• Analytical Science and Technology
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• v.6 no.5
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• pp.453-462
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• 1993

The retention behaviors of polystyrenes influenced by mixed solvents are examined in thermal field-flow fractionation(ThFFF). Experimental data are obtained with polystyrene samples of molecular weights of 35,000, 110,000, 200,000 and 470,000 dissolved in organic solvents. The pure and mixed solvents are tetrahydrofuran(THF), chloroform(CHL), cyclohexane(CH), and benzene(BZ), respectively. The values of retention ratio(R) and thermal diffusion coefficient($D_T$) are measured with change of molecular weight and composition of mixed solvents. Atempts are then made to correlate the measured values with various physicochemical parameters of polymers and solvents. Studies suggest that R is significantly increased with the density of solvent and a good correlation is found between them. $D_T$ values decreases in the mixed solvent having has a higher concentration of poor solvent.

• Journal of the Korean Chemical Society
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• v.39 no.11
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• pp.848-855
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• 1995

The influence of gravitational effect on the retention behaviors of polystyrene (PS) and polymethylmethacrylate (PMMA) in flat type thermal field flow fractionation (Thermal FFF) was studied. In the case of downward flow of mobile phase, the gravitational effect acting in the same direction of mobile phase flow increases as the angle of the system from the horizontal line (0˚to 60˚) increases. The decreasement of retention time of PS & PMMA was found. Also, the increasement of dimensionless λ values was found. And the difference in the retention time of PS & PMMA having different molecular weight decreases and also the resolution decreases. In the case of upward flow of mobile phase, the gravitational effect acting in the opposite direction of mobile phase flow increases as the angle of the system from the horizontal line (0˚to 60˚) increases. The increasement of retention time of PS & PMMA was found. Also, the decreasement of dimensionless λ values was found. And the difference in the retention time of PS & PMMA having different molecular weight increases and also the resolution increases.

• Analytical Science and Technology
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• v.30 no.4
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• pp.159-166
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• 2017

Exposure to UV light, i.e., UV-A (320-400 nm) or UV-B (290-320 nm) radiation, can cause skin cancer. Titanium dioxide ($TiO_2$) effectively disperses UV light. Therefore, it is used as a physical UV filter in many UV light blockers. Usually, the $TiO_2$ content in commercialized UV blockers is 25 % at most. To block UV-B, a chemical UV blocker, octyl-methoxy cinnamate (OMC) is used. OMC is commonly used in combination with $TiO_2$. In this study, $TiO_2$ and OMC were mixed in different proportions to produce UV blockers with different compositions. Also the changes in the sun protection factor (SPF) based on the composition and $TiO_2$ particle sizes were investigated. In order to analyze the $TiO_2$ particle size, dynamic light scattering (DLS) and asymmetrical flow field-flow fractionation (AsFlFFF) were used. The results showed that the SPF was influenced by the proportion of $TiO_2$ and OMC, where the proportion of $TiO_2$ induced a more significant influence. In addition, changes in the $TiO_2$ particle size based on the proportion of OMC were observed.

• Analytical Science and Technology
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• v.22 no.4
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• pp.285-292
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• 2009

It has been observed that, after long term storage, some ammunitions are misfired by tamping (combustionstopping) due to aging of the chemicals loaded in the ammunitions. Used in ammunitions are percussion powder which provides the initial energy, igniter which ignites the percussion powder, and a delay system that delays the combustion for a period of time. The percussion powder is loaded first, followed by the igniter and then the delay system, and the ammunitions explode by the energy being transferred in the same order. Tamping occurs by combustion-stopping of the igniter or insufficient energy transfer from the igniter to the delay system or the combustion-stopping of the delay system, which are suspected to be caused by low purity of the components, inappropriate mixing ratio, size distribution of particulate components, type of the binder, blending method, hydrolysis by the humidity penetrated during the long term storage, and chemical changes of the components by high temperature. Goal of this study is to find the causes of the combustion-stopping of the igniter and the delay system of the ammunitions after long term storage. In this study, a method was developed for testing of the combustion-stopping, and the size distributions of the particulate components were analyzed with field-flow fractionation (FFF), and then the mechanism of chemical change during long term storage was investigated by thermal analysis (differential scanning calorimetry), XRD (X-ray diffractometry), and XPS (X-ray photoelectron spectroscopy). For the ignition system, M (metal)-O (oxygen) and M-OH peaks were observed at the oxygen's 1s position in the XPS spectrum. It was also found by XRD that $Fe_3O_4$ was produced. Thus it can be concluded that the combustion-stopping is caused by reduction in energy due to oxidation of the igniter.

• Journal of the Korean Chemical Society
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• v.38 no.6
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• pp.427-434
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• 1994

The retention behaviors of poly(ethylene-co-vinyl acetate)s have been studied by thermal field-flow fractionation(ThFFF) with respect to effective separation and characterization of thermal diffusion coefficients($D_{\tau}$) as one of the physicochemical properties of polymers. The eight copolymers are different in vinyl acetate composition ranging from 25% to 70% and in molecular weight ranging from 110,000 to 285,000. The carrier solvents are THF, toluene and chlorobenzene which have different viscosities and thermal conductivities. It is shown that the retention of a copolymer is dependent on the type of the carrier, the molecular weight and chemical composition of the copolymer. The results show that the retention of a copolymer increases when either vinyl acetate composition or the molecular weight increase. $D_{\tau}$ values measured by experiments vary from 1.36∼5.97 $\cm^2/(s.K)$ depending on the copolymer composition and the type of the carrier solvent. These values increase $(r^2{\geq}0.928)$ with increase of weight % of vinyl acetate. THF is found to be the proper carrier solvent for separation of copolymers employed in this study due to the fact that a $D_{\tau}$ value greatly changes with variation of copolymer composition. From the above results, ThFFF can be used for separation of copolymers with similar molecular sizes but different compositions.

• BMB Reports
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• v.32 no.4
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• pp.414-418
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• 1999

A novel gene for malonyl-CoA decarboxylase was discovered in the mat operon, which encodes a set of genes involved in the malonate metabolism of Rhizobium trifolii (An and Kim, 1998). The subunit mass determined by SDS-PAGE was 53 kDa, which correspond to the deduced mass from the sequence data. The molecular mass of the native enzyme determined by field flow fractionation was 208 kDa, indicating that R. trifolii malonyl-CoA decarboxylase is homotetrameric. R. trifolii malonyl-CoA decarboxylase converted malonyl-CoA to acetyl-CoA with a specific activity of 100 unit/mg protein. Methylmalonyl-CoA was decarboxylated with a specific activity of 0.1 unit/mg protein. p-Chloromercuribenzoate inhibited this enzyme activity, suggesting that thiol group(s) is(are) essential for this enzyme catalysis. Database analysis showed that malonyl-CoA decarboxylase from R. trifolii shared 32.7% and 28.1% identity in amino acid sequence with those from goose and human, respectively, and it would be located in the cytoplasm. However, there is no sequence homology between this enzyme and that from Saccharopolyspora erythreus, suggesting that malonyl-CoA decarboxylases from human, goose, and R. trifolii are in the same class, whereas that from S. erythreus is in a different class or even a different enzyme, methylmalonyl-CoA decarboxylase. According to the homology analysis, Cys-214 among three cysteine residues in the enzyme was found in the homologous region, suggesting that the cysteine was located at or near the active site and plays a critical role in catalysis.