*3.8. Solubility Profile of RSP/RM-β-CD Kneaded Product*

The saturation shake-flask method was employed in order to evaluate the RSP solubility upon complexation with RM-β-CD. To this end, an excessive amount of drug substance and RSP/RM-β-CD kneaded product were added in 5 mL of phosphate buffer 0.1 M (pH 7.4), so that saturated solutions were obtained. The samples were shaken for

24 h at room temperature, and then the solutions were separated from the insoluble drug substance by filtration using a 0.45 µm nylon disk filter. After appropriate dilution, the filtrate was subjected to UV-spectrophotometric analysis at 277 nm. The RSP quantification was realized using a calibration curve. A set of RSP solutions in phosphate buffer 0.1 M with concentration in the range of 10–70 µg/mL were prepared, and their absorbance was recorded at 277 nm. The standard curve was obtained by plotting the absorbance (*A*) vs. the concentration (*C*); the equation of the RSP calibration curve is: *A* = 0.02801·*C* + 0.00677, with *R* = 0.99981.
