Abstract:In order to investigate and compare the similarities and differences of chemical composition of Rehmanniae radix, four-kind Rehmanniae radix (i.e., Radix rehmanniae, Radix rehmanniae preparata, Radix rehmanniae charcoal, and Radix rehmanniae preparata charcoal, shorted for RR, RRP, RRC and RRPC, respectively) were studied by infrared spectroscopy (FTIR) and their second derivative spectra were calculated. Their thermal performance changes during heat treatment were analyzed with a comprehensive thermal analyzer, and their surface chemical element content and microstructure were analyzed by X-ray energy spectrometer and scanning electron microscope (SEM). The results showed that four types of Rehmanniae radix had similar absorption peak position and shape, however, their absorption peak intensity was different. They all had absorption peaks of -OH, -CH, C=O and -NH of polysaccharides, alcohols and amino acid groups of Rehmanniae radix, among which the content of polysaccharide was higher in the dry root of Rehmanniae radix, while the absorption strength of RRC and RRPC significantly reduced in many peaks. The intensity and shape of second derivative of infrared spectra of four-kind Rehmanniae radix were quite different at the 1 200-500 cm-1 band. The four-kind Rehmanniae radix showed thermal weight loss due to the thermal decomposition of various polysaccharides, alcohols and amino acids under 190 ℃ ~ 350 ℃, and RR and RRP had significant thermal weight loss than that of RRC and RRPC. Compared with RR and RRP, RRC and RRPC had lower O element atomic content and higher C element atomic content were higher. These studies showed that the chemical composition was similar for four-kinds Rehmanniae radix, and RR and RRP had similar chemical composition and micro-structure, while RRC and RRPC had similar chemical composition and micro-structure. The content of polysaccharides and alcohols and amino acid in RRC and RRPC were significantly lower than that of RR and RRP.
