Recovery
The recovery of the four diterpenoids in plasma and urine was measured at three different QC concentrations: LQC, MQC and HQC (n = 5 for each concentration) for both pre-spiked standard of QC samples and post-spiked standard of blank plasma or urine. Extraction recoveries were calculated by comparing the peak area of pre-spiked standard in a blank matrix with the area of post-spiked standard in an extracted matrix at corresponding concentrations. To meet acceptance criteria, the recovery should be precise, accurate, and repeatable with %CV of recovery less than 15%.