Biomedical subjects

Zeineb Aturki

Publications and source records attributed to Zeineb Aturki.

6 recordsLinked to original sources

PubMed2006

Separation of basic compounds of pharmaceutical interest by using nano-liquid chromatography coupled with mass spectrometry.

Nano-liquid chromatography-mass spectrometry (nano-LC-MS) was evaluated for the separation of basic compounds of pharmaceutical interest. The separation of selected beta-blockers, namely nadolol, oxprenolol, alprenolol and propranolol in the presence of terbutaline was performed using two 75 microm I.D. capillaries packed with two different RP18 stationary phases (SP). The best results concerning resolution and efficiency were achieved using the SP where free silanol groups were not present. As expected, this latter SP proved to be very efficient and symmetry factors were observed mainly in the case of the more retained analytes. Baseline resolution of all studied basic compounds was achieved with the Cogent bidentate C18 silica phase (CBC18) eluting analytes at 800 nL/min with a mobile phase containing 500 mM ammonium acetate pH 4.5-water-methanol (1:8:91, v/v/v). The separated basic compounds were revealed using on-column UV detector at 205 nm and electrospray-ion-trap mass spectrometer (ESI-MS). The packed capillary was connected to the MS through a commercial sheath liquid interface or a sheathless nano-spray interface and in both cases the sensitivity was studied and the results compared. Limit of detection (LOD) as low as 0.1 ng/mL was measured for nadolol using the sheathless nano-spray interface and the capillary column packed with the CBC18 stationary phase.

Chromatography, Liquid↗

PubMed2006

On-line CE-MS using pressurized liquid junction nanoflow electrospray interface and surface-coated capillaries.

A simple and cost-effective laboratory-made liquid junction interface was used for coupling of CE with MS. In this device the capillary column and the spray tip were positioned in the electrode vessel containing appropriate spray liquid. The electrospray potential was applied on the electrode inside the liquid junction. A stable electrospray was produced at nanoliter per minute flow rates generated in the emitter tip without using an external pump. This arrangement provided high durability of the spray tip and independent optimization of the CE separation (use of coated capillaries) and ESI conditions. CE-MS analysis of mixtures of drugs, peptides, tryptic digests of proteins and biological fluids was optimized with respect to the effects of the distance between the separation capillary and electrospray tip and pressure applied on the liquid junction. The sensitivity of the system, in terms of the LOD (base peak monitoring) was below 10 ng/mL for the beta-blocker drugs and below 200 ng/mL for peptide analysis.

Adrenergic beta-Antagonists↗

PubMed2005

Rapid assay of vitamin E in vegetable oils by reversed-phase capillary electrochromatography.

A rapid capillary electrochromatographic (CEC) method for the analysis of vitamin E in vegetable oils is reported. Vitamin E consists of a group of eight isomers, tocopherols (TOHs) and tocotrienols. The separation of four TOHs (alpha-, gamma-, delta-TOH), alpha-tocopherol acetate (alpha-TOH-Ac), and an antioxidant compound, butylated hydroxytoluene (BHT) used to prevent TOH autoxidation, was optimized. The CEC experiments were carried out in a 75 microm inner diameter (ID) fused-silica capillary, partially packed with 3 microm C(18 )stationary phase (33 cm total length, 8.4 cm and 7 cm effective and packed lengths, respectively). The optimum mobile phase was a polar organic phase composed of a mixture of methanol-acetonitrile in the ratio 50/50 v/v containing 0.01% ammonium acetate, applying a voltage and temperature set at -25 kV and 20 degrees C, respectively. The tocopherols and the BHT were successfully separated within 2.5 min using the short-end injection method. Under these experimental conditions, repeatability of retention time and peak area, analyte detection and quantitation limits, linearity, precision, and accuracy were studied. The CEC method was applied to determine the content of TOHs in different commercially available oils of virgin olive, hazelnut, sunflower, and soybean. The extraction of vitamin E isomers from oil samples was achieved using methanol and a methanol-isopropanol mixture.

Butylated Hydroxytoluene↗

PubMed2005

Enantiomeric separation of mirtazapine and its metabolites by nano-liquid chromatography with UV-absorption and mass spectrometric detection.

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 microm 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 microg/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.

Chromatography, Liquid↗

PubMed2004

Separation of flavanone-7-O-glycoside diastereomers and analysis in citrus juices by multidimensional liquid chromatography coupled with mass spectrometry.

The major flavanone-7-O-glycoside constituents in citrus fruit juices (naringin, hesperidin, neohesperidin, narirutin, and eriocitrin) were separated as diastereomers by multidimensional liquid chromatography. The method consisted of coupling two HPLC columns: a reversed-phase (RP(18)) column was used for the separation of flavanone glycosides, which were, then, individually switched into a carboxymethylated beta-cyclodextrin (beta-CD)-based column and resolved as the corresponding stereoisomers. The method was used for the full analysis of flavanone glycosides in fresh hand-squeezed and commercial fruit juices by combining the quantitative estimation with the diastereomeric analysis. Quantitative data were in general consistent with previously reported data in this field. CC-LC isomer analysis was carried out by coupling the beta-CD column with a mass spectrometer operated with negative ion electrospray ionization (ESI-MS). The results showed that hesperidin was present in orange juices almost exclusively as the 2S isomer, whereas narirutin had mainly the 2R configuration. In grapefruit juices (2S)-naringin prevailed with the respect to the 2R isomer, whereas the opposite was true for narirutin. Lemon juices contained eriocitrin stereoisomers in equal amount (50% each), but hesperidin was almost exclusively found as the 2S isomer. Significant differences of the diastereomeric ratios were observed between freshly squeezed juices and juices from commercial sources.

Beverages↗

PubMed2004

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

The indirect resolution of five beta-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 beta-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.

Adrenergic beta-Antagonists↗