Analysis of Azithromycin in Human Plasma by LC–MS–MS

A simple sensitive and selective liquid chromatographic–tandem mass spectrometric method was developed and validated for the quantification of azithromycin in human plasma. Roxithromycin was used as the internal standard. The chromatographic separation was performed on a SunFire C18, 50 mm × 2.1, 3.5 μm column at 30 °C with mobile phase consisted of 1.54 g ammonium acetate, 250 mL water, 570 mL acetonitrile, 180 mL methanol and 0.6 mL glacial acetic acid. Flow rate was 0.2 mL min⁻¹. The work-up procedure involved a liquid–liquid extraction of the compounds. Mass spectrometric data were acquired in single ion monitoring. MRM mode of the ions 749.58 > 591.6 and 837.64 > 158.2 for azithromycin and roxithromycin, respectively. The method was validated in the concentration range of 2–1,000 ng mL⁻¹. Absolute recovery of azithromycin was 81.97%. Retention time for azithromycin was 0.9 and 1.1 min for roxithromycin. The run time was 2 min. This method was found suitable to analyse human plasma samples for application in pharmacokinetic, pharmacodynamic, bioavailability/bioequivalance studies.

     

Simultaneous LC–MS–MS Determination of Zolmitriptan and Its Active Metabolite N-Desmethylzolmitriptan in Human Plasma

A specific and sensitive liquid chromatography-electrospray ionization tandem mass spectrometry method was developed for the determination of zolmitriptan and N-desmethylzolmitriptan in human plasma. The analytes and the internal standard (IS) paroxetine were extracted by liquid–liquid extraction with a mixture of saturated ethyl acetate:dichloromethane (4:1) and were separated using an isocratic mobile phase on a XTerra RP18 column. The mobile phase used was acetonitrile: 5 mM ammonium acetate: formic acid (50:50:0.053, v/v/v). Zolmitriptan and N-desmethylzolmitriptan in a range of 0.25–20 ng mL⁻¹ were easily quantified. The validated method can be applied to pharmacokinetic and bioequivalence studies.

     

High resolution electronic absorption spectra of anisole and phenoxyl radical

High resolution absorption spectra of anisole and phenoxyl radical has been recorded in the vapor phase at room temperature by flash photolysis technique, and subsequent reactions have been investigated by kinetic spectroscopy. It was possible to follow the kinetics of the radical's decay which occurred predominantly by bimolecular recombination. The concentration of the phenoxyl radical calculated from the concentration of diphenoxyl molecules formed in the reaction cell during the optical pumping. The absolute extinction coefficient of this radical was measured from the absorption band at 291 nm, and found to be 0.95 x 10(+4) mol(-1) 1 cm(-1).     

Quantitative Determination of Fexofenadine in Human Plasma by HPLC-MS

A simple, rapid, sensitive and selective LC-MS method was developed and validated for quantification of fexofenadine in human plasma. The LC-MS system was operated under the positive electrospray ionisation mode (ESI). After liquid–liquid extraction, fexofenadine analysis was performed on a C₁₈ column with a mobile phase of acetonitrile: 10 mM ammonium acetate: formic acid, 70:30:0.1 (v/v/v) at a flow rate of 1 mL min⁻¹ by using loratadine as internal standard. The lower limit of quantitation was 3 ng mL⁻¹ for fexofenadine. The assay precision ranged between 1.05 and 12.56% and accuracy ranged between 82.00 and 109.07%. The validated method was successfully used to analyze human plasma samples in bioequivalence studies.

     

Simultaneous Determination of Carbamazepine and its Active Metabolite Carbamazepine-10,11-epoxide in Human Plasma by UPLC

A simple method for the determination of carbamazepine and its active metabolite carbamazepine-10,11-epoxide by ultra performance liquid chromatography (UPLC) with ultraviolet absorbance detection (TUV) was developed. The method involves a two-step protein precipitation by liquid–liquid extraction. Phenytoin sodium was used as the internal standard. The separation was carried out on Acquity C18 column with acetonitrile:methanol:KH₂PO₄ buffer (adjusting pH to 4.6 with 85% o-phosphoric acid) (180/180/170, v/v/v) as the mobile phase at a flow rate of 0.4 mL min⁻¹. Linear detection response was obtained for concentrations ranging from 50 to 5,000 ng mL⁻¹. The limit of quantification (LOQ) was 50 ng mL⁻¹. The method was validated successfully for the determination of carbamazepine and its active metabolite carbamazepine-10,11-epoxide, which can be applied through pharmacokinetics and bioequivalence studies.