Development of a sensitive LC-ESI-MS assay for 20(R)-ginsenoside Rh2 and its pharmacokinetic application in dogs: A case for the influence of micronization on traditional Chinese medicine

20(R)-ginsenoside Rh2 is being developed as a new antitumor drug. To contribute to its biopharmaceutical and pharmacokinetic study, a novel LC-ESI-MS method was described in this paper and was proved to be accurate, precise and rugged with a linearity range of 0.5–200 ng/ml (r2 = 0.9998) in dog plasma. The method procedure consisted of an economical and simple liquid–liquid extraction with satisfactory recovery (>70%), and a subsequent rapid analysis (within 9.5 min) which was performed on a Shimadzu LCMS2010A system (electrospray ionization, Q-array-octapole-quadrupole mass analyzer), with an ODS column (150 mm × 2.0 mm i.d., 5 μm) plus a C18 guard column for separation and ammonium chloride (500 μmol) as mobile phase additive. Chlorinated adducts of molecular ions [M + Cl]− of 20(R)-Rh2 at m/z 657.35 and internal standard digitoxin at m/z 799.55 were monitored in select ion monitoring (SIM) mode of negative ions. The method showed an excellent sensitivity that the limit of detection (LOD) and the lower limit of quantitation (LLOQ) of 20(R)-Rh2 were 0.1 and 0.5 ng/ml, respectively. This method was applied to a pharmacokinetic study of 20(R)-Rh2 in six dogs and the evaluation of the influence of micronization on pharmacokinetics. The results indicated micronization could remarkably improve the absolute bioavailability of 20(R)-Rh2.