Butylated hydroxyanisole
Inactive ingredient (antioxidant)
Measuring cell: DSC820
Pan: Aluminum 40 µl, hermetically sealed
Sample preparation: As received, no preparation
DSC measurement: Heating from 30 °C to 70 °C at 1, 2.5, 5, 10 und 20 K/min
Atmosphere: Nitrogen, 50 cm3/min
The DSC curves show the melting of butylated hydroxyanisole recorded at different heating rates. As expected the peak increases in size with increasing heating rates, which results in decreasing resolution. A second melting peak, which corresponds to the other modification of butylated hydroxyanisole, is observed only at lower heating rates. An additional factor of importance in the case of polymorphic transitions is the kinetics for transformation from one modification to the other. In the case described, most favorable heating rate for the detection of the second transition is 2.5 K/min. The heat of fusion of the first crystal modification is best measured at 10 K/min. Further experiments are required to determine the heat of fusion of the second crystal modification.
Heating rate K/min | Onset 1 °C | ΔH J/g | Onset 2 °C | ΔH J/g | Weight mg |
---|---|---|---|---|---|
1 | 59.2 | 95.0 | 62.6 | 2.7 | 1.360 |
2.5 | 59.9 | 82.1 | 63.8 | 17.6 | 4.929 |
5 | 59.4 | 85.5 | 62.9 | 2.9 | 1.607 |
10 | 60.2 | 100.2 | - | - | 4.516 |
20 | 61.1 | 99.3 | - | - | 4.398 |
With a suitable choice of the heating rates, it is possible to determine the melting point and the heat of fusion of the individual modifications of polymorphic substances, even when the melting points of the modifications lie close together.
The Influence of Heating Rate on the Detection of Polymorphism, Butylated Hydroxyanisole | Thermal Analysis Application No. HB845 | Application published in METTLER TOLEDO TA Application Handbook Pharmaceuticals