Investigation of pyrolysis process of caffeic acid in nitrogen using thermogravimetry-single drop microextraction-gas chromatography-mass spectrometry and Fourier transform infrared spectroscopy

The thermal decomposition behavior of caffeic acid was investigated using the thermogravimetry-single drop microextraction-gas chromatography-mass spectrometry (TG-SDME-GC-MS) and Fourier transform infrared spectroscopy. The heating rate and the air flow rate were set at 5 ℃/min and 400 mL/min,respectively. The evolved components of caffeic acid from thermogravimetry were extracted with ethanol by single drop microextraction in the temperature range of 160-360 ℃. Then the extract was separated and analyzed by GC-MS. Thus,the dynamic changes of the relative contents of 5 main pyrolysis products with the increase of temperature were identified and monitored. The alterations of functional groups of the solid residues at each weight-lose-point were analyzed by Fourier transform infrared spectroscopy. The results showed that the main reason for the weight loss of caffeic acid can be concluded to the generation of mass pyrocatechol at 240-360 ℃ and 4-ethylcatechol at 200-220 ℃. The molecular structure of caffeic acid was completely decomposed at 230 ℃. This method provides a significant approach for the investigation of the thermal decomposition behavior of material with the continuous rising of temperature.