亚临界水技术的应用研究进展

处于100℃～374℃, 0.1～22.1 MPa状态下的亚临界水在性质与应用方面与常温常压下的水明显不同.一方面,由于极性、黏度等的变化,亚临界水可以作为一种不同于常温常压下水的提取溶剂;本文将主要介绍其在提取精油、酚类及多糖等天然物质方面的应用.另一方面,亚临界水可以作为反应媒介.此外,本文还介绍了在亚临界水的体系中,通过水解、裂解等不同反应对生物质、塑料、石化资源等进行水热处理,制备燃料气体、生物油或者固体燃料等有回收价值产物的应用.     

土壤中不同极性污染物的亚临界水选择性萃取

研究了用亚临界水萃取技术选择性萃取土壤中3种不同极性的污染物:2,4-二氯酚(2,4-DCP)、4-氯联苯(4-PCB)和六氯苯(HCB)。研究了在不同温度下亚临界水对分析物的萃取效率。125℃时,萃取物主要是2,4-DCP;250℃时,主要萃取4-PCB和HCB。同时,研究了亚临界水萃取时间、萃取体积对3种物质的萃取效率的影响,确定了土壤中HCB的最佳亚临界水萃取条件为萃取水体积4mL,萃取时间75m in,萃取温度250℃。本方法用于实际样品中的HCB萃取,通过改变萃取温度,可以去除其它污染物对HCB测定的影响,测定结果与索氏提取-GC分析结果吻合较好。与USEPA标准方法8081A相比,本方法可以显著缩短萃取时间、简化净化步骤及减少有机试剂的用量。     

以亚临界水为流动相的高效液相色谱方法的进展

由于纯水在高温高压下形成亚临界液体水时氢键网络发生改变,导致其极性、粘度等物理性质产生较大的变化。以亚临界水为流动相的高效液相色谱方法(SubWC)是近年来发展起来的一种新型分离技术。SubWC的仪器系统可以采用通过改装的一般的气相色谱(GC)或液相色谱(LC)装置;分离色谱柱既可以采用液相色谱填充柱,也可以采用类似于GC的毛细管柱;选择性既可以通过调节柱系统的温度和压力,也可以通过在流动相中添加有机调节剂或盐类进行调节;检测既可用氢火焰离子化检测器检测,也可用紫外检测器检测,极大地拓宽了色谱分离和最佳条件选择的范围。SubWC无论在仪器系统、流动相的洗脱还是固定相的选择等方面均有一定的特征。这种新的分离模式目前尚处于研究与开发阶段,且多用于极性、中等极性样品的快速分离。     

蔬果中12种残留农药的亚临界水萃取研究

利用亚临界水可以定量萃取基质中绝大部分化合物的特点,借助加速溶剂萃取仪(ASE)将亚临界水萃取与固相吸附联用,通过在ASE萃取池中填加C18吸附层的方式改进了萃取吸附模式,优化了萃取温度,研究了亚临界水在萝卜、香瓜、苹果和白菜等蔬果基质中对异稻瘟净等12种农药的萃取效果,用气相色谱-串联质谱法(GC-MS/MS)进行检...     

La1-xSrxMnO3氧化物磁导率和介电常数的频率特性研究

采用溶胶．凝胶法制备了钙钛矿型La1-xSrxMnO3（x=0，0．2，0．4，0．6）氧化物多晶样品，样品粉料的平均粒径为70nm左右。对不同Sr含量的样品磁导率μr（μr=μ＇r＋iμ＂r）和介电常数εr（εr=ε＇r＋iε＂r）的频谱（50～1800MHz）的研究表明，不掺Sr时，LaMnO3氧化物的复磁导率不随着频率变化，其实部近似为0．8，而虚部近似为1．0，复介电常数却随着频率增加而单调下降，实部从33降到19，虚部从65降到5。掺入Sr后，复磁导率和复介电常数频谱曲线都为典型的弛豫型谱线，磁导率的共振频率随着掺杂增加从1420MHz减小到810MHz，而复介电常数的共振频率却随着Sr含量增加从231MHz增加到580MHz，并对相关动态磁化和电极化机制进行了讨论。     

纤维素超/亚临界水水解研究进展

纤维素作为天然可再生资源,由于其水解糖化技术的可行性和水解产物的重要性而受到人们的广泛关注。目前多种生物和化学技术应用于纤维素水解糖化的研究,其中超、亚临界水是纤维素水解的绿色新型水解技术之一,具有反应快、转化率高等特点。本文比较了纤维素在超、亚临界水中不同的水解机理和产物分布,归纳了反应温度、压力和时间以及催化剂和纤维素结构对超、亚临界水水解反应的影响,并且介绍了超、亚临界水水解技术联用在纤维素水解中的应用。     

用状态方程预测极性溶剂中多种气体的亨利常数

应用立方型链转子状态方程预测不同温度和压力下多种超临界气体在亚临界极性液体中的亨利常数,得到良好的结果.并从理论上加以分析和讨论.     

一类新的表面活性剂:长链烷基三苯基鏻盐(Ⅰ)——正十二烷基三苯基溴化鏻的合成及其表面活性初探

合成了正十二烷基三苯基溴化鏻,并用荧光探针法研究了它在水溶液中的表面活性。利用芘作为荧光探针,根据其单体荧光光谱中第3与第1振子带强度之比与其所处环境的极性之间的相关性,测定了该表面活性剂的临界胶束浓度为2.08×10^-3mol/L,它在水溶液中胶束内核的微极性为16.1(以介电常数表示)。     

过氧化氢的氧化还原问题

在分析化学中过氧化氫有时被用作氧化剂,有时被用作还原剂。根据湼克拉索夫的解释:“过氧化氫在酸性介貭中,此較明显地表現出氧化剂的作用,在碱性介貭中——还原剂的作用”。事实上并非完全如此。过氧化氫在酸性介貭中是可以表現出氧化剂的作用;但在碱性介貭中也能比較明显地表現出氧化剂的作用,而不是还原剂的作用;只有在强氧化剂的作用下才能表現出还原剂的作用。这个問題应該如何解释?作者根据参考材料,提出个人的看法。正确与否?希望大家指正。过氧化氫的性质和結构純过氧化氫是粘稠液体,它有比水更大的比重(1.4694/0℃)和比水更高的介电常数(水的介电常数84.4/0℃,过氧化氫的介电常数89.2/0℃),过氧化氫溶于水后介电常数升高,含有36%的过氧化氫水溶液的介电常数为120。过氧化氫是一种很好的极性溶     

超临界水的性质及其在化学反应中的应用

介绍了水的热物理性质、结构性质、离子积、扩散系数和粘度等在超临界区域的特殊性，以及超临界水溶液在介电常数、偏摩尔体积、溶解性和极性等方面的特殊性质，并阐述了超临界水的这种特殊性在化学反应和环境治理中的应用。     

Subcritical water chromatography: A green approach to high-temperature liquid chromatography

At temperatures and pressures lower than 374 degrees C and 218 atm, subcritical water has widely tunable properties such as dielectric constant, surface tension, viscosity, and dissociation constant achieved by simply adjusting the temperature with a moderate pressure to keep water in the liquid state. At elevated temperatures, water acts like a weak polar organic solvent. Thus, subcritical water has been used as a green eluent to replace hazardous solvents commonly used as organic modifiers in RPLC. Subcritical water chromatography (SBWC) is capable of separating polar, moderately polar, and even some nonpolar analytes. Most of these low molecular weight solutes are stable at elevated temperatures during a chromatographic run. Some new packing materials are also quite stable and robust at mild temperatures ranging from 80 to 150 degrees C. Advantages of SBWC include the elimination of hazardous organic solvents used in traditional RPLC, rapid analysis time, improved selectivity, temperature-dependent separation efficiency, temperature-programmed elution, and compatibility with both gas- and liquid-phase detectors. In this paper, the technical aspects as well as the applications of SBWC are reviewed. Topics addressed in this review include the unique characteristics of subcritical water, analytes separated by SBWC, packing materials tested for SBWC, the application of GC and LC detection techniques in SBWC, SBWC instrumentation development, temperature effects on SBWC separation, and models developed for separation in SBWC.     

Screening and determination of pesticides in soil using continuous subcritical water extraction and gas chromatography-mass spectrometry

In the present work the efficiency of water under subcritical conditions for the extraction of pesticides having a broad spectrum of polarities from soils was evaluated. The pesticides under study were carbofuran, hexachlorobenzene, dimethoate, simazine, atrazine, lindane, diazinon, methylparathion, alachlor, aldrin-R, metholachlor, chlorpyrifos, heptachlor epoxide, dieldrin, endrin, 4,4-DDT and metoxichlor. Optimization studies were carried out using a blank soil (Non-Polluted Soil 1, CLN-1, RTC) and a real soil which were previously spiked with the pesticide mixture and aged for 60 days. A laboratory-made aluminum oven with controlled temperature was used to carry out the leaching process with subcritical water, where it is placed a pre-heater and the extraction cell. The following variables were studied, keeping the pressure controlled about 1200 p.s.i.: the extraction temperature, the time of static and dynamic extraction and the flow-rate of water (1 p.s.i. = 6894.76 Pa). The extraction efficiency of the pesticides increases with the temperature trending to the quantitative extraction at temperatures near to 300 degrees C. After the extraction process, the analytes were transferred quantitatively to 5 ml dichloromethane, before the determination by GC-MS. The results indicate that under the optimized conditions mostly of the analytes are extracted quantitatively in 90 min with recoveries quite similar to those obtained by the standard Soxhlet extraction procedure. Alternatively, by using an extraction time of 25 min, the method can be used as screening for all the pesticides, with recoveries depending on their polarity.     

新铌酸盐Ba5LnZnNb9O30(Ln=Y,La)的合成、结构与介电性能

在BaO-Ln2O3-ZnO-Nb2O5(Ln=Y,La)体系中通过固相反应法合成了填满型钨青铜结构的新铌酸盐Ba5YZnNb9O30与Ba5LaZnNb9O30.采用X射线衍射分析和扫描电镜进行了结构分析,并进行了介电性能测试.结果表明,Ba5YZnNb9O30为弛豫性铁电体,10kHz时的居里温度为25℃;室温时为四方钨青铜结构铁电相,晶胞参数a=1.25255(4)nm,c=0.39530(2)nm;1MHz时陶瓷体的室温相对介电常数为456.Ba5YZnNb9O30在室温下为四方钨青铜结构顺电相,晶胞参数a=1.25731(3)nm,c=0.39812(2)nm;频率为1MHz时,其陶瓷的室温相对介电常数为316.     

Overview of the retention in subcritical fluid chromatography with varied polarity stationary phases

Retention and separation of achiral compounds in supercritical fluid chromatography (SFC) depend on numerous parameters: some of these parameters are identical to those encountered in HPLC, such as the mobile phase polarity, while others are specific to SFC, as the density changes of the fluid, due to temperature and/or pressure variations. Additional effects are also related to the fluid compressibility, leading to unusual retention changes in SFC, for instance when flow rate or column length is varied. These additional effects can be minimised by working at lower temperatures in the subcritical domain, simplifying the understanding of retention behaviours. In these subcritical conditions, varied modifiers can be mixed to carbon dioxide, from hexane to methanol, allowing tuning the mobile phase polarity. With nonpolar modifiers, polar stationary phases are classically used. These chromatographic conditions are close to the ones of normal-phase LC. The addition of polar modifiers such as methanol or ACN increases the mobile phase polarity, allowing working with less polar stationary phases. In this case, despite the absence of water, retention behaviours generally follow the rules of RP LC. Moreover, because identical mobile phases can be used with all stationary phase types, from polar silica to nonpolar C18-bonded silica, the classical domains, RP and normal-phase, are easily brought together in SFC. A unified classification method based on the solvation parameter model is proposed to compare the stationary phase properties used with the same subcritical mobile phase.     

Extraction of cloransulam-methyl from soil with subcritical water and supercritical CO2

Cloransulam-methyl was extracted from soil samples with supercritical CO2, subcritical water and conventional organic solvents. Supercritical CO2 was less efficient than conventional organic solvents; polarity modifiers had no impact on extraction efficiency. Extraction with supercritical CO2 exhibited a strong temperature dependence. Water was as effective as strong organic solvents for the extraction of cloransulam-methyl; however cloransulam-methyl hydrolyzed when extracted at 150 degrees C. Extraction temperature was the most important variable in increasing the efficiency and rate of extraction, while extraction pressure was not a significant variable.     

Relative Permittivities for Glucose+Glycine+Water Solution at 278.15 to 313.15 K

The relative permittivities(ε) for the glucose+glycine+water mixtures were measured at temperatures of 278.15 to 313.15 K. The experimental values for a complete data set were critically analyzed. The experimental va- lues were fitted to some empirical equations as the functions of temperature and/or compositions of the solution. At given temperatures and compositions of glycine, the dependences of the relative permittivities on the molar fraction of glucose(Glc) and glycine(Gly) can be described by a linear or quadratic equation, respectively. A comparison of the εGlc values of glucose solution with the εGla values of galactose solution indicates that the relative permittivities of the ternary solutions containing glucose are smaller than those containing galactose under the same conditions. This difference arises from the slight difference in the stereo-structures of the saccharide molecules.     

介电损耗法测定卤化银乳剂微晶体的离子电导

卤化银乳剂层在交变电场中显示出介电色散现象(Maxwell-Wagner效应),即在交变电场的频率f不同时,卤化银乳剂层的介电损耗ε″也不相同。根据ε″～1f,曲线可以计算卤化银微晶体的离子电导σ₂。我们注意到,不同类型的明胶具有不同的介电常数ε′₁,同一明胶在不同频率和真空度下所显示的ε′₁也有差别。含湿量的增大使乳剂的ε″_max,ε′_max和ε_∞的数值增大,使ε″～1gf曲线的低频端提高,使f_max向低频偏移。通过抽气严格控制样品含湿量是得到准确的σ₂的关键。此外,我们还考察了乳剂层的层数和电极的尺寸对f_max和σ₂值的影响。     

Carbon dioxide modified subcritical water chromatography

A novel method of increasing the elution strength in subcritical water chromatography (SWC) by adding CO2 to the water mobile phase is presented. Since the polarity of water reduces dramatically with increasing temperature, this property is used in SWC to create an isocratic mobile phase with tunable elutropic strength in reversed-phase separations. Unfortunately, thermal stability of the stationary phase dictates the upper temperature limit and therefore also the minimum available mobile phase polarity. As a result SWC is often not very effective at eluting non-polar analytes. However, when CO2 is blended into subcritical water, a considerable reduction in mobile phase polarity results and improves such separations. For example, in conventional SWC 1-octanol is not observed to elute from a PRP-1 column after several hours at the maximum column temperature of 200 degrees C. In contrast to this, when CO2 is present at 180atm (1atm=101325Pa) in the mobile phase, 1-octanol elutes with good peak shape in less than 4min at only 100 degrees C. The technique is applied to the separation of a variety of analytes which have previously been challenging or even not possible to analyze by conventional SWC. Further, the ability to use temperature and composition programming with the blended CO2/water mobile phase in SWC is also presented and discussed. Overall, the developed method considerably extends the range of non-polar analytes amenable to SWC analysis, while maintaining the beneficial conventional SWC features of flame ionization detection and environmental compatibility.     

类钙钛矿新铌酸盐Ba5LaTi2Nb3O18的合成、结构与介电特性

为满足现代通信技术小型化、集成化与高可靠性的迫切要求,探索具有高介电常数、低介电损耗与低温度系数的微波介电材料引起了材料科学、化学、物理和电子科学等领域科学工作者的广泛关注,并已开发出复合钙钛矿结构的Ba(Mg1/3Ta2/3)O3、Ba(Zn1/3Ta2/3)O3和钨青铜结构的Ba6-3xLn8+2x·Ti18O54及Ba2Ti9O20等实用化的高性能材料[1～7].这类材料均由氧八面体共顶连接,而且氧八面体内(B位)、外(A位)阳离子比例等于或略大于1,由此,我们推测在B位与A位阳离子比例略小于1的类钙钛矿结构中也极有可能存在具有优良介电性能的新材料,因此对通式为AnBn-1O3n(n=5,6,7,8)的系列新化合物进行了系统的合成、结构与介电性能研究[8,9].本文报道在BaO-La2O3-TiO2-Nb2O5体系中合成的具有5层类钙钛矿结构的新铌酸盐Ba5LaTi2Nb3O18,发现该材料具有较好的介电性能.