1,721,028 research outputs found
ANALYSIS OF CYCLOSPORIN A AND MAIN DEGRADATION IMPURITIES BY CYCLODEXTRIN– MODIFIED MICELLAR ELECTROKINETIC CHROMATOGRAPHY
No full textSeparation of the immunosuppressive drug cyclosporin A (CyA) from the closely related degradation impurities cyclosporin H (CyH, a CyA diastereomer) and isocyclosporin A (IsoCyA), was accomplished by means of cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC). Heptakis (2,3,6-tri-O-methyl)-beta-cyclodextrin (TM-betaCD) showed to be an effective modifiers of the sodium dodecyl sulfate (SDS) micellar system, allowing for the CD-MEKC separation of CyA from CyH and IsoCyA. By means of electric current measurements carried out using the capillary electrophoretic apparatus, the critical micelle concentration of SDS in the presence of different neutral cyclodextrins was estimated. Interestingly, it was found that TM-betaCD strongly inhibited the micellization of SDS compared to beta-, and hydroxypropyl-beta-cyclodextrin. This unusual behavior was considered to be a key factor of the specific ability of the methylated cyclodextrin in providing CD-MEKC separation of hydrophobic cyclosporins. The optimized method consisted of: 50 mM sodium dodecyl sulfate (SDS) in 50 mM tetraborate buffer (pH 9.2) supplemented with 15 mM TM-betaCD. The electrophoretic runs were performed at 30°C under the application of 22 kV in a fused-silica capillary (50 micron id, 64.5 cm total length, 56 cm length to the detector). The method was validated for linearity of CyA (within 0.25 – 5.00 mg/mL) and CyH and IsoCyA (within 0.25 – 5.0 %, w/w with respect to CyA), sensitivity (LOQ 5.0 microg/mL), accuracy and precision. The applicability of the method was proved by analysis of a commercially available pharmaceutical (gelatine capsules)
Enantioselective MEKC analysis of catechins in tea samples of different origin
No full textEnantioselective separation of catechin and gallocatechin was achieved by using micellar electrokinetic chromatography (MEKC) modified by cyclodextrin (HP-beta-CD). The analytical enantioseparation of these two catechins was found to be very useful because, for the first time, the presence of (-)-gallocatechin and (-)-catechin (chiral phytomarkers) in tea samples, was regarded as an index of thermal degradation of the product. More than twenty tea samples of different origin (China, Japan, Ceylon) were analysed; the chiral phytomarkers of degradation was found in some of the products proving the occured thermal degradation
Experimental design in capillary electrophoretic methods and development.
No full textExperimental design, in particular by means of multivariate methods has shown to be very useful in optimization and validation of analytical separations. In the communication, a brief survey of the use of experimental design - based otpimization techniques in capillary electrophoresis is presented
Analysis of catechins and xanthines in chocolate and Theobroma cacao by micellar electrokinetic chromatography after optimized extraction.
No full textDesign and variable optimization in the adsorptive stripping voltammetric determination of rufloxacin in tablets, human plasma and urine
No full textOptimization by Experimental Design of the adsorptive stripping voltammetric parameters in the determination of cinoxacin
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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