Journal of Thermal Analysis and Calorimetry, Vol. 72 (2003) 597–604
SPECIFICITY OF DECOMPOSITION OF SOLIDS IN
NON-ISOTHERMAL CONDITIONS
T. Vlase*, G. Vlase, M. Doca and N. Doca
West University of Timiºoara, Department of Chemistry, Str. Pestalozzi 16, RO-1900 Timiºoara,
Romania
Abstract
The thermal stability of the food additives Na metabisulphite, Na and K acetates, glutamic and citric
acids, respective of the pharmaceuticals nifedipine and acetyl salicylic acid was studied by means of
the non-isothermal kinetic (Friedman differential method).
The specificity of the thermal decomposition was characterized by identification of the bond to
be selective activated due to energy absorption at vibrational level. These bonds were assigned by
comparison of calculated wave numbers with the wave number of the IR spectra.
Keywords: compensation effect, IR wave number, isokinetic temperature, non-isothermal kinetics,
pharmaceutical and food additives
Introduction
Many years ago the thermal analysis earned its place as a current instrumentation
technique in assisting the analytical problems of pharmaceuticals [1]. A relative new
trend in this field is the study of the thermal stability of pharmaceuticals and food ad-
ditives in connection with the molecular architecture.
In an earlier paper [2] we suggested a correlation between the isokinetic temper-
ature and the wave number assigned to the bond responsible for the beginning of the
thermal decomposition of a certain compound. In this paper we extend this study to
some usual food additives and pharmaceuticals.
Experimental
The thermal curves were recorded with a MOM Derivatograph devices in static air at-
mosphere. For the thermal analysis, 100 mg samples were used, with heating rates of
20, 10, 5 and 2.5 K min–1.
The IR spectra were determined in KBr tablet for the initial, respectively the
thermal treated samples, using a NICOLET-510 FTIR Spectrometer.
The TG data were interpolated with logistical function and finally numerical
derivate. With the values of α, β(dα/dT) and T, the Friedman`s method for estimating
the non-isothermal kinetic parameters was used.
*
Author for correspondence: E-mail: tvlase@cbg.uvt.ro
1388–6150/2003/ $ 20.00
Akadémiai Kiadó, Budapest
© 2003 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht