*2.2. Quantification of the Drug Content in Formulations*

We quantified the nifedipine content in the formulations using a reverse-phase high-performance liquid chromatography (RP-HPLC) method. A C18 column, 90 Å, 5 µm, 3.9 × 150 mm (Resolve C18, Waters, Milford, MA, USA) was used as the stationary phase with a C18 guard column (Security Guard, Phenomenex, Torrance, CA, USA). A mobile phase composition of water/methanol/acetonitrile (50:25:25) was isocratically pumped at a flow rate of 1 mL/min. A high sensitivity flow cell for SPD-M30A diode array detector (Shimadzu, Kyoto, Japan) was used at 236 nm. The injection volume was 5 µL. Test solutions were prepared by dispersing 10 mg of the sample in 5 mL 0.1 M HCl to dissolve the calcium carbonate and calcium phosphate components of FCC. This was followed by sonicating the dispersions for 5 min to ensure complete dissolution of the carrier. A volume of 5 mL methanol was added in a subsequent step and the samples were sonicated again for 5 min. The solutions were diluted once more (1 mL to 10 mL) with the mobile phase and filtered through 0.45 µm syringe filters. All sample preparations were made in triplicate. The chromatographic measurements for each sample were carried out in triplicate. The absorbance was measured at a wavelength of 236 nm.
