2.5. Preparation of stock and working standard solutions
50 mg of curcumin working standard was weighed and transferred to a 50 mL volumetric flask and dissolved in 30 mL of methanol. The volumetric flask was shaken using ultrasonic vibrator for 5 min. The solution was diluted to volume with methanol. The stock standard solution had a concentration of 1 mg/mL of curcumin.