A survey on the occurrence of aflatoxin M1 in raw milk produced in Adana province of Turkey

During 2012, a total of 176 samples of raw milk obtained from dairy plants of Adana province of Turkey were analysed for the presence of aflatoxin M₁ (AFM₁). Aflatoxin M₁ analysis was carried out by centrifugation, liquid–liquid extraction, immunoaffinity column clean-up and high performance liquid chromatography with fluorescence detection (HPLC-FD). The limits of detection (LOD) and quantification (LOQ) of the analytical method were 0.021 μg kg⁻¹ and 0.025 μg kg⁻¹. Accuracy of the method obtained from bias ranged from 2.94 to 8.70. Aflatoxin M₁ was detected in 53 out of 176 samples analysed (30.1%). The ranges for positive samples were 0.042–0.552, 0.033–1.01, 0.047–0.150 and 0.025–0.102 μg kg⁻¹ in autumn, winter, spring and summer seasons, respectively. Thirty samples of raw milk (17%) were above the legal limits of Turkey and EU regulations.     

迎接深部开采高地温环境的挑战——岩石真三轴试验机地温模拟平台研究

为迎接深部开采高地温环境的挑战,提高真三轴试验设备的高地应力—高地温耦合能力,开展了岩石真三轴试验机地温模拟平台的研发工作.通过建立数值模拟(COMSOL)、变异系数法(RSD)与多属性决策问题理想解法(TOPSIS)相结合的真三轴高地应力—高地温耦合加载方案评估体系,对3种加温方案进行综合指标评估和方案优选.为了取得...     

Comparison of BEA, USY and ZSM-5 for the quantitative extraction of polycyclic aromatic hydrocarbons from water samples

The physicochemical properties of three commercial zeolites - namely BEA, USY and ZSM-5 - are compared for the water removal of 15 PAHs included in the US EPA priority pollutants list. The best percentages of extraction were obtained with BEA and varied from 85.2 ± 1.7% (benzo[g,h,i]perylene) to 99.6 ± 1.1% (pyrene). The correlation of physicochemical properties to the percentages of extraction suggests that the predominant factor for a successful extracting performance is the adsorption of PAHs to the external surface of the extracting material. This process is facilitated by relatively large total pore volumes, large average pore diameters and a homogeneous distribution of Lewis acid sites. The presence of the latter enhances extraction performance via π-electron interactions with the aromatic rings of the PAH.     

Parameters Optimization of Laser-Induced Breakdown Spectroscopy Experimental Setup for the Case with Beam Expander

Improvement of measurement precision and repeatability is one of the issues cur?rently faced by the laser-induced breakdown spectroscopy (LIBS) technique, which is expected to be capable of precise and accurate quantitative analysis. It was found that there was great poten?tial to improve the signal quality and repeatability by reducing the laser beam divergence angle using a suitable beam expander (BE). In the present work, the influences of several experimental parameters for the case with BE are studied in order to optimize the analytical performances: the signal to noise ratio (SNR) and the relative standard deviation (RSD). We demonstrate that by selecting the optimal experimental parameters, the BE-included LIBS setup can give higher SNR and lower RSD values of the line intensity normalized by the whole spectrum area. For validation purposes, support vector machine (SVM) regression combined with principal component analysis (PCA) was used to establish a calibration model to realize the quantitative analysis of the ash content. Good agreement has been found between the laboratory measurement results from the LIBS method and those from the traditional method. The measurement accuracy presented here for ash content analysis is estimated to be 0.31%, while the average relative error is 2.36%.     

大功率RSD开关多单元并联技术

为通过研究多单元并联技术来增大脉冲功率开关RSD(reversely switched dynistor)的功率容量,基于RSD的等离子体双极漂移模型,建立主回路和预充回路的RLC方程,采用四阶龙格-库塔方法迭代计算,得到两支路并联的RSD电流曲线。在一定的仿真条件下,RSD器件参数不同和支路电阻不同引起的电流不平衡率分别为3.56%和19.82%。在RSD并联实验中,内阻1.642mΩ的分流器和非对称连接引起的电流不平衡率分别为12.82%和20.71%。在3000μF主电容、2kV主电压下对并联的两个直径45mm的RSD堆体进行了大电流开通实验,得到了330μs脉宽下32.7kA的峰值电流。仿真和实验结果均表明,在高功率电流的快速开通机制中并联支路分流大小主要由回路参数决定,受RSD动态电阻影响很小。     

海星中皂苷总含量测定方法的研究

为了对海星中的总皂苷进行含量测定,本研究工作利用海星总皂苷能与香草醛-硫酸体系显色的特点,以提纯海星皂苷D262为标准品,26%香草醛乙醇溶液和75%硫酸为显色剂,用分光光度法对海星总皂苷的含量进行了测定,并系统研究了测定过程中的各种条件,确定了一种快速、简单、准确的海星总皂苷含量测定方法,标准曲线相关系数为0.99978。用此方法测得青岛海域罗氏海盘车和海燕中的皂苷总含量分别为0.0251%和0.0313%。相对标准偏差(RSD)分别为0.55%和0.33%,平均回收率分别为99.31%和97.57%。     

基于RSD方法随钻测井曲线实时对比技术研究

水平井测井曲线测深与真实垂直深度对比分析,依靠人工经验对曲线形态进行判断存在较大误差。提出了相对地层深度方法(Relative Strata Depth,RSD)用于水平井随钻测井曲线实时对比,RSD采用三次样条插值函数计算水平井测井曲线垂直深度及RSD刻度,将水平井测井曲线按照地层关系投影至垂直道上,实现多井测井曲线形态和数值的直接对比。该方法能够显著提高随钻测井曲线对比准确度、地质导向精度和工作效率。     

超高速半导体开关RSD的开通机理与大电流特性研究

基于反向注入控制RSD(Reversely Switched Dynistor)的大面积快速均匀开通、可无限串联、功率大、换流效率高、寿命长的特点,新开通机制的RSD将在脉冲功率技术中获得重要应用.本文研究了RSD的开通机理和开通条件,为器件开通特性的改进和预充电路的合理设计提供了依据;实验还表明,由小直径RSD的极限电流测试结果,可以用经验公式得到同类结构的任意通流面积RSD脉冲大电流耐量.     

基于脉冲变压器RSD直接式预充的设计与研究

基于反向开关晶体管(RSD)的工作原理,提出采用脉冲变压器隔离的直接式触发高压RSD,以解决系统对触发开关要求较高的问题。脉冲变压器的作用是隔离主放电回路的高压,同时在有限的时间内给RSD提供足够的预充电荷且经过一定的时间延迟后饱和。据此,利用变压器等效电路对其进行了设计,得到了变压器及电路的相关参数。利用电路仿真软件Saber仿真脉冲变压器的饱和特性,并进行了实验验证。最后以10kV电压通过RSD对负载放电为例,验证方案的可行性,得到峰值为12kA、底宽15μs、di/dt为2kA/μs的主电流。实验完毕,经测试,器件完好无损。     

Rapid determination of organophosphorous pesticides in leeks by gas chromatography–triple quadrupole mass spectrometry

A rapid multi-residue method was developed for the determination of 20 organophosphorous pesticide residues in leeks by gas chromatography coupled to triple quadrupole mass spectrometry (GC–QqQ-MS/MS). The method was based on the modified QuEChERS sample preparation method. After microwave pre-treatment, leek samples were extracted with acetonitrile containing acetic acid 0.1% and cleaned by dispersive solid phase extraction. The QqQ analyser acquired data in selected reaction monitoring (SRM) mode. Recoveries of 20 organophosphorous pesticides ranged from 81.0% to 109.4% with the relative standard deviations (RSD) below 10.4%. The limits of detection (LODs) were 0.07–1.5 μg/kg. The limits of quantitation (LOQs) ranged from 0.25 to 5 μg/kg. Ten leek samples were analysed for method application.