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Use of multivariate statistical techniques to optimize the separation of isoflavones by liquid chromatography

100%
Baranowska I., Magiera S., Baranowski J.
Open Chemistry
|
2011
|
vol. 9
|
issue 6
972-981
EN
The aim of this paper is to optimize and validate a high performance liquid chromatography (HPLC) method for separation and quantification of five isoflavones. A statistical central composite design was used to separate all peaks. These multivariate procedures were efficient in determining the optimal separation condition using resolution, capacity factor, asymmetry and number of theoretical plates. [...] The effective separation of the examined compounds was applied on a Develosil RP Aqueous AR 5 RP-30 column with a gradient mobile phase system and a DAD detector. The isolation and preconcentration of the isoflavones from urine and plasma samples were conducted by means of the solid-phase extraction (SPE). For optimize SPE conditions various sorbents were tested. Furthermore, high recoveries and good relative standard deviations were obtained when the samples were passed through the Oasis HLB column. The developed method was validated and successfully applied for determination of isoflavones in urine and plasma.
2
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Epitaxial graphene perfection vs. SiC substrate quality

64%
Teklinska D., Kosciewicz K., Grodecki K., Tokarczyk M., Kowalski G., Strupinski W., Olszyna A., Baranowski J.
Open Physics
|
2011
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vol. 9
|
issue 2
446-453
EN
Polytype instability of SiC epitaxial films was the main focus of attention in the experiment performed since this factor has a decisive influence on graphene growth, which was the second stage of the experiment. Layers deposited in various initial C/Si ratios were analyzed. Our observations indicate that the initial C/Si ratio in epitaxial growth is a crucial parameter determining which polytype will be grown, in particular for cubic (3C) or hexagonal (4H) polytypes. If the initial C/Si ratio was close to its final value, the dominant polytype was 4H. On the other hand, when the initial C/Si ratio was close to zero, 3C became the major polytype in spite of a non favourable growth temperature. The results for graphene growth on an epi-SiC layer and a bulk substrate, in which case the dominant polytype was 4H, are also presented. These results indicate that layers on epitaxial 4H-SiC are thicker, more relaxed and have better quality in comparison with samples on 4H-SiC substrates. Morphology and defects in SiC epilayers were analyzed using Nomarsky optical microscopy, scanning electron microscopy (SEM) and high resolution X-ray diffraction (XRD). Graphene quality was characterized by Raman spectroscopy.
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