BOGDAN TITA, ADRIANA FULIAS, MIRCEA STEFANESCU, ELEONORA MARIAN, DUMITRU TITA KINETIC STUDY OF SODIUM DICLOFENAC UNDER ISOTHERMAL CONDITIONS
The application of thermal methods is of great importance regarding the pharmaceutical problems such as the control of raw materials, the determination of purity, the qualitative and quantitative analysis of drug formulation, tests of thermal stability and compatibility, the determination of kinetic parameters etc. The purpose of a kinetic investigation is to calculate the kinetic parameters and kinetic model for the studied process. The results are further used to predict the system behaviour in various circumstances. A kinetic study regarding the sodium diclofenac thermal decomposition was performed under isothermal conditions in a nitrogen atmosphere, the temperature having the following values: 280, 285, 290, 295, 300°C. The TG/DTG data were processed by three methods: isothermal model-fitting, isothermal-isoconversional and Friedman’s isothermal-isoconversional. The model-fitting defines a single reaction step, while the model– free approach represented by isothermal-isoconversional methods gave dependences of the activation energy, of the extent of conversion. The obtained results are in good accord with the similar data which resulted in non-isothermal conditions from a previous work. The careful treatment of the kinetic parameters obtained under different thermal conditions was confirmed as necessary, as well as a different strategy of experimental data processing.
Keywords: sodium diclofenac, thermal analysis, TG/DTG/DTA, kinetic study