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991.
992.
Development of a Chromatographic Fingerprint of Tobacco Flavor by Use of GC and GC-MS 总被引:7,自引:0,他引:7
A new chromatographic fingerprinting method has been established for quality control of tobacco flavor. Three different extraction techniques, simultaneous distillation extraction (SDE), liquid–liquid extraction, and solid-phase microextraction were evaluated for isolation of the components of interest. After comparison of their performance, a combination of SDE and GC-MS was used for simple, reliable, and reproducible development of a chromatographic fingerprint of tobacco flavor. Twelve samples of the flavor from different batches were used to establish the fingerprint. Thirty-nine volatile components of the tobacco flavor samples, accounting for 86.54% of the total content, were identified and quantified. The 12 samples had 28 peaks in common. The method of fingerprint analysis was then validated on the basis of the relative retention times and relative peak areas of the common peaks, sample stability, and similarity analysis. The similarities of the 12 samples of tobacco flavor were >0.80, showing that samples from different batches were, to some extent, consistent. The chromatographic fingerprint developed was successfully used to differentiate tobacco flavor samples from tobacco extract prepared from tobacco leaf, both by similarity comparison and by principal-components projection analysis. The method can be used for quality control of tobacco flavor. 相似文献
993.
荧光法对光诱导野生型肌红蛋白和突变体(D44K)去氧的对照研究 总被引:1,自引:0,他引:1
用荧光法对光诱导野生型肌红蛋白(Mb)和突变体(D44K)去氧的过程进行对照研究。发现430nm是研究Mb(WT)和Mb(D44K)光照去氧的最佳激发波长。430nm激发时,Mb(D44K)在597.9nm和628.8nm处出现两个荧光发射峰,不同于Mb(WT)仅在597nm处出现一个荧光发射峰。经研究证明,628.8nm处荧光峰是Mb3 -H2O型中的H2O峰。光照也使此峰的荧光强度下降,但比去氧的速率慢。研究发现,597nm处Mb(D44K)的荧光效率比Mb(WT)的荧光效率低。传能实验表明Mb表面44位氨基酸由天冬氨酸突变为赖氨酸后,不影响Mb(D44K)中色氨酸和酪氨酸残基传递给铁卟啉的荧光效率,但使Mb(D44K)中色氨酸和酪氨酸残基的荧光效率变高。 相似文献
994.
995.
A rapid, selective and convenient liquid chromatography–mass spectrometric method for the simultaneous determination of paracetamol and caffeine in human plasma was developed and validated. Analytes and theophylline [internal standard (I.S.)] were extracted from plasma samples with diethyl ether-dichloromethane (3:2, v/v) and separated on a C18 column (150 × 4.6 mm ID, 5 μm particle size, 100 Å pore size). The mobile phase consisted of 0.2% formic acid–methanol (60:40, v/v). The assay was linear in the concentration range between 0.05 and 25 μg mL?1 for paracetamol and 10–5,000 ng mL?1 for caffeine, with the lower limit of quantification of 0.05 μg mL?1 and 10 ng mL?1, respectively. The intra- and inter-day precision for both drugs was less than 8.1%, and the accuracy was within ±6.5%. The single chromatographic analysis of plasma samples was achieved within 4.5 min. This validated method was successfully applied to study the pharmacokinetics of paracetamol and caffeine in human plasma. 相似文献
996.
997.
Feng H Liu X Gao W Chen X Wang J Chen L Lüdemann HD 《Physical chemistry chemical physics : PCCP》2010,12(45):15007-15017
Self-diffusion and structural properties of ammonia, methylamine and trimethylamine have been studied by molecular dynamics simulation in the temperature range between the melting pressure curve and 700 K at pressures up to 400 MPa. The calculation results agree well with the experiment, which suggests that one can use the simulation method as a powerful tool to obtain self-diffusion coefficients over wide range of temperatures and pressures, under which it is rather difficult for experiments. The local structures of such fluids are investigated by calculating radial distribution functions (RDFs), the numbers of hydrogen bonds and coordination numbers. The correlation between self-diffusion and structural properties, and the influence of temperature and pressure on them are discussed. The simulation results demonstrate that the temperature effects are more pronounced than the pressure effects on self-diffusion and structural properties, and the effect of hydrogen bonding on the translational dynamics in any of these systems is a minor factor, while it is mainly affected by the close packing of amine molecules. 相似文献
998.
999.
采用静电纺丝技术制备了PVP/[La(NO3)3+Fe(NO3)3]复合纳米纤维,在700℃下焙烧得到LaFeO3纳米纤维,再以CS2作为硫源进行硫化,成功制备了La2Fe2S5亚微米棒。利用XRD,SEM,EDS,宽频介电松弛谱仪等现代分析手段对样品进行了表征。XRD分析表明:将LaFeO3纳米纤维在CS2气氛中于900℃焙烧4 h得到纯相的La2Fe2S5亚微米棒,属于正交晶系,空间群为A21am。SEM分析表明:La2Fe2S5呈亚微米棒结构,直径和长度分别为851±122 nm和3.25±0.99μm。电分析表明:La2Fe2S5亚微米棒是较好的半导体材料。 相似文献
1000.