Linearity, range and lower limit of quantification (LLOQ)
Three calibration curves were calculated based on data from three consecutive days using twelve concentrations for each standard in plasma and urine. The coefficients of variation of AP1, AP3, AP4, and AP6, were 0.24–9.76, 0.58–11.48, 0.20–10.64, 0.53–10.26 for plasma, and 2.71–13.43, 2.57–10.46, 2.55–10.13, 1.69–10.88 for urine, respectively. Percent accuracies were 85.50–109.02%, 94.26–106.46%, 90.93–101.04%, 92.75–110.08% for plasma, and 91.14–103.01%, 92.41–106.39%, 90.39–105.42%, 91.22–110.17% for urine, respectively. The results show good linearity (> 0.99) for both plasma and urine over the range of 0.98–1000.00 ng/mL. This method established LLOQ for the four diterpenoids at 0.98 ng/mL in both plasma and urine. (Supporting information, Tables S3 and S4).