Validation and Application of an HPLC–UV Method for the Quantification of 3‐ <i>O</i> ‐Methylquercetin in Nasal Mucosa

> 0.99). Accuracy and precision met international regulatory acceptance criteria, with relative standard deviations below 5% for both intra-day and inter-day evaluations. It also demonstrated excellent robustness under deliberate variations in flow rate, temperature, and detection wavelength (RSD < 2.00%). Matrix effect (86.94%-110.28%) and recovery (85.21%-106.47%) results confirmed the reproducibility and the efficiency of the method. The applicability of the revalidated method was demonstrated through in vitro release, permeation, and retention experiments using Franz diffusion cells and porcine nasal mucosa. These findings demonstrate that the method is precise, sensitive, and robust, making it suitable for nasal permeation and retention studies of 3OMQ. Moreover, this analytical approach represents a reliable tool for in vitro and ex vivo pharmaceutical research, supporting the development and evaluation of nasal drug delivery systems for poorly soluble bioactive compounds, particularly flavonoid aglycones.