3.4. Dissolution Rate Measurement

The dissolution rates of ST-A and ST-B in distilled water and gastric juice pH 1.2 acid solution (in the presence of 0.2% SLS) at 37 °C were measured using a Thermo Scientific Evolution 300 UV-Vis spectrometer (Thermo Scientific, Waltham, MA, USA). For dissolution rate measurement, an excess quantity of drug was poured into 200 mL of water or gastric juice pH 1.2 acid solution, which was pre-heated to 37 °C and rotated at 150 rpm. The mixture was stirred for 120 min, and at specific time intervals, 2 mL of the sample was withdrawn and replaced with 2 mL of a fresh medium to maintain a total volume. The sample was then filtered through Whatman’s 0.45 μm syringe filter. The absorbance at λ_max of the obtained solution was determined. The concentrations of ST-A and ST-B were achieved by calculations based on the standard curves of Sor-Tos. Each concentration was measured three times in parallel and the average value was obtained.