Pyrolysis characteristics of Radix Rhizoma Rhei, Cortex Moudan Radicis, and Radix Sanguisorbae and correlations with the carbonizing process of Chinese herbs

Abstract

AimThe aim of the work is to study the pyrolysis characteristics of Radix Rhizoma Rhei, Cortex Moudan Radicis, and Radix Sanguisorbae in an inert atmosphere of argon (Ar), and to investigate the mechanism of the carbonizing process of the three traditional Chinese herbs. MethodsThe pyrolysis characteristics of the crude materials and their extracts were studied by thermogravimetry-mass spectrometry (TG-MS) in a carrier gas of argon, coupled with Fourier transform infrared spectrometry (FTIR) and scanning electron microscopy (SEM) methods. Correlation of the pyrolysis behaviors with the carbonizing process by stir-frying of traditional Chinese medicines was made. ResultsWithin the temperature range of 200–300 °C, which is the testing range for the study of the carbonizing process of Chinese herbs, the temperatures indicated by the maximum weight loss rate peak of the above three extracts were taken as the upper-limit temperatures of the carbonizing process of the herbs, and which were 200, 240 and 247 °C for Radix Rhizoma Rhei, Cortex Moudan Radicis, and Radix Sanguisorbae, respectively. The ion monitoring signal peaks detected by the TG-MS method corresponded with reports that the level of chemical components of traditional Chinese medicinal materials would decrease after the carbonizing process. It was confirmed by Fourier transform infrared spectrometry (FTIR) and scanning electron microscopy (SEM) methods that better results of “medicinal property preservation” could be obtained by heating at 200 °C for Radix Rhizoma Rhei, at about 250 °C for Cortex Moudan Radicis, and Radix Sanguisorbae, as the relative intensity values of the common peaks were among the middle of their three carbonized samples by programmed heating. ConclusionThe upper-limit temperatures of the carbonizing process for Radix Rhizoma Rhei, Cortex Moudan Radicis and Radix Sanguisorbae were 200, 240 and 247 °C respectively. It is feasible to research the mechanism and technology of the carbonizing process of traditional Chinese medicinal materials using thermogravimetry, Fourier transform infrared spectrometry, and scanning electron microscopy methods.