Fig. 4

Linearity of Epirubicin Quantification Using Traditional vs. True Dose Sampling Over Time. Linear regression plots showing the ratio of Epirubicin (AUC) to Doxorubicin (internal standard) across increasing Epirubicin concentrations (0–1000 nM). Dose–response curves of epi/doxo ratios under six conditions: direct analysis (a) and True Dose at five time points (b–f). Strong linearity (R² ≥ 0.99) was observed across 0–1000 nM Epirubicin, indicating analytical equivalence and stability.