Evaluation of thermal stability and kinetic of degradation for levodopa in non-isothermal conditions

Abstract

In this paper, we present the results obtained during the investigation of thermal stability of antiparkinsonian drug Levodopa in oxidative atmosphere and under non-isothermal conditions. As investigational tools, thermoanalytical methods were used along with ATR-FTIR spectroscopy and later completed with kinetic study for the main degradative process that occurs in the 260–330 °C temperature range, at four heating rates. Four kinetic methods were used as follows: ASTM E698 which leads to an activation energy of 209.72 kJ mol−1, while isoconversional methods suggested the values 177.6 ± 13.1 kJ mol−1 (Friedman) and 188.8 ± 4.5 kJ mol−1 (Kissinger–Akahira–Sunose), with a clear indication of multistep degradation. The last method used was NPK, which revealed that the degradation occurs in three steps, with different physical and chemical contributions with mean activation energy equal to 191.3 ± 9.5 kJ mol−1.