Multi-steps infrared spectroscopic characterization of the effect of flowering on medicinal value of Cistanche tubulosa

Multi-steps infrared spectroscopic methods, including conventional Fourier transform infrared spectroscopy (FT-IR), second derivative spectroscopy and two-dimensional infrared (2D-IR) correlation spectroscopy, have been proved to be effective methods to examine complicated mixture system such as Chinese herbal medicine. The focus of this paper is the investigation on the effect of flowering on the pharmaceutical components of Cistanche tubulosa by using the Multi-steps infrared spectroscopic method. Power-spectrum analysis is applied to improve the resolution of 2D-IR contour maps and much more details of overlapped peaks are detected. According to the results of FT-IR and second derivative spectra, the peak at 1732 cm−1 assigned to CO is stronger before flowering than that after flowering in the stem, while more CO groups are found in the top after flowering. The spectra of root change a lot in the process of flowering for the reason that many peaks shift and disappear after flowering. Seven peaks in the spectra of stem, which are assigned to different kinds of glycoside components, are distinguished by Power-spectra in the range of 900–1200 cm−1. The results provide a scientific explanation to the traditional experience that flowering consumes the pharmaceutical components in stem and the seeds absorb some nutrients of stem after flowering. In conclusion, the Multi-steps infrared spectroscopic method combined with Power-spectra is a promising method to investigate the flowering process of C. tubulosa and discriminate various parts of the herbal medicine.