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1.
In this work, the melting behaviors of nonisothermally and isothermally melt‐crystallized poly(L ‐lactic acid) (PLLA) from the melt were investigated with differential scanning calorimetry (DSC) and temperature‐modulated differential scanning calorimetry (TMDSC). The isothermal melt crystallizations of PLLA at a temperature in the range of 100–110 °C for 120 min or at 110 °C for a time in the range of 10–180 min appeared to exhibit double melting peaks in the DSC heating curves of 10 °C/min. TMDSC analysis revealed that the melting–recrystallization mechanism dominated the formation of the double melting peaks in PLLA samples following melt crystallizations at 110 °C for a shorter time (≤30 min) or at a lower temperature (100, 103, or 105 °C) for 120 min, whereas the double lamellar thickness model dominated the formation of the double melting peaks in those PLLA samples crystallized at a higher temperature (108 or 110 °C) for 120 min or at 110 °C for a longer time (≥45 min). © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 466–474, 2007 相似文献
2.
Equations between the differential order and the maximum of the fractional-order differential for the specified peak signals are developed based on the variation of the maximum of the specified peak signals at different orders. Also, equations between the differential order and the zero-crossing of the fractional-order differential of the specified peak signals are proposed according to the variation of the zero-crossing of the specified peak signals at different orders. Characteristic paramters of the Gaus- sian peak, Lorentzian peak, and Tsallis peak can be estimated using estimator I and estimator II which are obtained by the equations above. As a result, a new method is presented to resolve the overlapped peaks signal. Firstly, a fractional-order differential of the specified peak signals is obtained with the fractional-order differentiation filter. Then, characteristic paramters of the specified peak signals can be extracted using estimator I and estimator II. Finally, the Tsallis peak is used as a model to assign the overlapping peak signals correctly. Experimental results show that the proposed method is efficient and effective for the simulated overlapping peaks and detected overlapping voltammetric peak signals. 相似文献
3.
Gaston Bocaz-BeneventiRosa Latorre Marta FarkováJosef Havel 《Analytica chimica acta》2002,452(1):47-63
The application of the combination of experimental design (ED) and artificial neural networks (ANNs) for the quantification of overlapped peaks in capillary zone electrophoresis is described. When the total separation cannot be achieved by separation techniques, the use of ED-ANN can be a suitable approach. The unstability of EOF causes peak shift that has to be corrected in order to apply ED-ANN methods. In this work, normalization procedure of electropherograms with consequent application of ANNs for quantification purpose was developed. Both, spectra and electropherograms can be used as multivariate data. In general, both kinds of data were found to be suitable for unresolved peaks quantification by ED-ANN approach. 相似文献
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Summary Based on a thorough knowledge of the actual system precision significance testing of the primary eigen values, resulting from principal component analysis of the two-dimensional data array of HPLC with photodiode-array detection, is a powerful means to uncover unresolved chromatographic peaks. The implementation of this chemometric technique for assuring peak homogeneity and results showing the efficiency for two-component peaks in regard to spectral characteristics, chromatographic resolution and absorbance ratio of the investigated compounds are presented. 相似文献
6.
This paper describes the screening for metabolites of butoprozine, a new anti-anginal drug, in dog bile by means of reverse-phase HPLC. Although it does involve a simple clean-up step to remove a substantial amount of endogenous bile compounds, this screening method nevertheless avoids extraction of metabolites and thus allows all metabolites to be introduced into the chromatographic system. A single run of 100 minutes from 100% water to 100% methanol in a linear gradient effects adequate separation of the great majority of metabolites without interference from remaining endogenous compounds. Two methods of differentiating between metabolite peaks and endogenous peaks have been worked out. The first one makes use of 14C-labeled butoprozine by measuring the amount of radioactivity in the column effluent while simultaneously recording the UV absorbance. The second method compares continuous gradient chromatograms of bile recorded before and after butoprozine administration under very similar conditions. The latter method can be applied to both radioactive and non-radioactive materials. 相似文献
7.
Hong Shen James E. Mark Carl J. Seliskar Harry B. Mark Jr. William R. Heineman 《Journal of Solid State Electrochemistry》1997,1(3):241-247
One problem associated with using bare solid metal electrodes, such as gold and platinum, in stripping analysis to determine
heavy metal ions such as lead and copper ions in dilute solutions is that underpotential deposition (UPD) gives multiple stripping
peaks in the analysis of mixtures. These peaks are often overlapped and cannot be conveniently used for analytical purposes.
Bifunctional alkylthiols, such as 3-mercaptopropionic acid, with an ionizable group on the other terminal end of the thiol
can form self-assembled monolayers (SAMs) on the surface of the gold electrode. It is shown that such an SAM-modified gold
electrode minimizes the UPD effects for the stripping analysis of lead and copper. The anodic peak potential shifts and the
peak shape changes, indicating that the SAM changes the deposition and stripping steps of these heavy metal ions. Thus, the
sensitivity levels for both single species and mixtures can be significantly improved for the conventional solid electrodes.
The mechanism of the deposition reaction at the SAM-modified gold electrodes is discussed.
Received: 29 May 1997 / Accepted: 24 June 1997 相似文献
8.
利用脉冲射频空心阴极等离子体源激发含溴甲烷的工作气体产生等离子体,采用HR4000型高分辨力光谱仪测量了等离子体的发射光谱。通过光谱比较,在等离子体发射光谱图中得到了位于635.07,700.52 nm的溴原子的特征峰,并实验研究了工作气压和溴甲烷密度对溴原子特征峰强度的影响。实验结果表明:在相同的溴甲烷密度下,溴原子的特征峰强度随气压的升高而降低;在相同的气压条件下,溴原子的特征峰强度随溴甲烷密度的升高而升高;溴甲烷密度测量的精度高于1 g/m3。 相似文献
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