UV-Visible spectrophotometry (GENESYS 6 UV- Vis spectrophotometer, Thermo Scientific, Madison WI, US) was used to estimate the concentration of CA at a wavelength of 278 nm (United States Pharmacopeial Convention, 2000 ). The standard curve was linear across the range of 0.8 to 16 μg/mL (R2= 0.999).
pH-dependent saturation solubility measurements of CA were performed by adding a known excess amount of CA to 1 mL of 0.1 N HCl (pH 1.2), 0.1 M phosphate buffer (pH 6.8), or water. Samples were agitated using a mechanical shaker at 50 rpm (37 ± 0.5 °C) for 24 h. Samples were centrifuged at 10,000 rpm for 5 min and the supernatant was filtered, then diluted prior to UV-Vis spectrophotometric analysis at 278 nm. Phase solubility studies were performed for Kolliphor® TPGS and Gelucire® 44/14 at concentrations of 2–10% w/v in water by adding a known excess amount of CA. Samples were agitated in a water bath (37 ± 0.5 °C) for 48 h, then centrifuged at 10,000 rpm for 5 min. The supernatant was diluted and analyzed by UV-Vis spectrophotometry (Mader and Higuchi, 1970 ).
pH-dependent saturation solubility measurements of CA were performed by adding a known excess amount of CA to 1 mL of 0.1 N HCl (pH 1.2), 0.1 M phosphate buffer (pH 6.8), or water. Samples were agitated using a mechanical shaker at 50 rpm (37 ± 0.5 °C) for 24 h. Samples were centrifuged at 10,000 rpm for 5 min and the supernatant was filtered, then diluted prior to UV-Vis spectrophotometric analysis at 278 nm. Phase solubility studies were performed for Kolliphor® TPGS and Gelucire® 44/14 at concentrations of 2–10% w/v in water by adding a known excess amount of CA. Samples were agitated in a water bath (37 ± 0.5 °C) for 48 h, then centrifuged at 10,000 rpm for 5 min. The supernatant was diluted and analyzed by UV-Vis spectrophotometry (Mader and Higuchi, 1970 ).