pressure enabling their use at high flow rates during sample loading. Extraction and clean-up were highly efficient, and the good physical and chemical stability of the sorbent enables reuse up to 13 times. Graphical abstract ᅟ.

Magnetic dispersive micro solid-phase extraction and gas chromatography determination of organophosphorus pesticides in strawberries

Magnetic nanoparticles (MNPs) with different sizes and characteristics were synthesized to be used as a QuEChERS sorbents for the determination of seven organophosphorus pesticides (OPPs) in strawberries by gas chromatography analysis with flame photometric and mass spectrometry detection. To achieve the optimum conditions of modified QuEChERS procedure several parameters affecting the cleanup efficiency including the amount of the sorbents and cleanup time were investigated. The results were compared with classical QuEChERS methodologies and the modified QuEChERS procedure using MNPs showed the better performance. Under the optimum conditions of the new methodology, three spiking levels (25, 50 and 100 μg kg^-1) were evaluated in a strawberry sample. The results showed that the average recovery was 93% and the relative standard deviation was less than 12%. The enrichment factor ranged from 111 to 145%. The good linearity with coefficients of determination of 0.9904-0.9991 was obtained over the range of 25-250 μg kg^-1 for 7 OPPs. It was determined that the MNPs have an excellent function as sorbent when purified even using less amount of sorbents and the magnetic properties allowed non-use of the centrifugation in cleanup step. The new methodology was applied in strawberry samples from conventional and organic farming. The new sorbents were successfully applied for extraction and determination of OPPs in strawberries.

Carbon-Based Fe₃O₄ Nanocomposites Derived from Waste Pomelo Peels for Magnetic Solid-Phase Extraction of 11 Triazole Fungicides in Fruit Samples

Carbon-based Fe₃O₄ nanocomposites (C/Fe₃O₄ NCs) were synthesized by a simple one-step hydrothermal method using waste pomelo peels as the carbon precursors. The characterization results showed that they had good structures and physicochemical properties. The prepared C/Fe₃O₄ NCs could be applied as excellent and recyclable adsorbents for magnetic solid phase extraction (MSPE) of 11 triazole fungicides in fruit samples. In the MSPE procedure, several parameters including the amount of adsorbents, extraction time, the type and volume of desorption solvent, and desorption time were optimized in detail. Under the optimized conditions, the good linearity (R² > 0.9916), the limits of detection (LOD), and quantification (LOQ) were obtained in the range of 1–100, 0.12–0.55, and 0.39–1.85 μg/kg for 11 pesticides, respectively. Lastly, the proposed MSPE method was successfully applied to analyze triazole fungicides in real apple, pear, orange, peach, and banana samples with recoveries in the range of 82.1% to 109.9% and relative standard deviations (RSDs) below 8.4%. Therefore, the C/Fe₃O₄ NCs based MSPE method has a great potential for isolating and pre-concentrating trace levels of triazole fungicides in fruits.

Determination of Pesticides by Gas Chromatography Combined with Mass Spectrometry Using Femtosecond Lasers Emitting at 267, 400, and 800 nm as the Ionization Source

A standard sample mixture containing 51 pesticides was separated by gas chromatography (GC), and the constituents were identified by mass spectrometry (MS) using femtosecond lasers emitting at 267, 400, and 800 nm as the ionization source. A two-dimensional display of the GC/MS was successfully used for the determination of these compounds. A molecular ion was observed for 38 of the compounds at 267 nm and for 30 of the compounds at 800 nm, in contrast to 27 among 50 compounds when electron ionization was used. These results suggest that the ultraviolet laser is superior to the near-infrared laser for molecular weight determinations and for a more reliable analysis of these compounds. In order to study the conditions for optimal ionization, the experimental data were examined using the spectral properties (i.e., the excitation and ionization energies and absorption spectra for the neutral and ionized species) obtained by quantum chemical calculations. A few molecules remained unexplained by the currently reported rules, requiring additional rules for developing a full understanding of the femtosecond ionization process. The pesticides in the homogenized matrix obtained from kabosu ( citrus sphaerocarpa) were measured using lasers emitting at 267 and 800 nm. The pesticides were clearly separated and measured on the two-dimensional display, especially for the data measured at 267 nm, suggesting that this technique would have potential for use in the practical trace analysis of the pesticides in the environment.

Magnetic solid phase extraction using Fe3O4@SiO2@C8 nanoparticles performed in a narrow-bore tube followed by dispersive liquid–liquid microextraction for extraction and preconcentration of nine pesticides

In the present work, a new magnetic solid phase extraction method performed in a narrow-bore tube using synthesized Fe₃O₄@SiO₂@C₈ magnetic nanoparticles has been developed.

The Potential of Graphene as an Adsorbent for Five Pesticides from Different Classes in Rape Oil Samples Using Dispersive Solid-Phase Extraction

Isolation conditions for five pesticides (metazachlor, tebuconazole, λ-cyhalothrin, chlorpyrifos, and deltamethrin) from rape oil samples were examined using the dispersive solid-phase graphene extraction technique. To determine the optimal extraction conditions, a number of experimental factors (amount of graphene, amount of salt, type and volume of the desorbing solvent, desorption time with and without sonication energy, and temperature during desorption) were studied. The compounds of interest were separated and detected by an HPLC-UV employing a Kinetex XB-C18 column and a mobile phase consisting of acetonitrile and water flowing in a gradient mode. The optimized extraction conditions were: the amount of graphene 15 mg, desorbing solvent (acetonitrile) 5 mL, time desorption 10 min at 40°C, and amount of NaCl 1 g. The detection limit for metazachlor, tebuconazole, λ-cyhalothrin, and chlorpyrifos was 62.5 ng·g^-1, and for deltamethrin, it was 500 ng·g^-1. The obtained results lead to the conclusion that graphene may be successfully used for the isolation of the five pesticides from rape oil. However, their determination at low concentration levels, as they occur in real oil samples, requires the employment of appropriately highly sensitive analytical methods, as well as a more suitable graphene form (e.g., magnetically modified graphene).

Magnetic graphene coated inorganic-organic hybrid nanocomposite for enhanced preconcentration of selected pesticides in tomato and grape

The new magnetic graphene based hybrid silica-N-[3-(trimethoxysilyl)propyl]ethylenediamine (MG@SiO₂-TMSPED) nanocomposite was synthesized via sol-gel process, and used as an effective adsorbent in magnetic solid phase extraction (MSPE) of three selected pesticides followed by gas chromatography micro-electron capture detection (GC-μECD). The adsorbent was characterized using Fourier transform-infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET), Barrett-Joyner-Halenda (BJH), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDXS) techniques. The analytical validity of the developed method was evaluated under optimized conditions and the following figures of merit were obtained: linearity, 1-20μgkg^-1 with good determination coefficients (R²=0.995-0.999); limits of detection (LODs), 0.23-0.30μgkg^-1 (3×SD/m, n=3); and limits of quantitation (LOQ), 0.76-1.0μgkg^-1 (10×SD/m, n=3). The precision (RSD%) of the proposed MSPE method was studied based on intra-day (3.43-8.83%, n=3) and inter-day (6.68-8.37%, n=12) precisions. Finally, the adsorbent was applied to determination of pesticides in tomato and grape samples and good recoveries were obtained in the range from 82 to 113% (RSDs 5.1-8.1%, n=3).

Versatile magnetic carbon nanotubes for sampling and pre concentration of pesticides in environmental water

This article describes a simple, efficient, and versatile magnetic carbon nanotubes (MCNT) method for sampling and pre-concentration of pesticides in environmental water samples. The multi-walled magnetic carbon nanotubes were obtained by chemical deposition vapor (CVD) process. The MCNTs structures are formed of hydrophobic and hydrophilic fractions that provide great dispersion at any water matrix allowing simultaneously a high efficiency of pesticides sorption. Following the extraction, analytes were desorbed with minor amounts of solvent and analyzed by gas chromatography coupled mass spectrometry (GC/MS). The parameters amount of MCNTs used to extraction, desorption time, and desorption temperature were optimized. The method showed good linearity with determination coefficients between 0.9040 and 0.9733. The limits of detection and quantification were ranged between 0.51 and 2.29µgL^-1 and between 1.19 and 5.35µgL^-1 respectively. The recovery ranged from 79.9% to 111.6%. The method was applied to the determination of fifteen multiclass pesticides in real samples of environmental water collected in Minas Gerais, Brazil.

Magnetic solid phase extraction based on graphene oxide/nanoscale zero-valent iron for the determination of tetracyclines in water and milk by using HPLC-MS/MS

A magnetic solid-phase extraction (MSPE) based on graphene oxide/nanoscale zero-valent iron (GO/nZVI) coupled with HPLC-MS/MS was proposed for the determination of trace tetracycline antibiotics (TCs) in water and milk.

Fe3O4@Graphene Oxide@Ag Particles for Surface Magnet Solid-Phase Extraction Surface-Enhanced Raman Scattering (SMSPE-SERS): From Sample Pretreatment to Detection All-in-One

A multifunctional magnetic graphene surface-enhanced Raman scattering (SERS) substrate was fabricated successfully by the layer-by-layer assembly of silver and graphene oxide (GO) nanoparticles (NPs) on the magnetic ferroferric oxide particles (Fe3O4@GO@Ag). This ternary particle possesses magnetic properties, SERS activity, and adsorption ability simultaneously. Owing to the multifunction of this Fe3O4@GO@Ag ternary complex, we put forward a new method called a surface magnetic solid-phase extraction (SMSPE) technique, for the SERS detections of pesticide residues on the fruit peels. SMSPE integrates many sample pretreatment procedures, such as surface extraction, separation sample, and detection, all-in-one. So this method shows great superiority in simplicity, rapidity, and high efficiency above other standard methods. The whole detection process can be finished within 20 min including the sample pretreatment and SERS detection. Owing to the high density of Ag NPs, the detection sensitivity is high enough that the lowest detectable concentrations are 0.48 and 40 ng/cm(2) for thiram and thiabendazole, which are much lower than the maximal residue limits in fruit prescribed by the U.S. Environmental Protection Agency. This multifunctional ternary particle and its corresponding analytical method have been proven to be applicable for practical samples and also valuable for other surface analysis.

Preparation of size-controlled magnetite nanoparticles with a graphene and polymeric ionic liquid coating for the quick, easy, cheap, effective, rugged and safe extraction of preservatives from vegetables

Size-controlled magnetite nanoparticles (Fe3O4) with 200-1000nm were synthesized by co-precipitation method. Then Fe3O4@SiO2@G@PIL was synthesized and used as modified QuEChERS adsorbent for the determination of preservatives in vegetables. The size of about 200nm of Fe3O4 in Fe3O4@SiO2@G@PIL was selected as optimum size to clean-up. It not only exerted the nanometer features of magnetic nanoparticles, but also displayed the large specific surface area of graphene (G) and the solvent effects of polymeric ionic liquids (PILs). Various experimental parameters have been investigated. Under the optimized conditions, a simple, rapid and effective method for the determination of 20 preservatives residues in vegetables was established by modified QuEChERS to gas chromatography/mass spectrometry (GC-MS) analysis. The good linearity with correlation coefficients (R(2)) of 0.9972-0.9999 was obtained over the range of 0.02-2.00mg/L for 20 preservatives. The detection limits of the proposed method for 20 preservatives ranged from 0.82 to 6.64μg/kg. The adsorbent was successfully applied for extraction and determination of preservatives in vegetable samples, which thus was time-saving with keeping good clean-up performance.

Preparation of magnetic nanographene sorbent for extraction and quantification of targeted PPCPs in environmental water samples

Nano MGO provides the advantages of large surface area and reusability property for enrichment of selected PPCPs.