Matrix-free analysis of aflatoxins in pistachio nuts using parallel factor modeling of liquid chromatography diode-array detection data

In the present study a second-order calibration strategy for high performance liquid chromatography with diode-array detection (HPLC-DAD) has been developed using parallel factor analysis (PARAFAC) and has been applied for simultaneous determination of aflatoxins B₁, B₂, G₁ and G₂ in pistachio nuts in the presence of matrix interferences. Sample preparation was based on solvent extraction (SE) followed by solid phase extraction (SPE) on Bond Elut C18 cartridges. Since the sample preparation procedure was not selective to the analytes of interest, exploiting second-order advantage to obtain concentrations of individual analytes in the presence of uncalibrated interfering compounds seemed necessary. Appropriate pre-processing steps have been applied to correct background signals and the effect of retention time shifts. Transferred calibration data set obtained from standardization of solvent based calibration data has been used in prediction step. The results of PARAFAC on a set of spiked and naturally contaminated pistachio nuts indicated that the four aflatoxins could be successfully determined. The method was validated and multivariate analytical figures of merit were calculated. The advantages of the proposed method are using a low-cost SPE step relative to standard method of aflatoxin analysis (immune affinity column assay), a unique and simple isocratic elution program for all samples and a calibration transfer for saving both chemicals and time of analysis. This study show that coupling of SPE-HPLC-DAD with PARAFAC as a powerful second-order calibration method can be considered as an alternative method for resolution and quantification of aflatoxins in the presence of unknown interferences obtained through analysis of highly complex matrix of pistachio samples and cost per analysis can be reduced significantly.     

A rapid, acetonitrile-free, HPLC method for determination of melamine in infant formula

A simple, precise, accurate and validated, acetonitrile-free, reverse phase high performance liquid chromatography (HPLC) method is developed for the determination of melamine in dry and liquid infant formula. The separation is performed on a Kromasil C18 column (150 mm × 3.2 mm I.D., 5 μm particle size) at room temperature. The mobile phase (0.1% TFA/methanol 90:10) is pumped at a flow rate of 0.3 mL min⁻¹ with detection at 240 nm. Melamine elutes at 3.7 min. A linear response (r > 0.999) is observed for samples ranging from 1.0 to 80 μg mL⁻¹. The method provides recoveries of 97.2-101.2% in the concentration range of 5-40 μg mL⁻¹, intra- and inter-day variation in <1.0% R.S.D. The limit of detection (LOD) and limit of quantification (LOQ) values are 0.1 μg mL⁻¹ and 0.2 μg mL⁻¹, respectively.     

Rapid Photocrosslinkable Thermoresponsive Injectable Polyphosphazene Hydrogels

Rapidly photocrosslinkable and thermosensitive polyphosphazene polymers have been prepared to overcome the limitations associated with long UV exposure. Short UV exposure on the thermosensitive gels under mild conditions leads to quick photocrosslinking of the acrylate groups in the polymer network, and results in a dual crosslinked network with enhanced mechanical strength. The accelerated photocrosslinking can be attributed to the high reactivity of the acrylate double bond and hydrophobic interactions in the polymer network. The effects on the degree of photocrosslinking of the UV light intensity and the concentration of the photoinitiator were studied. In vitro and in vivo photocrosslinkings were accomplished within 120 and 180 s of exposure times, respectively. The degradation rate of the polymers depended on the degree of acrylate substitution in the polymer network. These results demonstrate that the injectable hydrogels with desired mechanical properties and degradation rates can be created in situ under mild photocrosslinkable conditions, and the dual crosslinkable acrylated poly(organophosphazenes) may hold great promise for biomedical delivery applications of biological molecules, cells, and drugs.

     

Synthesis and Properties of Hyperbranched Polyimides Combined with Silica

Summary: The novel hyperbranched polyimide - silica hybrid materials containing theoretically 16 wt% of an inorganic phase were prepared via a sol-gel process. An amine terminated polyimide precursor (hyperbranched polyamic acid) was prepared from commercially available monomers 4,4′,4″-triaminotriphenylmethane and 4,4′-oxydiphthalic anhydride in molar ratio 1:1. Tetramethoxysilane and/or 3-glycidoxypropyltrimethoxysilane (also used as a coupling agent) were used as silica precursors. During thermal exposition the polyimide precursor was transformed to hyperbranched polyimide and hydrolyzed alkoxy groups reacted mutually to form silica. The final products were self-standing films, whose structure was characterized by using IR and ¹³C and ²⁹Si solid state NMR spectroscopy. The influence of the amount of silica and/or coupling agent on their structure and thermal properties was described.     

Synthesis of fluorinated polybenzoxazoles with low dielectric constants

Two fluorinated aromatic bis(o‐aminophenol)s, 1,1‐bis(3′‐amino‐4′‐hydroxyphenyl)‐1‐(3′‐trifluoromethylphenyl)‐2,2,2‐trifluoroethane (6FAP) and 1,1‐bis(3′‐amino‐4′‐hydroxyphenyl)‐1‐(3′,5′‐ditrifluoromethylphenyl)‐2,2,2‐trifluoroethane (9FAP) were synthesized, which were allowed to polycondense with aromatic diacyl chlorides to afford the fluorinated aromatic polybenzoxazoles (PBOs) via a conventional two‐step procedure in which the low‐temperature solution polycondensation process was first performed to yield poly(o‐hydroxyamide)s (PHAs) followed by the thermal cyclodehydration to give the PBOs. Experimental results indicated that the PHAs had inherent viscosities in the range of 0.29–0.68 dL/g, showing excellent solubility in organic solvents. The PHAs could be thermally cyclodehydrated into the corresponding PBOs at 260–370 °C. The obtained PBOs exhibited enhanced glass‐transition temperature but decreased solubility with respect to the PHAs. The PBOs showed glass‐transition temperatures in the range of 315–337 °C and excellent thermal stabilities with 5% original weight‐loss temperatures (T₅) of >513 °C. Additionally, the PBO films had average refractive index of 1.5298–1.5656, birefringence of 0.0051–0.0092, and low dielectric constants of 2.57–2.70. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

高掺杂Ce,Gd(Y_(3-x-y)Ce_xGd_y)Al_5O_(12)荧光粉的发光下降及温度猝灭特性

采用高温固相法分别合成了不同Ce浓度掺杂的和固定Ce浓度为0.06不同Gd浓度掺杂的Y3Al5O12(YAG)系列荧光粉,通过测量其激发、发射光谱、漫反射光谱、荧光寿命和变温发射光谱,研究了掺杂元素的浓度对荧光粉发光性能的影响以及荧光粉发光的温度猝灭性质。研究结果表明:荧光粉发光强度随着Ce3+掺杂浓度和Gd3+掺杂浓度的提高均呈下降趋势。分析发现,荧光粉发光强度下降并非主要由浓度猝灭所引起,而是由于高浓度掺杂下发生YAG基质与Ce3+对激发光的竞争吸收,导致Ce3+对激发光的吸收量减少,从而影响发光强度。温度实验表明,随着温度的升高,荧光粉发光强度下降。Ce含量的改变对YAG:Ce荧光粉的热猝灭性质影响较小,Gd的掺杂使荧光粉的发射波长向长波方向移动,同时热猝灭现象严重。     

宽电压范围下阳极氧化制备TiO_2纳米管阵列及其热稳定性

采用电化学阳极氧化技术,以含有NH4F和H2O的甘油溶液为电解液,在宽氧化电压范围(20~100V)下于纯钛表面制备了结构高度有序的TiO2纳米管阵列。利用扫描电子显微镜(SEM)考察了阳极氧化工艺(氧化电压、NH4F浓度、环境温度、水分含量等因素)及退火处理对纳米管形貌的影响;采用X射线衍射分析(XRD)表征了不同氧化电压和退火前后TiO2纳米管阵列的物相;并从电流-时间曲线出发简要地分析了纳米管阵列的形成机理。结果表明,纳米管的内外径和管长随氧化电压的增大而增大;NH4F浓度和环境温度对纳米管形貌有一定的影响;水分含量的多寡决定了能否在高电压下自组装形成纳米管阵列;TiO2纳米管阵列具有良好的热稳定性,管状形貌可以保持到700℃;直接制备的TiO2纳米管阵列均为无定型结构,经450℃退火处理后,无定型的TiO2纳米管转变为锐钛矿相,而600℃退火处理后,部分锐钛矿相转变为金红石相。     

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%。     

高效液相色谱法检测畜禽肉中四环素类药物残留的条件优化

对畜禽肉中四环素类残留的检测方法进行改进,选用Na2EDTA-McIlvaine缓冲溶液作为提取液进行超声提取,经C18固相萃取小柱净化,脱溶剂后用流动相三氟乙酸-乙腈溶解,使用高效液相色谱-PDA检测器分段采集355 nm及270 nm波长下的色谱信息,对前处理方法及色谱条件进行优化。四环素、土霉素在0.01～1μg/g范围内,金霉素、多西环素在0.02～2μg/g范围内回收率为60%～85%,相对标准偏差小于5%,可以满足国家残留限量0.1～0.6μg/g的检测要求。     

Evaluating the Thermal Hazard of Double-Base Propellant SQ-2 by Using Microcalorimetry Method

The thermal decomposition behavior of double‐base rocket propellant SQ‐2 was studied by a Calvet microcalorimeter at four different heating rates. The kinetic and thermodynamic parameters were obtained from the analysis of the heat flow curves. The critical temperature of thermal explosion (T_b), the self acceleration decomposition temperature (T_SADT), the adiabatic decomposition temperature rise (ΔT_ad), the time‐to‐explosion of adiabatic system (t), critical temperature of hot‐spot initiation (T_cr), critical thermal explosion ambient temperature (T_acr), safety degree (SD) and thermal explosive probability (P_TE) were presented to evaluate the thermal hazard of SQ‐2.