PTV-LV-GC/MS/MS as screening and complementary method to HRMS for the monitoring of dioxin levels in food and feed

Recent developments in trapping efficiency inside ion trap mass spectrometer permitted to lower instrument detection limit (IDL). An IDL of 200 fg μl⁻¹ injected with a signal-to-noise ratio of 5:1 for tetrachlorodibenzo-p-dioxin (TCDD) was obtained by gas chromatography coupled to a quadrupole ion storage mass spectrometer in tandem mode (GC/MS/MS). Coupling large volume programmable temperature vaporizer (PTV-LV) injection to GC/MS/MS provides an alternative and complementary method to classical splitless-GC injection connected to high-resolution mass spectrometry (splitless-GC/HRMS) method for dioxin monitoring in food and feed.

An injection volume of 10 μl was found to be the best compromise between the sensitivity requirements and the robustness required for a high throughput method. PTV-LV-GC/MS/MS and Splitless-GC/HRMS were compared by performing analysis on five different matrices such as beef fat, yolk eggs, milk powder, animal feed and serum samples covering a concentration range of two orders of magnitude (i.e. 0.2–25 ng WHO-TEQ kg⁻¹). An analysis of variance (ANOVA) was carried out. Fisher tests pointed out that the method effect for all the 2,3,7,8 congeners was not significant, indicating that the null hypothesis (H₀: μ₁=μ₂=…=μ_n) was not rejected. Moreover, the interaction effects between methods and matrices were not significant for most of the 2,3,7,8 congeners. However, three congeners (2,3,7,8-TCDF; 1,2,3,4,7,8-HxCDD and 1,2,3,4,6,7,8-HpCDD) were characterized by P-values lower than the significance level (=0.05). In toxic equivalence (TEQ), the study showed that no significant bias was observed between the two methods. Consequently, PTV-LV-GC/MS/MS is an attractive technique and can be used as a cost effective complementary method to HRMS for dioxin levels monitoring in food and feed.     

Sample evaporation in conventional split/splitless GC injectors. Part 3: Retaining the liquid in the vaporizing chamber

As most sample liquids tend to pass through an empty injector insert at a speed which is too high to enable complete evaporation, movement of the liquid must be arrested before it reaches the column entrance. Stopping the liquid means deposition on to a surface; this, however, is possible only after the temperature of the surface has been cooled to (or below) the boiling point of the liquid (solvent). The performance of different means of stopping the liquid has been tested visually (by the method described in Part 2). Baffles on the wall of the injector insert had hardly any effect on evaporation: the band of liquid leaving the syringe needle performed a perfect slalorn around them. The inverted cup proved more efficient, but the best performance was obtained from a light plug of glass wool: owing to its low thermal mass, the first fibers to be met by the liquid are immediately cooled to the solvent boiling point, allowing the liquid to wet it. The sample liquid is sucked up by the glass wool, from where the sample evaporates relatively slowly, often over a period of several seconds.     

Light intensity and image visualization of GDI injector sprays according to nozzle hole arrangements

The light intensity measurement and image visualization of multi-hole injection spray due to different hole arrangements and hole numbers were investigated. The light intensities and behavior characteristics of the GDI spray were analyzed through the axial and diagonal spray penetration, cone angle, and spray area from the spray images by using the image visualization system and image analysis system. The atomization performance of GDI injectors was analyzed by the local and overall Sauter mean diameter (SMD) measurement.     

Influence of saddle-splay deformation on lyotropic chromonic liquid crystals confined between two coaxial cylinders

ABSTRACT

A striking feature of lyotropic chromonic liquid crystals confined in cylinder model exhibit double-twist director configurations. Evidence suggests that saddle-splay deformation is among the most important factors for the distortions of director. Previous researches limit the director to distort at a fixed plane (r-? plane) by using specific boundary conditions such as degenerate planar anchoring condition. In this work, we consider lyotropic chromonic liquid crystals confined between two coaxial cylinders with free-surface boundary conditions and Rapini-Papoular-type anchoring conditions. By using finite-difference iterative method to solve the numerical solution of Euler equation, we find that saddle-splay deformation leads to double-twist director configurations under free-surface boundary conditions, which consist of the result under degenerate planar anchoring conditions. Furthermore, at Rapini-Papoular-type anchoring conditions, saddle-splay deformation has a great influence on the director in the radial direction (r direction) and the director distorts in three-dimensional space. Remarkably, our method provides a more accurate theory basis for the measured values of saddle-splay elastic constant K_24。     

Eu（TTA）3AA-NBR/PVP同轴超细纤维的制备及荧光性能研究

用同轴静电纺丝制备了含有稀土铕配合物(Eu(TTA)3AA)的芯-壳结构的丁腈橡胶/聚乙烯吡咯烷酮(NBR/PVP)超细荧光纤维。考察了在外层PVP纺丝参数不变的情况下,改变芯层丁腈橡胶纺丝液的纺丝速度、Eu(TTA)3AA含量等对纤维形貌的影响。通过研究Eu(TTA)3AA-NBR/PVP同轴超细纤维中Eu(TTA)3AA微观结构、含量与纤维的荧光性能之间的关系,发现在同轴纤维形成过程中由于溶剂的快速挥发可使Eu(TTA)3AA形成无定形结构,进而在纤维中形成分子簇级别的分散,在Eu(TTA)3AA含量为30%时,同轴纤维比Eu(TTA)3AA粉末的荧光强度提高了2倍。     

增强型喷射器对爆轰波DDT过程的影响

在激波、火焰及射流同时存在的流场中,组织燃烧转爆轰过程是脉冲爆震发动机实现点火、起爆的关键问题。设计一类喷射器,采用C_2H_2/O_2/Ar反应,数值验证了该喷射器能增强爆震室燃料燃烧转爆轰的可行性,并讨论了流场中热点的点火机制。结果显示:该装置在流场中可激发不稳定性,产生漩涡,加速能量、质量的交换。流场产生热点,促进火焰速度加快,追赶前导激波。喷射器位置影响前导激波的运动速度。在一定范围内,前导激波速度越大,碰撞产生的热点越容易激发燃烧转爆轰过程。     

同轴静电纺丝技术制备Y2O3:Eu3＋@SiO2豆角状纳米电缆与表征

采用同轴静电纺丝技术, 以氧化钇、氧化铕、正硅酸乙酯(C₈H₂₀O₄Si)、无水乙醇、PVP和DMF为原料, 成功制备出大量的Y₂O₃:Eu^3＋@SiO₂豆角状纳米电缆. 用TG-DTA, XRD, SEM, TEM和荧光光谱等分析技术对样品进行了系统地表征． 结果表明, 得到的产物为Y₂O₃:Eu^3＋@SiO₂豆角状纳米电缆, 以无定型SiO₂为壳层, 晶态Y₂O₃:Eu^3＋球为芯, 电缆直径约为200 nm, 内部球平均直径约150 nm, 壳层厚度约为25 nm, 电缆长度＞300 μm. 纳米电缆内部为球状结构, 沿着纤维长度方向有序排列, 形貌均一. Y₂O₃:Eu^3＋@SiO₂豆角状纳米电缆在246 nm紫外光激发下, 发射出Eu^3＋离子特征的波长为614 nm的明亮红光. 对其形成机理进行了初步讨论.     

两共轴带电圆环的相互作用能和作用力

计算了两共轴均匀带电圆环的相互作用能,并求出它们之间的相互作用力,绘制出电场力的空间分布图,进而讨论了作用力和两圆环半径和中心距离等参量的关系.     

Development of GC–MS/MS method with programmable temperature vaporization large volume injection for monitoring of 17β-estradiol and 2-methoxyestradiol in plasma

Monitoring of estradiol and its metabolites in biological samples is essential for the accurate diagnosis of a number of endocrine diseases. In this study, a sensitive, precise and specific GC–MS/MS method for the quantification of 17β-estradiol (17-BE) and its main metabolite, 2-methoxyestradiol (2-MEOE), in plasma was developed and validated. Plasma concentrations of these steroids are currently investigated as diagnostic markers for pre-eclampsia, a systematic disorder of pregnancy and a leading cause of maternal and fetal morbidity and mortality worldwide.