多次顶空固相微萃取方法的原理及应用

详细讨论了多次顶空固相微萃取(MHS-SPME)技术的原理和影响因素,并与常用的固相微萃取(SPME)定量校正方法相比较,分析了该方法的优势和缺点。综述了多次顶空固相微萃取在食品、农业领域的应用情况,并对该方法存在的问题和发展前景进行了论述。     

微波辅助顶空固相微萃取GC-MS法分析柠檬草中挥发性成分

设计制作了一种微型底聚焦微波反应装置,用于辅助顶空固相微萃取,解决了无溶剂顶空提取的问题,建立了柠檬草样品中挥发性成分的微波辅助顶空固相微萃取方法。使用GC-MS法对柠檬草叶片和根茎萃取物中挥发性成分进行分析鉴定,分别得到37和46种化合物,结合峰面积归一法确定各组分的含量,其挥发性成分别占萃取物挥发总量的89.93%和77.29%。其中叶片和根茎中含量较高的挥发性成分都是橙花醛和香叶醛,叶片中的主要挥发性成分橙花醛(29.27%)和香叶醛(22.14%)的相对含量要明显优于根茎中橙花醛(8.61%)和香叶醛(7.76%)。研究为样品特别是固体样品挥发性成分的直接快速分析提供了一种稳定高效、简单快速的新方法,具有广泛的应用前景。     

HS-SPME结合GC-MS分析煎鸡蛋的挥发性风味成分

采用顶空固相微萃取与GC-MS联用方法对煎鸡蛋中挥发性成分进行提取与分析,考察萃取头、萃取温度和吸附时间对分析结果的影响,得到优化的顶空固相微萃取条件为:黑色萃取头(75μm Carboxen/PDMS),吸附温度75℃,吸附时间70 min。在优化的条件下分析,共鉴定出50种挥发性风味成分,其中,醛类16种(40.588%)、含氮化合物14种(23.639%)、醇类8种(7.156%)、烃类3种(4.800%)、酚类及杂环化合物3种(1.755%)、酮类3种(0.868%)及含硫化合物3种(0.563%)。鉴定出含量较高(相对质量分数大于2.5%)的物质有:2,5-二甲基吡嗪、3-甲基丁醛、2-甲基吡嗪、壬醛、苯甲醛、反,反-2,4-癸二烯醛、辛醛、2-甲基丁醛、反-2-癸烯醛、3,7-二甲基-1,6-辛二烯、1-辛烯-3-醇。     

固相微萃取-色谱-质谱分析聚丙烯产生的挥发性气体

采用顶空固相微萃取-气相色谱-质谱联用法,以聚二甲基硅氧烷为萃取头.在80℃下顶空吸附20 min,于250℃下解析5 min后进行气相色谱-质谱测定,定性地研究聚丙烯在经双螺杆挤出后产生的挥发性气体.聚丙烯样品的分析结果表明:其挥发性气体中共检测出28种组分,包括烷烃类、醛酮酸酯类、醇醚类及烯烃类化合物,其中以丙酮(14.12%)和2,4-二甲基庚烷(12.97%)的含量最多,并简要分析丙酮和2,4-二甲基庚烷的产生机理;顶空固相微萃取-气相色谱-质谱联用技术可以方便准确地检测出聚丙烯制品中的痕量挥发性气体.     

顶空固相微萃取结合气质联用仪分析五种酱香型白酒大曲中的风味化合物

以贵州仁怀市五种酱香型白酒大曲为研究对象,利用顶空固相微萃取-气相色谱-质谱联用仪研究大曲中风味化合物。实验共初步定性出141种化合物,五种酱香型白酒大曲所共有的化合物有11种,其中吡嗪类、酸类、醇类、酯类化合物相对含量较高,2,3,5,6-四甲基吡嗪是五种大曲中共有的相对含量最高的吡嗪类化合物。本文为后续深入研究酱香型大曲中的风味物质提供一定的参考。     

固相微萃取法萃取液态奶味香精挥发性香成分条件的优化

采用固相微萃取法,对液态奶味香精中的挥发性香成分进行了萃取条件的优化研究,得到了较佳的萃取条件。以23种奶味香料化合物组成的模拟奶味香精体系为研究对象,对预热温度(30~80℃),萃取时间(10~180 min),样品量(1~11 mL)和SPME纤维种类(65μm CWAX/DVB,65μm PDMS/DVB,75μm CAR/PDMS和50/30μm DVB/CAR/PDMS)4个因素进行了考察。发现这4个因素对香精中挥发性香成分萃取的选择性和对检出限的灵敏性均有显著性影响。结果表明,PDMS/DVB纤维对奶味香精中挥发性化合物的选择性最好,灵敏度最高,其次是DVB/CAR/PDMS。通过单因素实验,得到优化的固相微萃取条件是:预热温度50℃,萃取时间40 min,样品量5 mL。将得到的优化参数集中用于市售奶味香精样品分析,与对照组的固相微萃取结果相比,挥发性香成分的种类增加了30种,总峰面积增加了20倍,验证了固相微萃取参数优化的实用性。     

全叶青兰挥发性成分

采用顶空固相微萃取结合色谱质谱技术分析了全叶青兰中挥发性成分的组成和含量。结果表明,6 min和30 min的顶空吸附时间所测得的全叶青兰中挥发性成分的组分基本一致,但各组分所占的比例有一定差异。全叶青兰挥发性成分中以萜烯类为主的碳氢化合物约占其总质量的50%,醇类化合物约占20%,其他成分的质量分数高低依次为酯、酮、萜烯氧化物和醛类化合物,醚、胺及含硫化合物等质量分数极低。     

全叶青兰挥发性成分的研究

采用顶空固相微萃取结合色谱质谱技术分析了全叶青兰中挥发性成分的组成和含量。结果表明：6min和30min的顶空吸附时间所测得的全叶青兰中挥发性成分的组分基本一致,但各组分所占的比例有一定差异。全叶青兰挥发性成分中以萜烯类为主的碳氢化合物约占其总质量分数的50%,醇类化合物占到约20%,其它成分的含量高低依次为酯、酮、萜烯氧化物和醛类化合物,醚、胺及含硫化合物等含量极低。     

HS-SPME-GC-MS/MS法分析树苔及其提取物中的挥发性化学成分

为分析树苔及其提取物中的挥发性及半挥发性化学成分,通过单因素实验优化固相微萃取的萃取头、萃取温度、萃取时间和解吸时间,建立了一种测定树苔及其提取物中挥发性及半挥发性化学成分的顶空-固相微萃取-气质联用法(HS-SPME-GC-MS/MS),并用该方法分析了3种树苔提取物及2种树苔原料。结果表明:优化得到的固相微萃取条件为:0.5 g样品,65μm聚二甲基硅氧烷/二乙烯基苯粉色萃取头,萃取温度90℃,萃取时间20 min,解吸时间2 min; 5种树苔样品中共鉴定出338种(13类)挥发性及半挥发性化学成分,共检出成分有7种,3种树苔提取物主要共有特征成分为苔色酸乙酯、苔黑酚酸甲酯、赤星衣酸甲酯,2种树苔原料主要共有特征成分为苔黑酚酸甲酯。该方法前处理简便快捷、无溶剂损耗,适用于树苔样品的快速定性及半定量分析。     

恩施土家烟熏腊肉挥发性成分提取

以恩施土家烟熏腊肉为研究对象，分别采用索氏提取法、水蒸气蒸馏法、同时蒸馏萃取法和顶空固相微萃取法提取其挥发性物质，结合GC-MS技术对挥发性物质进行了定性定量分析与检测，并对比了各提取方法对挥发性物质分布与含量的影响。结果表明：在4种提取方法中烟熏腊肉挥发性物质种类分别为83种、53种、79种和62种，其中相同的挥发性物质有22种。这些挥发性物质分别为烃类、醇类、酚类、醛类、酸类、酯类、醚类及其他含硫含氮杂环化合物；各挥发性物质含量较大的为经顶空固相微萃取法提取得到的苯酚，为42016.73 ng/g。通过各挥发性物质的香气活度值(OAV)分析发现，对烟熏腊肉风味有贡献的主要风味物质59种，其中香气活度值较突出的为经顶空固相微萃取法提取得到的愈创木酚，高达10934。对比各提取方法结果发现，虽然不同提取方法各有优缺点，可以相互补充；但是通过顶空固相微萃取法得到的大部分挥发性物质相对含量比其他方法要高。同时对挥发物质进行了风味总结和嗅闻分析。     

Quantification of Phospholipids Classes in Human Milk

Phospholipids are integral constituents of the milk fat globule membranes and they play a central role in infants’ immune and inflammatory responses. A methodology employing liquid chromatography coupled with evaporative light scattering detector has been optimized and validated to quantify the major phospholipids classes in human milk. Phospholipids were extracted using chloroform and methanol and separated on C18 column. Repeatability, intermediate reproducibility, and recovery values were calculated and a large sample set of human milk analyzed. In human milk, phospholipid classes were quantified at concentrations of 0.6 mg/100 g for phosphatidylinositol; 4.2 mg/100 g for phosphatidylethanolamine, 0.4 mg/100 g for phosphatidylserine, 2.8 mg/100 g for phosphatidylcholine, and 4.6 mg/100 g for sphingomyelin. Their relative standard deviation of repeatability and intermediate reproducibility values ranging between 0.8 and 13.4 % and between 2.4 and 25.7 %, respectively. The recovery values ranged between 67 and 112 %. Finally, the validated method was used to quantify phospholipid classes in human milk collected from 50 volunteers 4 weeks postpartum providing absolute content of these lipids in a relatively large cohort. The average content of total phospholipids was 23.8 mg/100 g that corresponds to an estimated mean intake of 140 mg phospholipids/day in a 4-week old infant when exclusively breast-fed.     

The role of pH in thaumasite sulfate attack

The thaumasite form of sulfate attack (TSA) has been recognised in recent years as a distinct mechanism by which degradation of buried concrete can occur in the presence of an external source of sulfate ions. There is, however, disagreement about the role of pH. It has been proposed that attack by sulfuric acid, produced by oxidation of pyrite, is sometimes the primary cause of deterioration. Others believe that the acid is rapidly neutralised giving a higher concentration of sulfate ions in the ground, hence increasing the extent of attack. The aim of the laboratory study reported here was to understand the role of sulfuric acid in TSA by examining concrete cubes, made from three types of cement and two types of aggregate, immersed at low temperature in two solutions, one alkaline corresponding to BRE Design Sulfate Class DS-3 and the other acidic. It is concluded that the presence of acid does not promote the formation of thaumasite. Although degradation of the concrete was observed in acid conditions, the mechanism was not TSA as observed in alkaline conditions.     

Encapsulation of caesium-loaded Ionsiv in cement

The microporous material Ionsiv is used for ¹³⁷Cs removal from aqueous nuclear waste streams. In the UK, Cs-loaded Ionsiv is classed as an intermediate-level waste; no sentencing and disposal route is yet defined for this material and it is currently held in safe interim storage on several nuclear sites. In this study, the suitability of fly ash and blast furnace slag blended cements for encapsulation of Cs-Ionsiv in a monolithic wasteform was investigated. No evidence of reaction or dissolution of the Cs-Ionsiv in the cementitious environment was found by scanning electron microscopy and X-ray diffraction. However, a small fraction (≤ 1.6 wt.%) of the Cs inventory was released from the encapsulated Ionsiv during leaching experiments carried out on hydrated samples. Furthermore, it was evident that K and Na present in the cementitious pore water exchanged with Cs and H in the Ionsiv. Therefore, cement systems lower in K and Na, such as slag based cements, showed lower Cs release than the fly ash based cements.     

Thaumasite formation in a tunnel of Bapanxia Dam in Western China

A site investigation and sampling was carried out on a sulfate-attacked concrete structure in Bapanxia Hydraulic Power Plant in Western China. The concrete had been exposed to ground water containing substantial concentrations of salts (SO₄²⁻, CO₃²⁻ and Cl⁻) for about 6 years and was analyzed with X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), laser-Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. It is shown that a white mushy mixture consisting of thaumasite, ettringite, gypsum and calcite is present in the residual concrete. This paper reports the first instance of the thaumasite form of sulfate attack of concrete in China.     

Nonlinear ultrasonic evaluation of load effects on discontinuities in concrete

The presence of discontinuity surfaces in concrete structures, i.e. two or more layers in contact, may be an existing situation with evident relapses on damage formation and progression. Differences occur depending on the type of discontinuity, which could be a thin weaker layer or a pre-existing crack. The behavior of pre-existing interfaces is here studied by means of the Scaling Subtraction Method, a Nonlinear Ultrasonic Non-Destructive Technique, that revealed to be effective in describing the mechanical evolution of concrete samples with discontinuity surfaces under the effects of compressive loads.     

Linear and non-linear analysis of desorption processes in cement mortar

Based on the gathered experimental data concerning adsorption/desorption processes in cement mortar, it has been stated that the rate of these processes changes in time even if they proceed in stable conditions. In this paper an attempt is made to describe such processes by applying linear and non-linear diffusion theories for comparison. The main aim of these studies is to determine the diffusion coefficient by correlating the theoretically determined desorption isotherms with the experimental ones. The validation of the diffusion coefficient was accomplished through comparison of the theoretical desorption curves with the experimental data for narrow and broad ranges of the air humidity changes. The final conclusion is that the moisture transfer in hygroscopic porous materials for broad ranges of the air humidity changes should be modeled by the non-linear diffusion theory, in which the diffusion coefficient is a function of moisture content. The new material in this paper concerns very long time measurements in desiccators, and evaluation of the diffusion coefficient by an advanced optimization algorithm.     

Evolution of penetration resistance in fresh concrete

The objective of this research was to examine the setting of concrete through its penetration resistance; an experimental device, especially developed for this purpose was used, which consists of a system that lets a sphere fall on concrete from a certain height and then measures the depth of the crater. Forty-five samples were made with four different types of cement varying its quantity, water-cement ratio, at ambient temperature and humidity. A semiempirical model which explains the penetration resistance evolution in fresh concrete was proposed and experimentally demonstrated. The results are compared with the consolidation curves for soils represented by the logarithmic method. The proposed setting time was defined as the elapsed time between the placement of the concrete and the time when the depth of the crater is 18% of the initial one.     

Wavelet-based analysis of ultrasonic longitudinal and transverse pulses in cement-based materials

Ultrasonic pulse velocity has been used for decades to detect localized damage and to estimate concrete properties. More recent applications aim at diffuse damage characterization, such as environmental and mechanical damage. In most applications the methodology to calculate pulse speed is a very important issue. This work, applying continuous wavelet transform (CWT) to construct time-frequency signal representations, calculates frequency-dependent velocity of longitudinal and transverse ultrasonic pulses using wavelet scales. The method is applied to a total of 14 specimens of 5 different mixes and frequency-dependent velocities are calculated using four wavelet families. The CWT capability to decompose the inquiring pulse spectrum and analyze phase velocities is discussed with regard to wavelet, pulse type, and mixture. Frequency-dependent velocity of longitudinal pulses at lower frequencies (from 100 kHz up to 250 kHz) was proven to be much more sensitive to mix proportions than transverse pulses.     

The effect of nanoalumina silanisation in tetraglycidylether epoxy adhesive

The efficiency of different surface modifications on alumina nanoparticles on both filler dispersion and the final properties of the resulting adhesive nanocomposites have been investigated. A tetraglycidyldiaminodiphenylmethane (TGDDM) epoxy resin and three sample series of nanocomposites were prepared via in-situ incorporation of alumina nanoparticles into the reactor. The alumina/TGDDM nanocomposites were prepared individually using neat or non-treated alumina nanoparticles and two kinds of silane-grafted alumina nanoparticles, i.e., APS-treated alumina and GPS-treated alumina. The presence of different alumina nanoparticles in the epoxy matrices resulted in different states of nanofiller dispersion as revealed in SEM and AFM micrographs. It was elucidated that the silane treatment on alumina nanoparticles is crucial for the desired dispersion in the epoxy matrix. Besides, the appropriate filler dispersion resulted in improved thermal resistance and high degree of cure, especially for the adhesive nanocomposite containing APS-treated alumina nanoparticles. In adhesion tests, the shear strength was improved in both nanocomposites containing silane-grafted alumina with more pronounced values for the nanocomposite containing APS-treated alumina nanoparticles. The shear strength reached from 6.6 MPa for the neat epoxy adhesive to 10.2 MPa for the adhesive nanocomposite containing 5 wt % APS-treated alumina nanoparticles mainly due to high levels of dispersion of the high modulus alumina nanoparticles and effective interfacial interactions with the epoxy matrix. The adhesive peel strength of alumina/TGDDM nanocomposites showed a similar trend as in shear strength with more pronounced variations. A noticeable increase in the peel strength of the nanocomposites containing silane-grafted alumina nanoparticles appeared to correlate with greater levels of crack deflection and hence dissipation of fracture energy as observed in SEM pictures.     

蛇纹石吸附处理污水中重金属的实验研究

用蛇纹石做吸附剂 ,在温度为 70℃、吸附时间为 6h的条件下 ,可有效去除中性 (pH =7± 0 5 )水中的Cd2 +、Cu2 +、Fe3+、Pb2 +、Ni2 +,对上述离子的吸附容量依次为 0 5 0 8、2 0 5 0、2 0 0 0、0 2 98、0 2 32mg/g。用固定式吸附柱在所选条件下 ,对石油污水中Cd2 +、Cu2 +、Fe3+、Pb2 +、Ni2 +的去除率分别为 83 7%、89 5 %、90 7%、44 8%、5 3 5 % ,对合成水样去除率都在 99%以上。