## 3 Results and Discussion
The literature reports that the LOD and LOQ depend on various factors such as the method (e.g., spectrophotometric, fluorometric, mass spectrometry) and type/quantity of sample. [PERSON] et al. developed a methodology using chromatographic separation connected to a fluorometric detector [56]. The objective was to detect the concentration of nanomolars between 1 and 229 nmol/L of tRES loaded in lipid nanoparticles to evaluate in vitro intestinal assays, using Caco-2 cell monolayers. The authors showed a successfully quantification and low-cost analysis, enabling the improvement pharmacokinetic studies. In another study, the LOD and LOQ of tRES in polymeric nanoparticles, as recorded by chromatography with photodiode array, were found to be 1.29 \(\upmu\)g/mL and 4.29 \(\upmu\)g/mL, respectively [57]. While the sensitivity of the method has not been one of the selected parameters for its validation, the recorded LOD and LOQ confirm the capacity of our RP-HPLC-PDA to identify and quantify resveratrol. In addition, our method is easy, of straightforward implementation, and of low cost. Therefore, it has been used for in vitro studies. Stearic acid has been selected as the solid lipid from the preliminary screening of the solubility of tRES in a set of solid lipids (data not shown), while the surfactant combination has been based on reports from scientific literature [46]. SLN with a mean hydrodynamic diameter of 237.03 \(\pm\) 1.80 nm (F1.tRES) and 201 \(\pm\) 2.04 nm (F2.tRES), and a polydispersity index of 0.206 \(\pm\) 0.012 nm (F1.tRES) and 0.153 \(\pm\) 0.061 nm (F2.tRES) were obtained by ultrasound technique, and the validated method was applied for the quantification of tRES released from SLN in Franz diffusion cells. The drug release from SLN may occur either by diffusion from the nanoparticles surface or from the lipid matrix, or by erosion [58]. The in vitro release profiles of tRES from SLN are shown in Figure 4. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Parameters** & **Retention Time/(min.)** & **RSD/(\%)** \\ \hline \multirow{3}{*}{Flow} & 0.8 mL/min & 8.22 \(\pm\) 0.007 * & 0.52 \\  & 1.0 mL/min & 7.24 \(\pm\) 0.009 * & 0.64 \\  & 1.2 mL/min & 6.53 \(\pm\) 0.015 * & 0.52 \\ \hline \multirow{3}{*}{Column temperature} & 25 \({}^{\circ}\)C & 7.24 \(\pm\) 0.009 ** & 0.64 \\  & 30 \({}^{\circ}\)C & 7.15 \(\pm\) 0.100 ** & 0.26 \\ \cline{1-1}  & 35 \({}^{\circ}\)C & 7.06 \(\pm\) 0.006 ** & 0.70 \\ \hline \hline \end{tabular}  
* Not statistically significant (\(p\) \(<\) 0.05); ** Statistically significant (\(p\) \(>\) 0.05).  
\end{table} 
Table 3: Results of the robustness for quantification of tRES. There was no statistical difference (\(p<0.05\)) in tRES release between F1.tRES and F2.tRES, demonstrating that the addition of soy phosphatidylcholine in the formulation had no influence on the size and tRES release from the developed SLN. The first release of tRES was observed only 1 h after the beginning of the assay. For F1.tRES formulation, about 38.82 \(\pm\) 2.30 (\(\mu\)g/cm\({}^{2}\)) of the drug was released after 24 h, while for F2.tRES, about 41.03 \(\pm\) 4.28 (\(\mu\)g/cm\({}^{2}\)) of the drug was released within the same time frame. The tRES release data were adjusted using the mathematical models (zero-order and first-order kinetic, Higuchi, Weibull, and Korsmeyer-Peppas models) determining the linear regression. Table 4 summarizes the regression coefficients (R\({}^{2}\)) for tRES released from SLN. The criterion for selecting the most appropriate mathematical model was established to be the highest value of R\({}^{2}\). According to the obtained R\({}^{2}\) values (Table 4), the Weibull model was the one that best described the tRES release from SLN, which translates a complex release mechanism, involving simultaneously polymer chain relaxation and erosion during drug release. [PERSON] et al. [59] compared 13 mathematical models of kinetic release data of 32 drugs from 106 dispersions published in the literature [60].