Indirect resolution of beta-blocker agents by reversed-phase capillary electrochromatography

The 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

Aspartate analysis in formulations using a new enzyme sensor

Anal. Chim. Act

Enantiomeric separation of mirtazapine and its metabolites by using nano-liquid chromatography

Mirtazapine (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 \ub5m 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\u201315 and 10\u201340 \ub5g/mL, respectively (the highest value was obtained for the DEMIR enantiomers); correlation coefficients, 0.9993\u20130.9999; 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

Separation of catechins and methylxanthines in tea samples by capillary electrochromatography

PubMed: 19266552In 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 µm) 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 20°C. Precision, detection and quantification limits, linearity, and accuracy were investigated. A good linearity (R2 > 0.9992) was achieved over a concentration working range of 2-100 µg/mL for all the analytes. LOD and LOQ were 1 and 2 µg/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 analyte

Chiral separation of pesticides by coupled-column liquid chromatography application to the stereoselective degradation of fenvalerate in soil

Chiral separation of synthetic pesticides presenting more than one center of asymmetry was performed by multidimensional liquid chromatography. The method consisted of coupling two columns by means of a six‐port valve: an achiral column was used for the separation of the pesticide diastereomers, that were, then, individually switched into the chiral column and resolved as the corresponding enantiomers. In order to obtain optimum resolution conditions for pesticides existing as four (fenvalerate, propiconazole, and triadimenol) and eight (cyfluthrin) optical isomers, a number of coupled‐column systems constituted of an achiral (plain silica gel, γ‐cyanopropyl(CNP)‐, and γ‐aminopropyl(AMP)‐silanized silica gel) and a chiral [containing cellulose tris‐(3,5‐dimethylphenyl‐carbamate), (R)(−)‐N‐(3,5‐dinitrobenzoyl)‐phenylglycine(DNBPG), and (S)‐N‐1‐(α‐naphthyl) ethylaminocarbonyl‐(S)‐ter‐leucine, as the selectors] stationary phases were studied. Coupled‐column liquid chromatography (CC‐LC) proved to be a very effective strategy allowing the full resolution, with the exception of triadimenol, of all the investigated pesticides. The method was used for studying the stereoselective degradation of fenvalerate in soil under simulated laboratory conditions

Chiral interactions by capillary electrochromatography on multiple-interaction based stationary phases

The 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

Use of Hepta Tyr glycopeptide antibiotic as chiral selector in capillary electrophoresis.

A new glycopeptide antibiotic, MDL 63,246 (Hepta-tyr), of the teicoplanin family, has been evaluated in capillary electrophoresis for the resolution of chiral compounds of pharmaceutical and environmental interest. Electrophoretic separations were carried out in a polyacrylamide-coated capillary using the partial filling-counter current mode with aqueous-organic buffers in the pH range 4-6. Experimental parameters affecting resolution, such as antibiotic concentration, buffer pH, organic modifier type and capillary temperature, were studied. The Hepta-tyr antibiotic exhibited a high enantiorecognition capability towards the studied compounds at very low concentrations (1-2 mg/mL). The optimum experimental conditions were achieved by using a buffer at pH 5 containing acetonitrile at 25 degrees C