2.10. Assay of curcumin in C. longa extract
20 mg of curcumin standard was weighed and transferred to a 20 mL volumetric flask and dissolved in 15 mL of methanol. The volumetric flask was shaken using ultrasonicator for 5 min. The solution was diluted to volume with methanol. 20 mg of C. longa extract powder was weighed and transferred to a 20 mL volumetric flask and dissolved in 15 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 of curcumin and C. longa extract powder had a concentration of 1 mg/mL of curcumin. 0.2 mL of standard and extract powder solution was transferred to 10 mL volumetric flask and dissolved in methanol to give a concentration of 20 lg/mL. This sample was injected into HPLC in triplicate to determine the potency of C. longa extract powder. The content of curcumin in C. longa extract powder was calculated by dividing ratio of C. longa extract with ratio of standard times the potency of standard, where the ratio of standard or C. longa extract are calculated by dividing peak area of curcumin in standard or C. longa extract with the total area of three peaks comprising of curcumin, demethoxycurcumin and
bisdemethoxycurcumin.