Determination and toxicokinetics comparison of ketamine and S(+)-ketamine in dog plasma by HPLC-MS method

A simple and reproducible method was developed for the quantification of ketamine and S(+)-ketamine in dog plasma using a high-performance liquid chromatography system coupled to a positive ion electrospray mass spectrometric analysis. Solid-phase extraction was used for extracting analytes from dog plasma samples. The analytes were separated on a Zorbax SB C(18) column (100 x 2.1 mm, 3.5 microm) with acetonitrile-formate buffer (10 mM ammonium formate and 0.3% formic acid) (17 : 83, v/v) as mobile phase at a flow-rate of 0.2 mL/min. Detection was operated under selected ion monitoring mode. [M + H](+) at m/z 238 for ketamine and S(+)-ketamine and [M + H](+) at m/z 180 for phenacetin (internal standard) were selected as detecting ions, respectively. The method was linear in the concentration range 51.6-2580 ng/mL. The intra- and inter-day precisions (RSD %) were within 11.3% and the assay accuracies ranged from 80.0 to 101.4%. Their average recoveries were greater than 91.1% at all test concentrations. The analytes were proved to be stable during all sample storage, preparation and analysis procedures. The method was successfully applied to the toxicokinetics study and comparison of ketamine and S (+)-ketamine following intravenous administration to dogs.