## 3 Results and Discussion
### Physical and Chemical Characterization  
_FTIR analysis._ The purity of the two felodipine forms used in this study was investigated by infrared spectroscopy (FTIR) according to European Pharmacopoeia (Ph. Eur.) 10 th Edition monograph [26]. The FTIR spectra are presented in Figure 1a-d. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Formulation Code**} & \multicolumn{2}{c}{**\% of the Tablets’ Total Mass**} \\ \cline{2-3}  & **F18** & **F19** \\ \hline Felodipine & 5 & 5 \\ PEG 4000 & 5.4 & 5.4 \\ Propyl gallate & 0.05 & 0.05 \\ Methocel K100 & 15 & 15 \\ Methocel E50 & 5527.5 & 27.5 \\ Microcrystalline cellulose & 17.05 & 12.05 \\ Lactose monohydrate & 19 & 14 \\ Magnesium stearate & 21 & 21 \\ PVP K 30 & 10 & 20 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: F18 and F19 formulations, differing in PVP amounts. \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{**Ingredients**} & **Quantity (mg)** & **\% of the Tablets’ Total Mass** \\ \hline Felodipine & 10.00 & 5 \\ PEG 4000 & 10.80 & 5.40 \\ Propyl gallate & 0.10 & 0.05 \\ Methocel K100 & 30.00 & 15 \\ Methocel E50 & 55.00 & 27.50 \\ Microcrystalline cellulose & 24.10 & 12.05 \\ Lactose monohydrate & 28.00 & 14 \\ Magnesium stearate & 2.00 & 1 \\ PVP K 30 & 40.00 & 20 \\ \hline Total mass & 200.00 & 100.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Felodipine extended-release tablet formulation. From the FTIR spectra it was observed that the two feloipine forms have approximatively the same spectra as the reference. From Figure 1a can be seen that the peak attributed to the stretching vibration of the amino group v(N-H) appears at 3342 cm\({}^{-1}\), characteristic of the amorphous feloipine compound [27; 28]. This N-H stretching peak was shifted to 3370 cm\({}^{-1}\) in the crystalline feloipine forms. The peaks at 2942 cm\({}^{-1}\) and 1688 cm\({}^{-1}\) are attributed to C-H stretching and C=O stretching vibration, respectively. All the spectral bands, which appear in the FTIR spectra of the compounds are consistent with the FTIR spectra of the reference feloipine compound [29]. _Thermal analysis_: The DSC curves of the two feloipine forms, compared with the reference sample, are represented in Figure 2.  
The DSC analysis showed that the feloipine reference material had a lower melting point (143.9 \({}^{\circ}\)C) and the characteristic endothermal melting peaks of the two analysed feloipine forms were higher than the reference, proving the purity of the two samples. The melting point increased in the following order: feloipine reference sample (143.9 \({}^{\circ}\)C) < microcrystalline feloipine form (146.8 \({}^{\circ}\)C) < macrocrystalline feloipine form (148.51 \({}^{\circ}\)C). The higher melting points of the two feloipine forms may be explained by the more crystalline morphology of these samples. The lower melting point of microcrystalline feloipine form is due to the increased surface area of feloipine particles. This increase leads to an increase in heat-exchange efficiency [30]. The determined melting points agree with literature data [27; 31]. Figure 1: FTIR spectra of feloipine: macrocrystalline form—green line, microcrystalline form—blue line, reference—red line. (**a**) 4000–3000 cm\({}^{-1}\) range; (**b**) 3000–2000 cm\({}^{-1}\) range; (**c**) 2000–1000 cm\({}^{-1}\) range; (**d**) 1000–400 cm\({}^{-1}\) range. _Optical microscopy analysis._ Images of the two studied feloipine types, macrocrystalline felodipine (batch E0055518) and microcrystalline felodipine (batch 0057505) at different resolutions (4\(\times\), 10\(\times\), 40\(\times\) and 100\(\times\) objective) were collected. The optical images are represented in Figure 3 for macrocrystalline felodipine and Figure 4 for microcrystalline felodipine. In Figure 3, the tetrahedral aspect of the crystals and the surface heterogeneity can be seen. From Figure 4, the irregular round appearance of the microcrystalline felodipine form and the particles' tendency to agglomerate can be seen.