Analysis of acrylamide in food by isotope-dilution liquid chromatography coupled with electrospray ionization tandem mass spectrometry

A confirmatory method for the determination of low levels of acrylamide in different food products is presented. The method entails extraction of acrylamide with water, precipitation of matrix constituents with acetonitrile, and two clean-up steps consecutively over Isolute Multimode and cation-exchange cartridges. The final extract is analyzed by liquid chromatography (LC) coupled to positive electrospray ionization tandem mass spectrometry employing [13C3]-acrylamide as internal standard. For the chromatographic step, a LC column based on a polymethacrylate gel is employed which shows good retention of acrylamide under isocratic flow conditions (k' = 1.2). Mass spectral acquisition is done by selected reaction monitoring, choosing the characteristic transitions m/z 72-->55, 72-->54 and 72-->27. In-house validation data for breakfast cereals and crackers show good precision of the method, with intra- and interassay variation below 10%. The limits of detection for crackers and breakfast cereals, respectively are estimated at 15 and 20 microg/kg, and recoveries of fortified samples ranged between 58 and 76%. Furthermore, the method is applicable to a number of different food products, including biscuits, crisp bread, wafers, confectionery cocoa liquor, and nuts. Finally, the good results obtained in several small-scale interlaboratory tests provided additional confidence in the performance of the method.     

高效液相色谱法测定方便面中丙烯酰胺

建立了一种检测方便面中丙烯酰胺的液相色谱方法。萃取剂选择1g/L的蚁酸溶液,将萃取液以12000r/min,2℃离心18min,上清液再以14500r/min,0℃离心18min,可分离基质中淀粉、蛋白质、脂肪等干扰物;方法采用ZORBAX SB-C18(250mm×4.6mm,5μm)色谱柱,流动相为A(乙腈∶水=1∶24(V/V))和B(乙腈),流速0.5mL/min,在丙烯酰胺的最大吸收197nm处检测,提高了方法的检出限及回收率。该方法有良好的线性关系(r=1.00000),检出限为48.0μg/kg。回收率94.4%～109.8%,相对标准偏差为4.9%～5.6%。     

丙烯酰胺在聚乙二醇水溶液中聚合初期的液滴形成与成长过程

用动态激光光散射(DLS)在线观测了丙烯酰胺(AM)在聚乙二醇(PEG)水溶液中聚合初期液滴的出现、生长及聚并过程,考察了PEG分子量和浓度对聚合初期液滴尺寸的影响;用透射电镜(TEM)对聚合初期液滴形态的演变进行了观察,发现与DLS结果能很好吻合.用分光光度计对聚合体系分相点进行确定,采用溴化法测定了聚合体系临界分相时的转化率.随PEG分子量或浓度的升高,临界分相转化率逐渐减小;随温度的升高,临界分相转化率先减小后增大,在50℃左右出现最小值.用凝胶渗透色谱(GPC)对聚合体系临界分相时聚丙烯酰胺(PAM)的分子量进行了研究,变化趋势与临界分相转化率的变化一致.在上述基础上,提出了AM在PEG水溶液中聚合初期的液滴形成、成长机理.     

Synthesis of Acrylamide Molecularly Imprinted Polymers Immobilized on Graphite Oxide through Surface-Initiated Atom Transfer Radical Polymerization

A novel acrylamide (AA) molecularly imprinted polymer was synthesized by atom transfer radical polymerization (ATRP) on graphite oxide (GO) particles. Propionamide (PAM) was used as a dummy template molecule, hydroxy ethyl acrylate (HEA) as a functional monomer, ethylene glycol dimethacrylate (EDMA) as a crosslinking agent, and acetonitrile as both solvent and dispersion medium. Scanning electron microscopy (SEM) images and infrared spectroscopy (IR) confirmed that the molecularly imprinted polymers (MIP) were successfully grafted onto the surface of the GO particles. The corresponding adsorption kinetic curves and adsorption isotherms showed that the AA adsorption reached equilibrium after 5 h, with large amounts of AA being adsorped in the first 100 min. The maximum AA adsorption capacity was 123.48 µmol g^?1 according to Scatchard analysis, which indicated that the MIP possesses good AA adsorption capacity. This MIP-GO material was used to selectively determine AA in fried food samples.     

丙烯酰胺与丙烯酸十四酯共聚物的合成及性能研究

利用过氧化苯甲酰为引发剂探讨了丙烯酰胺（ＡＭ）和丙烯酸十四酯（ＴＡ）的自由基共聚合。重点讨论了合成条件如引发剂用量，单体配比、溶剂、温度等对共聚反应及共聚物对苯丙乳胶增稠性能的影响。并用ＩＲ和凯达定氮法表征了共聚物的组成，实验结果表明，ＡＭｔ ＴＡ进行沉淀聚合所得到的共物分子量足够大，可以作为疏水缔合型稠剂使用。     

A visual strip sensor for determination of iron

A visual strip has been developed for sensing iron in different aqueous samples like natural water and fruit juices. The sensor has been synthesized by UV-radiation induced graft polymerization of acrylamide monomer in microporous poly(propylene) base. For physical immobilization of iron selective reagent, the in situ polymerization of acrylamide has been carried out in the presence of 1,10-phenanthroline. The loaded strip on interaction with Fe(II) in aqueous solution turned into orange red color and the intensity of the color was found to be directly proportional to the amount of Fe(II) in the aqueous sample. The minimal sensor response with naked eye was found for 50 ng mL⁻¹ of Fe in 15 min of interaction. However, as low as 20 ng mL⁻¹ Fe could be quantified using a spectrophotometer. The detection limit calculated using the 3s/S criteria, where ‘s’ is the standard deviation of the absorbance of blank reagent loaded strip and ‘S’ is the slope of the linear calibration plot, was 1.0 ng mL⁻¹. The strip was applied to measure Fe in a variety of samples such as ground water and fruit juices.     

Development of monolithic enzymatic reactors in glass microchips for the quantitative determination of enzyme substrates using the example of glucose determination via immobilized glucose oxidase

A one-step procedure for the immobilization of glucose oxidase in fused-silica capillaries and in glass microchips was developed based on enzyme entrapment in a polyacrylamide-based monolithic column. The inner capillary surface was silanized with gamma-methacryloxypropyltrimethoxysilane (gamma-MAPS) to allow covalent binding of the gel to the surface. The composition of the polymer was optimized to prevent the formation of bubbles, allow liquid transportation by electroosmotic flow and to maintain the enzymatic activity. These requirements resulted in the addition of polyethylene glycol and poly(acrylic acid) to the acrylamide mixture. The gel containing the enzyme was formed in situ in the capillaries, respectively, in one channel of the microchip. In the microchip, it was limited to the sample injection channel by accordingly controlled silanization of the inner capillary surface. Glucose was detected via the amperometric determination of hydrogen peroxide. A linear correlation between signals and glucose concentration was observed from 0.05 to 1.1 mM glucose with a correlation coefficient of 0.999. The enzymatic monolithic microreactor showed no loss of activity during 8 h of continuous use and during storage in the running buffer at 4 degrees C for about 2 months. Interferents, such as ascorbic acid, were separated from the analyte electrophoretically, so that glucose could be quantified in diluted juices.     

气质联用法测定油炸型膨化食品中的丙烯酰胺

建立一种用气相色谱-质谱联用法检测油炸型膨化食品中丙烯酰胺含量的方法,通过水提取油炸型膨化食品中的丙烯酰胺、Carrez试剂除蛋白、正己烷抽提油脂,溴化衍生后生成2,3-二溴丙烯酰（2,3-DBPA）,气相色谱-质谱（GC-MS）特征离子定性,主要离子碎片（m/Z）：152、150、108、106,外标法定量.方法线性良好,线性范围为0.1-2μg/mL,相关系数达0.9986,检出限为0.02μg/mL,回收率为89.0％-93.4％,RSD值为2.42％-4.99％.该方法检出限低,回收率高,结果准确,适用于油炸型膨化食品中丙烯酰胺含量的测定.     

Fractal dimension and phase transition of graphene oxide (GO) doped polyacrylamide

Graphene Oxide (GO)- Polyacrylamide composites prepared between 5 and 50 μl GO were performed by Fluorescence Spectroscopy. The phase transition performed on the composites was measured by calculating the critical exponents, β and γ, respectively. In addition, fractal analysis of the composites was calculated by a fluorescence intensity of 427 nm. The geometrical distribution of GO in the composites was calculated based on the power law exponent values using scaling models. While the gelation proceeded GO plates first organized themselves into a 3D percolation cluster with the fractal dimension (D_f) of the composite, D_f = 2.63, then After it goes to diffusion limited clusters with D_f = 1.4, its dimension lines up to a Von Koch curve with a random interval of D_f = 1.14.     

Evaluation of molecularly imprinted membranes based on different acrylic copolymers

Polyacrylonitrile and its copolymers with different functional monomers (itaconic acid, acrylic acid and acrylamide) were synthesized via water-phase precipitation polymerization in order to prepare molecularly imprinted polymer (MIP) membranes with recognition properties for the flavonoid naringin (NR). Membranes were prepared by phase inversion technique using dimethylformamide (DMF) as the solvent and adding naringin as template molecule to the casting solution. For comparison, membranes without template (blank) were prepared and tested. All MIP membranes showed high specific binding capacity; among them, the membrane prepared with the copolymer containing acrylamide as functional group, showed the highest binding capacity. Blank membranes only showed non-specific binding. The bound template was totally recovered and regenerated membranes maintained their initial binding capacity after reuse.