• Natural Product Sciences
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• v.27 no.4
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• pp.264-273
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• 2021

Simultaneous quantification of multiple marker compounds in herbal medicine by high performance liquid chromatography (HPLC) analysis is still a challenge due to the complexity in various parameters to be considered and co-existing multi-components. As a case study, a reliable HPLC method for simultaneous quantification of paeoniflorin from Paeoniae Radix and decursin from Angelicae Gigantis Radix in various commercial herbal medicine was developed based on analytical quality by design (AQbD) strategy. As a first step, risk assessment was performed to select the critical method parameters (CMPs) which were decided as organic mobile phase ratio and column oven temperature. In order to evaluate the effect of the CMPs on critical method attributes (CMAs) of peak resolution and tailing, central composite design (CCD) was employed. The final chromatographic conditions were optimized as follows: column- C₁₈, 4.6 × 250 mm, 5 ㎛ particle size; mobile phase- A: acetonitrile, B: 0.1% acetic acid water; detection wavelength- 235 nm for paeoniflorin, 325 nm for decursin; column oven temperature- 25℃; flow rate- 1.0 mL/min; gradient mobile phase system as Time (min) : % A, 0:14, 25:14, 30:50, 60:50, 61:100, 65:100, 66:14, 75:14. The method was successfully validated according to the International Conference on Harmonization (ICH) guidelines and piloted for ten commercial herbal medicines.

• Bulletin of the Korean Chemical Society
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• v.31 no.3
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• pp.678-682
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• 2010

A doubly tethered chiral stationary phase (CSP) based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid were applied to the liquid chromatographic resolution of racemic tocainide, an antiarrhythmic agent, and its analogues. The chiral recognition efficiency of the doubly tethered CSP for tocainide and its analogues was generally greater than that of the corresponding singly tethered CSP especially in terms of the resolution ($R_S$). The resolution of tocainide and its analogues on the doubly tethered CSP were dependent on the content and the type of the organic and acidic modifiers in aqueous mobile phase and the column temperature. Especially, the retention behaviors of analytes on the doubly tethered CSP with the variation of the content of organic modifier in aqueous mobile phase were opposite to those on the corresponding singly tethered CSP and these opposite retention behaviors were rationalized by the lipophilicity differences of the two CSPs.

• Journal of the Korean Chemical Society
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• v.55 no.5
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• pp.751-755
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• 2011

A doubly tethered chiral stationary phase (CSP) based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid was applied to the resolution of various aryl ${\alpha}$-aminoalkyl ketones with the use of 80% ethanol in water containing 10 mM sulfuric acid as a mobile phase. The chiral resolution was quite successful, the separation factors (${\alpha}$) and the resolutions ($R_S$) being in the range of 1.39-2.05 and 3.18-5.22, respectively. The separation factors (${\alpha}$) on the doubly tethered CSP were slightly worse than those on the corresponding singly tethered CSP. However, the resolutions ($R_S$) on the doubly tethered CSP were generally greater than those on the corresponding singly tethered CSP. The chromatographic behaviors for the resolution of aryl ${\alpha}$-aminoalkyl ketones on the doubly tethered CSP were demonstrated to be dependent on the type and the content of the organic and acidic modifiers in aqueous mobile phase and the column temperature.

• Bulletin of the Korean Chemical Society
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• v.31 no.8
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• pp.2322-2328
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• 2010

A multiple solid-phase extraction (SPE) method was used with liquid chromatography, coupled with mass spectrometry (LC/MS), for the analysis of heterocyclic amines (HCAs) in human urine. Separation efficiencies based on the pH of the mobile phase and the types of columns were compared. An amide column showed better baseline separation and narrower HCA peak widths at pH 5.0 for the mobile phase than a $C_8$ column. Each SPE step, HLB, MCX, and HybridSPE, was optimized by controlling the pH conditions. The combined method with the three SPEs effectively removed interfering species that cause ion-suppression during HCA detection. Validation of the method, performed with SIM and SRM detection, showed correlation coefficients above 0.991 in the range 0.3 - 16.7 ng/mL. Recovery rates were 45.4 - 97.3% on the $C_8$ column and 71.8 - 101.4% on the amide column, and method detection limits were 0.11 - 0.65 ng/mL on the $C_8$ column and 0.12 - 0.48 ng/mL on the amide column. This method using multiple SPEs offers significant benefits for high-throughput determination of HCAs in urine.

• Journal of the Korean Chemical Society
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• v.32 no.2
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• pp.113-121
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• 1988

The retention mechanism and separation of various aromatic sulfonic and carboxylic acids on reversed-phase liquid chromatographic column were studied in the mobile phase containing dodecyltrimethylammonium bromide (DTAB). The retention mechanism was found to be followed the ion-interaction model where the DTAB occupies a primary layer at the stationary phase while the sample anions and other co-anions in the system compete for forming the secondary layer. The capacity factors of samples were influenced by the several factors such as pH, concentration of various organic solvents, co-anions in the mobile phase and functional groups in sample molecules. Some mixtures of organic samples were attempted to separate under optimum condition.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.2
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• pp.258-264
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• 2011

In this paper, we designed a frequency synthesizer with a low phase noise and fast lock time and excellent spurious characteristics using the offset-PLL(Phase Locked Loop) that is used in GSM(Global System for Mobile communications). The proposed frequency synthesizer has low phase noise using three times down conversion and third offset frequency of this synthesizer is created by DDS(Direct Digital Synthesizer) to have high frequency resolution. Also, this synthesizer has fast switching speed using DAC(Digital to Analog Converter). but phase noise degraded due to DAC. we improved performance using the DAC noise filter.

• JSTS:Journal of Semiconductor Technology and Science
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• v.17 no.3
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• pp.411-424
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• 2017

An all-digital delay-locked loop (DLL) for a mobile memory interface, which runs at 0.11-2.5 GHz with a phase-shift capability of $180^{\circ}$, has two internal DLLs: a global DLL which uses a time-to-digital converter to assist fast locking, and shuts down after locking to save power; and a local DLL which uses a phase detector with an adaptive phase sampling window (WPD) to reduce jitter accumulation. The WPD in the local DLL adjusts the width of its sampling window adaptively to control the loop bandwidth, thus reducing jitter induced by UP/DN dithering, input clock jitter, and supply/ground noise. Implemented in a 65 nm CMOS process, the DLL operates over 0.11-2.5 GHz. It locks within 6 clock cycles at 0.11 GHz, and within 17 clock cycles at 2.5 GHz. At 2.5 GHz, the integrated jitter is $954fs_{rms}$, and the long-term jitter is $2.33ps_{rms}/23.10ps_{pp}$. The ratio of the RMS jitter at the output to that at the input is about 1.17 at 2.5 GHz, when the sampling window of the WPD is being adjusted adaptively. The DLL consumes 1.77 mW/GHz and occupies $0.075mm^2$.

• Journal of the Korean Chemical Society
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• v.43 no.6
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• pp.656-662
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• 1999

We have obtained retention data of benzene, toluene, ethylbenzene, phenol, and acetophenone at 25, 30, 35, 40, 45 and 50 $^{\circ}C$ in 30/70, 40/60, 50/50, 60/40, 70/30, and 80/20 (v/v %) methanol/water eluents using a $C_18$ phase with a high ligand density. We drew van't Hoff plots from the data, and computed enthalpies and entropies of solute transfer from the mobile to the stationary phase. The cavity formation effect was found the major factor that governs the solute distribution between the mobile and stationary phases. The hydrophobic effect became significant in highly aqueous mobile phases. We also concluded that the Shodex C18-5B stationary phase was a polymer-like phase with a high ligand density, and followed a partially adsorption-like mechanism.

• Journal of Pharmaceutical Investigation
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• v.37 no.3
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• pp.187-192
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• 2007

A reversed phase HPLC analysis of atorvastatin (AS) standard solution was performed using diclofenac (DF) as internal standard. Column oven temperature, flow rate and the composition of the mobile phase were varied in order to determine a practical system setup using a C18 column and UV detector. Two C18 columns of different length were compared regarding their influence on the AS peak shape. Based on these preliminary experiments a validation study was performed utilizing a C18 column at $62^{\circ}C$ with a mobile phase consisting of sodium phosphate buffer (0.05 M, pH 4.0), methanol and acetonitrile (40:50:10, v/v/v). The detection limit for AS was $0.1{\mu}g/ml$ and inter- and intra-day calibration curves were linear over a concentration range of $0.2-50{\mu}g/ml$. Accuracy and precision were satisfactory in the AS concentration range of $0.5-50{\mu}g/ml$.

• Journal of Multimedia Information System
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• v.5 no.3
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• pp.155-162
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• 2018

Nowadays, the tracking technology of Quadrant Detector will become actual by new micro devices. Based on the past filed data of the reception experiment with COMETS satellite, we have studied on new device (AD8302, phase difference detector) was acquired and suspect its abilities. In 1998, we have developed a Quadrant Detector for mobile to track a weak signal from satellite on Ka band of COMETS. The Quadrant Detector is comprised of four dedicated feed components for reception under an environment of Nakagami - Rician fading, and one transmission and reception feed component. We were successful in receiving a 23 GHz beacon signal from ICE transponder of the COMETS and succeeded in tracking the satellite from a moving vehicle at speeds of approximately 10 ~ 20 Km/h on paved roads. In 2018, with new device AD8302, we have verified new QD system and performed a simulation, based on the past filed experiment. This new device shall be improving the tracking abilities from mobile body on the earth to the multimedia satellite.