• Analytical Science and Technology
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• v.6 no.4
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• pp.383-390
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• 1993

Retention behaviors of aliphatic and aromatic compounds were investigated with Van der Waals volume which represented the molecular size. The organic solvents, methanol, acetonitrile and tetrahydrofuran, were mixed with water at various ratio, respectively. The selectivity of organic solvents were tested by change of column temperature. The capacity factor was increased linearly according to the enlargement of molecular size. Therefore, Van der Waals volume was useful to predict the elution of organic molecules in reversed-phase column. The order of elution capacity of solvents was methanol

• Journal of Korean Society for Atmospheric Environment
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• v.27 no.5
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• pp.558-568
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• 2011

Hazardous volatile organic compounds (HVOCs) have been increasingly getting concern in urban air chemistry due to photochemical smog as well as its toxicity or potential hazards. In this study, we investigated their concentrations and the properties in tunnel, urban roadside and residential area. As a result, among 36HVOCs measured in this study, BTEX (benzene, toluene, ethylbenzene, xylene) and dichlorodifluoromethane, 1,2,4-trimethylbenzene, trichlorofluoromethane were detected above the concentration of $1{\mu}g/m^3$ in every sampling site and the most abundant compound was toluene. The other compounds were detected at trace level or below the detection limit. In addition, we found that three CFCs (chlorofluorocarbons), such as CFC-12, CFC-11, CFC-113, were persistently detected because of the emission in the past. Toluene to benzene ratio (T/B) at tunnel and roadside were calculated to be 4.3~5.3 and at residential area 15.4, suggesting that the residential area had several emission sources other than car exhaust. The ratio of X/E (m,p-xylene to ethylbenzene) ratio was calculated to be 1.8~2.1 at tunnel, 1.7 at roadside and 1.2 at residential area, which means this ratio reflected well the relative photochemical reactivity between these compounds. Good correlation between m,p-xylene and ethylbenzene ($r^2$ > 0.85) were shown in every study sites. This indicated that correlation between $C_2$-alkylbenzenes were not severely affected by 3-way catalytic converter. In this study, it was demonstrated that the concentration of benzene was very low, compared with national air quality standard (annual average of $5{\mu}g/m^3$). Its concentration were $2.52{\mu}g/m^3$ in roadside and $1.34{\mu}g/m^3$ in residential area. We thought this was the result of persistent policy implementation including the reduction of benzene content in gasoline enforced on January 1, 2009.

• Journal of the Korean Chemical Society
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• v.31 no.1
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• pp.55-63
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• 1987

The systematic investigation of the retention behaviors of 18 monosubstituted benzenes in reversed-phase liquid chromatography(RPLC) was studied in order to predict the separation possibility of their mixtures and study the contribution of substituent group to the retentions of solutes. The columns and mobile phases employed in this study were $\mu$ -Bondapak $C_{18}$, $\mu$-Bondapak phenyl columns and methanol/water, acetonitrile/water, and THF/water, respectively. The polar substituents such as phenol, aniline, acetophenone and benzonitrile have smaller capacity factor(k') values than benzene, while nonpolar ones such as alkylbenzenes and halobenzenes show larger k' value. The capacity factors of all solutes increased on both C18 bonded and phenyl bonded phases as the organic solvent content of three organic solvent-water mixtures decreased. The absolute differences in capacity factor(${\Delta}k$') between substituent and benzene were graphically shown for the prediction of the separation of the mixture and interpretation of the elution behavior of substituent. In addition, the selectivity of solvent system for the separation of the mixture was investigated in both two columns and three mobile phases.

• Korean Journal of Microbiology
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• v.47 no.1
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• pp.92-96
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• 2011

Rhodococcus sp. strain DK17 possesses three megaplasmids (380 kb pDK1, 330 kb pDK2, and 750 kb pDK3). The alkylbenzene-degrading genes (akbABCDEF) are present on pDK2 while the phthalate operons which are duplicated are present on both pDK2 (ophA'B'C'R') and pDK3 (ophABCR). DK17 with an optimal temperature of $30^{\circ}C$ showed no growth at $37^{\circ}C$. When transferred to $30^{\circ}C$, however, the $37^{\circ}C$ culture began to grow immediately, indicating that $37^{\circ}C$ is not lethal but stressful for DK17 growth. In addition, when exposed to $37^{\circ}C$ even for a short time, a part of DK17 cells lost the ability to degrade o-xylene (a model compound of alkylbenzenes). When two hundred colonies were randomly selected for colony PCR for pDK2-specific akbC, ophC', or pDK3-specific ophC, a total of 29 colonies were found to have lost at least one of the three genes. PFGE analysis clearly showed that all the mutants have different megaplasmid profiles from that of DK17 wild type, which are divided into five different cases: Type I (10 mutants, pDK2 loss and acquisition of a new ~700 kb plasmid), Type II (9 mutants, pDK2 loss), Type III (8 mutants, pDK3 loss and acquisition of a new ~400 kb plasmid), Type IV (1 mutant, pDK3 loss), and Type V (1 mutant, pDK2 and pDK3 loss and acquisition of the ~400 kb and ~700 kb plasmids). The above results showing that growth temperature changes can induce physical changes in bacterial genomes suggest that environmental changes in habitats including temperature fluctuations affect significantly the evolution of bacteria.