Decomposing or subliming? An investigation of thermal behavior of l-leucine

The thermal behavior of l-leucine under inert conditions was investigated by TGA, FTIR and TG–FTIR. The TG results showed that only one mass loss stage of more than 99% happened when l-leucine was under program heating with temperature ranging from 30 to 600 °C. The apparent activation energy, pre-exponential factor and the most probable model function were obtained by using of master plots method. The results of kinetic study showed that the decrease in mass of l-leucine was due to subliming rather than decomposing. And this was proved by the FTIR spectrum analysis and the directly observed subliming phenomenon. The results of TG–FTIR experiments showed that there was only one stage of decomposition process that happened after the subliming of leucine. The gas products were CO2, NH3, CO and some organic compounds such as 3-methyl-1-butanamine, and the main primary decomposition was decarboxylation.