• Proceedings of the Korean Radioactive Waste Society Conference
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• 2018.11a
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• pp.608-609
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• 2018

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2017.05a
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• pp.67-68
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• 2017

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2018.05a
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• pp.425-426
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• 2018

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2017.10a
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• pp.373-374
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• 2017

• Bulletin of the Korean Chemical Society
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• v.31 no.5
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• pp.1149-1154
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• 2010

Liquid chromatography/mass spectrometry using isotope dilution method has been established as a primary method for the measurement of cortisol in human serum. Verification of this method was accomplished by the participation in Consultative Committee for Amount of Substance-Metrology in Chemistry (CCQM) pilot study. Two levels of cortisol certified reference materials were prepared and certified by the established method. They were used as sample materials for the proficiency testing. The expanded uncertainty in the measurement of cortisol in human serum was approximately 1.2% at 95% confidence level. The results of the proficiency testing showed a good precision among the participants, but some bias to the certified values. This means that commercial field laboratories should keep traceability chain to SI unit through available reference measurement procedures and/or available reference materials.

• Mass Spectrometry Letters
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• v.8 no.3
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• pp.53-58
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• 2017

Glycated hemoglobin ($HbA_{1c}$) has been commonly used to screen and diagnose for patients with diabetes mellitus. Here the accelerated procedure of microwave-assisted sample treatment from acid hydrolysis to enzyme digestion followed by isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) was optimized and applied to measure $HbA_{1c}$ in an effort to speed up analysis time. First, two signature peptides of $HbA_{1c}$ and hemoglobin $A_0$ were certified with amino acid analysis by setting optimized acid hydrolysis conditions to $150^{\circ}C$, 1.5 h and $10{\mu}M$ sample concentration in 8 M hydrochloric acid. Consequently, the accurate certified peptides above were used as calibration standards to implement the proteolytic procedure with endoproteinase Glu-C at $37^{\circ}C$, 700 W for 6 h. Compared to the traditional method, the microwave heating not only shortened dramatically sample preparation time, but also afforded comparable recovery yields. The optimized protocol and analytical conditions in this study are suitable for a primary reference method of $HbA_{1c}$ quantification with full SI-traceability and other similar proteins in complex biological samples.

• Food Science and Biotechnology
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• v.15 no.1
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• pp.102-106
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• 2006

The phytoestrogens including isoflavones (genistein, daidzein, biochanin A, formononetin, and glycitein), coumestrol, and lignans (secoisolariciresinol, matairesinol, and anhydrosecoisolariciresinol) were quantified in edible sea vegetables from Korea. Sea vegetable samples were collected based on domestic consumption data. After hydrolysis of phytoestrogen glycosides in prepared samples, aglycones of phytoestrogens were extracted with diethyl ether and analyzed with isotope dilution gas chromatography-mass spectrometry in selected ion monitoring mode (ID-GC-MS-SIM). Total samples included 19 samples representing eight species. Most of the samples showed rather low concentrations, ranging from not determinated to $79.2\;{\mu}g/kg$ for isoflavones and from 106.4 to $694.8\;{\mu}g/kg$ for lignans. The daily intake of phytoestrogen from sea vegetables, estimated from the present data and domestic consumption data, was about $0.13\;{\mu}g/day$ for isoflavones and $2.0\;{\mu}g/day$ for lignans. When we compared these results with those from legumes, sea vegetables would not be considered the major source of phytoestrogens in the Korean diet.

• Bulletin of the Korean Chemical Society
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• v.28 no.5
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• pp.745-750
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• 2007

An isotope dilution-liquid chromatography/tandem mass spectrometric method was developed as a candidate reference method for the accurate determination of folic acid in infant milk formula. Sample was spiked with 13C5-folic acid and then extracted with phosphate buffer (pH 6) solution. The extract was further cleaned up by deproteinization followed by a C18 solid-phase extraction cartridge. The extract was analyzed by using LC/ ESI/MS/MS with selectively monitoring the collisionally induced dissociation channels of m/z 442 → m/z 295 and m/z 447 → m/z 295, which are the neutral glutamyl loss from the [M+H]+ ions of folic acid and 13C5-folic acid, respectively. LC/MS/MS chromatograms showed substantially reduced background from chemical noises compared to LC/MS chromatograms. Repeatability and reproducibility studies showed that the LC/MS/ MS method is a reliable and reproducible method which can provide less than 1.5 relative percentage of method precision.

• Korean Journal of Organic Agriculture
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• v.19 no.spc
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• pp.161-164
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• 2011

Nitrogen fixation by legumes can be valuable sources for organic farming. This study was to investigate the effect of different legume mixtures on nitrogen fixation and transfer to grasses on spring paddy field. Three different mixtures were used (rye+hairy vetch, Italian ryegrass+crimson clover, oat+pea) in a randomized complete block design with three replications and sowed in pots with different sowing rate (5:5 rye:hairy vetch,7:3=Italian:crimson, 6:4=oat:pea) on early March. $(^{15}NH_4)SO_4$ solution at. 99.8 atom%$^{15}N$ was applied to the each pot at the rate of 2kg N $ha^{-1}$ on $16^{th}$ April. Forage were harvested at ground level in heading stage and separated into legume and grass. Total N content and $^{15}N$ value were determined using a continuous flow stable isotope ratio mass spectrometry. DM yield of rye+vetch, Italian+crimson and oat+pea were 6,607, 3,213 and 4,312kg/ha, respectively. Proportion of N from fixation was 0.73(rye+vetch), 0.42(Italian+crimson) and 0.93(oat+pea). The percentages of N transfer from legume to grass were from 61% to 24% in different method by treatments and -35% to 21% in isotope dilution method.

• Mass Spectrometry Letters
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• v.9 no.4
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• pp.105-109
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• 2018

A certified reference material (CRM) for the analysis of inorganic nutrients in nutritional supplements has been developed. Accurate mass fractions of chromium (Cr), iron (Fe), copper (Cu), and zinc (Zn) were determined by isotope dilution inductively coupled plasma mass spectrometry (ID ICP/MS). The measurement results were used to assign certified values for the CRM, which were metrologically traceable to the definitions of the measurement units in the International System of Units (SI). Production of a candidate reference material (RM) and the certification processes are summarized. Each nutrient in the CRM showed good homogeneity, which was estimated using relative standard deviations of the measurement results of twelve bottles in a batch. This CRM is expected to be an important reference to improve reliability and comparability of nutrient analyses in nutritional supplements and related samples in analytical laboratories.