Dong-Hyug Yang

Dispersive liquid-liquid microextraction based on solidification of floating organic droplets followed by high performance liquid chromatography for the determination of duloxetine in human plasma.

A novel dispersive liquid-liquid microextraction method based on solidification of floating organic droplets (DLLME-SFO) technique was developed for the determination of duloxetine in human plasma samples by high performance liquid chromatography with fluorescence detection (HPLC-FLD). During the extraction procedure, plasma protein was precipitated by using a mixture of zinc sulfate solution and acetonitrile. After the protein precipitation step, duloxetine in an alkaline sample solution was quickly extracted by DLLME-SFO with 50 μL of 1-undecanol (extractant). Disperser was unnecessary because the small amount of remaining acetonitrile, which acts as a protein precipitating reagent, was also employed as a disperser; therefore, organic solvent consumption was reduced as much as possible. The emulsion was centrifuged and then fine droplets were floated to the top of the sample solution. The floated droplets were solidified in an ice bath and easily transferred. Various DLLME-SFO parameters such as extractant type, extractant amount, ionic strength, pH and extraction time were optimized. The chromatographic separation of duloxetine was carried out using ethanol as mobile phase. Validation of the method was performed with respect to linearity, intra- and inter-day accuracy and precision, limit of quantification (LOQ), and recovery. Calibration curves for duloxetine showed good linearity with correlation coefficients (r²) higher than 0.99. The method showed good precision and accuracy, with intra- and inter-assay coefficients of variation less than 15% (LOQ: less than 20%) at all concentrations. The recovery was carried out following the standard addition procedure with yields ranging from 59.6 to 65.5%. A newly developed environmentally friendly method was successfully applied to the pharmacokinetic study of duloxetine in human plasma and was shown to be an alternative green approach compared with the conventional solid-phase microextraction (SPME) and dispersive liquid-liquid microextraction (DLLME) techniques.

Species discrimination of Radix Bupleuri through the simultaneous determination of ten saikosaponins by high performance liquid chromatography with evaporative light scattering detection and electrospray ionization mass spectrometry

A simple, rapid and robust high performance liquid chromatography-evaporative light scattering detection (HPLC-ELSD) method was established for the species discrimination and quality evaluation of Radix Bupleuri through the simultaneous determination of ten saikosaponins, namely saikosaponin-a, -b(1), -b(2), -b(3), -b(4), -c, -d, -g, -h, and -i. These compounds were chromatographed on an Ascentis(®) Express C18 column with a gradient elution of acetonitrile and water containing 0.1% acetic acid at a flow rate of 1.0 mL/min. Saikosaponins were monitored by ELSD, which was operated at a 50°C drift tube temperature and 3.0 bar nebulizer gas (N(2)) pressure. The developed method was validated with respect to linearity, intra- and inter-day accuracy and precision, limit of quantification (LOQ), recovery, robustness and stability, thereby showing good precision and accuracy, with intra- and inter-assay coefficients of variation less than 15% at all concentrations. Furthermore, a high performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESI-MS) method was developed to certify the existence of ten saikosaponins, as well as to confirm the reliability of ELSD. The extraction conditions of saikosaponins from Radix Bupleuri were also optimized by investigating the effect of extraction methods (sonication, reflux and maceration) and various solvents on the extraction efficiencies for saikosaponins. Sonication with 70% methanol for 40 min was found to be simple and effective for extraction of major saikosaponins. This analytical method was applied to determine saikosaponin profiles in 20 real samples consisting of four Bupleurum species, namely B. falcatum, B. chinense, B. sibiricum and the poisonous B. longiradiatum. It was found that three major saikosaponin-a, -c and -d were the major constituents in B. falcatum, B. chinense, and B. longiradiatum, while one major saikosaponin (saikosaponin-c) was not identified from B. sibiricum. In addition, no saikosaponin-b(3) was detected in B. longiradiatum samples, indicating that the toxic B. longiradiatum may be tentatively distinguished from officially listed Bupleurum species (B. falcatum and B. chinense) based on their saikosaponin profiles. Overall the simultaneous determination of ten saikosaponins in Radix Bupleuri was shown to be a promising tool to adopt for the discrimination and quality control of closely related Bupleurum species.

Rapid chiral separation of racemic cetirizine in human plasma using subcritical fluid chromatography-tandem mass spectrometry

A method for fast chiral separation of cetirizine and quantitation of levocetirizine in human plasma using subcritical fluid chromatography with tandem mass spectrometry was developed and validated. The chromatographic separation was performed using a Chiralpak IE column (2.1 mm×150 mm, 5 μm) with an isocratic elution of CO2/organic modifier (55/45, v/v) at a flow rate of 0.85 mL/min. The organic modifier was composed of water/methanol (5/95, v/v). The makeup flow was optimized at water/methanol (10/90, v/v) and 0.2 mL/min. The most influential parameters on the separation of cetirizine affecting resolution, retention time and sensitivity were selected by fractional factorial design. The 3 selected factors were optimized by response surface methodology. Tandem mass spectrometry was used at electrospray ionization, positive ion mode, and multiple-reaction monitoring mode. Isotope-labeled cetirizine-d4 was used as the internal standard. The sample preparation of human plasma was conducted by solid phase extraction of hydrophilic-lipophilic balance (HLB) type. The developed method was validated for selectivity, linearity, precision, accuracy, recovery, limit of quantitation (LOQ), and limit of detection (LOD). The real human plasma samples were analyzed and the pharmacokinetic results were compared with results of previous research. The developed method was found to be reliable based on the similarity between the results of the current and previous methods. The chiral separation for cetirizine and economic feasibility were compared with those of previous studies using normal phase-HPLC or reversed phase-HPLC. The established analytical method could be successfully applied to pharmacokinetic study with reduction in the analysis time and costs.

Determination of residual arsenic compounds in chicken muscle by ultra-performance liquid chromatography coupled with ultraviolet detection after pre-column derivatization with toluene-3,4-dithiol.

A simple and sensitive derivatization method using toluene-3,4-dithiol as a derivatization reagent for the simultaneous analysis of seven arsenic compounds (roxarsone, nitarsone, p-arsanilic acid, o-arsanilic acid, phenylarsonic acid, phenylarsine oxide, and mono-methylarsonic acid) in chicken muscle was developed and validated by ultra-performance liquid chromatography coupled with ultraviolet detection (UPLC-UV). The structure of the derivatized arsenic compounds was confirmed by liquid chromatography-ion trap mass spectrometry or gas chromatography-mass spectrometry. Optimization of the derivatization reaction conditions was carried out by investigating the influence of reagent concentration, buffer or additive acids, temperature, and time. The optimized conditions were a derivatization reagent concentration of 20mg/mL with 0.05mol/L HCl as an additive acid at 60°C for 15min. In this study, baseline separation of arsenic compounds could be achieved within 13min, except for phenylarsonic acid and phenylarsine oxide whose derivatized products are equal. The developed method was successfully validated and applied to 12 chicken muscle samples from Korean districts and other countries.

Environmentally friendly determination of urinary trans, trans-muconic acid for biological monitoring of benzene exposure by green high-performance liquid chromatography

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 (150 mm×2.0 mm I.D., 5 μm) column with a mobile phase of 10 mM KH₂PO₄ containing 0.1% H₃PO₄ 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 (r²=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.

Determination of calcium content and dissolution characteristics of oyster shell by ICP-AES

An ICP-AES method for determination of calcium content and dissolution characteristics of oyster shell (Ostrea gigas) has been developed and validated. Total calcium content in oyster shell was determined using ICPAES. The dissolution characteristics, which would reflect the composition of polymorphs and calcium salts in oyster shell, were also evaluated by dissolution test. The total calcium contents ranged from 31.8 to 39.9% and the dissolution ratios varied from 62.7 to 83.6% (n