2.3. Plasma sample preparation
The stored plasma samples were allowed to thaw at room temperature
before processing. The plasma samples were centrifuged
at 4000 rpm for 10 min, an aliquot (0.96 ml) was
pipetted into a 10 ml polypropylene tube and acetonitrile
(2.0 ml) was added. The mixture was vortex mixed briefly,
and after standing for 5 min at room temperature, the mixture
was centrifuged at 4000 rpm for 20 min. the supernatant was
carefully transferred into vial and injected into HPLC system