Determination of tubuloside B by LC-MS/MS and its application to a pharmacokinetic study in rats.

Tubuloside B, a novel neuroprotective phenylethanoid, is a major active constituent of Cistanche tubulosa and Cistanche deserticola. A specific and sensitive liquid chromatography tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the quantification of tubuloside B in rat plasma. Sample preparation was conducted through a protein-precipitation extraction with methanol using tubuloside A as internal standard (IS). Chromatographic separation was achieved using a Capcell Pak C18 column (2.0 × 50 mm, 5 µm) with a mobile phase of methanol-10 mm ammonium acetate buffer (70:30, v/v) in an isocratic elution. Mass spectrometry analysis was performed in negative ionization mode with selected reaction monitoring transitions at m/z 665.1 → 160.9 for tubuloside B, and m/z 827.1 → 160.9 for IS. Calibration curves were linear over the range of 1.64-1640 ng/mL for plasma samples samples (R2 > 0.990). The lower limit of quantification (LLOQ) was 1.64 ng/mL. The intra- and inter-day accuracy was between 92.3 and 113.0% with the RSD <9.23% at all LLOQ and quality control levels. Finally, this method was successfully applied in the pharmacokinetics study of tubuloside B after intravenous administration.

Validated LC-MS/MS method for the quantification of sciadopitysin in rat plasma and its application to pharmacokinetic and bioavailability studies in vivo.

A sensitive and rapid LC-MS/MS method was developed and validated for quantitation of sciadopitysin in rat plasma using amentoflavone as an internal standard. Sample processing was accomplished after deproteinization with 150 µL aliquot of acetonitrile. Chromatographic separation was achieved using an Agela C18 column with an isocratic mobile phase comprising 2 mm ammonium acetate-acetonitrile (35:65, v/v) at a flow rate of 0.4 mL/min. Detection was performed by selection reaction monitoring on a triple-quadrupole mass spectrometer following the transitions m/z 579 → 547 and 537 → 375 for sciadopitysin and internal standard, respectively, in the negative ionization mode. The calibration curve was linear from 2.90 to 1160 ng/mL for sciadopitysin. Intra- and inter-day precisions were in the ranges 4.1-11.4 and 5.7-9.1% for sciadopitysin. Sciadopitysin was stable under different stability conditions. The validated assay was applied to pharmacokinetic and bioavailability studies in rats.