Determination of pH

Immediately before mixing, the pH of the IR solution (nominal concentrations of 0.61 mg/mL and 0.65 mg/mL, as listed in Table 1) and each of the 3 LV solutions (7.20, 2.72, and 1.36 mg/mL, as listed in Table 1) was measured. Immediately after the solution for each treatment scenario was mixed (in a glass container), its pH was measured. The pH meter (Accumet model 925, Fisher Scientific, Nepean, Ontario) was standardized on each day on which pH was to be measured using commercially available buffer solutions (Fisher Scientific). The pH was recorded to the nearest 0.001 unit but is reported to 2 decimal places.

Visual Inspection

Before and immediately after mixing (time 0) and after 0.5 h, 1 h, and 24 h, each of the 54 experimental solutions was visually inspected against both a black background and a white background for precipitate, colour changes, and clarity. The samples for physical inspection were removed from the respective containers and placed in glass test tubes before inspection to avoid misinterpretations related to the opacity of the container. After inspection, solutions were centrifuged (3000 rpm, 1500g) for 10 min to pellet any precipitate that might have formed. The supernatant was also visually inspected. tadalis sx