DSC Calibration, Heating Rate Independence
Sample
Zinc (calibration standard, purity > 99.999 %)
Application
Standard for calibration
Conditions
Measuring cell: DSC821e
Pan: Alumina 40 µl, with pierced lid
Sample preparation: Zinc pellet, pressed flat and premelted
DSC measurement: Heating from 350 °C to 475 °C at 5, 10 and 20 K/min. All measurements are performed with the same sample. Cooling rate is 5 K/min.
Atmosphere: Nitrogen, 50 cm3/min
Interpretation
The DSC curves show the melting of zinc at different heating rates. If displayed with respect to temperature, the peak area increases with increasing heating rates. The heat of fusion is however the integral of the heat flow with respect to time. This is just as independent of the heating rate as the melting point.
Evaluation
The onset temperature and the heat of fusion of zinc are determined.
| Measured | Measured | Measured | Ref. value | |
|---|---|---|---|---|
| Heating rate | 5 | 10 | 20 | K/min |
| Melting point (onset) | 419.5 | 419.6 | 419.8 | 419.7 °C |
| Heat of fusion | 107.0 | 107.0 | 107.1 | 107.0 J/g |
Conclusion
The calibration data of an instrument are affected by many factors such as the heating rate, the purge gas used, the sample pan material and the temperature range used. Only when these effects can be taken into account in the calibration data, are results obtained that are independent of measurement parameters, as is shown in this example of the melting point and the heat of fusion.
DSC Calibration, Heating Rate Independence | Thermal Analysis Application No. HB804 | Application published in METTLER TOLEDO TA Application Handbook Pharmaceuticals