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Chiral interactions by capillary electrochromatography on multiple-interaction based stationary phases
No full textThe direct resolution of neutral amino acid and amino alcohol derivatives by pressurized
capillary electrochromatography (p-CEC) is reported. Separations were performed on columns
packed with multiple-interaction based chiral stationary phases (CSPs) in reversedphase
mode, using borate buffer/acetonitrile mixtures as the eluent. Two CSPs were used:
3,5-dinitrobenzoyl-(R)-phenylglycine (DNB-PGLY)- and 3,5-dinitrobenzoyl-(R)-naphthylglycine
(DNB-NGLY)-silica bonded, respectively. Baseline separations of N-benzoyl-b-naphthylamide
derivatives of phenylalanine and leucine were accomplished on DNB-PGLY-CSP in
less than three minutes, and on DNB-NGLY-CSP within about 3.5 minutes, with a comparable
efficiency of 160.000 plates per meter. As expected, DNB-NGLY-CSP showed
higher selectivity for the compounds under study. The R-isomer eluted before the S-isomer
on both CSPs. The effect of the buffer pH on the efficiency of the columns was also studied.
With buffer pH over the values of 8–8.5, free residual c-aminopropyl groups on the silica
particles seemed do affect neither selectivity nor resolution. At these mobile phase conditions
calculated efficiency against electroosmotic flow plot is consistent with that generally obtained
in CEC, providing a reduced plate height of about 1.8 at a linear velocity of
0.5 mm s)1. With buffer pH values under 7.0, protonation of the free aminopropyl groups
strongly affected the resolution with the result of higher retention and lower solute mass
transfer
Separation of catechins and methylxanthines in tea samples by capillary electrochromatography
No full textIn this paper, the simultaneous separation of several polyphenols such as (+)-catechin, ( – )-epicatechin, ( – )-epigallocatechin, theophylline, caffeine in green and black teas by capillary electrochromatography (CEC) was developed. Several experimental parameters such as stationary phase type, mobile phase composition, buffer and pH, inner diameter of the columns, sample injection, were evaluated to obtain the complete separation of the analysed compounds. Baseline resolution of the studied polyphenols was achieved within 30 min by using a capillary column (id 100 lm) packed with bidentate C18 particles for 24.5 cm and a mobile phase composed of 5 mM ammonium acetate buffer pH 4 with H2O/ACN (80:20, v/v). The applied voltage and the temperature were set at 30 kV and 208C. Precision, detection and quantification limits, linearity, and accuracy were investigated. A good linearity (R2 A 0.9992) was achieved over a concentration working range of 2 – 100 lg/mL for all the analytes. LOD and LOQ were 1 and 2 lg/mL, respectively, for all studied compounds.
The CEC method was applied to the analysis of those polyphenols in green and black tea samples after an extraction procedure. Good recovery data from accuracy studies ranged between 90% and 112% for all analytes
Indirect resolution of beta-blocker agents by reversed-phase capillary electrochromatography
No full textThe indirect resolution of five P-adrenoreceptor blocking agents (propranolol, oxprenolol, pindolol, metoprolol, and atenolol) using precolumn derivatization with (+)-1-(9-fluorenyl)ethyl chloroformate (FLEC), and capillary electrochromatography (CEC) is reported. Three octadecylsilanized (ODS) silica gel-based stationary phases, differing in particle diameter and carbon surface density for suitability of determination of the enantiomeric composition of these substances in drugs and biological fluids, were studied. Under optimum separation conditions, all the investigated compounds were baseline-resolved within acceptable analysis times (i.e., between 10-16 min). The resolution values ranged between 1.80 and 1.14, and the separation factors were in no case less than 1.07. The possible use of the developed CEC method for the determination of enantiomeric composition of P-adrenoreceptor blocking agents in drug substances was investigated. A study, in which the enantiomers of metoprolol were examined regarding specificity, reproducibility, limit of detection, and ruggedness, was developed in accordance with some analytical procedures for method validation
Enantioselective separation of the novel antidepressant mirtazapine and its main metabolites by CEC
No full textAnalysis of synthetic cannabinoids in herbal blends by means of nano-liquid chromatography.
No full textIn this study, a rapid and simultaneous separation of 12 synthetic cannabinoids and Δ(9)-tetrahydrocannabinol (Δ(9)-THC) in herbal blends was obtained by means of nano-liquid chromatography (nano-LC). The nano-LC experiments were performed in a 100μm i.d. capillary column packed with Cogent(®) bidentate C(18) silica particles for 25.0cm. All compounds were resolved using an isocratic elution mode in less than 30min. A mobile phase containing ACN/MeOH/H(2)O/formic acid 69/5/25/1 (v/v/v/v) was employed for the chromatographic separation. The developed analytical method was validated in terms of precision, linearity, sensitivity and accuracy. Under optimal nano-LC-UV conditions, the resulting RSD percentages for intra-day and inter-day repeatability, related to retention time and peak area, were below 2.98 and 6.40%, respectively. Limits of detection and quantification were 0.2 and 0.5μg/mL, respectively, for all the studied compounds. Linearity was assessed in the concentration range of interest for all analytes with determination coefficients r(2)≥0.9975. The method was then applied to the determination of synthetic cannabinoids in herbal blends. Quantitative analyses of the cannabimimetic compounds in six products showed that there was a wide difference in the concentration of the studied compounds among different products. Further, the nano-LC system was coupled with a mass spectrometer measuring the MS and MS-MS spectra to unequivocally identify the cannabinoids present in smoking mixtures
Enantioseparation of mirtazapine and its metabolites in biological fluids by capillary electrochromatography and nano-liquid chromatography
No full textEnantiomeric separation of mirtazapine and its metabolites by using nano-liquid chromatography
No full textMirtazapine (MIR) and two of its main metabolites, namely, 8-hydroxymirtazapine and N-desmethylmirtazapine, were separated in totheir enantiomers by nanoLC in a laboratory-made fused-silica capillary column (75 μm ID) packed with a vancomycin modified silica stationary phase. The simultaneous separation of the three couples of the studied enantiomers was achieved in less than 33 min, using an experimentally optimized mobile phase delivered in the isocratic mode. Optimization of the mobile phase composition was achieved by testing the influence of the buffer pH and concentration, the water concentration, the organic modifier type and concentration, and on the retention and resolution of the analytes. The optimum mobile-phase composition contained 500 mM ammonium acetate pH 4.5/water/MeOH/MeCN, 1:14:40:45 v/v/v/v. Using a UV detector at 205 nm, the method was validated studying several experimental parameters such as LOD and LOQ, intraday and interday repeatability, and linearity. Good results were achieved: LOD and LOQ were in the range 5–15 and 10–40 μg/mL, respectively (the highest value was obtained for the DEMIR enantiomers); correlation coefficients, 0.9993–0.9999; the intraday and interday precision was acceptable (RSD < 2%) using an internal standard. The method was tested for the separation of the studied enantiomers in an extracted (solid-phase) serum sample spiked with standard racemic mixture of MIR and its two metabolites. Finally, the nanoLC system was connected to a mass spectrometer through a nanoelectrospray interface and the MS, MS2, and MS3 spectra were acquired showing the potential of the system used for characterization and identification of the separated analytes
Going 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
Use of nano-liquid chromatography for the analysis of glycyrrhizin and glycyrrhetic acid in licorice roots and candies
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