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Lee, Jaeick,Lee, Seunghwa,Kim, Byungjoo,Lee, Joonhee,Kwon, Oh-Seung,Cha, Eunju Korean Society for Mass Spectrometry 2018 Mass spectrometry letters Vol.9 No.1
A quantitation method for free amino acids in human serum was developed using a stepwise-dilution method and a bimodal cation exchange (CEX)/hydrophilic interaction liquid chromatography (HILIC)-tandem mass spectrometry system equipped with an electrospray ionization source (ESI/MS/MS). This method, which was validated using quality control samples, was optimized for enhanced selectivity and sensitivity. Dithiothreitol (DTT) was used as a reducing agent to prevent the oxidation of a serum sample ($50{\mu}L$), which was then subjected to stepwise dilution using 3, 30, and 90 volumes of acetonitrile containing 0.1% formic acid. Chromatographic separation was performed on an Imtakt Intrada Amino Acid column ($50mm{\times}3mm$, $3{\mu}m$) in mixed mode packed with CEX and HILIC ligands embedded in the stationary phase. Underivatized free amino acids were eluted and separated within 10 min. As a result of the validation, the precision and accuracy for the inter- and intraday assays were determined as 2.11-11.51% and 92.82-109.40%, respectively. The lowest limit of quantification (LLOQ) was $0.5-4.0{\mu}g/mL$ and the matrix effect was 80.22-115.93%. The proposed method was successfully applied to the quantitative analysis of free amino acids in human serum.
Lee, Jaeick,Yoo, Hye Hyun,Rhim, Kwang Jin,Sohn, Dong-Ryul,Kim, Dong-Hyun John Wiley Sons, Ltd. 2007 Rapid communications in mass spectrometry Vol.21 No.7
<P>The in vitro and in vivo metabolism of a novel PDE 5 inhibitor, SK3530, was investigated in rats. Bile, plasma, feces, urine and liver samples were collected and analyzed using a high-performance liquid chromatography (HPLC) system equipped with ultraviolet (UV), mass spectrometric and radioactivity detectors. After a single oral administration, the mean radiocarbon recovery was 92.32 ± 6.26%, with 91.25 ± 6.25 and 1.07 ± 0.21% in the feces and urine, respectively. The biliary excretion of radioactivity for the first 24 h period was approximately 38.82%, suggesting that SK3530 is cleared by hepatobiliary excretion. In vitro incubation of SK3530 with rat and human liver microsomes resulted in the formation of twelve and ten metabolites, respectively. SK3530 was extensively metabolized to twenty different metabolites, including three glucuronide and three sulfate conjugates in rats. The structures of these metabolites were elucidated based on MS<SUP>n</SUP> spectral analyses. Six major metabolic pathways were identified in the rat: N-dealkylation and oxidation of the hydroxyethyl moiety; N,N-deethylation and hydroxylation of the piperazine ring; hydroxylation of the propyl group and sulfate conjugation. An additional metabolite due to aromatic hydroxylation was also identified in hepatic microsomes. Copyright © 2007 John Wiley & Sons, Ltd.</P>
Lee, Sang Kyu,Kim, So-Hee,Kim, Ho Jun,Yoo, Hye Hyun,Kwon, Oh Seung,In, Moon Kyo,Jin, Changbae,Kim, Dong Hyun,Lee, Jaeick John Wiley Sons, Ltd. 2010 Rapid communications in mass spectrometry Vol.24 No.21
<P>Amphetamine (AP) and amphetamine-type stimulants, methamphetamine (MA) and N,N-dimethylamphetamine (DMA), are known as central nervous system stimulants, and their abuse throughout the world has recently increased. Since it is difficult to physically distinguish among AP, MA and DMA, analysts may not be aware of what abusers have administered. In this study, following the detection of specific metabolites of AP, MA and DMA as biomarkers in abuser urines, a rapid and sensitive method was developed for the identification and classification of AP-type stimulants abusers. After the simple filtration of the urine samples, the samples were directly analyzed using a liquid chromatography/tandem mass spectrometry system with selected reaction monitoring (SRM)-triggered quantitation-enhanced data-dependent MS/MS (QED-MS/MS) for the simultaneous qualitative and quantitative analysis of p-hydroxy AP, p-hydroxy MA, p-hydroxy DMA, AP, MA, DMA and DMA N-oxide. The determination of p-hydroxy AP, p-hydroxy MA, AP, MA, DMA and DMA N-oxide was accurate and reproducible, with the limits of quantitation of 5 ng/mL in urine. When applied to the urine samples of suspected AP-type stimulants abusers, the abused drugs were precisely identified between MA and DMA abusers. Copyright © 2010 John Wiley & Sons, Ltd.</P>
Lee, Illjoo,Park, Hyungkwon,Kim, Jaeick,Lee, Changhee Elsevier Sequoia 2016 Surface & coatings technology Vol.307 No.1
<P><B>Abstract</B></P> <P>Heavy steel automotive parts have been replaced with aluminum-based lightweight materials worldwide. In particular, grey cast iron engine blocks, which are very heavy components in vehicles, have been replaced by aluminum-silicon hypoeutectic alloys in order to reduce emissions and fuel consumption. However, aluminum alloys are not able to withstand severe engine cylinder conditions due to their poor mechanical properties. In this study, a Mo blended ferrous coating was fabricated using atmospheric plasma spraying to replace the grey cast iron liner in the automotive cylinder bore. Five fractions of Mo, 0, 5, 10, 15, and 20wt%, with ferrous powder were prepared to investigate the effect of Mo on the microstructure and mechanical properties of coatings. All of the Mo-added coating layers showed significantly improved mechanical properties, such as hardness and wear resistance compared to that of grey cast iron. However, as Mo content exceeded 10wt% of the blend, the tribological properties gradually degraded due to brittle fracture of Mo. As a result, 10wt% Mo blended with ferrous powder provided optimized mechanical properties and can be substitute for grey cast iron liners in the automotive industry.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Mo-added ferrous coating to protect the automotive engine was investigated and it showed excellent mechanical properties. </LI> <LI> The Mo fraction was optimized to maximize the tribological property and minimize the amount of Mo. </LI> <LI> The effect of Mo fraction in the coating later was proven by various mechanical property measurements. </LI> <LI> The effect of Mo on fracture mechanism was investigated based on the microstructure analysis. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Lee, Jaeick,Yoo, Byung-Chul,Lee, Hyo-Suk,Yoo, Hee-Won,Yoo, Hye-Hyun,Kang, Min Jung,Kim, Dong-Hyun Lippincott Williams Wilkins, Inc. 2006 Therapeutic drug monitoring Vol.28 No.1
The purpose of this study was to develop an analytical method for the determination of 2&vprime;-fluoro-5-methyl-&bgr;-l-arabinofuranosyl uracil triphosphate (L-FMAU-TP) in human peripheral blood mononuclear cells (PBMCs), and its application in the determination of cellular levels of L-FMAU-TP in PBMCs isolated from patients treated with 2&vprime;-fluoro-5-methyl-&bgr;-l-arabinofuranosyl uracil (L-FMAU). An ion-pairing liquid chromatography (IPC) method, coupled with negative ion electrospray ionization tandem mass spectrometry (ESI-MS/MS), was developed for the accurate and repeatable detection of L-FMAU-TP, with a limit of detection of 1.6 pmol/10 cells. The calibration curve for L-FMAU-TP was linear over the concentration range 1.6 to 80 pmol/10 cells. The intra- and inter-day precision was lower than 11.2%, and the accuracy was between 97.1 and 106.9%. When applied to the determination of L-FMAU-TP in PBMCs isolated from HBV-infected patients undergoing L-FMAU treatment, the levels reached a steady state concentration 4 weeks after daily single oral administration of 20 mg L-FMAU, and these levels were maintained for up to 12 weeks, but then decreased 12 weeks after drug cessation. The terminal half-life of L-FMAU-TP in PBMCs after drug cessation was estimated to be 15.6 days.
Lee, Yujin,Seo, Eunji,Park, Jun Young,Bae, Kwang-Hak,Lee, Jaeick,Cha, Sangwon Korean Society for Mass Spectrometry 2018 Mass spectrometry letters Vol.9 No.4
Since accumulation of chemicals in deciduous teeth can occur from the second trimester of fetal development to shedding, a deciduous tooth has been considered as an attractive biomatrix for estimating individual chemical exposures recently. Therefore, detection of organic chemicals from teeth has received an increasing attention in exposomics research. Most previous studies on organic chemical analysis of teeth not only focused on a few targeted chemicals but also ignored potential contaminants from an enamel surface or a dental pulp. Recently, our group started developing a multi-class organic analysis method for deciduous teeth and tried to find a proper incubation condition of tooth materials. Our results showed that incubation with methanolic HCl provided the best performance among tested.