7.5.1. Drug Content

Drug content was estimated by placing one dose (7.5 mg) equivalent microemulsion formulation in a 100 mL volumetric flask and adding a small volume of methanol, which solubilizes the microemulsion. Finally, the volume was made up to 100 mL, with a pH 6.4 phosphate buffer. It was shaken well for about 1 h in a shaker followed by centrifugation then analyzed. The resultant solution was filtered through Whatman filter paper, and the absorbance was measured at 228 nm using a UV-visible spectrophotometer [18]. To calculate the concentration of mirtazapine in the samples, the straight line equation obtained from regression anlaysis was used. The equation was obtained from the standard calibration plots, which were conducted in simulated nasal fluid, was well as a pH 6.4 phosphate buffer. The calibration curve of mirtazapine in the pH 6.4 phosphate buffer was found to obey Beer-Lambert's law within the linearity range of 10–60 µg/mL, with a regression coefficient value of 0.992 at 228 nm, while in simulated nasal fluid, it was within the linearity range of 2–20 µg/mL, with a regression coefficient value of 0.991 at 228 nm.
