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ABSTRACT: A high-temperature liquid chromatographic technique is employed for the separation of commercially available polymer additives to enhance the resolution and speed. Separation efficiencies and elution behaviors for seven phthalate plasticizers and five antioxidants are evaluated at elevated column temperatures and with a thermal gradient. Diamondbond C18 (octadecylsilica), Zirchrom PS (zirconia-based polystyrene), and Zirchrom PBD (zirconia-based polybutadiene) columns are selected for the study because of their thermal stability. The temperature programming is controlled with a column oven in conjunction with an independent mobile phase preheater and a post-column effluent cooling assembly. Van't Hoff plots show that the reverse-phase liquid chromatography mechanism is maintained over a wide range of column temperatures. A 1% increase of acetonitrile in the mobile phase is estimated to have a comparable effect as a 7-7.5 degrees C column temperature increase on the retention time changes.
Journal of chromatographic science 02/2007; 45(1):16-21. · 0.88 Impact Factor
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ABSTRACT: A simple and convenient liquid chromatographic method has been developed and applied to the analysis of the novel aminothiazolecarboxamide fungicide, ethaboxam, in soil and crops. After the isolation and concentration of analyte from soil and crops, clean-up and separation of sample solutions are performed by high-performance liquid chromatography with online solid-phase extraction. Good linearity (r2 > 0.9995), recovery [for soil, 95.3-98.4%, and crops (grape, red pepper), 92.9-95.9%], and repeatability are achieved in the calibration range of 0.1-10.3 microg/mL. The limit of detection is the 2.5 parts per billion (ppb) (40 g of soil) and the 20 ppb (25 g of crops), respectively. This assay method shows the suitability for the residual analysis of ethaboxam in soil and crops.
Journal of chromatographic science 09/2004; 42(7):366-70. · 0.88 Impact Factor
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ABSTRACT: We have used density functional theory to study palladium-based catalysts commonly used for the polymerization of norbornene derivatives with an ester group. Exo-exo, exo-endo, and endo-endo isomers of catalyst complexes were investigated; the endo-endo isomer was the most stable and inactive due to an intramolecular interaction between Pd and O of the carbonyl group. Phosphine groups are effective in minimizing the Pd-O interaction in the endo-endo isomer and P(C6H11)3 was found to be the most efficient reagent. The intramolecular Pd-O interactions were estimated using model complexes, and it was demonstrated that they play a crucial role in stabilizing the endo-endo isomer.
Journal of Molecular Modeling 11/2003; 9(5):304-7. · 1.80 Impact Factor
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ABSTRACT: The interaction of poly(styrene-co-allyl alcohol) and aliphatic polyester was studied using FT-IR spectroscopy. The hydrogen bonding between two polymers was investigated by monitoring C=O and OH stretching modes with the variation of concentration and temperature. The phase-separated morphology was also observed using FT-IR imaging, where the spectroscopic analysis of each phase is available.
Applied Spectroscopy 10/2003; 57(9):1058-62. · 1.66 Impact Factor
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ABSTRACT: A pre-column derivatization liquid chromatographic method has been developed for the analysis of aminoglycoside antibiotics using phenylisocyanate as a derivatization reagent. Derivatives including kanamycin, neomycin and gentamicin were formed by reaction of the analytes with phenylisocyanate in the presence of triethylamine. Phenylisocyanato groups were attached to corresponding amino groups of aminoglycoside and their molecular mass was confirmed by liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS). The experimental conditions for derivatization and separation of aminoglycoside derivatives were optimized and validated. A simple liquid chromatographic method for the determination of aminoglycoside antibiotics was demonstrated.
Biomedical Chromatography 10/2003; 17(6):396-403. · 1.97 Impact Factor
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ABSTRACT: Melagatran is an active thrombin inhibitor showing oral and parenteral bioavailability for antithrombotic therapy. A simple and convenient liquid chromatographic method has been developed and applied to the analysis of melagatran in rabbit plasma. The clean-up and separation of the sample solutions were performed by automated on-line column switching HPLC. The method validation shows the suitability of the column switching liquid chromatographic system for the quantitation of melagatran in biological fluids.
Biomedical Chromatography 10/2003; 17(6):373-5. · 1.97 Impact Factor
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ABSTRACT: Enantiomeric separation of pyrethroic acid methyl and ethyl esters was examined on cellulose-based chiral stationary phases (CSPs): chiralcel OD (cellulose tris(3,5-dimethylphenyl carbamate)) and chiralcel OF (cellulose tris(4-chlorophenyl carbamate)). The good resolution of pyrethroic acid esters was achieved on chiralcel OD and OF. Separation factors ranged from 1.19-5.12 for Chiralcel OD and 1.00-1.59 for chiralcel OF. Hexane/2-propanol (100:0.15, v/v %) was used as the eluent. The resolution capability of CSPs was greater chiralcel OD than chiralcel OF in the case of the pyrethroic acid esters. The flow rate was 0.8 ml/min and detection was set at 230 nm. The results of the chromatographic data and molecular mechanics suggest that steric effect was a major factor in the enantioseparation. Furthermore, the hydrogen bond between analytes and CSP played an important role in the chiral recognition.
Chirality 04/2003; 15(3):276-83. · 2.35 Impact Factor
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ABSTRACT: Reversed-phase high-performance liquid chromatography is widely used in the analysis of drug substances and their metabolites. The interaction of quinolones with residual silanol in a silica-based C18 stationary phase causes peak broadening and bad peak shapes and makes it hard to resolve the peak separations. This unusual interaction is studied and finally can be removed by masking the residual silanol of a silica-based C18 stationary phase, then good peak separation is achieved. We have chosen four new quinolones and ciprofloxacin and improved the peak shapes by optimizing the pH of the eluent and the quantity of the additive (N,N-dimethyloctylamine, approximately 0-40 mM) in the monomeric C18 stationary phase. The elution behavior of quinolones in the polymeric C18 stationary phase is compared with that in the monomeric C18 stationary phase under the same eluent condition. Good peak symmetry and a high plate number are achieved by this technique, which are hardly obtained with the conventional silica-based C18 stationary phase. Based on these results, we present data of the influence of the eluent composition such as pH, buffer, and additive concentration on the peak shape.
Journal of chromatographic science 09/2002; 40(7):369-76. · 0.88 Impact Factor
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The Journal of Antibiotics 07/2002; 55(6):598-601. · 1.65 Impact Factor
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ABSTRACT: A liquid chromatographic method for the determination of the aminoglycoside kanamycin in varicella vaccine is described. Kanamycin sulfate was derived with phenylisocyanate (PIC) and triethylamine for 10 min at 70°C and chromatographed on a alkylamide-bonded column, Suplex pKb-100. A derivative of kanamycin sulfate was attached to four phenylisocynato groups and that molecular mass was confirmed with liquid chromatography–electrospray ionization mass spectrometry (LC–ESI-MS). The kanamycin-PIC derivative was found to have a retention time of 11.7 min using an eluent composed of 40% acetonitrile in water at 1.2 ml/min column flow-rate. Detection was at a wavelength of 240 nm. Recoveries ranging from 97.5 to 99.8% were found. The correlation coefficient was greater than 0.9998 over the range between 10 and 100 μg/ml. The method precision of within-day assay showed a 0.5 to 4.0% coefficient of variation (n=5) ranging from 10 to 70 μg/ml of kanamycin concentration levels. Kanamycin-PIC derivative in reaction solution was stable for 24 h at room temperature. A simple and efficient method for the analysis of the kanamycin in varicella vaccine was developed and validated.
Journal of Chromatography B: Biomedical Sciences and Applications.
