Stock solutions of doxycycline hyclate (DOX) and oxymetazoline hydrochloride (OXY) (500 mg L -1 ) were prepared by dissolving 0.05 g of each pure drug in 100 mL distilled water.
Working standard solutions were prepared by suitable dilution of the stock standard solution with distilled water. 2 M NaOH was prepared by dissolving 20 g of NaOH (Merck) in 250 mL distilled water, and working solutions were prepared by appropriate dilution with the same solvent. Diazotized 4-aminoacetophenone (DAAP) solution (5×10 -3 M) was prepared daily by dissolving 0.0675 g of 4-aminoacetophenone (Merck) in 5 mL ethanol, 20 mL distilled water and 2 mL of 0.8 M hydrochloric acid (Merck, 37% w/v) in a 100 mL volumetric flask. The mixture was cooled to 0-5 °C for 5 min using an ice-bath. Then 0.0345 g of sodium nitrite (Fluka) was added and the mixture was stirred. After 5 min, the volume was made up to the mark with the addition of cooled distilled water.
Working standard solutions were prepared by suitable dilution of the stock standard solution with distilled water. 2 M NaOH was prepared by dissolving 20 g of NaOH (Merck) in 250 mL distilled water, and working solutions were prepared by appropriate dilution with the same solvent. Diazotized 4-aminoacetophenone (DAAP) solution (5×10 -3 M) was prepared daily by dissolving 0.0675 g of 4-aminoacetophenone (Merck) in 5 mL ethanol, 20 mL distilled water and 2 mL of 0.8 M hydrochloric acid (Merck, 37% w/v) in a 100 mL volumetric flask. The mixture was cooled to 0-5 °C for 5 min using an ice-bath. Then 0.0345 g of sodium nitrite (Fluka) was added and the mixture was stirred. After 5 min, the volume was made up to the mark with the addition of cooled distilled water.