Abstract
Thermal analysis is one of the most widely used methods for studying the solid state of pharmaceutical substances.
TG/DTG and DSC curves provide important information regarding the physical properties of the pharmaceutical compounds (stability, compatibility, polymorphism, kinetic analysis, phase transitions etc.).
The purpose of a kinetic investigation is to calculate the kinetic parameters and the kinetic model for the studied process. The results are further used to predict the system’s behaviour in various circumstances.
A kinetic study regarding the diazepam, nitrazepam and oxazepam thermal decomposition was performed, under non-isothermal and isothermal conditions and in a nitrogen atmosphere, for the temperature steps: 483, 498, 523, 538 and 553 K. The TG/DTG data were processed by three methods: isothermal model-fitting, Friedman’s isothermal-isoconversional and Nomen-Sempere non-parametric kinetics.
In the model-fitting methods the kinetic triplets (f(α), A and E a) that defines a single reaction step resulted in being at variance with the multi-step nature of diazepines decomposition. The model-free approach represented by isothermal and non-isothermal isoconversional methods, gave dependences of the activation energies on the extent of conversion.
It is very difficult to obtain an accord with the similar data which resulted under non-isothermal conditions from a previous work.
The careful treatment of the kinetic parameters obtained in different thermal conditions was confirmed to be necessary, as well as a different strategy of experimental data processing.
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Tiţa, B., Marian, E., Tiţa, D. et al. Comparative kinetic study of decomposition of some diazepine derivatives under isothermal and non-isothermal conditions. J Therm Anal Calorim 94, 447–452 (2008). https://doi.org/10.1007/s10973-008-9146-4
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DOI: https://doi.org/10.1007/s10973-008-9146-4