• Proceedings of the PSK Conference
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• 2002.10a
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• pp.394.2-394.2
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• 2002

A sensitive and selective reversed-phase LC-ESI-MS method to quantitate pseudoephedrine in human plasma was developed and validated. Phenacetin was used as an internal standard. Samples were prepared simply by acetonitrile precipitation without an evaporation step. Chromatographic separation was achieved on a XTerra MS C18 column ($150{times}2.1$ mm I.D.. 3.5 $\mu\textrm{m}$ particles). using gradient elution with 0.5% (v/v) trifluoroacetic acid (TFA) in water and 0.5% (v/v) TFA in methanol at a flow-rate of 0.1 ml/min. (omitted)

• Proceedings of the PSK Conference
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• 2002.10a
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• pp.401.2-401.2
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• 2002

To study the pharmacokinetics of triflusal, more reliable and sensitive analytical method of triflusal in plasma sample was developed. Analytical method of triflusal in human plasma was developed using semi-microbore HPLC equipped with automated column switching system. p- Toluic acid, which is structural analogue of triflusal. was used as an internal standard and 2 M HCI was employed as a stabilizer. The load phase and mobile phase were prepared using acetonitrile and 20 mM $KH_{2}PO_{4}$ with the volume ratios of 10:90 (pH 2.5) and 43:57 (pH 2.3), respectively. (omitted)

• Journal of Food Hygiene and Safety
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• v.5 no.4
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• pp.213-217
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• 1990

A simple and practical method for the determination of caffeine in coffee, black tea and green tea was studied. The analysis of caffeine was performed by reverse phase high perfomance liquid chromatography using a ${\mu}-Bondapak$ C18 column at isocratic condition with methanol-acetic acid-water (20: 1: 79) on UV detector at 280 nm. The extraction and clean-up of caffeine in sample is based on combing a simple pretreatment with the use of a Sep-Pak Alumina A cartridge. The average recoveries of caffeine from several samples were 95.2 -101.3%, the relative standard deviation for the whole procedure was 0.10 ~ 0.62%, and the detection limit of caffeine in sample solution was about $0.1\;\mu\textrm{g}\;per\;ml$.

• Toxicological Research
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• v.29 no.3
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• pp.203-209
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• 2013

A simple and rapid liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for the quantification of ${\varepsilon}$-acetamidocaproic acid (AACA), the primary metabolite of zinc acexamate (ZAC), in rat plasma by using normetanephrine as an internal standard. Sample preparation involved protein precipitation using methanol. Separation was achieved on a Gemini-NX $C_{18}$ column ($150mm{\times}2.0mm$, i.d., 3 ${\mu}m$ particle size) using a mixture of 0.1% formic acid-water : acetonitrile (80 : 20, v/v) as the mobile phase at a flow rate of 200 ${\mu}l/min$. Quantification was performed on a triple quadrupole mass spectrometer employing electrospray ionization and operating in multiple reaction monitoring (MRM) and positive ion mode. The total chromatographic run time was 4.0 min, and the calibration curves of AACA were linear over the concentration range of 20~5000 ng/ml in rat plasma. The coefficient of variation and relative error at four QC levels were ranged from 1.0% to 5.8% and from -8.4% to 6.6%, respectively. The present method was successfully applied for estimating the pharmacokinetic parameters of AACA following intravenous or oral administration of ZAC to rats.

• Korean Journal of Environmental Agriculture
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• v.29 no.3
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• pp.247-256
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• 2010

A high-performance liquid chromatographic (HPLC) method was developed to determine buprofezin residues in hulled rice and fruits. The buprofezin residue was extracted with acetone and the extract was stepwise purified by liquid-liquid partition and Florisil column chromatography. For rice samples, acetonitrile/n-hexane partition was additionally employed to remove nonpolar lipids. Reversed phase HPLC using an octadecylsilyl column was successfully applied to separate buprofezin from sample co-extractives, as detected by ultraviolet absorption at 250 nm. Recovery experiment at the limit of quantitation validated that the proposed method could evidently determine the buprofezin residue at the level of 0.02 mg/kg. Mean recoveries from hulled rice, apple, pear, and persimmon samples fortified at three tenfold levels were in the range of 80.8~85.2%, 89.1~98.4%, 88.8~95.7% and 90.8~96.2%, respectively. Relative standard deviations of the analytical method were all less than 5%, irrespective of sample types. A selected-ion monitoring LC/mass spectrometry with positive electrospray ionization was also provided to sensitively confirm the suspected residue.

• Mass Spectrometry Letters
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• v.11 no.1
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• pp.10-14
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• 2020

Riboflavin is a water-soluble vitamin, which serves as a precursor to flavin mononucleotide and flavin adenine dinucleotide. This study aimed to develop a simple and rapid liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis for the quantification of riboflavin in the Beagle dog plasma. This method utilized simple protein precipitation with acetonitrile and ¹³C₄, ¹⁵N₂-riboflavin was used as an internal standard (IS). For chromatographic separation, a hydrophilic interaction liquid chromatography (HILIC) column was used with gradient elution. The mobile phase consisted of 0.1% (v/v) aqueous formic acid with 10 mM ammonium formate and acetonitrile with 0.1% (v/v) formic acid. Since riboflavin is an endogenous compound, 4% bovine serum albumin in phosphate buffered saline was used as a surrogate matrix to prepare the calibration curve. The quantification limit for riboflavin in the Beagle dog plasma was 5 ng/mL. The method was fully validated for its specificity, sensitivity, accuracy and precision, recovery, and stability according to the US FDA guidance. The developed LC-MS/MS method may be useful for the in vivo pharmacokinetic studies of riboflavin.

• Bulletin of the Korean Chemical Society
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• v.33 no.7
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• pp.2224-2228
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• 2012

This study describes the ability of capillary electrochromatography (CEC) for the determination of imidacloprid and carbendazim in tomato samples. A novel liquid crystal crown ether modified hybrid silica monolithic column was synthesized, characterized and developed as separation column for the first time. Baseline separation of imidacloprid and carbendazim could be achieved using a mobile phase containing 90% (v/v) 20 mmol/L phosphate buffer (pH 7.0) and 10% (v/v) acetonitrile. The matrix matched calibration curves were linear with correlation coefficient $r^2$ > 0.9998 in the range of 0.20-10.00 mg/L. The limits of detection for imidacloprid and carbendazim were 0.061 and 0.15 mg/kg, respectively, which were below the maximum residue limits established by the European Union as well as Codex Alimentarius. Average recoveries for imidacloprid and carbendazim varied from 101.6-108.0% with relative standard deviations lower than 6.3%. This method was applied to the analysis of tomatoes collected from local markets.

• Bulletin of the Korean Chemical Society
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• v.29 no.6
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• pp.1173-1178
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• 2008

A simple and sensitive high-performance liquid chromatographic method was developed for the simultaneous identification of enrofloxacin and its active metabolite ciprofloxacin in chicken muscle. Norflorxacin imprinted polymers synthesized in water-containing systems show high selectivity to enrofloxacin and ciprofloxacin in an aqueous environment. Using these water-compatible imprinted polymers as selective adsorbents in the solid-phase extraction of enrofloxacin and ciprofloxacin from chicken samples, the remaining biological matrix could be quickly washed out from the imprinted column while enrofloxacin and ciprofloxacin were selectively retained and enriched. Analytical separation was performed on a $C_{18}$ column using acetonitrile-water as a mobile phase and fluorescence detection. Good linearity was obtained from 0.8 to 500 ng/g (r > 0.998) with relative standard deviation of less than 3.9%. The mean recoveries of enrofloxacin and ciprofloxacin from chicken muscle were 80.6-94.5% and 77.8-91.8% at three different concentrations. The limits of determinations based on S/N=3 were 0.07 ng/g and 0.09 ng/g, which are below the maximum residue limits established in many countries.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.7
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• pp.485-494
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• 2013

An efficient extraction method was developed for the analysis of 16 perfluorinated compounds (PFCs) in fish samples. We compared the recoveries from the Ion-Pairing Extraction (IPE), Liquid-Liquid Extraction (LLE), Solid-Phase Extraction (SPE), IPE + SPE method with varying the injection time of the internal standard. As a result, IPE method with the internal standard before extraction was evaluated as the most effective pretreatment method. The RPM (Revolution Per Munite) and pH in IPE-before method were additionally adjusted and the more efficient pretreatment method was established. The total 33 fish samples including liver and gut samples were collected from Korean markets and analyzed PFCs with developed pretreatment method of this study. Total 16 PFC levels in fish samples ranged from ND to 1.67 ng/g with 100% detection frequency. The average PFCs concentrations of muscle, liver and gut samples from fish were compared and showed the following trend: liver (17.8 ng/g) > gut (13.3 ng/g) > muscle (1.67 ng/g). The PFC levels in fish samples were similar or lower than other available previous results of foreign studies.

• Food Science and Biotechnology
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• v.18 no.6
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• pp.1470-1475
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• 2009

The seed coat of the black soybean contains 3 main anthocyanins such as delphinidin-3-O-$\beta$-glucoside, cyanidin-3-O-$\beta$-glucoside, and petunidin-3-O-$\beta$-glucoside. As a part of our effort on discovering and breeding new black soybean cultivars which possesses specific anthocyanin component rich, we determined the anthocyanin profiles of the 2 cultivars recently developed soybean cv. Gaechuck #1 and cv. Gyeongsang #1, using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and compared their content and identity with those of previously known 10 cultivar controls. The Cosmosil-$5C_{18}$-AR-II column were selected for the analysis because of the best peak separation. The column temperature was set up at $35^{\circ}C$. The mobile phase consisting of water containing 0.5%(v/v) formic acid and methanol gave good separation between the 3 anthocyanin analytes and internal standard (quercetin 3-O-$\beta$-rutinoside) and peaks with suppressed tail. The MS/MS spectra of each individual anthocyanin standard were detected in positive electron spray ionization (ESI) modes. It was disclosed that the anthocyanin contents of the soybean cv. Gaechuck#1 and cv. Gyeongsang#1 are roughly higher than those of the 10 controls.