Selective determination of chloramphenicol at trace level in milk samples by the electrode modified with molecularly imprinted polymer

A novel voltammetric sensor for determination of chloramphenicol (CAP) in milk samples was introduced. The CAP selective molecularly imprinted polymer (MIP) and non imprinted polymer (NIP) were synthesized and then added to the carbon paste (CP) electrode composition in order to prepare MIP-CP electrode. The MIP, embedded in the carbon paste electrode, acted as the selective recognition element and pre-concentrator agent for CAP. CAP was extracted in the electrode for a definite time and then it was analyzed by differential pulse voltametry, found to be an effective determination method. The MIP-CP showed very high CAP recognition ability, compared to NIP-CP. The electrode washing, after CAP extraction, led to an enhanced selectivity. Various factors, known to affect the response behavior of the electrode, were investigated and optimized. This sensor showed a linear response range of 8.0 × 10⁻⁹−1.0 × 10⁻⁶ M and lower detection limit of 2.0 × 10⁻⁹ M (S/N = 3). The sensor was successfully applied to the determination of CAP in milk samples.     

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.     

Synthesis and characterisation of a selective adsorbent based on the molecularly imprinted polymer for the removal of cloxacillin antibiotic residue from milk

In recent decades, environmental pollution has been a subject of growing concern. This is partly due to the overuse of antibiotics, the consequent drug resistance and the discharge of drugs into the environment. The aim of this study was to synthesise molecularly imprinted polymer (MIP) particles via a noncovalent procedure for the removal of cloxacillin from milk. Accordingly, the effects of operational parameters such as pH, contact time and MIP dosage were studied. The performance of MIP particles in removing cloxacillin from livestock milk samples proved that these adsorbents can effectively help to reduce drug contamination from dairy sources.     

新型分子印迹聚合物修饰的选择性离子源结合电喷雾电离质谱快速检测莠灭净和莠去津

基于分子印迹聚合物修饰铁片（molecularly imprinted polymer modified iron sheet,MIPIS）制备了一种选择性的敞开式质谱离子源,结合电喷雾电离质谱,构建一种快速检测食品基质中莠灭净和莠去津痕量残留的方法。分子印迹聚合物以氰草津为模板,使用甲基丙烯酸和苯胺在水溶液中聚合而成。将MIPIS作为萃取尖端对豆奶粉、小麦和牛奶中的莠灭净和莠去津进行富集,随后作为敞开式质谱离子源结合电喷雾电离质谱直接进行检测。结果显示,在0.2～200μg/L范围内线性良好,相关系数R2为0.998 2和0.999 7,检出限和定量限分别为0.2～0.5μg/kg和0.6～1.5μg/kg,在3个加标水平下回收率在81.05%～109.66%。该方法操作简单,灵敏度高,省时高效,无需长时间的色谱分离,适用于食品中痕量三嗪类农药残留的快速检测。     

Preparation of Molecularly Imprinted Polymer Monolith with an Analogue of Thiamphenicol and Application to Selective Solid-Phase Microextraction

A molecularly imprinted polymer (MIP) monolith has been prepared and characterized. Its application to the assay of thiamphenicol in milk with high-performance liquid chromatography?Cphotodiodes array detector was validated. The newly developed MIP monolith was produced using an analogue to thiamphenicol as the template molecule to avoid major traditional drawback associated with MIPs of residual template bleeding. The MIP monolith synthesized in a micropipette tip could be connected with syringes in different sizes simply to perform solid-phase microextraction process without any other treatment. This molecularly imprinted polymer monolith microextraction (MIPMME) method showed high selectivity and enrichment ability for thiamphenicol (TAP). Several parameters affecting MIPMME were investigated, including the flow rate, volume, pH and salt concentration of sample, the type and volume of washing solution, and the type and flow rate of eluent. The recovery of this method for TAP was investigated and high recoveries of 93.5?~?96.8% from milk were obtained with relative standard deviations less than 6.3%.     

Molecularly imprinted solid-phase extraction of fumonisin B analogues in bell pepper,rice and corn flakes

A molecularly imprinted polymer (MIP) for the recognition of fumonisin B analogues (FB) using 2-(diethylamino) ethyl methacrylate (DEAEM) as functional monomer and trimethylolpropane trimethacrylate (TRIM) as cross-linker was prepared by bulk polymerization in acetonitrile. Fumonisin B₁ (FB₁) was used as a template molecule. A molecularly imprinted solid-phase extraction (MISPE) procedure was developed for further application in the analysis of FB. The performance of the MIP throughout the clean-up of spiked bell pepper, rice and corn flake sample extracts was compared with the results obtained when using non-imprinted polymer, C₁₈, strong anion exchange and immunoaffinity sorbents. Extracts were analysed for FB with liquid chromatography-tandem mass spectrometry (LC-MS/MS) after clean-up. Depending on the food matrix and the concentration range of the fumonisins, recoveries after MISPE varied from 62 to 86%, from 62 to 83%, and from 67 to 81% for fumonisin B₁ (FB₁), fumonisin B₂ (FB₂) and fumonisin B₃ (FB₃), respectively. The selectivity of the synthesized MIP for mycotoxins belonging to the group of FB was confirmed by evaluating cross-reactivity from analogue structures and other mycotoxins. Analysis of 39 naturally contaminated samples (corn flakes) by liquid chromatography tandem mass spectrometry indicated that the synthesized MIP could be an excellent alternative for clean-up and pre-concentration of FB in food samples. Pearson correlations between immunoaffinity clean-up and MISPE were calculated and amounted to 0.923 for FB₁, 0.808 for FB₂, and 0.759 for FB₃. It was shown that the developed MIP could be reused more than 50 times. The synthesis of an FB₁ imprinted polymer and its application in food analysis is reported for the first time.     

Removal of estrogenic pollutants from contaminated water using molecularly imprinted polymers

A synthetic molecularly imprinted polymer (MIP) sorbent for estrogenic compounds was prepared using a noncovalent imprinting technique. MIP microspheres sized from 1 to 2 microm were synthesized in acetonitrile by using alpha-estradiol as the template, acrylamide as the functional monomer, and trimethylpropanol trimethacrylate as the cross-linker. When compared with the nonimprinted polymer (NIP), the MIP showed outstanding affinity toward alpha-estradiol in aqueous solution with a binding site capacity (B(max)) of 380 nmol mg(-1) MIP, imprinting effect of 35, and a dissociation constant (Kd) of 38 microM. The MIP exhibited significant binding affinity toward other related estrogenic compounds such as beta-estradiol, diethylstilbestrol, estriol, and estrone, suggesting that this material may be appropriate for treating a complex mixture of estrogenic pollutants. The feasibility of removing estrogenic compounds from environmental water by the MIP was demonstrated using lake water spiked with alpha-estradiol. In addition, the MIP reusability without any deterioration in performance was demonstrated for at least five repeated cycles.     

沙拉沙星分子印迹聚合物的制备及其性能研究

以沙拉沙星为模板分子,甲基丙烯酸为功能单体,乙二醇二甲基丙烯酸酯为交联剂,采用本体聚合制备沙拉沙星的分子印迹聚合物。通过振荡吸附实验对模板分子和功能单体的比例进行优化。印迹聚合物和空白聚合物的等温吸附线表明,印迹聚合物形成的孔穴对沙拉沙星的吸附量高于空白聚合物。在吸附过程中模板分子沙拉沙星与印迹聚合物形成两种结合位点,两种结合位点的解离常数分别为0.321μg/mL和1.577μg/mL,对沙拉沙星最大表观吸附量分别为1.249mg/g和3.222mg/g。吸附动力学实验结果显示聚合物对沙拉沙星的吸附在7h达到平衡,选择性试验表明印迹聚合物对沙拉沙星具有较好的吸附特性。     

Chemiluminescence sensors based on molecularly imprinted polymers for the determination of organophosphorus in milk

As a food adapted to all kinds of people, milk has a high nutritional value. Because milk is a complex biological matrix, detecting illegal compounds is often difficult. As a common pesticide, organophosphorus (OP) residues caused by nonstandard use may be ignored, which is a threat to milk quality. In this study, using coumaphos as template molecule, the synthesized molecularly imprinted polymer (MIP) can specifically recognize 7 kinds of OP. Then, the MIP was used as an identification element to prepare a chemiluminescence sensor on a 96-well microplate for the determination of OP residues in milk samples. Due to the 4-(imidazol-1-yl)phenol-enhanced luminol-H₂O₂ system, the sensitivity of the system is very high; the detection limits of 7 OP including coumaphos, fenthion, chlorpyrifos, parathion, diazinon, fenchlorphos, and fenitrothion were 1 to 3 pg/mL, and the half maximal inhibitory concentrations were 1 to 20 ng/mL. The intraday recoveries of 7 OP were in the range of 86.1 to 86.5%, and the interday recoveries were in the range of 83.6 to 94.2%. Furthermore, the sensor can be reused up to 5 times. Therefore, the MIP-based chemiluminescence sensor can be used as a routine tool to detect OP residues in milk samples.     

Molecularly Imprinted Layer-Coated Silica Gel Particles for Selective Solid-Phase Extraction of Pefloxacin and Enrofloxacin from Milk Samples

This study describes the synthesis of a molecularly imprinted polymer (MIP) as a novel solid-phase extraction adsorbent. The MIP consisted of pefloxacin (PEF) as a template, methacrylic acid (MAA) as a functional monomer, and silica gel particles as a support. The MIP was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and static adsorption. The MIP allowed the selective extraction of the fluoroquinolones PEF and enrofloxacin (ENR) and the simultaneous elimination of interfering components from milk matrices. Good linearity was obtained in a range of 2.5–500 ng?mL^?1, with correlation coefficients (R ²) >0.999. The average recovery rates of PEF and ENR ranged from 92.04 to 98.31 %, and the detection limits were 0.8–1.5 ng?mL^?1. This work provides a sensitive and selective tool for the detection of PEF and ENR residues in milk and potentially in other foods.     

Study on a Molecularly Imprinted Solid-Phase Extraction Coupled to Capillary Electrophoresis Method for the Determination of Trace Trichlorfon in Vegetables

How to determine the pesticide residues in vegetable is an urgent problem. In this study, we reported a new method of solid-phase extraction coupled to capillary electrophoresis (SPE–CE) based on a molecularly imprinted polymer (MIP) for determination of trace trichlorfon. The electrophoretic conditions and factors which affected the molecularly imprinted solid-phase extraction were optimized. Under optimal conditions, the linear ranges of the calibration graph were 0.1 μg/L to 10 mg/L. The limit of detection (LOD) and method quantitation limit (MQL) were 4.9 and 16.2 μg/kg, respectively. With a flow rate of 2.5 mL/min for 50 mL loading, an enrichment factor of 160 was obtained. The relative standard deviation (RSD) for five replicate extractions of 0.01 mg/L trichlorfon standard solution was 4.5 %. The blank cucumber, lettuce, and radish samples spiked with trichlorfon at three levels were extracted and determined by this presented method with recoveries ranging from 77.6 to 93.2 %. Moreover, this proposed methodology was successfully applied to the quantitative detection of the trichlorfon residues in the leek samples, and the results were in good agreement with that obtained by the gas chromatography method.     

A new method based on electrospray ionisation ion mobility spectrometry (ESI-IMS) for simultaneous determination of caffeine and theophylline

In this work for the first time, simultaneous analysis of caffeine and theophylline was done by ion mobility spectrometry (IMS) only, without a powerful separation technique (e.g., HPLC). Ion mobility spectrometry with low cost, inexpensive maintenance and very fast analysis makes an attractive technique for the simultaneous determination of the caffeine and theophylline in foodstuff samples and biological matrices. In this study, the extraction protocol using molecular imprinted polymer-solid phase extraction (MIP-SPE) was successfully used to directly extract caffeine and theophylline from real samples. The results obtained provided the detection limits of 0.2 and 0.3 μg mL⁻¹ for caffeine and theophylline, respectively. The linear dynamic range of about two orders of magnitude was obtained for these compounds. Also, the proposed method was used to analyse various real samples of green tea and spiked human plasma, and the obtained results confirmed the capability of ESI-IMS for simultaneous detection of caffeine and theophylline.     

Selective trace analysis of sulfonylurea herbicides in water and soil samples based on solid-phase extraction using a molecularly imprinted polymer

A molecularly imprinted polymer (MIP) was synthesized using the herbicide metsulfuron-methyl (MSM) as a template, 2-(trifluoromethyl)acrylic acid as a functional monomer, divinylbenzene as a cross-linker, and dichloromethane as a porogen. This polymer was used as a solid-phase extraction material for the quantitative enrichment of five sulfonylureas (nicosulfuron, thifensulfuron-methyl, metsulfuron-methyl, sulfometuron-methyl, and chlorsulfuron) in natural water and soil samples and off-line coupled to a reversed-phase HPLC/diode array detection (HPLC/DAD). Washing solvent was optimized in terms of kind and volume for removing the matrix constituents nonspecifically adsorbed on the MIP. It has been shown that the nonspecific binding ability of the sulfonylureas to the polymer largely increased along with increasing the concentration of Ca2+ ions in the water sample, whereas complexation of divalent ions with EDTA eliminated this interference completely. The stability of MIP was tested by consecutive percolation of water sample, and it was shown that the performance of the MIP did not vary even after 200 enrichment and desorption cycles. Recoveries of the five sulfonylureas extracted from 1 L of tap water and surface water samples such as river water and rainwater at a 50 ng/L spike level were not lower than 96%. The recoveries of sulfonylureas extracted from 10-g soil sample at the 50 microg/kg level were in the range of 71-139%. Depending on the particular compound, the limit of detection varied from 2 to 14 ng/L in water and from 5 to 12 microg/kg in soil samples. The MIP was also compared with a commercially available C-18 column and an immunoaffinity support with encapsulated polyclonal anti-MSM antibodies in sol-gel glass.     

混合三模板分子印迹固相萃取柱应用于粮谷中三唑类农药的检测

建立了采用混合三模板分子印迹固相萃取-高效液相色谱法分离检测粮谷样品中3种三唑类杀菌剂残留的方法。以联苯三唑醇、腈菌唑、烯唑醇为混合模板分子,采用本体聚合法合成了具有高选择性的混合三模板分子印迹聚合物,以该聚合物为填料制备混合三模板分子印迹固相萃取柱,并结合高效液相色谱法检测粮谷中联苯三唑醇、腈菌唑、烯唑醇残留。结果表明,以20 mL水为淋洗剂,15 mL甲醇为洗脱剂,并在最佳色谱条件下,联苯三唑醇、腈菌唑、烯唑醇的平均回收率分别为74.0%~82.4%、79.0%~86.2%、77.5%~85.1%,相对标准偏差(RSD)≤4.4%,该混合三模板分子印迹聚合物对3种杀菌剂具有特异性吸附能力,该分析方法可用于样品中三唑类杀菌剂残留的分离检测。     

基于分子印迹整体柱的在线固相萃取-液相色谱联用测定奶粉中四环素类兽药残留

目的建立高交联结构的分子印迹整体柱(molecularly imprinted polymer monolithic column,MIP-MC)制备方法,利用在线固相萃取与液相色谱联用技术检测奶粉样品中四环素类兽药残留。方法在不锈钢色谱柱中,以土霉素为模板,甲基丙烯酸和甲基丙烯酸羟乙酯为功能单体,乙二醇二甲基丙烯酸酯和双季戊四醇六丙烯酸酯为交联剂,偶氮二异丁腈为引发剂,在丙酮-甲醇-十二醇混合溶剂中,制备了分子印迹整体柱。将整体柱与液相色谱联用,在线固相萃取奶粉中的四环素类兽药残留。结果在最佳在线固相萃取条件下,获得了较高的富集因子(19.3)和净化效果。四环素类在0.05、0.25和0.5 mg/kg 3个加标水平下,回收率为84.2%~103.4%,相对标准偏差为1.37%~4.87%,方法检出限(S/N=3)和定量限(S/N=10)分别为8.48~11.74?g/kg和28.24~39.09?g/kg。结论该在线固相萃取方法简单快速、灵敏性高、选择性好,适用于奶粉中四环素类抗生素残留的测定。     

Determination of 14 aminoglycosides by LC-MS/MS using molecularly imprinted polymer solid phase extraction for clean-up

An LC-MS/MS method for screening 14 aminoglycosides in foodstuffs of animal origin is presented. Its scope includes raw materials and processed ingredients but also finished products composed of milk, meat, fish, egg or fat. Aminoglycosides are extracted in an acidic aqueous solution, which is first recovered after centrifugation, then diluted with a basic buffer and finally purified by molecularly imprinted polymer-solid phase extraction (MIP-SPE). Analytes are detected within 8 min by ion-pair reversed phase LC-MS/MS. Due to the large range of foodstuffs involved, the variability of matrix effects led to significant MS signal variations. This was circumvented by systematically extracting each sample twice, i.e. ‘unspiked’ and ‘spiked’ at the screening target concentration of 50 µg kg^?1. The method was validated according to the European Community Reference Laboratories Residues Guidelines giving false-negative and false-positive rates ≤3% for all compounds. Ruggedness of the method was further demonstrated in quality control operations by a second laboratory. The 14 aminoglycosides in water-based standard solutions were stable for up to 6 months when stored at either ?80°C, ?20°C or at 4°C storage temperatures.     

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.     

采用替代模板硅胶表面接枝制备棒曲霉素分子印迹聚合物及其性能研究

以棒曲霉素为目标分子,5-羟甲基糠醛为干扰物,6-羟基烟酸为替代模板分子,通过对硅胶表面进行硅烷化并接枝后共聚,制备基于硅胶表面修饰的分子印迹聚合物.借助红外检测和元素分析对聚合物的制备进行评价,并通过固相萃取-高效液相联用以及振荡吸附法对所得聚合物的吸附特性进行研究.试验结果表明这种分子印迹聚合物对棒曲霉素表现出特异性吸附,而对干扰物5-羟甲基糠醛吸附较少:在固相萃取中两者吸附率分别为93.97％和76.89％,振荡吸附中吸附量分别为0.654 μg/mg和0.496 μg/mg.该聚合物能被有效地应用于SPE-HPLC法测定苹果汁和相关苹果产品中的棒曲霉素.     

An Electrochemical Nanosensor Based on Molecularly Imprinted Polymer (MIP) for Detection of Gallic Acid in Fruit Juices

The molecularly imprinted polymer (MIP)-based electrochemical sensor has been attending recently, due to their exceptional advantages and specificity. Here, we successfully designed and fabricated a novel electrochemical nanosensor for determination of gallic acid (GA) based on its specific MIP. The MIP was synthesized using precipitation polymerization technique, via polymerization of methacrylic acid as a functional monomer. The MIP was applied in the multiwalled carbon nanotube-modified carbon paste electrode (MWCNT–CPE), and similarly, MIP and MWCNT-modified CPE (MIP–MWCNT–CPE) was prepared, which acted as the selective recognition element and pre-concentrator agent for GA. The effect of different factors such as quantity of MIP and MWCNT, GA solution pH, and GA accumulation time on an oxidation current of accumulated GA at the electrode were investigated and optimized by central composite design (CCD) as a an experimental design and response surface methodology. The results showed that fabricated nanosensors (MIP–MWCNT–CPE) have higher sensitivity compared with bare CPE, MWCNT–CPE, and MIP–CPE. This sensor showed a linear response range of 0.12–380.0 μM and detection limit of 47.0 nM. Finally, the nanosensor was applied to determine GA in apple, pineapple, orange juices, and a commercial green tea drink as real samples with satisfactory results.     

Immunochromatographic lateral-flow test strip for the rapid detection of added bovine rennet whey in milk and milk powder

An immunochromatographic lateral-flow test dipstick test was developed for the fast detection of bovine rennet whey in liquid milk and milk powder. The test is based on the binding of casein glycomacropeptide (cGMP) by two specific anti-bovine κ-casein monoclonal antibodies and has a visual detection limit of around 15 ng mL^?1 for cGMP and 1% (v/v) for rennet whey in milk using standards and spiked samples. The dipstick performance was evaluated in a collaborative trial using skim milk powder and raw, pasteurized and UHT milk. The suitability of the dipstick was demonstrated in comparison with gel permeation-high performance liquid chromotography and a colorimetric method, by analysing 60 raw milk samples collected from farms in Brazil. The dipstick results correlated well with the HPLC results and were more reliable than those obtained with the colorimetric method. The dipstick test correctly identified all raw milk samples with a rennet whey content above 4%.