Fig. 4. DSC Thermograms of Different Samples of Acetaminophen
Key: a, sample 1: native acetaminophen; b, sample 2: preheated to 180 °C and then quickly cooled to 25 °C; c, sample 3: preheated to 80 °C and then cooled to 25 °C; d, sample 4: preheated to 135 °C and then cooled to 25 °C. Solid line: first heating; dotted line: second heating.
1550 and 1448cmϪ1 (Fig. 3c→Fig. 3d) indicates that over 85 °C the irregular crystal form of the glassy acetaminophen was transformed to the regular crystal form. 85°C was the temperature for recrystallization of the glassy acetaminophen.