Heat contact method was performed under a polarized microscope equipped with an electric desk heater (Hot Stage). Certain amount of artesunate was placed on glass objects, covered, heated to melt and allowed to recrystallize again. Afterwards, the nicotinamide powder was placed right on the glass cover boundary. The sample system was heated again until all the nicotinamide melts. The melting nicotinamide was allowed to move and made contact with the surface of artesunate crystal. The area of contact (contact zone) between artesunate and nicotinamide were observed for the growth of new crystals under polarizing microscope at 200x magnification.
The cocrystals formation was recorded using a digital camera [6].