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101.
Ke-Shun Liu 《Journal of the American Oil Chemists' Society》1994,71(11):1179-1187
Theoretically, preparation of fatty acid methyl esters (FAMEs) deals with reversible chemical reactions in a complex system.
Methodologically, there are numerous ways, generally characterized by the type of catalysts used and steps involved. Although
there are more than a half dozen common catalysts, the majority fall into either acidic (HCl, H2SO4 and BF3) or alkaline types (NaOCH3, KOH and NaOH), with each having its own catalytic capability and application limitations. In terms of steps, many conventional
methods, including those officially recognized, consist of drying, digestion, extraction, purification, alkaline hydrolysis,
transmethylation/methylation and postreaction work-up. Although these methods are capable of providing reliable estimates
if some precautions are taken, they are cumbersome, time-consuming and cost-inefficient. A new approach has been to transmethylate
lipidsin situ. Due to its simplicity, high sensitivity, comparable reliability and capability to determine total fatty acids, the method
of direct transmethylation is finding a unique place in lipid determination. Regardless of which method is used, quantitative
methylation requires chemists to take precautions at every step involved, particularly during FAME formation and subsequent
recovery steps. Evidently, there is an urgent need for more systematic studies, guided by the chemical principle of reactions
involved and physicochemical properties of regents and end products, into factors affecting these steps. Hopefully, this will
lead to an improved method, which measures lipid composition in biological materials not only with high accuracy but also
with high efficiency and minimum costs. 相似文献
102.
103.
用于重离子核反应实验测量的纵向电场气体电离室 总被引:1,自引:0,他引:1
本文报道了一种新型的大动态范围,多叠层探测器系统组件之一的纵向电场气体电离室的构造,性能和在中能得离子核反应实验中的应用。 相似文献
104.
应用烃类直接检测技术预测天然气藏 总被引:1,自引:0,他引:1
柴达木盆地位于青藏高原北部,是中国大型含油气盆地之一,历经40年的勘探,发现了丰富的油气资源。柴达木盆地东部地区是第四纪沉降与沉积中心,区内第二系生储气岩厚度大、分布广、第四纪新构造运动形成的同生沉积构造发育、保存完整、具有形成大中型天然气田的地质条件。此外,由于该地区含气地层时代新、埋藏浅、成岩与胶结作用差、含气层厚度大、孔渗性好,加之构造条件简单,人文干扰小、是应用烃直接检测技术寻找天然气的有 相似文献
105.
介绍了用气相色谱分析叔丁醇两步氧化制甲基丙烯酸液相产物的组成,该分析方法能够分析液相产物中的醛类,酮类和酸类化合物共计9个组分,C2-C4有机酸无记忆效应,其色谱峰不拖尾,该分析方法的相对标准偏差≤8.5%,回收率在94.5%-103.7%之间,是一种快速,准确,操作简单的分析方法。 相似文献
106.
A rapid and easy analysis method for polymers is presented. The method involves sample preparation by SFE, separation of the extracted compounds by SFC and simultaneous quantitative detection by FID, as well as identification of unknowns by MS. The applications illustrate how structural research work and routine polymer analysis can be done with this time saving method. 相似文献
107.
Sylvia V A Uzochukwu Esther Balogh Owen G Tucknot Mervyn J Lewis Patrick O Ngoddy 《Journal of the science of food and agriculture》1994,64(4):405-411
Palm wine and pasteurised palm sap volatiles were collected, concentrated on a Tenax GC and analysed by gas chromatography and gas chromatography-mass spectrometry. Eighty-two components were identified: 47 esters, 9 alcohols, 5 acids, 6 carbonyls, 2 acetals, 4 terpenes and 9 hydrocarbons. These had all been found previously in conventional wines. Odour evaluation of the separated palm wine components as they eluted suggested that no one compound is responsible for the characteristic palm wine odour. The acetates of higher alcohols and the ethyl esters of straight-chain aliphatic C6-C10 acids seemed to be important and may play a big role in imparting the fruity nuances of characteristic palm wine odour. Their association with alcohols seemed also to be necessary for the expression of typical palm wine odour. The qualitative difference between palm sap aroma and palm wine aroma appeared to be due mainly to the presence of these esters and alcohols in palm wine and their apparent absence from palm sap, as well as to the presence of some low-boiling esters and alcohols in palm sap and their apparent absence from palm wine. 相似文献
108.
������ú��������˲ʱѹ������ 总被引:7,自引:0,他引:7
煤层气采出有扩散和渗流两个过程,比常规天然气层中的渗流方程复杂。煤层气由煤层流入井筒的过程为:随着煤层中水的不断采出,地层压力下降,吸附在煤层中的煤层气被解吸出来,并扩散至割理,割理中的气体渗流到达井筒。采用非平衡态吸附模型,研究单相煤层气在煤体和割理中的流动规律。在拟稳态流和不稳态流的数学模型假设下,用气体标准压力代替Langmuir吸附公式中的压力,得到气层中标准压力所满足的方程。如果考虑无限大地层或有界圆形封闭和定压地层,最终得到井底无量纲准压力及其导数的解。 相似文献
109.
丙酰芸苔素内酯的气相色谱分析 总被引:3,自引:0,他引:3
采用毛细管柱气相色谱法,以(22E,24S) 2,22 二烯 5α 豆甾 6 酮为内标,对丙酰芸苔素内酯进行定量分析。色谱条件为12m× 0.53mm,膜厚1.5μm(CBP 1固定液)熔融石英毛细管柱,柱温为305℃,检测器、汽化室温度为320℃,载气流速为20mL/min。该方法检测丙酰芸苔素内酯质量分数的平均标准偏差为0.39%,平均回收率为100.4%。方法操作简便,定量准确。 相似文献
110.
I. Hole T. Tybell J. K. Grepstad I. Wrnhus T. Grande K. Wiik 《Solid-state electronics》2003,47(12):2279
Heteroepitaxial LaFeO3(1 1 0) thin films with a thickness of 150 nm were grown on LaAlO3(0 0 1) by reactive sputtering in an inverted cylindrical magnetron geometry. Equilibrium conductivity was measured as a function of partial pressure of oxygen at T=1000 °C, and logσ plotted vs. logP(O2) showed a minimum in conductivity for P(O2)=10−11 atm and a linear response between 10−10 and 1 atm. This linear response makes thin films of LaFeO3 a promising material for oxygen sensor applications. We have also measured the time response of the film conductivity upon an abrupt change in the partial pressure of ambient oxygen from 10−2 to 10−3 atm, which was determined at 60 s for T=700 °C and <3.5 s at T=1000 °C. 相似文献