Ring‐expansion polymerization of meso‐lactide catalyzed by dibutyltin derivatives

Meso‐Lactide was polymerized in bulk at 60, 80, and 100 °C by means of three different types of catalysts: dibutyltin sulfides (2,2‐dibutyl‐2‐stanna‐1,3‐dithiolane and 2,2′‐dibutyl‐2‐stanna‐1,3‐dithiane), dibutyltin derivatives of substituted catechols (BuCa, CyCa, and BzCa), and dibutyltin derivatives of 2,2′dihydroxybiphenyl (SnBi) and 2,2′‐dihydroxy‐1,1′‐binaphthyl (SnNa). Only the latter two catalysts were active at 60 °C. The architecture of the resulting polylactides depends very much on the structure of the catalyst and on the temperature. At the lowest temperature (60 °C), SnBi and SnNa mainly yielded even‐numbered linear chains, but SnNa also yielded even‐numbered cycles at 100 °C and short reaction times. In contrast, BuCa, CyCa, and BzCa mainly yielded odd‐numbered cycles, although the same catalysts yielded even‐numbered linear chains when benzylalcohol was added. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 749–759     

液相色谱-串联四极杆飞行时间质谱和超高效液相色谱-串联三重四极杆质谱用于检测牛肉中的刚果红

建立了牛肉中刚果红的检测方法。定性方法采用液相色谱-串联四极杆飞行时间质谱对未知物进行质谱谱图库匹配,定量分析采用超高效液相色谱-串联三重四极杆质谱。牛肉样品中的刚果红经液液萃取净化后,采用Agilent ZORBAX Eclipse Plus C₁₈ Rapid Resolution HD色谱柱(50 mm×2.1 mm, 1.8 μm)进行分离,流动相为95%(体积分数)甲醇,流速为0.2 mL/min。AB 4000⁺三重四极杆质谱仪在电喷雾负离子化(ESI)及MRM模式下定量。结果显示,刚果红在0.03~1 mg/L浓度范围内,线性关系良好(相关系数为0.9998),精密度良好(RSD小于5%),回收率为88%~91%,检出限约为0.01 mg/L。本方法快速简便,重现性好,可以为牛肉及其他肉制品中刚果红的定量提供良好的解决方案。     

Effects of longitudinal wave on the resonance behavior of an electrode-separated piezoelectric sensor in liquids

An electrode-separated piezoelectric sensor (ESPS) was constructed and its operation in the liquid phase was characterized. When the surface of the separated-electrode reflects the weak longitudinal wave (LW) back to the surface of the quartz disc where it was generated, the interaction of the reflected LW with the main thickness-shear wave of the quartz disc is a potential error source. In this study, the influence of the LW effect on the response of the ESPS was investigated by an impedance analysis method. It was shown that all the impedance response parameters shift periodically as a function of the distance between the separated-electrode and the quartz crystal. The LW effect depends markedly on the surface conditions, including the shape, area, position, angle and roughness, of the separated-electrode. When a rough, non-parallel or ball electrode was used, the influence of the LW could be decreased greatly. The influence of the air/liquid interface on the reflection of the LW was efficiently screened in the ESPS.     

全二维气相色谱/飞行时间质谱法定性筛查鱼肉组织中含卤有机污染物

采用全二维气相色谱/飞行时间质谱(GC×GC-TOFMS),建立了鱼肉样品中含卤有机污染物的定性和定量分析方法.鱼肉样品用正己烷丙酮(1∶1,V/V)提取,凝胶色谱和复合硅胶柱净化,浓缩富集,全二维气相色谱联用飞行时间质谱(DB-5MS毛细管色谱柱联HT-8色谱柱)检测.软件自动识别后,经三步筛查,共鉴定出含氯或溴化合物72种,其中包括33种多氯联苯,9种有机氯农药,4种多溴联苯醚,4种DDT代谢产物,2种氯代茴香醚,2种氯苯乙烯,1种氯代茴香硫醚及1种甲基三氯生.另外,从质谱信息上看,有16种化合物明显含氯或含溴,但是因为缺少必要的谱库信息不能准确识别.采用外标定量法,对鱼肉样品中检出的主要的10种多氯联苯和1种多溴联苯醚进行了准确定量分析.     

体外大鼠肠道菌群代谢脱氧雪腐镰刀菌烯醇的研究

运用超高效液相色谱串联四级杆/飞行时间质谱(UPLC-Q/TOF-MS)识别和确定脱氧雪腐镰刀菌烯醇( Deoxynialenol,DON)在大鼠肠道菌群体外代谢模型中的代谢产物,同时运用高效液相色谱串联三重四级杆质谱定量分析DON含量变化,比较各段肠管中厌氧菌群的代谢能力.结果表明,DON不能被大鼠小肠菌群代谢,而能被其大肠菌群代谢为脱环氧代谢产物脱环氧-脱氧雪腐镰刀菌烯醇(Deepoxy-deoxynialenol,DOM).定量测定结果显示,大肠中盲肠菌群代谢能力最强.     

Optimization of a quadrupole ion storage trap as a source for time‐of‐flight mass spectrometry

Designs of a quadrupole ion trap (QIT) as a source for time‐of‐flight (TOF) mass spectrometry are evaluated for mass resolution, ion trapping, and laser activation of trapped ions. Comparisons are made with the standard hyperbolic electrode ion trap geometry for TOF mass analysis in both linear and reflectron modes. A parallel‐plate design for the QIT is found to give significantly improved TOF mass spectrometer performance. Effects of ion temperature, trapped ion cloud size, mass, and extraction field on mass resolution are investigated in detail by simulation of the TOF peak profiles. Mass resolution (m/Δm) values of several thousand are predicted even at room temperature with moderate extraction fields for the optimized design. The optimized design also allows larger radial ion collection size compared with the hyperbolic ion trap, without compromising the mass resolution. The proposed design of the QIT also improves the ion–laser interaction volume and photon collection efficiency for fluorescence measurements on trapped ions. Copyright © 2011 John Wiley & Sons, Ltd.     

超高效液相色谱-四极杆-飞行时间质谱法快速测定水产品中微囊藻毒素和节球藻毒素

通过超声提取、固相萃取纯化、超高效液相色谱-四极杆-飞行时间质谱(UPLC-Q-TOF-MS)联用技术快速测定水产品中的微囊藻毒素-RR、-YR、-LR和节球藻毒素.分别采用选择离子监测质荷比(m/z)为519.84、1045.66、995.67、825.54分子离子峰进行定量分析.该法检出限为5.0～10.0μg/kg,在浓度0.02～5mg/kg的范围内,峰面积与样品浓度呈良好线性关系;4种藻毒素的回收率为76.2％～93.7％,相对标准偏差为2.0％～7.1％.采用上述方法对45个太湖水产品样品进行测定,发现有少量水产品中存在藻毒素污染,其中微囊藻毒素-RR最高含量为15.2μg/kg,微囊藻毒素-LR最高含量为0.84μg/kg,MC-YR、节球藻毒素均未检出.此方法可作为监测水产品体内蓄积藻毒素的分析方法.     

钒氧阴离子团簇与小分子碳氢化合物反应的实验和理论研究

为了在分子层次上揭示相关催化反应的机理, 人们对过渡金属氧化物团簇与碳氢化合物分子反应进行了大量研究. 相比于过渡金属氧化物团簇阳离子, 阴离子对一些碳氢化合物的活性弱得多, 因此研究还很少. 在本工作中, 我们通过激光溅射产生钒氧团簇阴离子VxOy, 产生的团簇在接近热碰撞条件下与烷烃(C2H6和C4H10)以及烯烃(C2H4和C3H6) 在一个快速流动反应管中进行反应, 飞行时间质谱用来检测反应前后的团簇分布. 在VxOy与烷烃的反应中, 生成了产物V2O6H-和V4O11H-; 在与烯烃的反应中, 产生了相应的吸附产物V4O11X-(X=C2H4或C3H6). 密度泛函理论计算表明: V2O-6和V4O-11可以活化烷烃(C2H6和C4H10)的C—H键, 也可以与烯烃(C2H4和C3H6)发生3+2环化加成反应形成一个五元环结构(-V-O-C-C-O-), C—H键活化与环加成反应都需经历可以克服的反应能垒. 理论计算与实验观测结果相符合. V2O-6和V4O-11团簇都具有氧原子自由基(O·或O-)的成键特征, 活性O-物种也经常出现在钒氧催化剂表面, 因而本研究在分子水平上, 揭示了表面活性氧物种与碳氢化合物反应的机理.     

超高效液相色谱-四极杆串联飞行时间质谱分析黄酮类化合物及小毛茛茎叶的成分

为了探索液相色谱-质谱联用(LC-MS)技术在快速识别中药及天然产物成分中的应用,以黄酮对照品为研究前体,药用植物小毛茛为研究对象,采用超高效液相色谱/二极管阵列检测器-电喷雾四极杆串联飞行时间质谱(UPLC/DAD-ESI/Q-TOF MS)分析了黄酮类化合物同系物及同分异构体的色谱、质谱特性。结果显示:黄酮氧苷和黄酮碳苷的紫外吸收光谱及二级质谱具有显著性差异,糖苷化位置同保留时间、二级质谱碎片及相对丰度具有相关性。将该方法应用于小毛茛茎叶醇提液的分析,结合其酸水解液的分析,解析了22个黄酮醇糖苷和3个苷元。方法简便,具有可操作性。     

Effective medium theory expressions for the effective diffusion in chromatographic beds filled with porous, non-porous and porous-shell particles and cylinders. Part I: Theory

Using the permeability analogue of the diffusion and partitioning processes occurring in a chromatographic column, the different Effective Medium Theory (EMT) models that exist in literature for the electrical and thermal conductivity have been transformed into expressions that accurately predict the B-term band broadening in chromatographic columns. The expressions are written in such a form that they hold for both fully porous and porous-shell particles, and both spherical and cylindrical particles are considered. Mutually comparing the established EMT-expressions, it has been found that the most basic variant, i.e., the Maxwell-based expression, is already accurate to within 5% for the typical conditions encountered in liquid phase chromatography, independently of the exact microscopic morphology of the packing. For most typical values of the intra-particle diffusion rate and the species retention factors, it is even accurate to within 1%. If even higher accuracies are needed, more elaborate EMT-expressions are available. The modelling accuracy of all explicit EMT-expressions is much better than the residence time weighted (RTW) B-term expressions that have been used up to now in the field of chromatography, where the error is typically on the order of 10% and more. The EMT-models have also been used to establish expressions for the obstruction and tortuosity factor in packings of non-porous particles. The EMT has also been applied to the meso-porous zone only, yielding an expression for the intra-particle diffusion coefficient that can be used without having to specify any obstruction factor. It has also been shown that the EMT also provides a very simple but exact expression to represent the way in which the solid core obstructs the effective intra-particle diffusion in the case of porous-shell particles. This obstruction factor is given by γ(part)=2/(2+ρ3) for spherical particles and γ(part)=1/(1+ρ3) for cylinders. Back-transforming the obtained expressions, a set of simple explicit expressions has been obtained that allow to directly obtain the intra-particle diffusion coefficient (D(part)) from peak parking or B-term constant measurements. Using these expressions, it could be demonstrated that the traditionally employed RTW-model yields D(part)-values that display an erroneous retention factor dependency, even in cases where the RTW-model appears to be able to closely fit the peak parking measurements.