Molecularly Imprinted Polymer as Sorbent for Solid-Phase Extraction Coupling to Gas Chromatography for the Simultaneous Determination of Trichlorfon and Monocrotophos Residues in Vegetables

In this study, a molecularly imprinted polymer (MIP) was prepared using the mixture of trichlorfon and monocrotophos as the mixed template. The imprinted polymer was characterized and exhibited good recognition ability and fast adsorption–desorption dynamic toward the trichlorfon and monocrotophos. Using this imprinted polymer as sorbent, a new method of molecularly imprinted solid-phase extraction coupled to gas chromatography for the simultaneous determination of two organophosphate pesticides residues was developed. Under optimal condition, the linear range was 0.005–10.0 mg/l. At a loading flow rate of 2.0 ml/min for loading 100 ml, the detection limits were 0.28 μg/l for trichlorfon and 0.090 μg/l for monocrotophos, the peak area precision (RSD) for five replicates was 4.23–4.50 %. The blank rape samples spiked with two organophosphate pesticides at 0.05 and 0.1 mg/l levels were determined by this method with recoveries ranging from 89.41 % to 95.12 %. Moreover, this method was successfully applied to the quantitative detection of the trichlorfon and monocrotophos residues in leek samples.     

Molecularly Imprinted Solid-Phase Extraction Coupled with High-Performance Liquid Chromatography for the Determination of Trace Trichlorfon and Monocrotophos Residues in Fruits

In this study, a novel molecularly imprinted polymer (MIL@MIP) that could selectively recognize the trichlorfon and monocrotophos was synthesized using metal-organic framework MIL-101 as support material. The prepared MIL@MIP was characterized by Fourier transform infrared, thermogravimetric analysis, scanning electron microscope, static adsorption, kinetic adsorption, and competitive adsorption analyses. Using this material as sorbent, a new method of molecularly imprinted solid-phase extraction coupled with high performance liquid chromatography for simultaneous determination of trichlorfon and monocrotophos was established. Under optimal conditions, the limit of detection (LOD) of this method for trichlorfon and monocrotophos detection was 0.011 and 0.015 mg/kg, respectively. The relative standard deviation (RSD) for five replicates of 0.05 mg/L trichlorfon and monocrotophos mixed solutions was within the range of 1.8 to 3.7 %. Apple and pear samples spiked with the two kinds of organophosphate pesticides were extracted and determined by using this method with good recoveries ranging from 86.5 to 91.7 %. Moreover, this method was successfully applied for the detection of the two organophosphate pesticides in strawberry samples.     

Direct Competitive Biomimetic Immunoassay Based on Quantum Dot Label for Simultaneous Determination of Two Pesticide Residues in Fruit and Vegetable Samples

In this study, trichlorfon and chlorpyrifos conjugated to CdSe/ZnS quantum dots with different emission wavelengths were adopted as labels. A hydrophilic imprinted film synthesized directly on the surface of a 96-well plate was used as the antibody. A direct competitive biomimetic immunoassay method for simultaneous determination of trichlorfon and chlorpyrifos in fruits and vegetables was developed. Under optimal conditions, the limit of detection of this method was 18.0 μg/L for chlorpyrifos (55 mg/kg for sample) and 19.0 μg/L for trichlorfon (45 mg/kg for sample). Orange and carrot samples spiked with chlorpyrifos and trichlorfon were extracted and determined by this method with recoveries ranging from 77.8 to 92.0%. The method was applied for detection of chlorpyrifos and trichlorfon residues in banana and apple samples, and the results correlated well with those obtained using gas chromatography.     

Preparation of a Hydrophilic Molecularly Imprinted Polymer and Its Application in Solid-Phase Extraction to Determine of Trace Acrylamide in Foods Coupled with High-Performance Liquid Chromatography

A hydrophilic molecularly imprinted polymer was synthesized using acrylamide (C₃H₅ON) as the template and 2-acrylamido-2-methylpropane sulfonic acid as the functional monomer. This imprinted polymer was characterized by static and kinetic adsorption experiments, and results showed that it exhibited with good recognition ability and fast adsorption–desorption dynamics toward acrylamide in an aqueous environment. Using the prepared material as sorbent, a method of molecularly imprinted solid-phase extraction coupled with high-performance liquid chromatography for analysis of acrylamide in foods was developed. Under the optimized conditions, the limit of detection (S/N?=?3) of this method for acrylamide was 72.0 ng/L, and the RSD for five replicate extractions of 10 μg/L acrylamide was 4.7 %. The blank potato samples spiked with acrylamide at different levels of 0.125, 0.250, and 0.50 μg/g were extracted and determined respectively by this developed method, and recoveries ranging from 91.5 to 95.1 % were obtained. Finally, commercial samples of twisted cruller and potato chip were quantitatively analyzed by this method.     

Molecularly Imprinted Nanosilica Solid-Phase Extraction for Bisphenol A in Fish Samples

This paper reports a method using molecularly imprinted nanosilica as the solid-phase extraction sorbent to extract bisphenol A (BPA) from fish samples. The selective extraction efficiency of BPA from its structure-analogous by molecularly imprinted solid-phase extraction (MISPE) was compared with commercial C18 SPE column. The reproducibility of MISPE and optimal flow rate of sample were studied. There was a linear correlation in the concentration range of 0.7–114.1 μg l^?1 of BPA (r?=?0.997). The limit of detection (LOD) based on three times ratio of signal to noise was 0.11 μg l^?1. Under optimal conditions, the proposed method was applied to the analysis of BPA in fish samples. The amount of BPA in bream was 4.00 μg kg^?1, and both concentrations of BPA in crucian and weever were below the LOD. The recoveries of BPA standard solution spiked with fish samples were in the range of 92.56–102.3 % with the relative standard deviation less than 10 %.     

Evaluation of a Selective Approach for the Determination of 5-Nitroimidazoles in Aquaculture Products by Capillary Liquid Chromatography Using Molecularly Imprinted Solid-Phase Extraction

Capillary liquid chromatography with UV detection is proposed for the determination of 5-nitroimidazole residues in aquaculture products. The separation was carried out in a C18 column at 20 °C, using a mobile phase consisting of water and acetonitrile, at 7 μL/min and 320 nm as detection wavelength. Furthermore, full loop injection mode (8 μL) was selected and water was considered as injection solvent. The optimized method was applied to the monitoring of nine 5-nitroimidazoles, including three metabolites, in crab, salmon, prawn, and velvet swimming crab. Molecularly imprinted solid-phase extraction has been evaluated for sample cleanup. The method was characterized in all the matrices in terms of linearity (R ² ≥ 0.9964), precision (repeatability, RSD ≤ 7.9%, and reproducibility, RSD ≤ 11.1%) and trueness (recoveries between 80.4 and 108.7%). Decision limits, CCα, ranging from 0.2 to 1.5 μg/kg and detection capabilities, CCβ, from 0.2 to 1.8 μg/kg, were obtained.     

分子印迹杂化介孔硅胶材料的制备及固相萃取-高效液相色谱法测定鳕鱼中氟喹诺酮类兽药残留

目的建立一种分子印迹介孔硅胶材料的制备方法,并用于鳕鱼中氟喹诺酮类药物残留的选择性富集。方法采用分子印迹技术和共缩聚法合成了苯基和氨基功能化的新型分子印迹杂化介孔硅胶材料。在最佳条件下,采用固相萃取-高效液相色谱法测定鳕鱼中氧氟沙星、洛美沙星和沙拉沙星3种氟喹诺酮类药物残留。结果在最佳固相萃取条件下,获得了较高的富集倍数(8.56)。在鱼样中,添加0.05、0.10和0.50 mg/kg的方法回收率为79.2%~95.2%,相对标准偏差为2.2%~4.9%,方法检出限(S/N=3)和定量限(S/N=10)分别为6.82~14.45?g/kg和22.73~48.45?g/kg。结论该样品处理方法选择性好、简单、快速,可用于鳕鱼中氟喹诺酮类药物残留的分离检测。     

Development of a Direct Competitive Biomimetic Enzyme-Linked Immunosorbent Assay Based on a Hydrophilic Molecularly Imprinted Membrane for the Determination of Trichlorfon Residues in Vegetables

In recent years, there has been an increasing demand on the determination of trace trichlorfon residues in fresh vegetables. In this study, a sensitive direct competitive biomimetic enzyme-linked immunosorbent assay (BELISA) method was developed for the determination of trichlorfon based on a hydrophilic imprinted membrane, which was directly synthesized on the well surface of MaxiSorp polystyrene 96-well plate through bulk polymerization technology. This novel imprinted membrane was characterized with high binding ability and specificity. Under the optimal conditions, the sensitivity (IC₅₀, half maximal inhibitory concentration) and the limit of detection (LOD, IC₁₅) of this method were 6800 ± 60 μg/L and 6.8 ± 0.20 μg/L, respectively. This BELISA method had been applied to the determination of trichlorfon with good recoveries ranging from 106.0 to 110.5%, and the results were correlated with that obtained by the gas chromatography method. Moreover, this method was applied to quantitative detection of trichlorfon residues in the leek samples.     

Preparation and Evaluation of Histamine Imprinted Polymer as a Selective Sorbent in Molecularly Imprinted Solid-Phase Extraction Coupled with High Performance Liquid Chromatography Analysis in Canned Fish

A series of molecularly imprinted polymers (MIPs) were prepared against histamine. Different template/monomer ratios were applied to optimize the imprinting condition. Methacrylic acid (MAA) as a functional monomer and Chloroform as a solvent were applied in polymerization process. The binding properties of MIPs were studied in comparison with a blank non-imprinted polymer. The optimized polymer, with a histamine/MAA ratio of 1/4, was selected as a sorbent in molecularly imprinted solid-phase extraction (MISPE) of histamine from canned fish. Scatchard analysis of MIP-histamine interactions revealed two types of binding sites for MIP: high affinity (K_D?=?11.11 μM) and low affinity (K_D?=?333.3 μM). The MISPE procedure was calibrated and a recovery of 76.5–97.6 % was obtained. The intra-and inter-day precision values were less than 5.70 % and 10.1 %, respectively. The selectivity of MISPE for histamine was also studied in comparison with some other structurally similar amines, which could be simultaneously present in canned fish. The performance of the imprinted polymer was examined and the results indicated that its good selectivity and affinity for histamine was very promising. Therefore, the proposed calibrated method could be applied in selective extraction and analysis of histamine in canned fish.     

Molecularly imprinted solid-phase extraction coupled to liquid chromatography for determination of Sudan dyes in preserved beancurds

New molecularly imprinted microspheres synthesized by suspension polymerisation using phenylamine and naphthol as mimic template were successfully applied as selective sorbents for the solid-phase extraction used for the simultaneous determination of four Sudan dyes from preserved beancurd products. The obtained imprinted microspheres showed good recognition and selectivity to the four Sudan dyes in aqueous solution and the affinity could be easily controlled by adjusting the property of the solution. Under the selected experimental condition, the recoveries of the Sudan dyes in preserved beancurds at three spiked levels were ranged between 90.2-104.5% with the relative standard deviation of less than 6.8%. The limit of detection (LOD) and limit of quantification (LOQ) based on a signal-to-noise of 3 and 10 were in the range of 0.005-0.009 μg g⁻¹ and 0.015-0.030 μg g⁻¹, respectively. Comparing with alumina and C₁₈-based extraction, the selectivity and repeatability of molecularly imprinted solid-phase extraction (MISPE) were obviously improved. This method could be potentially applied for the determination of Sudan dyes in complicated food samples.     

Determination of Sulfonamides in Chicken Meat by Magnetic Molecularly Imprinted Polymer Coupled to HPLC-UV

In this work, Fe₃O₄ magnetic nanoparticles were synthesized and modified by a molecularly imprinted polymer for easy and selective extraction and determination of sulfonamides in chicken meat samples. Imprinted polymer magnetic nanoparticles were characterized by Fourier transform infrared spectroscopy, X-ray diffraction pattern, thermal analysis, and scanning electron microscope micrograph. The template was removed by methanol elution. The effective parameters on extraction and determination of sulfonamides on the sorbent such as eluent type, extraction solvent, and adsorption and desorption times were optimized. Sulfonamide separation and determination were performed by high-performance liquid chromatography–UV. The linear ranges for sulfonamides were 0.5–150 μg/L and the limits of detection were 0.1–0.5 μg/L. Relative standard deviations were within 4.3–5.4 %. The method showed good selectivity for extraction of sulfonamides in real samples.     

The Mesoporous Porphyrinic Zirconium Metal-Organic Framework for Pipette-Tip Solid-Phase Extraction of Mercury from Fish Samples Followed by Cold Vapor Atomic Absorption Spectrometric Determination

In this study, the highly stable mesoporous porphyrinic zirconium metal-organic framework, namely PCN-222/MOF-545 (Zr-MOF), was prepared and used for pipette-tip solid-phase extraction of Hg(II). As a high-capacity sorbent, 4 mg of the Zr-MOF was placed into a conventional pipette tip and used, for the first time, for the fast extraction and preconcentration of mercury ions. For desorption, 50 μL of 10% HCl was used by 15 repeated aspirating/dispensing cycles, and Hg ions in elusion were measured by a cold vapor atomic absorption spectrometer. Affecting parameters on extraction efficiency were studied, and optimum conditions were established as amount of sorbent 2 mg, pH was adjusted to 5.0, the eluting volume was 15 μL, and extraction was performed on 1.8 mL of the sample. The optimal number of aspirating/dispensing cycles for extraction and desorption of analytes was found to be 10 and 15 cycles, respectively. The limit of detection of the method was found to be 20 ng L^?1 with a relative standard deviation of ≤3.1% (for seven replicate analyses of 20 μg L^?1 of mercury). Adsorption capacity and enrichment factor were 35.5 mg g^?1 and 120-fold, respectively. The proposed method was successfully applied for the determination of Hg(II) ions in fish samples.     

A Novel Molecularly Imprinted Polymer Based on Carbon Nanotubes for Selective Determination of Dioctyl Phthalate from Beverage Samples Coupled with GC/MS

Phthalates represent a potential risk for humans, since they are ubiquitous environmental contaminants. Efficient extraction and purification procedures are demanded for the detection of low concentration levels of phthalates. In this work, a novel type of molecularly imprinted polymers coated onto the surface of vinyl functionalized multi-walled carbon nanotubes was synthesized and coupled with gas chromatography–mass spectrometry (GC/MS) for the selective separation and determination of dioctyl phthalate (DOP) in beverage samples. The morphology, structure property, and thermostability of the resultant polymers were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The adsorption properties of the prepared polymers were investigated by equilibrium rebinding and competitive experiments. The resultant imprinted nanomaterials exhibited high capacity and favorable selectivity. In addition, the feasibility of the developed method using the obtained imprinted polymers as a solid-phase sorbent coupled with GC/MS for the selective isolation and determination of DOP in different beverage samples was demonstrated. Under optimal conditions, the limit of detection of the proposed method for DOP was 2.3 ng L^?1. DOP spiked at three levels of concentration in beverage samples was extracted and determined through the application of the present method, with recoveries ranging from 88.6 to 93.0 % with relative standard deviations less than 5.6 %.     

Highly Selective Determination of Chrysoidine in Foods Through a Surface Molecularly Imprinted Sol–Gel Polymer Solid-Phase Extraction Coupled with HPLC

A highly selective determination method for chrysoidine, an industrial azoic dye banned in foods, was developed through a novel molecularly imprinted polymer (MIP) online solid-phase extraction coupled with high-performance liquid chromatography. The MIP was firstly synthesized by a surface molecular imprinting technique in combination with a sol–gel process and characterized by FT-IR and adsorption experiments. The MIP exhibited high selectivity and high adsorption capacity for chrysoidine and offered a fast kinetics for the adsorption and desorption of chrysoidine. A number of parameters, including the pH of loading solution, the sample loading flow rates, and eluting time of analyte, were carefully optimized to improve the extraction efficiency. Under the optimal experimental conditions, for a 50-mL sample solution, the enrichment factor was 279 and the detection limit (S/N?=?3) was 6 ng L^?1. The linear plots with r ²?>?0.99 were achieved over a range of 0.04–40 μg L^?1, and the peak area precision (relative standard deviation) for nine parallel determinations was below 6.32 %. This method was employed for quantitative determination of chrysoidine in oil bean curd, yellow croaker, and paprika with satisfactory recoveries (89.3–97.6 %).     

水兼容性分子烙印固相萃取-高效液相色谱法测定鸡肉中氟喹诺酮类药物残留

目的：建立分子烙印固相萃取-高效液相色谱测定鸡肉中氟喹诺酮类药物残留的新方法。方法：以甲基丙烯酸为功能单体,恩诺沙星为模板分子,在强极性溶剂甲醇-水体系中制备分子烙印聚合物,考察和评价分子烙印聚合物的特性。鸡肉样品经乙腈提取浓缩后过分子烙印固相萃取柱,乙腈-三氟乙酸(99:1,V/V)洗脱液由高效液相色谱分离和荧光法检测。结果：高亲合力的结合位点的解离常数为Kd1=7.19×10-5 mol/L,最大表观结合位点数Qmax,1=110.19μmol/g;低亲和力结合位点的解离常数为Kd2=2.44×10-3mol/L,最大表观结合位点数Qmax,2 = 965.51μmol/g。氧氟沙星、诺氟沙星、环丙沙星和恩诺沙星等氟喹诺酮类药物的校准曲线在1.0～500 μg/kg范围内呈良好的线性关系(r≥0.9991),检出限(S/N=3)为0.06～0.09μg/kg,平均回收率为75.4%～86.4%(n=3),相对标准偏差小于6%。结论：以水兼容性分子烙印固相萃取-高效液相色谱法可实现氟喹诺酮药物的有效分离和灵敏测定。     

Fast Preconcentration of Pesticide Residues in Oilseeds by Combination of QuEChERS with Dispersive Liquid–Liquid Microextraction Followed by Gas Chromatography-Mass Spectrometry

A fast, efficient, and simple method for determination of pesticide residues in pumpkin seeds has been developed combining QuEChERS and dispersive liquid–liquid microextraction (DLLME) followed by gas chromatography and mass spectrometry (GC-MS). Parameters affecting the DLLME performance such as solvent selection and volume of extractive and dispersive solvent, salt effect, and extraction time were studied. Under the selected conditions (50 μL extractive solvent chloroform, 1 mL QuEChERS extract, and 3 mL water), the developed method was validated. Linearity was evaluated at nine concentrations in the broad range of 0.1–500 μg/kg with correlation coefficients from 0.9842 to 0.9972. The relative standard deviations at lowest calibration level varied from 0.3 to 22 %. Under the optimum conditions, an enrichment factor was 6–17-fold and detection limits 0.01–12.17 μg/kg were achieved. Finally, the developed and validated method was successfully applied for the extraction and determination of pesticide residues in 16 real samples with 2 positive findings below maximum residue limits (MRL). Limits of detection (LODs) of the proposed method are below the MRLs established by the European Union.     

Rapid determination of Alternaria mycotoxins in tomato samples by pressurised liquid extraction coupled to liquid chromatography with fluorescence detection

ABSTRACT

A sensitive and reliable method using pressurised liquid extraction (PLE) followed by molecularly imprinted solid phase extraction (MISPE) and high performance liquid chromatography with fluorescence detection (HPLC–FLD) has been developed for the analysis of alternariol (AOH) and alternariol monomethyl ether (AME) in tomato samples. Influence of several extraction parameters that affect PLE efficiency were evaluated for the simultaneous extraction of both mycotoxins in the selected samples. AOH and AME were optimally extracted using MeOH/water (25:75, v/v) at 70°C as solvent, a pressure of 1000 psi and a single extraction cycle. The resulting PLE extracts were pre-concentrated by molecularly imprinted solid phase extraction (MISPE) cartridges followed of analysis by HPLC with fluorescence detection (λ_exc = 258, λ_em = 440 nm). The proposed method was applied to the analysis of AOH and AME in fortified tomato samples (20–72 µg· kg–1) with recoveries of 84–97% (RSD < 8%, n = 6) for AOH and 67–91% (RSD < 13%, n = 6) for AME. The detection limit for AOH and AME were 7 and 15 µg· kg^–1, respectively. The ensuing PLE–MISPE–HPLC–FLD method was validated for the analysis of both mycotoxins in tomato samples in accordance with European Commission Decision 2002/657/EC.     

Simultaneous Determination of Flumequine and Oxolinic Acid Residues in Aquatic Products Using Pressurized Capillary Electrochromatography

A rapid method for detection of flumequine (FQ) and oxolinic acid (OA) residues from fish tissues was established using pressurized capillary electrochromatography (pCEC). Residual FQ and OA were extracted from fish tissue samples with acidified acetonitrile and purified on an Oasis HLB C₁₈ solid-phase extraction column. The extract was then analyzed by pCEC with the mobile phase (pH?=?3) consisting of acetonitrile and 15 mM ammonium acetate (45: 55, v/v, respectively) at the flow rate of 0.07 mL/min, detection wavelength of 324 nm, and applied voltage of ?10 kV. Baseline separation of FQ and OA was achieved in 10 min; both drugs showed good linearity in the range of 0.2–5 μg/mL. The recoveries of FQ and OA were between 82 and 92 % (relative standard deviation?=?3.63–5.96). The limits of detection for FQ and OA were 0.1 and 0.08 mg/kg, respectively.     

Development and Comparison of Sample Preparation Techniques for Chromatographic Analysis of Sulfonamide Residues in Bovine Milk

Most studies to determine sulfonamide residues in milk samples have used solid-phase extraction as the sample preparation technique. However, the quick, easy, cheap, effective, rugged, and safe (QuEChERS) method, introduced in 2003, has been used in the extraction of various compounds in food matrices. This study aimed to evaluate two sample preparation techniques: solid-phase extraction and QuEChERS, for chromatographic analysis of sulfonamides (sulfathiazole, sulfamethazine, and sulfadimethoxine) in bovine milk. The chromatographic parameters and the QuEChERS extraction procedure were developed by using different experimental designs, obtaining good peak resolution, recovery, precision, accuracy, linearity, selectivity, and limits of detection and quantification. In contrast, using solid-phase extraction, acceptable recoveries and selectivity were not achieved, despite the number of articles published that have applied this sample preparation technique for sulfonamide analysis. As a result of the experiments performed, probably sulfonamides are retained together with other components of the matrix in the sample pretreatment step (prior to its addition in the cartridge containing solid phase), which is an important part of solid-phase extraction with raw whole milk. Therefore, QuEChERS is a better method than solid-phase extraction for the analysis of sulfonamide residues in milk. Validation tests demonstrated that the method is appropriate, within the maximum residue limit (0.1 mg kg^?1). Moreover, it was possible to use a lower amount of solvent compared with previously published articles (6 mL against 10 or 15 mL).     

Magnetic Mixed Hemimicelles Solid-Phase Extraction of Three Food Colorants from Real Samples

Introducing a specific clean extraction procedure with a minimal matrices effect for food colorant determination is still a challengeable topic and highly recommended. Mixed hemimicelle solid-phase extraction method, based on cetyltrimethylammonium bromide-coated Fe₃O₄/SiO₂ nanoparticles as a novel, simple, and fast preconcentration method, was applied for preconcentration and fast isolation of three synthetic food colorants in foodstuff matrices prior to HPLC-UV-vis determination. The influence of different parameters on extraction efficiency such as surfactant amount, sample pH, time of extraction, desorption condition, and nanoparticles concentration was optimized. Under the optimized conditions, a preconcentration factor of 100 was achieved by extracting 10 mL sample. The limit of detection for the three synthetic food colorants including Tartrazine, Sunset yellow FCF, and Quinoline yellow is 2.50, 1.25, and 2.12 μg/L, respectively. The proposed method was applicable for extraction and preconcentration of three food colorants in various food samples with the food dye contents in the range of 13–105 μg/L.