• Korean Journal of Environmental Agriculture
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• v.25 no.4
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• pp.359-364
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• 2006

Reversed-phase high-performance liquid chromatography (HPLC) techniques were developed to quantify abamectin (ABM) in paprika (Capsicum annum). Separation was achieved on a $C_{18}$ ODS column with a mobile phase of acetonitrile/water (96/4, v/v) mixture in an isocratic elution at the flow tate of 1.2 mL/min for avermectins (AVMs). The retention times were 8.0 and 9.7mins for AVM $B_{lb}$ and AVM $B_{1a}$, respectively. Residual AVMs (sum of AVM $B_{1a}$, AVM $B_{1b}$ and 8,9-Z-AVM $B_{1a}$) in the vegetable were extracted with acetonitrile, and the silica solid-phase extraction cartridges were used to purify the extract. AVMs were derivatized using trifluoroacetic acid and 1-methylimidazole, and the derivatives were determined with a fluorescence detector (excitation at 365 nm and emission at 470 nm). High and consistent recoveries, ranging from 93% to 115%, were obtained for AVM $B_{1a}$ and 8, 9-Z-AVM $B_{1a}$ at fortified levels of $20{\mu}g/kg\;and\;200{\mu}g/kg$ for paprika. The limit of quantitation (LOQ) was $2{\mu}g/kg$. The residual levels of AVMs in paprika in a field experiment from one day to seven days after the last application decreased from 18.40 to $7.59{\mu}g/kg$. The half-life $(T_{1/2})$ of AVMs in paprika was 1.47 days.

• Bulletin of the Korean Chemical Society
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• v.28 no.5
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• pp.737-744
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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 acrylamide in potato chips, starch-rich foodstuff cooked at high temperature. Sample was spiked with 13C3-acrylamide and then extracted with water. The extract was further cleaned up with an Oasis HLB solid-phase extraction (SPE) cartridge and an Oasis mixed-phase cation exchange (MCX) SPE cartridge. The extract was analyzed by using LC/ESI/Tandem MS in positive ion mode. LC with a medium reversed-phase (C4) column was optimized to obtain adequate chromatographic retention and separation of acrylamide. MS was operated to selectively monitor [M+H]+ ions of the analyte and its isotope analogue at m/z 72 and m/z 75, respectively. Sample was also analyzed by the LC/MS with selectively monitoring the collisionally induced dissociation channels of m/z 72 → m/z 55 and m/z 75 → 58. Compared to the LC/MS chromatograms, the LC/MS/MS chromatograms showed substantially reduced background chemical noises coming from solvent clusters formed during ESI spray processes and interferences from sample matrix. Repeatability and reproducibility studies showed that the LC/MS/MS method is a reliable and reproducible method which can provide a typical method precision of 1.0% while the LC/MS results are influenced by chemical interferences.

• Analytical Science and Technology
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• v.25 no.6
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• pp.460-466
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• 2012

An environmentally friendly, so-called green, high performance liquid chromatography method was developed and validated for the determination of trans, trans-muconic acid (t,t-MA) in human urine as a biomarker of benzene exposure. After urinary t,t-MA was extracted and enriched using solid-phase extraction, a MF-Ph1 SG80 ($150mm{\times}2.0mm$ I.D., 5 ${\mu}m$) column with a mobile phase of 10 mM $KH_2PO_4$ containing 0.1% $H_3PO_4$ was used for isocratic separation of t,t-MA with UV detection at 259 nm. The calibration curve was constructed in the range of 0.1-5.0 mg/L with good linearity ($r^2$=0.9992). The intra-day and inter-day precision (as RSD) were 0.9-8.5% and 3.1-4.5%, respectively. The average recovery ranged from 97.5% to 101.7%. The green sample preparation and separation with no organic solvents were successfully achieved. The validated method would be suitable for the routine biological monitoring of benzene exposure in the occupational settings.

• Analytical Science and Technology
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• v.31 no.1
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• pp.39-46
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• 2018

Carbaryl and seven organophosphorous pesticides were analyzed simultaneously using on-line solid phase extraction (on-line SPE) coupled with liquid chromatography tandem mass spectrometry (LC/MS/MS). The target pesticides are Carbaryl, Methyl demeton, Fenitrothion, Malathion, Parathion, Phenthoate, Diazinon, and EPN. This method includes the direct injection of $500{\mu}L$ in the water sample, a 15 min separation period using a rapid resolution liquid chromatography system with on-line SPE, and detection through electrospray ionization (ESI) positive mode. The percentage of recovery of all pesticides ranged from 85.3 % to 100 %. This method showed an accuracy of ${\geq}90.0%$, possessing limits of detection and quantification within 0.05 to $0.28{\mu}g/L$ and 0.16 to $0.89{\mu}g/L$, respectively. The correlation coefficients (r) for the calibration curves within a range of 0.5 to $8.0{\mu}g/L$ were higher than 0.99. The evaluation results showed the efficacy of the method for all contents, and no pesticides were detected in the water quality sample.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.9
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• pp.894-899
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• 2010

We coordinated the experiments with ozone pretreatment and two-phase anaerobic digestion using solid-liquid separation to raise the efficiency of sludge volume reduction and obtained the following results. The pre-treatment with ozone reduced the solid concentration in the average of TSS $8.3{\pm}2.0%$ TSS and $9.2{\pm}}2.8%$ VSS. Of the organic material, TCOD decreased $5.1{\pm}2.4%$, but SCOD showed $72{\pm}6.5%$ increased, which was due to destruction of the cell wall and dissolution of icell media by the powerful oxidative stress of ozone. During the two-phase anaerobic digestion process, we achieved the reduction of $21.5{\pm}3.4%$ TSS, $20.2{\pm}8.4%$ VSS, $32.1{\pm}7.9%$ TCOD and $22.1{\pm}7.2%$ SCOD in average. The maximum methane gas production were 177.6 mL per g TSS, 210.8 mL per g VSS, 127.0 mL per g TCOD and 1452.0 mL per g SCOD, respectively. Solid material reduction through the two-phase anaerobic digestion and MLE (Modified Ludzack-Ettinger) processes were 93.8% of TSS and 92.0% of VSS. We concluded that suggested two-phase anaerobic digestion and MLE process could achieve the reasonable production of biogas and a maximum reduction of the sludge volume.

• Bulletin of the Korean Chemical Society
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• v.34 no.9
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• pp.2760-2764
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• 2013

Geniposide is a biologically active ingredient of gardenia fruit. A liquid chromatography-tandem mass spectrometric method was developed and validated for the determination of geniposide in rat plasma. The plasma samples were pretreated by solid-phase extraction and introduced into a BDS Hypersil $C_{18}$ column ($50{\times}2.1mm$, $5{\mu}m$) for chromatographic separation. The mobile phase consisted of 0.1% formic acid and 0.1% formic acid in acetonitrile, and gradient elution was performed at a flow rate of 0.25 mL/min. For mass spectrometric detection, multiple reaction monitoring was performed via an electrospray ionization source in positive mode. The calibration curve for geniposide was linear ($r^2=0.997$) in the concentration range of $0.005-1{\mu}g/mL$. The intra- and inter-day accuracies and precisions fulfilled the required criteria (${\pm}15%$). The developed method was subsequently used for pharmacokinetic analysis of geniposide after oral administration to rats at a dose of 50 mg/kg. The mean maximum plasma concentration of geniposide was $0.68{\pm}0.29{\mu}g/mL$ at $0.44{\pm}0.13h$, and the mean area under the plasma concentration versus time curve was $1.46{\mu}g{\cdot}h/mL$.

• Applied Chemistry for Engineering
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• v.29 no.5
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• pp.613-619
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• 2018

In this study, various influent sludge pre-treatment methods and the internal recirculation of thickened sludge from effluents using a liquid/solid separation unit were adopted to investigate their effects on the sludge digestion and methane production in a combined mesophilic anaerobic and thermophilic aerobic sludge digestion process. A lab-scale combined sludge digestion process was operated during 5 phases using different feed sludge pre-treatment strategies. In phase 1, the feed sludge was pre-treated with a thermal-alkaline method. In contrast, in phases 2, 3 and 4, the internal recirculation of thickened sludge from the effluent and thermal-alkaline, thermal, and alkaline pre-treatment (7 days) were applied to the combined process. In phase 5, the raw sludge without any pre-treatment was used to the combined process. With the feed sludge pre-treatment and internal recirculation, the experimental results indicated that the volatile suspended solid (VSS) removal was drastically increased from phases 1 to 4. Also, the methane production rate with the thermal-alkaline pre-treatment and internal recirculation was significantly improved, showing an increment to 285 mL/L/day in phase 2. Meanwhile, the VSS removal and methane production in phase 5 were greatly decreased when the raw sludge without any pre-treatment was applied to the combined process. Considering all together, it was concluded that the combined process with the thickened sludge recirculation and thermal-alkaline pre-treatment can be successfully employed for the highly efficient sewage sludge reduction and methane gas production.

• Bulletin of the Korean Chemical Society
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• v.32 no.8
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• pp.2637-2642
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• 2011

A new ultrasonic-assisted micellar extraction and cloud-point pre-concentration method was developed for the determination of major saikosaponins, namely saikosaponins -A, -C and -D, in Radix Bupleuri by high performance liquid chromatography with evaporative light scattering detection (HPLC-ELSD). The non-ionic surfactant Genapol X-080 (oligoethylene glycol monoalkyl ether) was chosen as the extraction additive and parameters affecting the extraction efficiency were optimized. The highest yield was obtained with 10% (w/v) Genapol X-080, a liquid/solid ratio of 200:1 (mL/g) and ultrasonic-assisted extraction for 40 min. In addition, the optimum cloud-point pre-concentration was reached with 10% sodium sulfate and equilibration at $60^{\circ}C$ for 30 min. Separation was achieved on an Ascentis Express C18 column (100 ${\times}$ 4.6 mm i.d., 2.7 ${\mu}M$) using a binary mobile phase composed of 0.1% acetic acid and acetonitrile. Saikosaponins were detected by ELSD, which was operated at a $50^{\circ}C$ drift tube temperature and 3.0 bar nebulizer gas ($N_2$) pressure. The water-based solvent modified with Genapol X-080 showed better extraction efficiency compared to that of the conventional solvent methanol. Recovery of saikosaponins ranged from 93.1 to 101.9%. An environmentally-friendly extraction method was successfully applied to extract and enrich major saikosaponins in Radix Bupleuri.

• Korean Journal of Veterinary Service
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• v.27 no.1
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• pp.17-29
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• 2004

A multiresidual analysis was performed to determine 12 sulfonamides(sulfacetamide, sulfadiazine, sulfisomidine, sulfathiazole, sulfapyridine, sulfamerazine, sulfamethazine, sulfamonomethoxine, sulfisoxazole, sulfamethoxazole, sulfaquinoxaline, and sulfadimethoxine) in beef and pork simultaneously. The multiresidual analysis for the sulfonamides currently used was able to analyze 5 kinds of sulfonamides at the same time. The method of this 12 sulfonamides multiresidual analysis in this study was matrix solid-phase dispersion(MSPD) by high performance liquid chromatography (HPLC) and liquid chromatography mass spectrometry (LC/MS). The recovery rate of the materials was measured by MSPD method with 3 different extraction solvents; Dichloromethane, DCM: Ethylacetate(3:1), DCM:EA(9:1). Also, samples (84 beef and 205 pork samples) which were positive by EEC-4 plate test from 2001 to 2003 were tested to investigate the kinds of sulfonamides using HPLC. The results from the study were as follows; 1. The recovery rate of the materials was measured by MSPD method with 3 different extraction solvents; Dichloromethane, DCM:Ethylacetate(3:1), DCM:EA(9:1). The method of extraction solvent with DCM:ethyl acetate(9:1) was the most excellent(87.7∼99.3%) in separation and reappearance. 2. In the LC/MS analysis. of sulfonamides, signal to noise ratio was showed relatively high in the positive mode and special ion in the quality analysis was determined via [M+H]$\^$+/ and m/z 156. A spectrum of sulfonamides was showed from all 12 sulfonamides. 3. The samples positive by the EEC-4 plate, a screening test method, were categorized by sulfonamides through Charm II and confirmed the kinds of sulfonamides through HPLC. 1) Among 84 beef samples positive by EEC-4 plate, 20 samples were positive by Charm II and identified as 7 sulfamethazine, 9 sulfadimethoxine, 1 sulfamonomethoxine and 3 unknown status. 2) Among 205 pork samples positive by EEC-4 plate, 42 samples were positive by Charm II and identified as 19 sulfamethazine, 1 sulfadimethoxine, 4 sulfamonomethoxine and 5 unknown status.

• Journal of Powder Materials
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• v.4 no.2
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• pp.113-121
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• 1997

The densification of the compacts of Co+32%Cr+20%W+l.5%C, Co+32%Cr+20%W+3.0%C and Co+32%Cr+20%W+4.5%C sintered under $H_2$ gas or vacuum was investigated. The effect of V and B addition on the densification was also investigated. The densification of these compacts were always incomplete regardless of sintering atmosphere, temperature and time. The amounts of oxygen and carbon in compacts sintered in $H_2$ for 3.6ks at 1523K were 0.105~0.160 mass% and 0.33~0.89 mass%, respectively. And those in vacuum were 0.028~0.032% and 0.957~4.08%, respectively. Relative density(Ds) of Co+29%Cr+17%W+3.0%C compact containing 6%V and Co+32%Cr+20%W+2.97%C compact containing 0.03%B were 99 and 100%, respectively, indicating complete densification by solid phase sintering. Victors hardness of sintered compacts containing 6%V or 0.03%B were 632 and 568, showing 50~60% increase in comparison to those without V or B. These results can be explained in terms of oxidation/reduction of oxides and equilibrium pressure of CO in isolated pore, instead of presence of liquid formation and grain boundary separation from pores due to large grain growth.